[email protected], IEM CSIC, Spaindigital.csic.es/bitstream/10261/167616/1/EPS-Plasmas Praga 2018-Tanarro-Plenary Lecture...• Since the discovery of CH and CN radicals in ISM ( 1940),

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45th Conf. Plasma PhysicsJuly 2‐6 2018, Prague

R. J. Peláez, J. L. Doménech, V. J. Herrero, B. Alemán, C. Bermúdez, S. I. Ramírez,E. Moreno, K. Lauwaet, G. Santoro,

J. A. Martín‐Gago, J. R. Pardo, J. Cernicharo, F. Beltrán, J. M. HernándezP. de Vicente, J. D. Gallego and the Team of Yebes Observatory

Funding: Spanish grants CSD2009‐00038 “ASTROMOL”, FIS2016‐77726‐C3‐1‐PEU grant ERC‐2013‐Syg 610256 “NANOCOSMOS”

[email protected], IEM‐CSIC, Spain

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• Interstellar molecular clouds are the place of star formation and molecules play a key role in this process.

• Molecules cool efficiently the gas heated by gravity collapse and reduce the ionization degree much more efficiently than atoms, contributing to decouple the gas from electromagnetic fields.

• Molecular species are the product of a rich chemistry, and their study allows to find out relevant properties of these regions.


INTRODUCTION

• Since the discovery of CH and CN radicals in ISM (1940), more than 200 molecular species have been found by spectroscopic methods, containing up to 70 atoms.

• 80% have been detected with radio astronomy, that is,mm wavelengths, by their pure rotational transitions.

• Valid for NON symmetric species, with dipole moment ≠ 0.


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• Radio astronomy is very useful for the characterization of very cold IS regions, where only molecular levels very close to the ground state are populated.

• It provides very high spectral resolution.

• It is particularly convenient to study molecular clouds, as comparedwith visible and UV, due to the different opacities of the media to be crossed by the radiation.


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Dark molecular clouds are composed mainly of H2 and Dust(15% mass of galaxies)

UV and visible ( large opacity )

FIR and Radio( good transparency )

Dark molecular cloud Barnard 68 , T 16 K

Unlike UV and visible light, scattered or absorbed by interstellar dust, longer wavelengths can pass through the microscopic particles.


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Earth’s Atmosphere presents high transmittance for radio waves, which increases markedly with increasing altitude and dryness

Wavelength

Atmosph

ericTran

smission

300 250 200 150 100 50

Frequency (GHZ)

1.0

0.8

0.6

0.4

0.2

0.0

South PoleAtacama desert, Chile (very dry)Hanoi, Vietnam(very humid)

O2 O2

H2O

O3

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Nowadays, the most recent generation of radio‐telescopes, like ALMA, provides more sensitivity and angular resolution than all the previous

ones to search molecules in space.

ALMA (Atacama Large Mm/sub‐mm Array)Atacama Desert (Chile), 2400 m altitude


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PRESENT WORK: USE OF RADIO ASTRONOMY TECHNIQUES

TO DETECT ROTATIONAL EMISSIONS IN LABORATORYCOLD PLASMAS AT ROOM TEMPERATURES.

40 m Radio Telescope of Yebes Observatory, Guadalajara, Spain


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102 103 104 105 106 107 108 109

10-2 10-1 100 101 102 103 104 1051010

1015

1020

1025

1030

1010

1015

1020

1025

1030

Ne (

m- 3

)

E (eV)

T (K)

Fusion reactor core

Flame

Laser focus

SolidsLiquids

Interplanetaryspace

Solar corona

Solar photosphere

Solar core

Jupiter core

Si crystal

Lightning

Fusion plasma edge

ArcGlow

Discharges

PLASMA

ColdPlasmas

IonospheresAuroras

IntestellarMedia (ISM)

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Glow Discharge ReactorsLength 100 cm

Density 2.5 x 1015 cm‐3 (0.1 mbar)

Column density in line of sight:Stable species 10 17 cm‐2

Radicals (1%) 1015 cm‐2

Ions (0.01%) 1013 cm‐2

Molecular CloudsLength 1019 cm

Density 104‐105 cm‐3

Column density in line of sight

H2 1022 cm‐2

CO 1018 cm‐2

HCN, HCO+, C2H, CN, CS 1014 cm‐2


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BASIC EXPERIMENTAL SCHEME


13.56 MHz Generator

+ MatchingREACTOR

Hot Load300 K

Diff. PumpQuadr.

Mass Spec.

Gas Input

COLD LOAD

Gas Output

UV & visibleEmission

Coil

PLASMAEMISSION

BackgroundEmission

• Versatile Reactor devoted to study Gas Phase, Plasma Chemistry in ICP discharges & Photochemistrywith UV lamps.

• HEMT Heterodine Receivers for broad band, high resolution, rotational emission spectroscopy.

