WITCH status + Simbuca, a Penning trap simulation program S. Van Gorp, M. Breitenfeldt, V. De Leebeeck,T. Porobic, G. Soti, M. Tandecki, F. Wauters, N

WITCH status + Simbuca, a Penning trap simulation program

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S. Van Gorp, M. Breitenfeldt , V. De Leebeeck,T. Porobic, G. Soti, M. Tandecki, F. Wauters, N. Severijns (K.U.Leuven, Belgium),

M. Beck, P. Friedag, C. Weinheimer (Univ. Munster, Germany),M. Beck (Univ. Mainz, Germany),

V. Kozlov, F. Gluck (Univ. Karlsruhe, Germany),D. Zakoucky (NPI-Rez, Prague, Czech)

Motivation

EXP: |CS/CV| < 0.07 |CT/CA| < 0.09

H = gP

j =S;V;A ;T ;P (ÃpOj Ãn)(ÃeOj (Cj +C

0

j °5)Ãn) +h:c:H = g

X

j =S;V;A ;T ;P

(ÃpOj Ãn)(ÃeOj (Cj +C

0

j °5)Ãn) +h:c: (1)H = gX

j =S;V;A ;T ;P

(ÃpOj Ãn)(ÃeOj (Cj +C

0

j °5)Ãn) +h:c: (1)

=>Search for scalar (or Tensor) Interactions

Low energy (couple 100 eV)! Need for scattering free source

Simon Van Gorp - Scientific meeting - 16.02.20112/21

m

Experimental Setup


35Ar: voltage dependent discharge

Still a small ionization is visible which depends onthe retardation barrier voltage…

Nov 2009 run on 35Ar

6 seconds spectrumRetardation voltage (0 -> 500V) from 1.5-3.5s

Increase (instead of decrease) in count rate was observed.


g-> create e- ionization collisions with gas molecules secondary electrons and positive ions; secondary emissionon cathode due to positive ion impact more electrons more ionization collisions more secondary electrons and ions

avalanche, self sustained discharge

+

+

e +

+

+

e

e

e

e

e

e

e

ionization

secondary electron emission

- -

Unwanted discharges: Townsend dischargeTownsend discharge (bad vacuum, with or without magnetic field)


trapped e- spend long time between cathode and anode large pathlength increased probability for discharge, even in good vacuum

Penning Discharge (good vacuum, with magnetic field)

+

+

e ++

+

e

ee

e

eee

ionization

secondary electron emission

- -

Unwanted Penning Traps


Unwanted Penning Trap in WITCH

Retardation barrier for ions=

Potential well for e-

Installation of a wire in the spectrometer.If an e- hits this wire it will be picked up by the power supply and lost.

Simon Van Gorp - Scientific meeting - 16.02.2011

7/21

The spectrometer wire

Measurement on 144Eu (June 2010) with the wire installed

-> no ionization was seen

Before: 40MBq 60Co 20% effect after: 40MBq 241Am

450V0V

spec

tro

met

er

po

ten

tial

(V

)

450V0V


The spectrometer wire

Good correspondence between simulation and experimental data.

The creation of the ionization can be stopped with installing a wire.

We understand the ionization effect andMore tests with a centered wire will be done

sp

ec

tro

me

ter

po

ten

tia

l (V

)

450V0V

2.7 MBq 137Cs source4-5% effect seen BUT- Bad vacuum conditions- 90x more intense source than 60Co- Wire is still not in the centre


WITCH Status - Planning June 2009:

• Measurement with 144Eu, unfortunately a mixed cocktail beam from ISOLDE. Too low statistics to extract a recoil spectrum.

November 2009:• Faulty thermocouple while baking caused a bad temperature read-

out which resulted in a bad connections to all trap electrodes…• Magnetic Shielding works. WITCH can work in parallel with REX-

ISOLDE! January 2010:

• New traps installed Now – May/June:

• Testing of the traps and the wire with a more intense source. May-June 2011

• Measuring a recoil spectrum on 35Ar


Simulation Motivation Data analysis by particle tracking routine to recreate a spectrum. A good

understanding of the source of ions is needed.

