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Book of Abstracts12th International Workshop on
Electric Probes in Magnetized Plasmas 2017
Naklo 2017
IWEP 2017September 4 - 7N A K L OS L O V E N I A
12th International Workshop on Electric Probes in Magnetized Plasmas
Book of Abstracts
12th International Workshop on Electric Probes in Magnetized Plasmas
2017
Naklo 2017
Organizers: Nuclear Society of Slovenia
and Jožef Stefan Institute
Reactor Physics Department
Jamova cesta 39 SI-1000 Ljubljana
Slovenia
www.nss.si/iwep2017/
Book of Abstracts 12th International Workshop on Electric Probes in Magnetized Plasmas 2017 Naklo 2017 Editor: ddr.Tomaž Gyergyek Published by: Nuclear Society of Slovenia Jamova cesta 39 SI-1001 Ljubljana Web: www.djs.si E-mail: [email protected] Printed 50 copies. Printed by DEMAT d.o.o.. Not for sale.
CIP - Kataložni zapis o publikaciji Narodna in univerzitetna knjižnica, Ljubljana 533(082) INTERNATIONAL Workshop on Electric Probes in Magnetized Plasmas (12 ; 2017 ; Naklo) Book of abstracts / 12th International Workshop on Electric Probes in Magnetized Plasmas, [also] IWEP 2017, September 4-7, Naklo, Slovenia ; [organizers Nuclear Society of Slovenia and Jožef Stefan Institute Reactor Physics Department ; editor Tomaž Gyergyek]. - Ljubljana : Nuclear Society of Slovenia, 2017 ISBN 978-961-6207-41-6 1. Gyergyek, Tomaž 2. Društvo jedrskih strokovnjakov Slovenije 3. Inštitut Jožef Stefan (Ljubljana). Reaktorski center (Podgorica) 290715136
Previous meetings organized by the Nuclear Society of Slovenia • First Meeting of Nuclear Society of Slovenia, Bovec, Slovenia, June 1992 • Regional Meeting: Nuclear Energy in Central Europe, Present and Perspectives,
Portorož, Slovenia, June 1993 • PSA/PRA and Severe Accidents ‘94, Ljubljana, Slovenia, April 1994 • Annual Meeting of NSS ‘94, Rogaška Slatina, Slovenia, September 1994 • 2nd Regional Meeting: Nuclear Energy in Central Europe, Portorož, Slovenia, September 1995 • 3rd Regional Meeting: Nuclear Energy in Central Europe, Portorož, Slovenia, September 1996 • 4th Regional Meeting: Nuclear Energy in Central Europe, Bled, Slovenia, September 1997 • Nuclear Energy in Central Europe `98, Čatež, Slovenia, September 1998 • Nuclear Energy in Central Europe `99 with Embedded Meeting Neutron Imaging Methods to
Detect Defects in Materials, Portorož, Slovenia, September 1999 • 20th International Conference on Nuclear Tracks in Solids, Portorož, Slovenia, August 2000 • Nuclear Energy in Central Europe 2000, Bled, Slovenia, September 2000 • Nuclear Energy in Central Europe 2001, Portorož, Slovenia, September 2001 • Nuclear Energy for New Europe 2002, Kranjska Gora, Slovenia, September 2002 • Nuclear Energy for New Europe 2003, Portorož, Slovenia, September 2003 • Nuclear Energy for New Europe 2004, Portorož, Slovenia, September 2004 • Nuclear Energy for New Europe 2005, Bled, Slovenia, September 2005 • Nuclear Energy for New Europe 2006, Portorož, Slovenia, September 2006 • Nuclear Energy for New Europe 2007, Portorož, Slovenia, September 2007 • Nuclear Energy for New Europe 2008, Portorož, Slovenia, September 2008 • Nuclear Energy for New Europe 2009, Bled, Slovenia, September 2009 • Nuclear Energy for New Europe 2010, Portorož, Slovenia, September 2010 • Nuclear Energy for New Europe 2011, Bovec, Slovenia, September 2011 • Nuclear Energy for New Europe 2012, Ljubljana, Slovenia, September 2012 • Nuclear Energy for New Europe 2013, Bled, Slovenia, September 2013 • Nuclear Energy for New Europe 2014, Portorož, Slovenia, September 2014 • Nuclear Energy for New Europe 2015, Portorož, Slovenia, September 2015 • Nuclear Energy for New Europe 2016, Portorož, Slovenia, September 2016
Committees
Members of the committees are listed in alphabetic order.
International Scientific Committee
Michael LAUX, Germany, Chair
John ALLEN, UK Gheorghe DINESCU, Romania Åshild FREDERIKSEN, Norway
James Paul GUNN, France Tomaž GYERGYEK, Slovenia
Carlos HIDALGO, Spain Mark KOEPKE, USA
Emilio MARTINES, Italy Hans Werner MÜLLER, Germany
Tsviatko POPOV, Bulgaria Jens Juul RASMUSSEN, Denmark Roman SCHRITTWIESER, Austria
Carlos SILVA, Portugal Reiner STENZEL, USA
Organizing Committee
Tomaž Gyergyek, Chair
and Editor of Book of Abstracts
Saša Bobič Mateja Južnik Jernej Kovačič Urška Turšič
Nina Udir Bojan Žefran
Welcome
International Workshops on Electric Probes in Magnetized Plasmas (IWEP) take place every second year since 1993. They are devoted to understanding and solving problems associated with electric probes in either magnetized or unmagnetized plasmas. The 12th International Workshop on Electric Probes in Magnetized Plasmas 2017 (IWEP 2017) takes place in Hotel Marinšek in Naklo, Slovenia from 4th to 7th of September 2017 and is organized by the Nuclear Society of Slovenia. This Society has a long tradition of successful organization of scientific conferences and workshops. The organizers have received 18 abstracts. All the abstracts were approved by the International Scientific Committee and are published in this book of abstracts.
