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)

Motivation EXP: |C S /C V | < 0.07 |C T /C A | < 0.09 =>Search for scalar (or Tensor) Interactions Low energy (couple 100 eV)!  Need for scattering free source Simon Van Gorp - Scientific meeting /21

mm Experimental Setup Simon Van Gorp - Scientific meeting /21

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

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 + + e e e e e e e e ionization secondary electron emission - - Unwanted discharges: Townsend discharge Townsend discharge (bad vacuum, with or without magnetic field) Simon Van Gorp - Scientific meeting /21

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 e e e e e e ionization secondary electron emission - - Unwanted Penning Traps Simon Van Gorp - Scientific meeting /21

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 /21

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

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 and More tests with a centered wire will be done spectrometer potential (V) 450V0V 2.7 MBq 137 Cs source 4-5% effect seen BUT - Bad vacuum conditions - 90x more intense source than 60 Co - Wire is still not in the centre Simon Van Gorp - Scientific meeting /21

WITCH Status - Planning June 2009: Measurement with 144 Eu, 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 35 Ar Simon Van Gorp - Scientific meeting /21

Simulation Motivation Data analysis by particle tracking routine to recreate a spectrum. A good understanding of the source of ions is needed. WITCH: 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 Parameters to characterize Temperature (=Energy) # ions Position distribution Simon Van Gorp - Scientific meeting /21

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 - … Simon Van Gorp - Scientific meeting /21 [2]: http://arxiv.org/abs/astro-ph/

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 factorCPU and GPU simulation time Simon Van Gorp - Scientific meeting /21

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 Simon Van Gorp - Scientific meeting /21 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 Simon Van Gorp - Scientific meeting /21

Penning traps B: radial confinement E: axial confinement Three independend motions: * fast cyclotron w + (mass dependent) * Harmonic oscillation at w z * slow magnetron w - (mass independent) These eigenmotions can be excited independently Possibility of mass selectivity/purification Simon Van Gorp - Scientific meeting /21

Quadrupole excitation Mass selective excitation on the frequency w c = 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 Simon Van Gorp - Scientific meeting /21

Quadrupole excitation – movie Argon (150 ions ) and Chlorine (ions) mixture 1) 10ms w c excitation quadrupole excitation 2) 5ms w - dipole excitation 3) w c excitation quadrupole excitation Simon Van Gorp - Scientific meeting /21

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

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. Simon Van Gorp - Scientific meeting /21

WITCH History Simon Van Gorp - Scientific meeting first recoil spectrum measured 124 In First notice of discharges Electrodes could not be operated as intended 2007 physics run 35 Ar Discharges returned Stable 35 Cl + domination in the beam Trap-halflife of 35 Ar + was 8 ms Electrodes could not be operated as planned 2008 Technical improvements Vacuum upgrade All-metal buffer gas 23/24 spectrometer potential (V) 500V 0V

Discharges: example Simon Van Gorp - Scientific meeting  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 1)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 Coulomb force scales with O(N 2 ) Tree methods (Barnes Hut, PM, P 3 M, PIC, FMM) reduces this to O(N log N) 25/12 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? Simon Van Gorp – TCP Saariselkä /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 60 Co as before (70% of the source strength, t 1/2 ~ 1925d)  Clear effect on background 20% higher when 450 V only 2.5 cps Much more decays are expected for 35 Ar 450V 0V spectrometer potential (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 35 Ar in 2007 Isobaric contamination from 35 Cl During the run: 25 times more Cl than Ar Charge exchange with buffer gas We couldn’t cool the ion cloud, because the ions were neutralized before being cooled Secondary ionization ‘Noise’/discharges showing up when switching the spectrometer

Simon Van Gorp - Scientific meeting Electropolishing the electrodes beforeafter 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 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 line force is the output of each line [2]: T. Hamada and T. Iitaka, arXiv.org:astro-ph/ , 2007

Simon Van Gorp - Scientific meeting Improving the vacuum Vacuum system dry 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 VBL teflon electrode connections gone installation of NEG coated chambers non-UHV compatible materials gone (Zn, …) HBL untouched

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 obtained SPACCE01 -2 kV-1.4 kV -2 kV SPACCE kV -2 kV -8 kV SPEINZ V -500 V -500V SPDRIF kV -550 V -8 kV SPDRIF kV -7 kV -9 kV SPACCE01 SPACCE02 SPEINZ01 SPDRIF01 SPDRIF02 Detector MCP Compensation magnet

Simon Van Gorp – TCP Saariselkä /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