• Cold Load at the backend to minimize mm background radiation (+ movable Hot Load for calibration).

Additional equipment:

• Quadrupole Mass Spectrometry • Visible Emission Spectroscopy

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Very weak signalP 10‐15 W, F 30‐300 GHz

HeterodyneDetectionAmplification

Frequency Down ConversionProcessing by FFTS

Gain 120 dB IF 2 GHz

RadioReceiver

Low NoiseAmplifier Mixer IF

Amplifier

LocalOscillators( 1 … n )

IFoutput

IF FilterFast Fourier TransformSpectrometer

15 K, He Cryostat


Careful noise reduction is essential

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TWO CAMPAIGNS OF EXPERIMENTS TWO INDEPENDENT EQUIPMENTS

1.‐ Proof of concept in the 40 m Radio Telescope of YebesObservatory (Spain) (2016/2017).

2.‐ New set‐up devoted to Laboratory Astrophysics in the Yebes Observatory location (2018).


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1. PROOF OF CONCEPT IN THE 40 m RADIO TELESCOPE OF YEBES OBSERVATORY


100 steps

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Prototype Reactor

• Designed to be used in the 40 m telescope • Dimensions: 40 cm length x 25 cm diameter• Gas flow or static conditions 10‐2 ‐ 10‐1 mbar• RF discharge: 13.56 MHz, 5‐60 W• Windows: 9.6 mm thickness Fused Silica or 70 m Upilex polyimide film, non parallel between them.

Plasma Chemistry

Photochemistry

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HEMT Heterodine Q band Receiverused in the 40 m Radio Telescope

• Spectral Range = 30‐50 GHz • Instantaneous Bandwidh = 2 GHz• 2 FFTS (65536 channels/u) Resolution = 38 kHz

Two Sampling Modes for Noise Reduction• ON/OFF technique (sample in/sample out) the common one in Astronomy

• Frequency Switching ±24 MHz (for plasma experiments)

Reactor

Mirrors System

Receiver


300 250 200 150 100 50

Frequency (GHZ)

Atmosph

ericTran

smission

1.0

0.8

0.6

0.4

0.2

0.0South Pole, Atacama, ChileHanoi, Vietnam

Q band 16

Cold Load

• 40 m Antenna towards the Zenith (89o)(clear blue sky) TB = 42 K at 45 GHz

• Load of liquid N2 (cloudy or rainy weather) TB = 77 K


Mirrors

N2 Load

RemovableMirror

Reactor

Mirrors

Signal fromAntenna

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70 m UpilexWindows

Implosion Risk!


Tests of interference effects of the windows on the background signal

70 m Upilex

9.6 mm thickness Fused Silica

• 9.6 mm Fused Silica: similar thickness to Q band wavelengths (6‐9 mm).• 70 m Upilex: much lower interferences, but dangerous for warping at

vacuum and giving rise occasionally to loud implosions.

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• The discharge didn’t induce any coupling with the radio receivers. • Astronomical observation of a SiO maser signal from the star TX

Cam through the reactor showed identical results with PLASMA ON/OFF.

Test of interferences between Receivers and RF discharge

TX CamSiO, v=1

PLASMA ON

PLASMA OFF

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• 80% of molecular species discovered in the ISM contain at least one carbon atom Study focused on different carbon containing molecules of astrophysical interest.

Particular showcases:

• Rotational emissions of OCS and its plasma products. • Species produced with O2 plasmas used for reactor cleaning


EXPERIMENTAL RESULTS

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Line profile and intensity vs. OCS gas pressure

PartialPressure(mbar)0.300.150.060.007

Tempe

rature

(K)

Voigt Profile: Pressure

broadening

Doppler Profile: Temperaturebroadening


Low working pressures lead to significantly higher resolution, with not so large intensity loss

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OCS 0 J=4‐3

OCS 0 J=4‐30.50 mbar

Plasma Off

0.15 mbar Plasma Off

On/Off

Frequency switching 0.15 mbar

Plasma On(5 W)

OCS, 0.5 mbar, no plasma• On/Off Acquisition • The 2 J=4‐3 doublet of OCS

and OC34S ( 0.025 mbar) were detected.


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OCS, 0.15 mbar, plasma (5 W) • Frequency Switching (±24 MHz)• OCS dissociation 70%• 2 /0 intensities evince a rotational temperature change:

Plasma Off (300 K) vs. Plasma On (450 K)

CS radical produced in OCS plasma, 0.15 mbar, 50 W

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2

1

0

T B(K)

‐5 0 5(‐0) (MHz)

0 = 48990.957 MHz

CS J=1‐0

During the discharge, Sulphur was deposited on the walls, which got very dirty and smelly


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O2 cleaning discharge after Sulphur & Carbondeposition by the former OCS plasma: SO2 generation

• 0.1 mbar O2, 60 W.

• SO2 (40 bar), detected in 2 min.