Place and time of Workshop
The Workshop will take place in Hotel Marinšek in Naklo, Slovenia. Address: Hotel Marinšek d.o.o. Glavna Cesta 2 4202 Naklo Slovenija, EU From: Monday, September 4, at 12:00 To: Thursday, September 7, at 12:00
Registration
Registration desk opening hours: Monday, September 4: 12:00 to 18:00 Tuesday, September 5: 9:00 to 12:00
Social Activities
Welcome Reception: Monday, September 4 Workshop Lunch: Tuesday, Wednesday and Thursday. Lunch is included in the registration fee and will be served from 12:00 - 13:30. Workshop Trip: Wednesday, September 6 Workshop Dinner: Wednesday, September 6
Workshop Program
Monday, September 4
12:00-16:00 Arrival and registration 16:00 Opening Ceremony Paper no. 101 16:15 – 16:45
Measurements with cold and emissive probes in a High Power Impulse Magnetron Sputtering discharge (HiPIMS) R. Schrittwieser
Paper no. 102 16:45-17:15
Design and Status of the Electrostatic Probe System for the SPIDER Experiment M. Spolaore
Paper no. 103 17:15 – 17:45 Electric Probe Measurements in Uniform and Strongly Magnetized Plasma Produced by Glow-Discharge in Halbach Array S. Costea
19:00 Welcome cocktail
Tuesday, September 5 Paper no. 104 9:00 – 9:30
Slabbing Model for Kinetic Description of ion Thrusters Plasma Plumes: Propagator Integral Method Solutions J. M. Donoso
Paper no. 105 9:30-10:00
Kinetic Analysis of Weakly ionized Plasmas in presence of collecting and emissive walls J. Gonzales
Paper no. 106 10:00-10:30
A Study of the Electron Energy Probability Function in the Plume and Channel of a low-power Hall Thruster M. Tichy
10:30-11:00 Coffee break Paper no. 107 11:00-11:30
Multiprobe Characterization of Plasma Flows for Space Propulsion J. Damba
Paper no. 108 11:30-12:00
Langmuir Probe Measurements in the Early Hydrogen Discharge of GLAST-III Tokamak A. Qayyum
Lunch Paper no. 109 16:00 – 16:30
Measurements of Densities of Gas Constituents in a Discharge Device with a Large Wall Probe I. P. Kurlyndskaya
Paper no. 110 16:30-17:00
Spatial Distribution of Plasma Parameters in Gas Aggregation Nanocluster Source A. Kolpakova
Wednesday, September 6 Paper no. 111 9:00-9:30
Determination Of Anisotropic Ion Velocity Distribution Function In Intrinsic Gas Plasma. Theory A. Grabovskiy
Paper no. 112 9:30 – 10:00
Determination Of Anisotropic Ion Velocity Distribution Function In Intrinsic Gas Plasma. Probe Method A. Grabovskiy
Paper no. 113 10:00 – 10:30
Feasibility, Strategy, Methodology, and Analysis of Probe Measurements in Plasma under High Gas Pressure V. Demidov
10:30-11:00 Coffee break Paper no. 114 11:00 – 11:30
Current-Voltage and Floating Potential Characteristics of Cylindrical Emissive Probes from a Self-consistent Full-Kinetic Model X. Chen
Paper no. 115 11:30 – 12:00
Current Density Distribution Along the Cylindrical Probe in Magnetized Plasma G. Popa
Lunch 15:00 – 18:30 Workshop trip 20:00 Workshop dinner
Thursday, September 7 Paper no. 116 9:00 – 9:30
Disturbances of ICP Plasmas by Langmuir Probes with Uninsulated Protecting Shields V. Riaby
Paper no. 117 9:30-10:00
The Radial-Motion-Only (RMO) and Orbital-Motion (OM) Methods for Calculating Velocity Distribution Functions in a Spherical Probe Scenario S. Kuhn
Paper no. 118 10:00-10:30
Some Experiments with the Tunnel Probe in a Low-Temperature Magnetized Plasma J. Kovačič
10:30 Closing ceremony
Abstracts
Disclaimer The content of abstracts published in the book of abstracts is the responsibility of the authors concerned. The organizer is not responsible for published facts and technical accuracy of the presented data.
101.1
Measurements with cold and emissive probes in a High Power Impulse Magnetron Sputtering discharge (HiPIMS)
Roman Schrittwieser
Institute for Ion Physics and Applied Physics, University of Innsbruck
Technikerstr. 25
A-6020 Innsbruck, Austria
Bernd S. Schneider, Stefan Costea, Ovidiu Vasilovici, Codrina Ionita
Institute for Ion Physics and Applied Physics, University of Innsbruck
Technikerstr. 25
A-6020 Innsbruck, Austria
[email protected], [email protected], [email protected],
Tiberiu Minea, Daniel Lundin
Laboratoire de Physique des Gaz et des Plasmas, LPGP, Université Paris-Sud, Université Paris-
Saclay
Bat. 210, rue H. Becquerel,
F-91405 Orsay Cedex
[email protected], [email protected]
A combination of two Cold Langmuir Probes (CLP)
and one Electron Emissive Probe (EEP) was used for local
measurements of plasma (ion) density ni, plasma potential
pl and electron temperature Te, with high temporal resolu-
tion, only limited by the data acquisition system (see Fig. 1).
The ion density was determined as usual from the ion satura-
tion current Iis:
eB
i
p
is
i
Tk
m
eA
In
7,0
, (1)
with Ap being the effective probe area for ion collection, mi
the ion mass and kB the Boltzmann constant. The relation be-
tween pl and the floating potential Vfl of a CLP is given by:
e
TV
I
I
e
TV
e
fl
is
ese
flpl
ln (2)
Here Ies is the electron saturation current. By means of an EEP we have
the possibility to estimate pl (notwithstanding the pending discussions
on the reliability of EEP for measuring pl). Combining an EEP and a
CLP, Te can be derived by converting Eq. (1):
flpleV
e
T (3)
Probe measurements of pl and Te were carried out in two differ-
ent plasma discharges mounted in the same vacuum chamber (Fig. 2).
The first discharge consisted of an inductively coupled plasma using a
radio-frequency (RF) power supply. Good agreement between the new
probe and a commercial "Smart Probe" was found. In the second case,
similar measurements were carried out in a High Power Impulse Magne-
tron Sputtering discharge (HiPIMS) (Fig. 2 shows the probes' positions).
We also measured the full time-traces of pl and Te during a 40 µs
HiPIMS and evidence for a possible ion acoustic wave launched at the
onset of the discharge pulse were found.
Fig. 1: The probe with two cold and one emissive
sive Langmuir probe.
Fig. 2: Position of combined probe
and the Smart Probe in the HiPIMS)
101.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
102.1
Design and Status of the Electrostatic Probe System for the SPIDER Experiment
M. Spolaore
M. Brombin, R. Cavazzana, G. Serianni, R. Pasqualotto, N. Pomaro, C. Taliercio
Consorzio RFX (CNR, ENEA, INFN
Università di Padova, Acciaierie Venete SpA) Corso Stati Uniti 4
35127 Padova, Italy
The neutral beam injector, an additional heating system for the ITER project, will be optimized in the NBI
test facility under construction in Padova. The facility includes the SPIDER ion source representing the full size
prototype for the production of negative ions, based on RF plasma with expected beam 100kV energy and 50A
current. The source will be equipped with a system of 84 electrostatic probes for the investigation of the
homogeneity of plasma parameters, such as plasma density, electron temperature, and plasma potential and
possibly of the Electron Energy Distribution Function. Measurements will be performed in the extraction region
of the ion source, where most of the extracted negative ions are produced. The system consists of 2D arrays of
different sensors, covering the Plasma Grid (PG) surface and the Bias Plate (BP), which are the components facing
the plasma in the extraction region. The probe system design accounts for the constraints related to the need of
embedding the sensors within the PG and BP. It has been carried out with the aim of providing sensors easy
maintenance and enough robustness to withstand the experimental operation of SPIDER. A special machining of
the insulating part has been adopted in order to avoid sensor short circuit due to deposition of metals such as
caesium or copper on the BP and PG surfaces during the operation of the SPIDER source. Given the RF plasma,
a particular attention is paid to the RF conditioning of the current collected by the probes in order to minimize the
spurious effects on the voltage-current characteristic of the sensors. In order to test in advance the electrostatic
sensor and to check possible weak points in the design, prototype sensors were manufactured and successfully
tested in plasma conditions as similar as possible to the plasma which will be produced in the SPIDER source.
The system is presently being installed on the SPIDER grids. In this contribution the overall system
description and status will be provided, including the in-vessel and ex-vessel parts, following the path from the
sensors up to the conditioning electronics and the acquisition system.
102.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
.
103.1
Electric Probe Measurements in Uniform and Strongly Magnetized Plasma
Produced by Glow-Discharge in Halbach Array
Stefan Costea Institute for Ion Physics and Applied Physics, University of Innsbruck
Technikerstraße 25b/3
A-6020 Innsbruck, Austria
Ovidiu Vasilovici, Bernd S. Schneider, Roman Schrittwieser, Codrina Ionita
Institute for Ion Physics and Applied Physics, University of Innsbruck Technikerstraße 25b/3
A-6020 Innsbruck, Austria
[email protected], [email protected], [email protected], codri-
For many experiments and applications, plasma is confined using magnetic fields, especially in fusion-
relevant devices. There are two ways of producing external magnetic fields: by strong electric currents in coils or
by permanent magnets. Coils have the advantage of varying the magnetic field strength by changing the electric
current flowing through them but for high currents a cooling system has to be implemented. Permanent magnets
can deliver magnetic fluxes into the gap of a magnetic circuit without continuous consumption of energy. We
present a way to produce highly-magnetized plasma using a special magnet assembly, known as the Halbach ar-
ray, able to produce a homogeneous magnetic flux density across a cylindrical gap region. Electric probes were
used to characterise this highly magnetized plasma.