WITCH: 106-7 ions per cycle -> Computer simulations are dominated

by the Coulomb interaction calculationSolution: use a Graphics card to simulate Coulomb interactions. Development of

the Simbuca simulation package

Parameters to characterize • Temperature (=Energy)• # ions• Position distribution


Chamomile scheme: practical usage

Function provided by Hamada and Iitaka [2]:

Gravitational force ≈ Coulomb Force

Conversion coefficient:

Needed: - 64 bit linux - NVIDIA Graphics Card that supports CUDA - CUDA environment v3.x

Not needed: - CUDA knowledge - …

2 2 grav coulomb e

Mm QqG k F r F rr r

cunbody1_force(xj, mj, xi, eps, ai, nmax, nmax)

2

;eCoulomb

q ka ai

m


[2]: http://arxiv.org/abs/astro-ph/0703100 , 2007

GPU vs CPU•GPU blows the CPU away. The effect becomes more visible with even more particles simulated.•Simulating 4000 ions with a quadrupole excitation for 100ms with buffer gas. Takes 3 days with a GPU compared to 3-4 years with a CPU!

GPU improvement factor CPU and GPU simulation time


Simbuca overview Simbuca is a modular Penning Trap simulation package that can be applied to simulate:

• Charged particles (+/- /N charges) • Under the influence of B and E fields• With realistic buffer gas collisions• Coulomb interaction included• Can run on GPU and CPU• http://sourceforge.net/projects/simbuca/ • http://dx.doi.org/10.1016/j.nima.2010.11.032


Simulation of Ion Motion in a Penning trap with realistic BUffer gas collisions and Coulomb interaction using A Graphics Card.

Usage of the program

WITCH• Behavior of large ion clouds• Mass separation of ions

Smiletrap (Stockholm)• Highly charged ions• Cooling processes

ISOLTRAP (CERN)• In-trap decay• Determine and understand the mass selectivity in a Penning trap

ISOLTRAP(Greifswald)• isobaric buncher, mass separation and negative mass effect

CLIC (CERN)• Simulate bunches of the beam


Penning traps

B: radial confinement

E: axial confinement

Three independend motions: * fast cyclotron w+ (mass dependent)

* Harmonic oscillation at wz

* slow magnetron w- (mass independent)

These eigenmotions can be excited independently Possibility of mass selectivity/purification


Quadrupole excitation Mass selective excitation on the frequency wc = q.B/m

Continuous conversion between Magnetron and cyclotron radii.The cyclotron radius is cooled by Buffer gas collisions-> mass selective centering/cooling of ions

The size of the final ion cloud one can

reach is influenced by the Coulomb

interaction


Quadrupole excitation – movie

Argon (150 ions ) and Chlorine (ions) mixture1) 10ms wc excitation quadrupole excitation

2) 5ms w- dipole excitation

3) wc excitation quadrupole excitationSimon Van Gorp - Scientific meeting - 16.02.2011

18/21

frequency scans• The effect of the Coulomb interaction is not yet understood• All highly depended on mass, amplitudes, times of excitations…


# particles / 100

Conclusion The WITCH experiment

• New traps installed• We understand the small ionization trap in the spectrometer• More tests with a (centered) wire will be done before the next beam time• The Magnetic shielding works -> WITCH can work in parallel with REX-ISOLDE

The Simbuca Code• A big simulation-time gain to calculate Coulomb interactions on a GPU• A new tool to investigate how large ion clouds are behaving and to explain

observed frequency shifts• Necessary for WITCH and being used by other groups• Will be compared to experimental data in upcoming months


Thank you for your attention

Acknowledgements

Retardation spectrometer

A potential barrier is applied and the #ions going over the barrier are counted with an MCP detector.

This potential barrier is changed -> A spectrum is measured.


WITCH History


2006 first recoil spectrum measured 124In• First notice of discharges• Electrodes could not be operated as intended

2007 physics run 35Ar• Discharges returned• Stable 35Cl+ domination in the beam• Trap-halflife of 35Ar+ was 8 ms• Electrodes could not be operated as planned

2008• Technical improvements

• Vacuum upgrade• All-metal buffer gas

23/24

spec

trom

eter

pot

entia

l (V)

500V

0V

Discharges: example


Huge increase in count rate Can happen in couple of hours/minutes Unexpected Some discharges only happen in combination with a g source

The energy barrier was set to +500 V in the first 3.4 seconds. After this the spectrometer switches to 0 V and it awaits the next cycle.

