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WITCH status + Simbuca, a Penning trap simulation program

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. Severijns (K.U.Leuven, Belgium) , M. Beck, P. Friedag, C. Weinheimer (Univ. Munster, Germany) , M. Beck (Univ. Mainz, Germany) ,

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WITCH status + Simbuca, a Penning trap simulation program

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  1. 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. 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)

  2. Motivation EXP: |CS/CV| < 0.07 |CT/CA| < 0.09 =>Search for scalar (or Tensor) Interactions Low energy (couple 100 eV)! • Need for scattering free source 2/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  3. ~7m ExperimentalSetup 3/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  4. 35Ar: voltage dependent discharge • Nov 2009 run on 35Ar • 6 seconds spectrum • Retardation voltage (0 -> 500V) • from 1.5-3.5s • Increase (instead of decrease) in count rate was observed. • Still a small ionization is visible which depends on • the retardation barrier voltage… 4/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  5. + e + ionization e e + e e + e e secondary electron emission e + Unwanted discharges: Townsend discharge - - Townsend discharge (bad vacuum, with or without magnetic field) g-> create e- ionization collisions with gas molecules  secondary electrons and positive ions; secondary emission on cathode due to positive ion impact  more electrons  more ionization collisions  more secondary electrons and ions avalanche, self sustained discharge 5/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  6. - e + ionization + + e e e + e e e secondary electron emission e + Unwanted Penning Traps Penning Discharge (good vacuum, with magnetic field) - trapped e-spend long time between cathode and anode large pathlength  increased probability for discharge, even in good vacuum 6/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  7. 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

  8. The spectrometer wire • Before: 40MBq 60Co 20% effect after: 40MBq 241Am spectrometer potential (V) 450V 450V 0V 0V • Measurement on 144Eu (June 2010) with the wire installed • -> no ionization was seen 8/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  9. The spectrometer wire • 2.7 MBq137Cs source • 4-5% effect seen BUT • - Bad vacuum conditions • - 90x more intense source than 60Co • - Wire is still not in the centre spectrometer potential (V) 0V 450V • Good correspondence between simulation and experimental data. • The creation of the ionization can be stopped with installing a wire. • We understand the ionization effect and • More tests with a centered wire will be done 9/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  10. 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 10/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  11. Simulation Motivation • Data analysis by particle tracking routine to recreate a spectrum. A good understanding of the source of ions is needed. • Parameters to characterize • Temperature (=Energy) • # ions • Position distribution • WITCH: 106-7 ions per cycle • -> Computer simulations are dominated by the Coulomb interaction calculation • Solution: use a Graphics card to simulate • Coulomb interactions. Development of the Simbuca simulation package 11/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  12. 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]: http://arxiv.org/abs/astro-ph/0703100 , 2007 12/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  13. 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 13/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  14. Simbucaoverview • 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. 14/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  15. 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 15/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  16. 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 16/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  17. 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 17/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  18. Quadrupole excitation – movie • Argon (150 ions ) and Chlorine (ions) mixture • 10ms wc excitation quadrupoleexcitation • 5ms w- dipole excitation • wc excitation quadrupole excitation 18/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  19. frequency scans • The effect of the Coulomb interaction is not yet understood • All highly depended on mass, amplitudes, times of excitations… # particles / 100 19/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  20. 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-timegain 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 20/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  21. Acknowledgements Thank you for your attention

  22. 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. 22/21 Simon Van Gorp - Scientific meeting - 16.02.2011

  23. 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 500V spectrometer potential (V) 0V Simon Van Gorp - Scientific meeting - 10.06.2009

  24. 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 discharges Townsend discharge (bad vacuum) Vacuum breakdown (sharp electrodes) Penning Discharge (combination of B and E field) Simon Van Gorp - Scientific meeting - 10.06.2009

  25. Coulomb interactions • Coulomb force scales with O(N2) • Tree methods (Barnes Hut, PM, P3M, PIC, FMM) • reduces this to O(N log N) • 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 Simon Van Gorp – TCP Saariselkä- 14.04.2010

  26. Why a GPU? • 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 Simon Van Gorp – TCP Saariselkä- 14.04.2010

  27. 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 cps Much more decays are expected for 35Ar spectrometer potential (V) 450V 0V Michaël Tandecki - Werkbespreking – 09/12/2009

  28. 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

  29. Charge exchange: improvements He-57 gas bottle All-metal reducer Needle valve To turbo pump NEG pump All-metal angle valves Full-range gauge Michaël Tandecki - Werkbespreking – 09/12/2009

  30. 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, because the ions were neutralized before being cooled • Secondary ionization‘Noise’/discharges showing up when switching the spectrometer Michaël Tandecki - Werkbespreking – 09/12/2009

  31. 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! Simon Van Gorp - Scientific meeting - 10.06.2009

  32. Chamomile scheme • Calculating gravitational interactions on a Graphics Card via the Chamomile scheme from Hamada and Iitaka (in 2007). • 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 line • force is the output of each line [2]: T. Hamada and T. Iitaka, arXiv.org:astro-ph/0703100, 2007 Simon Van Gorp – TCP Saariselkä- 14.04.2010

  33. Improving the vacuum • Vacuum systemdry scroll pumps instead of rotary pumps extra valves in front of turbos for ‘vacuum safety’ • Detector electropolishing of surrounding electrode • Spectrometer redesign of some electrodes electropolishing of re-acceleration electrodes NEG foil around biggest retardation electrode • Traps better Ti (>< Al) structure buffer gas system is ‘all-metal’ now NEG foil + resistive heater around the traps • VBLteflon electrode connections gone installation of NEG coated chambers non-UHV compatible materials gone (Zn, …) • HBLuntouched Simon Van Gorp - Scientific meeting - 10.06.2009

  34. High voltage / re-acceleration Michaël Tandecki - Werkbespreking – 09/12/2009

  35. High voltage / re-acceleration Michaël Tandecki - Werkbespreking – 09/12/2009

  36. High voltage / re-acceleration SPACCE01SPACCE02SPEINZ01SPDRIF01SPDRIF02Detector MCP Compensation magnet Optimal settings normal settings Recently obtainedSPACCE01 -2 kV -1.4 kV -2 kV SPACCE02 -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 Michaël Tandecki - Werkbespreking – 09/12/2009

  37. Simbucaoverview • 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/ Simon Van Gorp – TCP Saariselkä- 14.04.2010

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