An ideal Halbach array is a ring magnet where the po-
larization direction varies continuously along the circumfer-
ence such that the magnetic flux increases in the enclosed
space and reduces or cancels outside it. In practice, typical
Halbach cylinders are built using discrete permanent magnets
each with its own magnetization direction, approximating the
Halbach magnetic distribution [1]. Choosing the orientation of
each segment appropriately, the fields will all add at the centre.
We simulated the magnets’ positions in order to obtain a
uniform and homogenous magnetic field and the optimum cyl-
inder bore diameter, using Quick Field v6.1 Student Edition
(Figure 1). The input parameters for the magnetic material
were set according to the technical datasheet of the magnets.
For our experimental device, 8 identical 50×15×15 mm
Nd2Fe14B cubic bar magnets were used to produce a 0,5 T
magnetic field. The plasma was produced inside the 22×22×45
mm magnetized region by a glow discharge. Two electrodes were placed in such a way that the electrical field is
parallel with the magnetic field lines, one electrode was grounded and the other was biased with negative voltag-
es of a few hundreds of volts.
REFERENCES
[1] C.K. Chandrana, J.A. Neal, D. Platts, B. Morgan, P. Nath, "Automatic alignment of multiple magnets into
Halbach cylinders", Journal of Magnetism and Magnetic Materials, 381, 2015, pp. 396-400.
Figure 1: Magnetic flux simulation of exper-
imental Halbach array.
y x
103.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
104.1
Slabbing Model for Kinetic Description of ion Thrusters Plasma Plumes: Propagator Integral Method Solutions
José Manuel Donoso Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio (ETSIAE), Technical University of Madrid
Plaza del Cardenal Cisneros, 3 28850, Madrid, Spain
Jorge González, Luis Conde Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio (ETSIAE), Technical University of Madrid
Plaza del Cardenal Cisneros, 3 28850, Madrid, Spain
[email protected], [email protected]
The comprehension of the phenomena involved in plasma thrusters devices, where ions can be
accelerated to high velocities, is of relevant importance to improve the efficiency and designing of these engines,
as well as to ensure a correct interpretation of plasma diagnostics measurements [1,2]. Usually, fluid model
equations mislead upscaling diffusive kinetic effects that remains to mesoscopic or fluid scales. We present an
extension of the previously stated one-dimensional collisional velocity-space kinetic model [3,4], for weakly
ionized plasmas, to describe a plasma plume column in physical space. We propose a slabbing model to compute
the transient ion distribution function by including elastic collisions and charge-exchange contributions. The
plasma is spatially sectioned into a set of contiguous interconnected slabs, transversal to the direction of the
flows carried from the ionization chamber to the exhaust area. For each plasma slab, the kinetic nonlinear
equation is solved by the semi-analytical stable Integral Propagator Method, which allows the computation of the
non-local energy and mass flows of the analysed plasma species. This firstly offered global kinetic treatment
does not require the local thermodynamic equilibrium hypothesis and it establishes a feasible tool able to detect
and describe phenomena, as the merging of two distinguishable ions populations with high and low energy, in
accordance to several experimental results [1,5].
REFERENCES
[1] Zun. Zhang, H. Tang, J. Ren, Zhe. Zhang, J. Wang, Rev. Sci. Instrum. 87, 2016 pp. 113502
[2] J. C. Adam, A. Héron, and G. Laval, “Study of stationary plasma thrusters using two-dimensional fully
kinetic simulations”, Phys. Plasmas, 11, 2004, pp. 295-305
[3] J. M. Donoso and J. J. Salgado, “Nonlinear Fokker–Planck–Landau integral propagator (II): Transport far
from equilibrium,” J. Phys. A, Math. Gen. 39, 2006, pp. 587–600
[4] J. Gonzalez, J. M. Donoso, and S. P. Tierno, ”Three species one-dimensional kinetic model for weakly
ionized plasmas”, Phys. Plasmas, 23, 2016, pp. 062311
[5] J. Gonzalez, S. P. Tierno, J. M. Donoso, "Comparison between experimental Langmuir probes and three
species one-dimensional kinetic simulations", Phys. Plasmas, 23, 2016, pp. 103514
104.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
105.1
Kinetic Analysis of Weakly ionized Plasmas in presence of collecting and emissive walls
Jorge González Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio (ETSIAE), Technical University of Madrid
Plaza del Cardenal Cisneros, 3 28850, Madrid, Spain
José Manuel Donoso Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio (ETSIAE), Technical University of Madrid
Plaza del Cardenal Cisneros, 3 28850, Madrid, Spain
Plasma-wall interaction is an unavoidable phenomenon in plasma science that is always under theoretical
and experimental consideration. This interaction essentially involves charge emission and collection processes
that may perturb the whole plasma inside a device [1]. A wide range of processes appears when a plasma
interacts with a wall, such as the thermionic emission, discharges, that may govern the plasma dynamics and the
confinement. Many fluid [2] and kinetic [3] models attempt to describe this scenario, accounting for various
phenomena under different time and spatial scales. In this work, some kinetic models to describe the dynamics of
Weakly Ionized Plasmas in front of a metallic flat wall are presented. In these plasmas elastic collisions between
charges and neutrals play a relevant role to properly describe the dynamics of the system [4]. Kinetic
descriptions provide an excellent tool to deal with the processes of disparate intensities, time scales and origin
that appear in the plasma-wall system. Phenomena such as the self-consistent electric field and electric density
currents, or the interaction between charges and neutrals, can be deeply analysed at kinetic scale to determine its
relevance in the system dynamics. It is found that a proper description of this complex system is only possible
with a self-consistent study that includes significant possible microscopic effects to elucidate and to understand
macroscopic measurable effects.
To solve the proposed models, the Propagator Integral Method [5] is employed. Since this method
provides a physically meaningful time evolving solution, as a semi-analytical method, it allows to accounting for
many phenomena of disparate time and spatial scales simultaneously, without affecting the method consistency.
REFERENCES
[1] M. Campanell, "Entire plasmas can be restructured when electrons are emitted from the boundaries", Phys.
Plasmas, 22, 2015, pp. 040702
[2] T. Gyergyek, B. Jurčič-Zlobec, M. Čerček, J. Kovačič, "Sheath structure in front of an electron emitting
electrode immersed in a two-electron temperature plasma: a fluid model and numerical solutions of the
Poisson equation", Plasma Sources Sci. Technol., 18, 2009, pp. 035001
[3] J. Sheehan, I. Kaganovich, H. Wang, D. Sydorenko, Y. Raitses, N. Hershkowitz, "Effects of emitted
electron temperature on the plasma sheath", Phys. Plasmas, 21, 2014, pp. 063502
[4] J. Gonzalez, S. P. Tierno, J. M. Donoso, "Comparison between experimental Langmuir probes and three
species one-dimensional kinetic simulations", Phys. Plasmas, 23, 2016, pp. 103514
[5] J.M. Donoso, A. Jimenez, J. Gonzalez, L. Conde, "Integral propagator method as a kinetic operator to
describe discontinuous plasmas", J. Phys. Conf. Ser, 768, 2016, pp. 012004
105.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
106.1
A Study of the Electron Energy Probability Function in the Plume and Channel of a low-power Hall Thruster
Milan Tichý1 1Charles University, Faculty of Mathematics and Physics
Ke Karlovu 3
121 16 Praha 2, Czech Republic
Aude Pétin2, Pavel Kudrna1 and Stéphane Mazouffre2 2Institut de Combustion, Aérothermique, Réactivité et Environnement (ICARE), CNRS
1C Avenue de la Recherche Scientifique
45100 Orléans, France
[email protected], [email protected], [email protected]
The local properties of the electrons in the plasma emitted by a thruster such as the electron density, the
electron temperature and the electron energy distribution function are studied most effectively by electric probes.
