witch status + simbuca, a penning trap simulation program s. van gorp, m. breitenfeldt, v. de...
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WITCH status + Simbuca, a Penning trap simulation program
sdsd
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
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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.
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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)
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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
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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.
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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
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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
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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
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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
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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
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[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
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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
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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
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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
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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
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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
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frequency scans• The effect of the Coulomb interaction is not yet understood• All highly depended on mass, amplitudes, times of excitations…
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# 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
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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.
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WITCH History
Simon Van Gorp - Scientific meeting - 10.06.2009
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
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spec
trom
eter
pot
entia
l (V)
500V
0V
Discharges: example
Simon Van Gorp - Scientific meeting - 10.06.2009
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)
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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?
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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)
Michaël Tandecki - Werkbespreking – 09/12/2009
Charge exchange (with Ar)
Situation in 2007:
• ‘Charge exchange half-life’ in REXTRAP; 75 ms
in WITCH; 8 ms (= not enough to cool)
Michaël Tandecki - Werkbespreking – 09/12/2009
Charge exchange: improvements
NEG pump
He-57 gas bottle
All-metal reducer
Needle valve
To turbo pump
Full-range gauge
All-metal angle valves
Michaël Tandecki - Werkbespreking – 09/12/2009
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
Simon Van Gorp - Scientific meeting - 10.06.2009
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
Simon Van Gorp – TCP Saariselkä- 14.04.2010
Calculating gravitational interactions on a Graphics Card via the Chamomile scheme from Hamada and Iitaka (in 2007).
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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
Simon Van Gorp - Scientific meeting - 10.06.2009
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
Michaël Tandecki - Werkbespreking – 09/12/2009
High voltage / re-acceleration
Michaël Tandecki - Werkbespreking – 09/12/2009
High voltage / re-acceleration
Michaël Tandecki - Werkbespreking – 09/12/2009
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
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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/