3 types of discharges1)Townsend discharge (bad vacuum)2)Vacuum breakdown (sharp electrodes)3)Penning Discharge (combination of B and E field)

24/24

Coulomb interactions

Simon Van Gorp – TCP Saariselkä- 14.04.2010

Coulomb force scales with O(N2) Tree methods (Barnes Hut, PM, P3M, PIC, FMM)

reduces this to O(N log N)

25/12

2coulomb e

QqkF rr

Space is divided in nodes. Which are subdivided A node has the total charge and mass, and is located on the centre of mass. Approx. long range force by aggregating particles

into one particle and use the force of this one particle

Scaled Coulomb Force puts more weight to the charge of one ion to simulate more ions. Works well [1]

[1]: D. Beck et al, Hyp. Int. 132, 2001

Why a GPU?


26/12

GPU -high parallelism-very fast floating point calculations-SIMD structure (pipelining!)

Stream processor≈ CPU= Comparable with a factory assembly line with threads being the workers

Geforce 8800 GTX

Michaël Tandecki - Werkbespreking – 09/12/2009

Secondary ionization (2009) July 2009; measurement with same 60Co as

before (70% of the source strength, t1/2 ~ 1925d)

Clear effect on background 20% higher when spec@ 450 V

only 2.5 cpsMuch more decays areexpected for 35Ar

450V

0V

spec

tro

met

er p

ote

nti

al (

V)


Charge exchange (with Ar)

Situation in 2007:

• ‘Charge exchange half-life’ in REXTRAP; 75 ms

in WITCH; 8 ms (= not enough to cool)


Charge exchange: improvements

NEG pump

He-57 gas bottle

All-metal reducer

Needle valve

To turbo pump

Full-range gauge

All-metal angle valves


Most important issues with 35Ar in 2007

Isobaric contamination from 35ClDuring the run: 25 times more Cl than Ar

Charge exchange with buffer gasWe couldn’t cool the ion cloud, becausethe ions were neutralized before being cooled

Secondary ionization‘Noise’/discharges showing up when switching the spectrometer


Electropolishing the electrodes

before after

2 cm

Most probably the reason why the huge discharge in the spectrometer is gone.

Discharge with g-source gone!

31/24

Chamomile scheme


Calculating gravitational interactions on a Graphics Card via the Chamomile scheme from Hamada and Iitaka (in 2007).

32/12

Why a GPU?-parallelism!-only 20 float operations-CUDA programming

language for GPU’s

i-particles piece available for each ‘assembly line’j-particles piece presents itself sequentially to each lineforce is the output of each line

[2]: T. Hamada and T. Iitaka, arXiv.org:astro-ph/0703100, 2007


Improving the vacuum Vacuum system

dry scroll pumps instead of rotary pumpsextra valves in front of turbos for ‘vacuum safety’

Detectorelectropolishing of surrounding electrode

Spectrometerredesign of some electrodeselectropolishing of re-acceleration electrodesNEG foil around biggest retardation electrode

Trapsbetter Ti (>< Al) structurebuffer gas system is ‘all-metal’ nowNEG foil + resistive heater around the traps

VBLteflon electrode connections goneinstallation of NEG coated chambersnon-UHV compatible materials gone (Zn, …)

HBLuntouched


High voltage / re-acceleration





Optimal settings normal settings Recently obtainedSPACCE01 -2 kV -1.4 kV -2 kVSPACCE02 -10 kV -2 kV -8 kV SPEINZ01 -200 V -500 V -500VSPDRIF01 -10 kV -550 V -8 kV SPDRIF02 -10 kV -7 kV -9 kV

SPACCE01

SPACCE02

SPEINZ01

SPDRIF01

SPDRIF02

Detector MCP

Compensation magnet


37/12

Simbuca overview Simonion is a modular Penning Trap simulation package.

Reading external fieldmaps Trap excitations 3 different integrators 2 buffergas routines Can run on CPU and GPU Compile with g++ or icpc A root analysis file is provided A Makefile is provided

http://sourceforge.net/projects/simbuca/

Documents

WITCH status + Simbuca, a Penning trap simulation program S. Van Gorp, M. Breitenfeldt, V. De Leebeeck,T. Porobic, G. Soti, M. Tandecki, F. Wauters, N