Since the power deposition on the probe is high when measuring inside the channel of a Hall thruster, one type
of plasma thruster for spacecraft propulsion, the probes are as a rule fixed on a fast moving translation stage [1].
The electron energy distribution function (EEDF) or the electron energy probability function (EEPF)
belong among the most interesting electron properties, since it describes both the electron density as well as the
electron mean energy also in the case when the EEDF deviates from Maxwellian. Several groups have attempted
the measurements of the EEDF in the thruster channel and plasma plume using the Langmuir probe, e.g. [2,3].
The studied Hall thruster is a 200 W class thruster able to deliver a thrust of 10 mN when operated at
250V and 1.0 mg/s xenon mass flow rate [4]. The thruster was placed inside a 1.8m long and 0.8m in diameter
stainless-steel vacuum chamber. The associated pumping system is composed of a large dry pump (400m3/h), a
200 l/s turbomolecular pump to evacuate light gases and a cryogenic pump with a typical surface temperature of
35 K (8000 l/s) to get rid of the propellant gas. A background pressure of 2×10−5 mbar was achieved in the
working conditions - xenon mass flow rate of 1.0 mg/s and input power of 250W. The Langmuir probe used in
this work was made of a 0.2 mm in diameter tungsten wire. The non-collecting part of the wire was insulated by
a 100 mm long and 2 mm in diameter alumina tube. The length of the collecting part was 1 mm.
The measured EEPF’s confirm the idea that the EEPF near the thruster exit plane is composed of two
groups of electrons [2,5]: The first group is extracted from the hollow cathode by the electric field having a
component along the magnetic field near the cathode region. On arriving at the channel exit, these electrons are
deflected by the strong radial magnetic field in the vicinity of the thruster exit and become involved in a E B
drift motion. This magnetized beam of electrons has in our Hall thruster an energy around 120 eV. The second
group consists of slower electrons produced by ionization inside the thruster channel and accelerated by the
electric field at the channel exit. The EEPF’s measured downstream of the thruster give a logical picture on how
the magnetized beam of electrons merges into the EEPF body. At large distances the EEPF becomes Maxwellian
and one can observe a decrease in both the electron temperature and density due to the expansion process.
REFERENCES
[1] K. Dannenmayer and S. Mazouffre, “Compact high-speed reciprocating probe system for measurements
in a Hall thruster”, Rev. Sci. Instrum. 83, 2012, 123503.
[2] V. Yu. Fedotov and A. A. Ivanov, G. Guerrini, A. N. Vesselovzorov, and M. Bacal, “On the electron
energy distribution function in a Hall-type thruster”, Physics of Plasmas 6, 1999, 4360.
[3] K. Dannenmayer, S. Mazouffre, P. Kudrna and M. Tichy, “The time-varying electron energy distribution
function in the plume of a Hall thruster”, Plasma Sources Sci. Technol. 23, 2014, 065001.
[4] A. Leufroy, T. Gibert, A. Bouchoule, “Characteristics of a permanent magnet low-power Hall thruster”,
Proc. of the 31th International Electric Propulsion Conference (Ann Arbor), IEPC-2009-083, 2009.
[5] F. Taccogna, “Monte Carlo Collision method for low temperature plasma simulation”, J. Plasma Physics
81, 2015, 305810102.
106.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
107.1
Multiprobe Characterization of Plasma Flows for Space Propulsion
Julius Damba
Department of Applied Physics. ETSI Aeronáutica y del Espacio. Universidad Politécnica de Madrid
Plaza Cardenal Cisneros 3, 28040 Madrid, Spain
P. Argente1, P.E. Maldonado2, A. Cervone2, J. L. Domenech-Garret1 and L. Conde1 1 Department of Applied Physics. ETSI Aeronáutica y del Espacio. Universidad Politécnica de Madrid
Plaza Cardenal Cisneros 3, 28040 Madrid, Spain 2 Department of Space Engineering. Delft University of Technology.
Kluyverweg 1, 2629HS Delft. The Netherlands
Plasma engines for space propulsion generate plasma flows (also denominated plasma plumes) having
supersonic ion groups with typical speeds in the order of tens of kilometres per second. The mapping of the
plasma potential, electron and ion densities and temperatures as well as the ion energy distribution function
(IEDF) are important ground tests to study the plasma
expansion process and also the performance of plasma
engines. Diagnostics of plasma streams using a four-grid
retarding potential analyzer (RPA) [1], emissive probe (EP),
Langmuir probe (LP), and Faraday cup (FC) mounted on a 3-
D displaced multiprobe stand is discussed.
The response of such electric probes in relation with
the presence of supersonic ions in the plasma stream will be
explored, specifically the existence of secondary electron
emission due to impact of energetic ions with the RPA
internal surfaces on the voltage–current characteristic curves.
Spatial profiles of the plasma potential and charged
particle densities obtained with LP and EP probes
characterize the length and radial collimation of the plasma plume. The two-peaked IEDFs shown in the figure
above are characteristic of a mesothermal plasma flow [2–4] and can be seen as superpositions of two ion
populations. The low-energy group is constituted by ions with low random speeds whereas fast ions reach
supersonic velocities along a fixed direction. The reduction in peak heights and fast-ion energy losses observed
in the figure provide information concerning the energy relaxation [5–8] length along the engine axis of
symmetry. Furthermore, the relation between the observed energy relaxation lengths and mean free paths
corresponding to the different collisional processes will be discussed.
Finally, we examine the connection between the plasma stream properties and the space propulsion
performance of our ALPHIE (alternative low power hybrid ion engine) plasma thruster.
REFERENCES
[1] C. Bohm, J. Perrin, Rev. Sci. Instrum. 64 (1) (1993).
[2] Zun. Zhang, H. Tang, J. Ren, Zhe. Zhang, J. Wang, Rev. Sci. Instrum. 87 113502 (2016).
[3] Y. Hu, J. Wang, IEEE Transactions on Plasma Science 43 (9) (2015).
[4] M. Merino, E. Ahedo, IEEE Transactions on Plasma Science 43 (1) (2015).
[5] M. Capitelli et al., Chemical Physics Letters 316 (2000) 517–523.
[6] Z. Wang et al., Phys. Plasmas 21, 072703 (2014).
[7] U. Hohenester et al., Eur. Phys. J. B 5, 143–152 (1998).
[8] M. Shihab et al., Appl. Phys. B (2016) 122:146.
107.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
108.1
Langmuir Probe Measurements in the Early Hydrogen Discharge of GLAST-III Tokamak
A. Qayyum, F. Deeba, S. Ahmad, S. Hussain
National Tokamak Fusion Program, 3329 Islamabad, Pakistan
[email protected], [email protected], [email protected], [email protected]
Triple Langmuir probe has been developed and successfully applied for time resolved measurements in
the first hydrogen discharge of GLAST-III spherical tokamak started with electron cyclotron heating (ECH).
Diagnostic measurements provide insights into expected and unexpected physics issues of the initial discharge.
Triple Langmuir probe (TLP) has the ability to give time-resolved measurements of floating potential (Vfloat),
electron temperature (Te), and ion saturation current (Isat ne√kTe). The evolution of ECH-assisted pre-ionization
and subsequent current formation phases in one shot are well envisioned by probe measurements. Probe data
seem to correlate with microwave absorption and subsequent light emission. Intense fluctuations in the current
formation phase advocate for efficient equilibrium and feedback control systems. A noticeable change in the
profile's shape of floating potential, electron temperature, ion saturation current (Isat) and light emission is
observed with changing hydrogen fill pressure and vertical field.
