Conclusions

1. Conclusions • The TPC idea, now 32+ years old, continues to evolve, with new ideas and innovations! Paris TPC Symposium

2. Conclusions • The TPC idea, now 32+ years old, continues to evolve, with new ideas and innovations: • “It is a bit shocking when one’s children grow up and do things that you can’t do, that you didn’t imagine they could do, and that they probably shouldn’t be able to do” Paris TPC Symposium

3. From 10 to 10,000 particles Paris TPC Symposium

4. e+ e– collisions PEP-4/9 TOPAZ DELPHI ALEPH pp collision (CDF) pp collisions (FNAL) v - N collisions T2K ICARUS N - N collisions NA49 STAR ALICE Rare decays and events   e  (TRIUMF)   decay (UCI, EXO,…) WIMP - N collisions Space & Astronomy  imaging  polarimetry TPC Applications Paris TPC Symposium

5. TPC Instrumentation • Advances in gas gain devices: • GEM • Micromegas • Advances in electronics • Signal processing ASICs • Ultra-low noise design • Hybrid systems: gas gain + pixel ASICs • Negative Ion TPC - NITPC (DRIFT) Paris TPC Symposium

6. Concept for - Spectroscopy with High Energy Resolutionbased on aNegative-Ion TPC (NITPC) David Nygren LBNL Paris TPC Symposium

7. Concept: • The negative-ion TPC: • proposed by Jeff Martoff (Temple U) • demonstrated by the DRIFT collaboration • Basic notion: • Capture event images on electronegative gas • Drift ion images to readout plane • Strip electrons from ions in high electric field • Amplify signals with standard MWPC plane Paris TPC Symposium

8. NITPC Characteristics • Diffusion of ions during drift is thermal:  = 0.07 mm (L/E)1/2{L in cm, E in kV/cm}  = ~70 m for 100 cm drift, E = 1 kV/cm  = ~210 m for 100 cm drift, E = 0.1 kV/cm • Drift of ions can be very slow: v = E ~ 0.1 - 10 m/second HV can be rather low: 10’s of kV • Event track length: 2 Mev  or -conversion: ~10 -15 cm in 20 bar xenon  Event images drift in over ~1 second Paris TPC Symposium

9. Event Detection Concept: • Since ion drift is so slow, fast detectors like micromegas or GEM may be able to detect the arrival times of individual ions; if so: • Energy of an event is determined by counting up all associated detected pulses; if so: • Energy resolution would approach the limit imposed by fundamental statistics. Paris TPC Symposium

10. “Intrinsic” Energy Resolution • Example: 136Xe  decay event: E = 2.5 MeV • high-pressure xenon gas (HPXe) •  = 0.1 g/cm3 (~20 bars) • Total event track length: 10 - 15 cm • Total ionization = E/W = N • N ~115,000 electron/ion pairs N2 = FN (F = Fano factor: 0.05 < F < 0.17) let F = 0.17 N = (FN)1/2 ~ 140 electrons rms (with Penning effect - could be much less) Paris TPC Symposium

11. “Intrinsic” Energy Resolution… E/E  2.35 x N/N(FWHM)  E/E = 2.9 x 10-3FWHM (Xe) ************************* The Gold Standard:Germanium diode E/E ~ 1.25 x 10-3 FWHM (Ge) Optimally, this xenon detector would have an energy resolution only ~2.3 x worse than germanium Paris TPC Symposium

12. Tracking “Requirement” • Choose pad/pixel diameter D to give a suitable number of distinct Hits along track • For 136Xe decay example, choose: D = 4 mm; this provides 160/4 = 40 “Hits” per 2.5 MeV • Pad size directly affects ion arrival rate… and: Presence of pad edges means that pulse sharing will occur, with impact for counting statistics: zero, single, double & triple counting of pulses can occur Paris TPC Symposium

13. Event Detection “Requirement” Individual electron signals must be detected with “high efficiency” • “high efficiency” preserves E/E • ion density is not “too high” - (pile-up) • gas gain is adequate - (finite threshold) • pulse-pair resolution is “good” - (rise/fall) Paris TPC Symposium

14. “High Detection Efficiency” • It appears that the impact of the total detection inefficiency is very mild: • Assume a low averageefficiency:  = 95% • Then the loss n = N x (1- ) = 5750 ions • If gaussian, the variation L = n1/2 = 76 • In quadrature: = (762 + 1402)1/2 = 160 E/E = 3.3 x 10-3FWHM (Xe) E/E is increased by only ~13% ( = 95%) Paris TPC Symposium