• SO2 was produced first, and quickly disappeared in favor of CO and CO2

SO2142,12 – 133,1

47913.427 MHz)


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Concentrations are estimated with MADEX Code (Cernicharo 2012)


Proof of concept published in Astronomy & Astrophysics

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Lessons learned from the former experimentsin the radio telescope

• Radio‐astronomy techniques can be used successfully to perform rotational spectroscopy and chemical simulations in laboratory.

• Estimated sensitivity can be as good as 0. 1 bar of CS in the Q band. Better sensitivity and broader spectral range is expected in the W band.

• Special care is needed to get the lower background temperatures and best observing procedures.

• Windows material should provide as low interferences and noise as possible and allow safe operation => Teflon seems the best choice


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2.‐ NEW SET‐UP FOR LABORATORY ASTROPHYSICS Yebes Observatory

Former Campaignsin 40 m Telescope

New ExperimentsLocation

Control room of an 13.5 m old telescope covered with spherical dome (1980’s)


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EQUIPED WITH Q AND W BAND RECEIVERS A LARGER REACTOR AND CRYOGENIC COLD LOADS


New Reactor (1 m x 0.6 m)16 FFTS

Q & W band Radio‐Receiversin a single housing

Mirrors

FRONT ENDSIDE VIEW

RF Source & Matching

Gas Mixing

VacuumPumps

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Teflon corrugated windows

optimized for W band

New Reactor

Cold Load: He Cryostat at 17 K

Mirrors

BACK END

Visible Spectrometer

MassSpectrometer

29Plasma

RECEIVERS

• Two receivers in a single cryostat set‐up: Q band = 32‐50 GHz ( = 9.1 – 6 mm)W band = 72‐116 GHz ( = 6.4 – 2.7 mm) with 3 sub‐bands: L (72‐90 GHz), M(84‐102 GHz), H (98‐116 GHz)

• Q band and one of W sub‐bands can operate simultaneously.Each one is connected to 8 FFTS2.5 GHz, 1.5 x 106 channels

Instantaneous Bandwidth = 18 GHz Resolution = 38 kHz

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300 250 200 150 100 50

Frequency (GHZ)

Atmosph

ericTran

smission

1.0

0.8

0.6

0.4

0.2

0.0

Q ban

d

W ban

d



1. OFF/ON technique: Cell empty / Cell full 2. Frequency Switching (± 37 MHz) 3. Load switching : without cell evacuation, but using the hot

load and an additional cold load next to the receivers as references

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SAMPLING MODES FOR NOISE REDUCTION

Mobile Mirror to switch between Hot Load and Internal Cold Load

in front of the Receiver

EXPERIMENTAL RESULTS (May‐June 2018)

Precursors and plasma products of pure gases and mixtures containing carbon atoms, like for example:

• CH3CN• CH4 + N2• O2 (used for reactor cleaning)

Very low pressures ( tens of bar) can be used at stable plasma conditions, reducing line‐widths and improving signal detection.


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CH3CN without discharge, 25 bar, 11 min/sub‐band

All vibrational excited states < 0.1 eV detected

13 C/12 C = 1% 0.25 bar CH3

13CN15 N/14 N = 0.4% 0.1 bar CH3C15N

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Remaining CH3CN(0.5 bar) > 80% precursor dissociation

Plasma of CH3CN (3 µbar, 20 W, 80 s)HC3N (0.006 bar) & HCN (0.4 bar) produced

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Reactor cleaning with 20 µbar, O2 plasma, after CH3CN discharge

HCN and CO produced in the discharge were detected.


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HCN (0.085 bar) = 2.98 D

CO (8 bar) = 0.12 D Dirtiness deposited

on the reactor walls

Plasma of 13 µbar CH4 + 19 µbar N2 , 20 W (40 min)Main component of Titan atmosphereCH3CN, HCN and HC3N produced in the discharge were detected.

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HCN (0.4 bar)CH3CN (0.01 bar)

HC3N (0.015 bar)


Reactor cleaning with O2 plasma after the CH4 + N2 dischargeCO (5 µbar) , HCN (0.1 µbar) and HNCO (0.3 µbar) were detected


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(0.3 µbar)

0.1 µbar

(5 µbar)

1. The technique is very useful to measure frequencies of molecular species with high accuracy and sensitivity, and to derive their rotational constants with high precision.

2. It allows to detect and identify minor products in cold plasmas, even with very complex precursor mixtures, and contribute to the identification of the kinetic processes.

3. These experiments open new and very encouraging opportunities to laboratory astrophysics and to possible collaborations between astronomers and plasma specialists.


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Thank you very muchfor your attention!

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Documents

[email protected], IEM CSIC, Spaindigital.csic.es/bitstream/10261/167616/1/EPS-Plasmas Praga 2018-Tanarro-Plenary Lecture...• Since the discovery of CH and CN radicals in ISM ( 1940),