Plots show the effect of vertical field on electron temperature measured by triple Langmuir probe during
the evolution of two phases in one shot. It is clear from probe signals that two region of electron temperature
corresponding to ECH pre-ionization and plasma current formation can be easily recognized. Moreover, plasma
stays for longer time with vertical field corresponding to 40 V charging voltage.
REFERENCES
[1] A. Qayyum, N. Ahmad, S. Ahmad, Farah Deeba, Rafaqat Ali, S. Hussain," Time-resolved measurement
of plasma parameters by means of triple probe", Rev. Sci.Instrum.,84, 2013,pp. 123502
[2] C. Theiler, I. Furno, A. Kuenlin, Ph. Marmillod, A. Fasoli, "Practical solutions for reliable triple probe
measurements in magnetized plasmas",Rev. Sci. Instrum. 82, 2011, pp.013504
0 1 2 3 4 5 6
0
5
10
0
5
10
0
10
20
300
20
40
0
20
40
0
20
40
t[ms]
VF(100V)
Dependence of electron temperature on Vertical field
VF(80V)
VF(60V)
VF(40V)
VF(30V)
Te[e
V]
VF(20V)
Photographic image of GLAST-III Spherical Tokamak
108.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
109.1
Measurements of Densities of Gas Constituents in a Discharge Device with a Large Wall Probe
I. P. Kurlyandskaya, A. A. Kudryavtsev
INTEPH Technologies LLC
Springboro, OH 45066, USA
[email protected], [email protected]
S. F. Adams, J. A. Miles
Air Force Research Laboratory
WPAFB, OH 45433, USA
[email protected], [email protected]
V. I. Demidov, M. E. Koepke
West Virginia University
Morgantown, WV 26501, USA
[email protected], [email protected]
An approach leading to the development of gas analytical detectors has been previously reported [1,2].
This approach is based on the use of a large electric wall probe to measure fine structures associated with atomic
and molecular plasma processes at the high-energy portion of the electron energy distribution function (EEDF)
in the near-cathode plasma. The large-area wall probe provides increased sensitivity of the gas detector.
However, the additional potentials that are necessary to apply to the probe during the measurements can
significantly change the properties of the entire plasma in the discharge [3], thus altering the EEDF, which the
probe is attempting to measure. As a result, each measured EEDF can be associated with a different plasma for
different energies (probe potentials). This is not an issue, though, as the exact knowledge of the undisturbed
EEDF is not really important for measurements of densities of gas constituents. The result of the measurements
can be corrected by calibrating with known gas mixtures. Even though the ratios of the high-energy electron
features in the EEDF change with probe potential, the presence of a specific target gas component can still be
monitored from the measured EEDF.
In this work, a short (without positive column) dc discharge with cold cathode and conducting walls was
used in experiments at gas pressures of a few Torr [1]. For the investigated conditions, the plasma is collisional
and one might expect that maxima corresponding to arising energetic electrons are proportional to the first
derivative of electron current with respect to the probe potentials (collisional probe theory) [4]. However, it is
experimentally shown that the maxima are proportional to the second derivative of electron current with respect
to the probe potentials (as in collisionless theory [4]). The reason for this discrepancy is unknown and still
should be investigated. Measurements have been conducted in Helium-Argon gas mixtures with content of
Argon from 0.002 to 5% and calibration of the device has been demonstrated.
REFERENCES
[1] V. I. Demidov, S. F. Adams, J. Blessington, M. E. Koepke M. E., J. M. Williamson, “Short dc discharge
with wall probe as a gas analytical detector”, Contributions to Plasma Physics, 50, 2010, 808-813.
[2] V. I. Demidov, S. F. Adams, J. A. Miles, M. E. Koepke, I. P. Kurlyandskaya, “Suprathermal Electron
Energy Spectrum and Nonlocally Affected Plasma-Wall Interaction in Helium/Air Micro-Plasma at
Atmospheric Pressure”, Physics of Plasmas, 23, 2016, 103508.
[3] S. F. Adams, E. A. Bogdanov, V. I. Demidov, M. E. Koepke, A. A. Kudryavtsev, I. P. Kurlyandskaya,
“Control of Plasma Properties in a Short Direct Current Glow Discharge with Active Boundaries”,
Physics of Plasmas, 23, 2016, 024501.
[4] V. A. Godyak, V. I. Demidov, “Probe Measurements of Electron Energy Distributions in Plasmas: What
Can We Measure and How Can We Achieve Reliable Results? (Invited review)”, Journal of Physics D:
Applied Physics, 44, 2011, 233001.
109.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
110.1
Spatial Distribution of Plasma Parameters in Gas Aggregation Nanocluster Source
Anna Kolpaková
Dept. of Surface and Plasma Science
Faculty of Mathematics and Physics, Charles University
V Holešovičkách 2
18000, Prague 8, Czech Republic
Artem Shelemin, Pavel Kudrna, Milan Tichý, Hynek Biederman
Charles University
V Holešovičkách 2
18000, Prague 8, Czech Republic
[email protected], [email protected]
Gas aggregation cluster sources (GAS) are widely used for production of nanoparticles (NPs) ranging from
metallic to plasma polymer ones. The special version of GAS based on planar magnetron as a plasma source [1]
has become more popular recently. GAS usually work with pressures at least one order of magnitude higher than
what are typical for magnetrons optimized for deposition [2]. At sufficiently high pressure the material sputtered
from the target creates nanoparticles within the aggregation chamber. These nanoparticles are dragged by the flow
of a carrier gas downstream and transported through an orifice to the substrate located in the deposition chamber
with reduced pressure, where they are physically cooled by adiabatic expansion. For better understanding of
nucleation, formation, and electric charge of NPs there is an urgent need to determine plasma parameters inside
the aggregation chamber.
For that purpose the special “diagnostic GAS” with axially movable magnetron has been constructed [3].
This system is equipped with optical emission spectroscopy, quadrupole mass spectrometry, quartz crystal
microbalance, and probe diagnostic. The last mentioned technique may provide plasma parameters with spatial
resolution in two dimensions by means of radially movable probe.
Different plasma-based methods have been developed that enabled deposition of plasma-polymerized
nanoparticles using RF plasmas. In our case nylon-sputtered nanoparticles were prepared by means of gas
aggregation cluster source based on a planar RF magnetron that involves a low-temperature plasma in the process
of production of nanoparticles. GAS was equipped with a nylon target which was sputtered in pure Ar. Aggregation
chamber pressure was varied, which resulted in two studied situations: (1) discharge without nanoparticles and (2)
discharge with production of nanoparticles in pure argon.
The spatial profiles of plasma parameters were obtained by means of heated probe. Such construction
minimizes the deposition of polymer layer on the probe surface. Heating current kept the probe clean of insulating
nylon films that would otherwise depreciate the probe data.
REFERENCES
[1] H. Haberland, M. Mall, M. Moseker, Y. Qiang, T. Reiners, Y. Thurner, "Filling of micron-sized contact
holes with copper by energetic cluster impact", J. Vac. Sci. Technol. A, 12 (5), 1994, pp. 2925-2930.
[2] P. J. Kelly, R. D. Arnell, "Magnetron sputtering: a review of recent developments and applications",
Vacuum, 56, 2000, pp. 159-172.
[3] A. Shelemin, O. Kylián, J. Hanuš, A. Choukourov, I. Melnichuk, A. Serov, D. Slavínska, H. Biederman,
"Preparation of metal oxide nanoparticles by gas aggregation cluster source", Vacuum, 120, 2015, pp. 162-
169.