15. 2. Ion density at readout plane? • Primary ionization density: • dE/dx of  particle - well understood • Diffusion - very “small” - negligible! • Gas density and average Z - can be chosen • “Secondary” ionization density: • Capture length  of electronegative gas additive • Can be chosen to match needs - very flexible!  “fuzz factor” of tracks may be optimized! Paris TPC Symposium

16. Ion density at readout plane?… • Goal: ion density is ~independent of angle • Track density: 115,000/150 mm = 766/mm • Choose a fuzz factor  of D mm • track smeared along E-field: e-z/ • density for tracks || to E-field unchanged • density for tracks  to E-field stretched out • Diffusion during drift changes the numbers slightly Paris TPC Symposium

17. 3. Adequate Gas Gain? •  depends on gain spectrum of gain device Crudely: • Assume electronic noise of ~200 e- rms • Set threshold at 4 = 800 e- (noise-less) • If a S/N of 15 is chosen, then • Gas gain needed = 12,000 (rough estimate)  High gas gain probably necessary Paris TPC Symposium

18. 4. Pulse-pair Resolution OK? • Estimate an arrival time distribution; • Choose a very slow drift velocity: v = 400 mm/s Density for tracks || to E-field unchanged by fuzz factor • (766 ions/mm)x(400mm/s) = ~3 x105 ions/second • Crudely: ~3 ions every 10 s Density for tracks  to E-field ~ unchanged if D =  • (766 ions/mm x 4/4) x(400mm/s) = ~3 x105/mm-second • Crudely: ~3 ions every 10 s Paris TPC Symposium

19. Pulse-pair Resolution OK?… • Roughly, ions arrive at a rate of 3 x 105/s over an pad/pixel area of about 12 mm2 , independent of track orientation. • If a 3% loss is allocated, this corresponds roughly to a pulse-pair resolution t = 100 x 10-9 seconds This seems possible… Paris TPC Symposium

20. Electronics • Each readout channel is equipped with a counter that integrates for ~100 s. • Average count: 30 (~8 bits adequate) • Time-stamps added (10 kHz clock!) • No counts, no output datum • Buffers included, as needed, for DAQ Paris TPC Symposium

21. Summary of Issues • Is all this possible at high pressure? • Must be able to strip electrons from ions • Must realize fairly high gas gain • High speed performance OK? • Gas gain device must produce fast signals • Front-end electronics must have high bandwidth • Must realize low electronic noise or high gas gain • Low noise probably requires one pixel per channel • Maybe some exploration of new ions is needed? Paris TPC Symposium

22. Perspective • Choosefuzz factor to match pixel  • Detector response then becomes roughly independent of track orientation • MeV  tracks imaged with good 3-D quality ~40 hits/ event with space ~0.2 mm rms Paris TPC Symposium

23. Perspective • Energy resolution appears to be excellent and very forgiving of efficiency losses, even up to 10%! • Penning mixture could lead to greater ionization, with even smaller intrinsic fluctuations • F ~ 0.05  N = (FN)1/2 ~ 80 electrons rms • Energy resolution would be comparable to Ge diode! • Need a molecule with IP around 7 eV (TEA?) Paris TPC Symposium

24. “Energy Resolution” • Optimistically: • Intrinsic fluctuations: 80 e– rms • Inefficiency fluctuations: 80 e– rms • In quadrature: 113 E/E ~ 2.30 x 10-3 FWHM (Xe) E/E ~ 1.25 x 10-3 FWHM (Ge) Paris TPC Symposium

25.  decay: daughter atom tagging • If significant ion mobility differences exist, and if even one single electron is liberated promptly at the cathode HV plane, it will be detected at the readout plane. • This highly constrained “echo” pulse is a “birth detection” with equivalent power to the Ionization Imaging Chamber scheme. Paris TPC Symposium

26. Summary • It seems possible to realize large-scale, high- resolution. direction-sensitive / detection if the gas-gain + electronic performance is achieved. • Possible applications: • Large-area  spectroscopy @ room temperature, with energy resolution competitive with Ge diodes • 0-v double beta decay searches in 136Xe • Compton -cameras in low-rate applications • …… Paris TPC Symposium