110.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
111.1
Determination of Anisotropic Ion Velocity Distribution Function in Intrinsic Gas Plasma. Theory
Aleksandr Mustafaev, Artem Grabovskiy, Oscar Murillo
Saint Petersburg Mining University
21 line of the Vasilievskiy Island, h. 2
199106, Saint Petersburg, Russia
Vladimir Soukhomlinov
Saint Petersburg State University
Universitetskaya emb., h. 7-9
199034, Saint Petersburg, Russia
Ion velocity distribution function (IVDF) researches are vital for a wide range of modern applications:
plasma technologies, ion surface treatment, technology of selective etching and creation of relief by ion
bombardment, new generation of nanoelectronics (single-electron transistors, spintronics, etc) [1, 2]. In this
context, the development of reliable theories for IVDF in different discharges, in particular, in DC self-sustained
discharge plasmas are of special interest.
This paper deals with development of theory for IVDF, based on the analytic solution of the Boltzmann
kinetic equation for ions in the plasma of their parent gas under conditions, when the resonant charge exchange
is the predominant process, and an ion acquires on its mean free path a velocity much higher than the
characteristic velocity of thermal motion of atoms. The presence of an ambipolar field of an arbitrary strength is
taken into account. It is shown that the ion velocity distribution function is determined by two parameters and
differs substantially from the Maxwellian distribution. Comparison of the results of calculation of the drift
velocity of He+ ions in He, Ar+ in Ar, and Hg+ in Hg with the experimental data shows their conformity. The
results of the IVDF calculation correctly describe the experimental data on its measurements.
Analysis of the result shows that in spite of the presence of the strong field, the IVDF’s are isotropic for
ion velocities lower than the average thermal velocity of atoms. With increasing ion velocity, the distribution
becomes more and more extended in the direction of the electric field.
REFERENCES
[1] H. Abe, M. Yoneda and N.Fujiwara. Jpn. J. Appl. Phys. 2008. Vol.47. P. 1435.
[2] Michael A. Lieberman. Bull. of the APS. 2010. Vol. 55. N 7. P. 105.
111.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
112.1
Determination of Anisotropic Ion Velocity Distribution Function on Intrinsic Gas Plasma. Probe Method
Aleksandr Mustafaev, Artem Grabovskiy
Saint Petersburg Mining University
21 line of the Vasilievskiy Island, build. 2
199106, Saint Petersburg, Russia
Vladimir Soukhomlinov
Saint Petersburg State University
Universitetskaya emb., build. 7-9
199034, Saint Petersburg, Russia
The ion velocity distribution function (IVDF) is of interest in cases, associated with the study of
plasmachemical reactions occurring with the participation of ions, the determination of ion mobility in the
plasma object, processes of heating of the neutral plasma component, and a series of others. Among technical
applications, we note modern plasma nanotechnologies, fine ion purification of the surface of products, and the
technology of creating reliefs on the surface owing to selective etching during bombardment by ion fluxes. In
this context, the development of reliable probe methods for IVDF measurements in different discharges, are of
great importance.
Despite the significant amount of theoretical works [1-4], the experimental investigations of IVDF are
almost absent, except paper [5], where IVDF in the plasma of DC discharge was determined. The Doppler shift
of ion lines in the argon discharge was measured spectroscopically at the observation along the discharge axis in
[5], and, judging by its value, a conclusion was made about the average ion velocity, which was on the order of
104 сm/s under the conditions of experiments.
In this paper a new probe method for the IVDF determination was proposed. For the first time, the ion
distribution function over energies and directions of the motion for Hg+ ions in Hg, He+ in He and Ar+ in Ar has
been measured at the arbitrary value of the electric field using the plane one-sided probe. The experiment is
carried out under conditions when the ion velocity, acquired at the mean free path, is on the order of and larger
than the average thermal velocity of atoms and resonance recharging is the dominating process in plasma. The
main requirement, limiting the region of the applicability of the method, is the small thickness of the near-probe
Debye layer in comparison with the probe sizes.
The obtained results make it possible to conclude that, in independent gas discharge plasma, even at
moderate fields, where E/P=10-20 V/(cm∙Torr), the ion distribution function can have noticeable anisotropy and
can strongly differ from the Maxwellian distribution.
REFERENCES
[1] Smirnov B.M., Zh. Tekh. Fiz., 1966, vol. 36, p. 1864.
[2] Perel’ V.I., Zh. Eksp. Teor. Fiz., 1957, vol. 32, p. 526.
[3] Fok V.A., Zh. Eksp. Teor. Fiz., 1948, vol. 18, p. 1048.
[4] Golant V.E., Zhilinskii A.P., Sakharov S.A., Osnovy fiziki plazmy (Fundamentals of Plasma Physics),
Moscow: Atomizdat, 1977.
[5] Frish S.E. and Kagan Yu.M., Zh. Eksp. Teor. Fiz., 1947, vol. 17, p. 577.
112.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
113.1
Feasibility, Strategy, Methodology, and Analysis of Probe Measurements in Plasma under High Gas Pressure
Vladimir Demidov
West Virginia University
White Hall
26501, Morgantown, USA
Mark Koepke, Mikhail Malkov
West Virginia University
White Hall
26501, Morgantown, USA
[email protected], [email protected],
At present, most published probe measurements of electron energy distribution function (EEDF) f() and
electron density n are conducted by using a Langmuir probe and interpreted by using the Langmuir formula [1]
𝑰(𝑽) =𝟐𝝅𝒏𝒆𝑺
𝒎𝟐 ∫ 𝒇(𝜺)(𝜺 − 𝒆𝑽)𝒅𝜺,∞
𝒆𝑽 (1)
where I is the probe current, e is the elementary charge, S is the probe surface, m is the mass of electron, V is the
probe potential and is the electron energy. From Eq. 1 it is simple to obtain the Druyvesteyn formula with
double differentiation over probe potential [1]
𝒇(𝜺) =𝒎𝟐
𝟐𝝅𝒏𝒆𝟑 ×𝒅𝟐𝑰
𝒅𝑽𝟐. (2)
In practice, the application of Eq. 1 and 2 is restricted by an important requirement: the mean free path of
electrons is assumed to be much greater than the probe radius r and Debye length rd. As a result, in noble gases,
the probe method is inapplicable for gas pressure higher than 10 Torr. For the last 50 years, a number of theories
and methods have been developed to extend probe measurements of EEDFs to higher gas pressure [3,4].
However, analysis using most of these theories and methods seldom appears in the literature.
This talk will review existing theories and previous probe measurements of EEDFs at higher gas pressure.
An explanation of whether or not the measurements are realizable and reliable, an enumeration of the most
common sources of measurement error, and an outline of proper probe-experiment design elements that
inherently limit or avoid error will be presented. Additionally, we describe recent EEDF-measurement
developments in higher-pressure plasma conditions, including electron spectroscopy analysis. This summary of
the authors’ experiences gained over decades of practicing and developing probe diagnostics is intended to
inform, guide, suggest, and detail the advantages and disadvantages of probe application in plasma research.
REFERENCES
[1] H. M. Mott-Smith, I. Langmuir, “The Theory of Collectors in Gaseous Discharges”, Phys. Rev. 28, 1926,
pp. 727-763.
[2] M. J. Druyvesteyn, “Der Niedervoltbogen”, Z. Phys. 64, 1930, pp. 781-798.
[3] J. D. Swift and M. J. R. Schwar, Electrical Probes for Plasma Diagnostics, Iliffe Books, London, 1970.
[4] Y. B. Golubovsky, V. M. Zakharova, V. I. Pasunkin, and L. D. Tsendin, “Probe measurements of the
electron energy distribution under diffusion conditions”, Sov. J. Plasma Phys. 7, 1981, pp. 340-344.
113.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
114.1
Current-Voltage and Floating Potential Characteristics of Cylindrical Emissive Probes from a Self-consistent Full-Kinetic Model
Xin Chen
Universidad Carlos III de Madrid
Escuela Politécnica Superior, Avd. de la Universidad 30
28911, Leganés (Madrid), Spain
G. Sánchez-Arriaga
Universidad Carlos III de Madrid
Escuela Politécnica Superior, Avd. de la Universidad 30
28911, Leganés (Madrid), Spain
To model the sheath structure around a cylindrical emissive probe (EP), difficulties arise due to the space-
charge effects and the possible non-monotonic character of the potential profile. For instance, in space conditions,
where probe radius can be comparable to the Debye length (R ≈ λDe) due to low plasma density and the ion
temperature is not negligible compared to electron temperature, it is essential to include the orbital effects and to
solve the non-monotonic potential profile without ambiguity. A full-kinetic model based on Orbital Motion Theory
(OMT) was not available until very recently [1]. The OMT takes advantage of three conserved quantities,
distribution function f, transverse energy E, and angular momentum J, to transform the stationary Vlasov-Poisson
system into a single integro-differential equation. For a stationary collisionless unmagnetized plasma, this equation
describes self-consistently the probe characteristics. A numerical scheme can solve this equation and find the radial
profile of the electrostatic potential for arbitrary parameters. Then, the current versus voltage characteristics and
the floating potential versus probe temperature curves can be computed. The goal of this work is to make extensive
parametric analysis in order to determine the I-V characteristics and the floating-potential-versus-probe-
temperature curves and to analyse their dependence on key dimensionless parameters, for instance, the probe-to-
Debye-length ratio, the probe-to-electron-temperature ratio, the ion-to-electron-temperature ratio, and the work-
function-to-electron-temperature ratio. As shown by the results, the floating potential - at which a cylindrical
emitter collects/emits zero net current – can be positive relative to the plasma potential and depends on the probe
radius, instead of being about one electron temperature below the plasma potential as predicted by the classical
planar theory. The results from the extensive parametric analysis have been used to obtain fitting laws for both I-
V characteristics and the floating potential curves. The former can provide the probe potential at which the
transition between operational regimes (e.g, OML collection, SCL emission) occurs. The latter can be useful for
determining the plasma potential by using the EP floating-potential technique. Besides probe theory and plasma
diagnostics, the results of this work can also benefit space applications and technology such as Low Work function
Tethers (LWTs) for space debris removal [2] and spacecraft charging.
REFERENCES
[1] Xin Chen, G. Sanchez-Arriaga, “Orbital Motion Theory and Operational Regimes for Cylindrical Emissive
Probes”, Phys. Plasmas 24, 2017, pp. 023504.
[2] G. Sanchez-Arriaga, Xin Chen, “Modelling and Performance of Electrodynamic Low-Work-Function
Tethers with Photoemission Effects”, to be published in J. Propul. Power.
114.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
115.1
Current Density Distribution Along the Cylindrical Probe in Magnetized Plasma
Gheorghe Popa
Alexandru Ioan Cuza University, Faculty of Physics
Blvd. Carol I, 11
700506, Iasi, Romania
Claudiu Costin1, Ilarion Mihaila2 1Alexandru Ioan Cuza University, Faculty of Physics
2Alexandru Ioan Cuza University, Integrated Center of Environmental Science Studies in the North-Eastern
Development Region (CERNESIM)
Blvd. Carol I, 11
700506, Iasi, Romania [email protected], [email protected]
Cylindrical probes are frequently used for magnetized plasma diagnostic, being one of the most
affordable tools. Extensive analysis of both theoretical model and experimental technique were published in
many textbooks [1] and general review articles [2]. The presence of a magnetic field induces a strong anisotropy
of the plasma, making the probe characteristic strongly depend on the probe orientation with respect to the
direction of the magnetic field lines. There are two main orientations: along and perpendicular to the magnetic
field lines, but intermediate angles are also possible. The reported experimental results showed that probe
characteristics exhibit different shapes for the two main orientations, even if the same plasma volume was
investigated. In some experimental conditions, even a negative slope might appear in the electronic part of the
probe characteristic when the cylindrical probe is parallel to the magnetic field lines [3]. On the other hand,
Stamate & Ohe showed that the space charge sheath may cause particular focalization of the ions collected by a
negatively biased probe, demonstrating a non-uniform distribution of the current density at the probe surface in
an unmagnetized plasma [4]. To the best of our knowledge, there are no published results concerning the
distribution of the current density along the probe length, when the probe is parallel to the magnetic field lines.
Consequently, the present work reports experimental and simulation results of the distribution of the local
current density along the probe, having the probe bias and the magnetic field strength as parameter. A cylindrical
probe (tungsten wire of 0.5 mm in diameter) was placed in a magnetized plasma column produced in a
previously described experimental device [3]. The probe length was modified by moving the wire along a
ceramic tube, which assures the insulation of the rest of conducting wire within the supporting shaft. The basic
idea is to record the probe characteristic for different probe lengths in an axially uniform plasma region and the
same stationary conditions (typically Ar pressure of 1 mTorr, discharge current intensity of 0.5 A, but variable
magnetic field strength up to 0.45 T). The probe was placed along the axis of the magnetized plasma column,
aligned with the magnetic field lines. Probe characteristics were recorded starting with a plane probe, when only
the top cross section of the W wire is exposed to plasma, followed by cylindrical probes with different lengths
(up to the total length of 5 mm). Under the hypothesis that the local plasma potential does not change along the
probe length, the current density at the probe surface was calculated for each segment of the probe.
REFERENCES
[1] O. Auciello, D.L. Flamm, Plasma Diagnostics: Discharge Parameters and Chemistry, Acad. Press, 2013.
[2] G.F. Matthews, “Tokamak plasma diagnosis by electrical probes”, Plasma Phys. Control. Fusion, 36,
1994, pp. 1595–1628.
[3] I. Mihaila, M. L. Solomon, C. Costin, G. Popa, “On Electrical Probes Used in Magnetized Plasma
Diagnostics”, Contributions to Plasma Physics, 53(1), 2013, pp. 96-101.
[4] E. Stamate, K. Ohe, “On the Surface Condition of Langmuir Probes in Reactive Plasmas”, Appl. Phys.
Lett., 78, 2001, pp. 1-3.
115.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
116.1
Disturbances of ICP Plasmas by Langmuir Probes with Uninsulated Protecting Shields
Valentin Riaby
Research Institute of Applied Mechanics and Electrodynamics (RIAME) of the Moscow Aviation
Institute (National Research University), 5 Leningrad Rd., 125080 Moscow, Russia
Valery Godyak Electrical Engineering and Computer Science Dept., University of Michigan, Ann Arbor, 48109
Michigan, USA and RF Plasma Consulting, Brookline, 02446 Massachusetts, USA
Benjamin Alexandrovich
Plasma Sensors, Brookline, 02446 Massachusetts, USA
Pavel Masherov
RIAME
Vladimir Savinov and Valery Yakunin
Moscow State University named after M.V. Lomonosov, Physical Dept., 119991 Moscow, Russia
[email protected]; [email protected]
Probe diagnostics of xenon inductively coupled plasma (ICP) has been carried out using two cylindrical
classic Langmuir probes. One of them was straight and could move radially and the other, L-shaped one could
move along plasma area and revolve around its axis. The purpose was to study plasma “tablet” 146 mm in
diameter and 39 mm thick at pressure 2 mTorr by measurement of its plasma parameter spatial distributions.
This “tablet” represented one half of gas discharge space that was located in front of an ion extracting grate
(IEG) of an ion thruster model in which an external planar antenna coil enhanced with ferrite core was used.
Such measurements were necessary for correct calculations of IEG accelerating cells and subsequent
manufacturing of this system. Probe measurements were arranged with the automated VGPS-12 probe station of
Plasma Sensors Co., USA that provided accurate plasma diagnostics due to the most advanced achievements of
nowadays’ experimental physics included into its control program and circuit engineering of the VGPS-12 probe
station. Measurements with probes 0.15 mm in diameter and of different lengths resulted in the selection of
probe tip’s length lp=10 mm that practically excluded local plasma perturbations caused by the first probe holder.
Diagnostic results for spatial plasma parameter distributions in the common cross-section showed
noticeable differences of both probe readouts. Their analysis based on the previous authors’ research of large
uninsulated metallic bodies’ behaviour under floating potential in contact with plasmas showed that the said
measurement discrepancies could be caused by use here of grounded, uninsulated externally probe shields that
protected probe circuits against RF interferences. Physical consideration of the grounded probe shields and the
ones under floating potential in contact with plasmas proved that they both behaved as short-circuited,
asymmetrical double Langmuir macro-probes that caused disturbances of the discharge structure decreasing
plasma or discharge currents and plasma ionization level and providing electrical power loss in the probe shields.
So this phenomenon could be considered as the reason for qualitative error fields of probe measurements. Beside
that a combination of two probe forms in the present experiments allowed for determination of quantitative scale
of measurement errors caused by L-shaped probe. In the common plasma “tablet” cross-section a point was
found at its periphery where only L-shaped probe caused disturbances lowering electron temperature and
concentration by up to 15% and plasma potential by about 30%. Besides from the axis to periphery of plasma
“tablet” it decreased plasma floating potential from positive area to zero level and then made it negative.
According to physical essence of this phenomenon, thus found discharge structure damage and plasma
parameter perturbations can be eliminated by deposition of dielectric layer upon probe shields.
116.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
117.1
The Radial-Motion-Only (RMO) and Orbital-Motion (OM) Methods for Calculating Velocity Distribution Functions in a Spherical Probe Scenario
Siegbert Kuhn
Institute for Theoretical Physics, University of Innsbruck
Technikerstrasse 21A
A-6020 Innsbruck, Austria
Alif Din
Theoretical Physics Division, PINSTECH
P.O. Nilore, Islamabad
44000, Islamabad, Pakistan
We consider the time-independent collisionless plasma-probe transition (PPT) region around a negatively
biased non-emissive spherical probe, extending from the probe radius p
r to the presheath-entrance radius p s
r .
The particle species involved are thermal electrons and cold ions entering the PPT region at p s
r . Their velocity
distribution functions (VDFs) are denoted by , ,s
r tf r v v , with ,s e i the respective species index and
,r t
v v the radial and tangential velocity components, respectively.
The VDF of a particle species essentially moving in the radial direction can be calculated in the “radial-
motion-only (RMO)” approximation ( 0t
v ), whereas that of a particle species with a non-negligible
tangential velocity spread requires application of the full “orbital-motion (OM)” method. While the former is
fairly straightforward, the latter is based on the concept of “trajectory integration” [1], structurally represents a
boundary-value problem and turns out to involve some tricky mathematics.
In this paper, the general formalism and the ensuing equations for the RMO and OM methods will be
presented and discussed in detail. Then, these methods will be specifically applied to calculating the VDFs of the
cold ions and the thermal electrons, respectively, in the entire PPT region. Ultimately, the Poisson equation
appropriate for the scenario considered will be set up and solved numerically [2] to obtain the potential profile in
the sheath and presheath regions at moderate negative values of the probe bias.
REFERENCES
[1] S. Kuhn, “The Physics of Bounded Plasma systems (BPS's): Simulation and Interpretation”, Contrib.
Plasma Phys., 34 (4), 1994, pp. 495–538.
[2] A. Din and S. Kuhn, “Numerical Matching of the Sheath and Presheath Solutions for a Spherical Probe in
Radial-Motion theory”, Phys. Plasmas, 21, 2014, pp. 103509-1–6.
117.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
118.1
Some Experiments with the Tunnel Probe in a Low-Temperature Magnetized Plasma
Jernej Kovačič
Reactor Physics Department, Jožef Stefan Institute
Jamova cesta 39
SI-1000, Ljubljana, Slovenia
Tomaž Gyergyek
University of Ljubljana, Faculty of Electrical Engineering
Tržaška cesta 25
SI-1000, Ljubljana, Slovenia
tomaž[email protected]
James P. Gunn
CEA, IRFM
F-13108 Saint-Paul-Lez-Durance, France
Experiments were performed using a Tunnel Probe (TP) inside the weakly-ionised plasma of the Linear
Magnetized Plasma Device (LMPD). The TP is designed as a concave probe, which annihilates the problem of
sheath expansion in the ion branch of the I-V characteristic. As the ion saturation current is consequently well
defined, the plasma density can be more accurately calculated and the ratio between the ion saturation currents on
the two collectors (ring and the back-plate) can be used to derive the electron temperature. The TP has repeatedly
been used with success on the former Tore-Supra tokamak and will be used on its upgraded version – the WEST
tokamak – as well [1, 2], however it was never used in a low-temperature plasma.
We studied the feasibility of the TP use in a low-temperature plasma for direct measurements of plasma
temperature and density. The various probe characteristic dimensions, such as the distance between the two
collectors, the aperture size and the probe radius were varied to see influence of the individual probe feature. We
also varied the level of magnetization of the charged particle species, the background gas pressure (which
influences the electron energy distribution function), the plasma density (important for the ratio between the λD
and the ion Larmor radius). The sensitivity of the probe alignment to the magnetic field lines was also studied. We
found, that the ion saturation current does not necessarily saturate and that the probe works according to
expectations only in a limited amount of regimes.
.REFERENCES
[1] J. P. Gunn et al, "Tunnel Probes for Measurements of the Electron and Ion Temperature in Fusion Plasmas
", Rev. Sci. Instrum., 75, 2004, pp. 4328-4330
[2] J. P. Gunn et al, “Simultaneous DC Measurements of Ion Current Density and Electron Temperature Using
a Tunnel Probe”, J. Phys.: Conf. Series, 700, 2016, 012018
118.2
Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017
Authors index
Adamas S. F. 109.1 Popa G. 115.1 Ahmad S. 108.1 Qayyum A. 108.1 Alexandrovich B. 116.1 Riaby V. 116.1 Argente P. 107.1 Sánchez-Arriaga G. 114.1 Biederman H. 110.1 Savinov V. 116.1 Cervone A. 107.1 Schneider B. S. 101.1, 103.1 Chen X. 114.1 Schrittwieser R: 101.1, 103.1 Conde L. 104.1, 107.1 Shelemin A. 110.1 Costea S. 101.1, 103.1 Soukhomlinov V. 111.1, 112.1 Costin C. 115.1 Spolaore M. 102.1 Damba J. 107.1 Tichy M. 106.1, 110.1 Deeba F. 108.1 Vasilovici O. 101.1, 103.1 Demidov V. I. 109.1, 113.1 Yakunin V. 116.1 Din A. 117.1
Domenech-Garret J. L. 107.1
Donoso J. M. 104.1, 105.1
Godyak V. 116.1
Gonzáles J. 104.1, 105.1
Grabovskiy A. 111.1, 112.1
Gunn J. P. 118.1
Gyergyek T. 118.1
Hussain S. 108.1
Ilarion M. 115.1
Ionita C. 101.1, 103.1
Koepke M. E. 109.1, 113.1
Kolpaková A. 110.1
Kovačič J. 118.1
Kudrlyandskaya I. P. 109.1
Kudrna P. 106.1, 110.1
Kudryavtsev A. A. 109.1
Kuhn S. 117.1
Lundin D. 101.1
Maldonando P. E. 107.1
Malkov M. 113.1
Masherov P. 116.1
Mazouffre S. 106.1
Miles J. A. 109.1
Minea T. 101.1
Murillo O. 111.1
Mustafaev A. 111.1, 112.1
Pétin A. 106.1
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