1. Progress on high pressure gas filled RF cavity test program K. Yonehara & A. Tollestrup APC, Fermilab 3/4/121MAP collaboration meeting 2012

2. Milestone 800 MHz Vacuum cavity 800 MHz HPRF cavity P. Hanlet et al., Proceedings of EPAC’06, TUPCH147 3/4/122MAP collaboration meeting 2012 2002: R.P. Johnson and D. Kaplan proposed new RF concept and obtained SBIR/STTR fund First high pressure RF (HPRF) cavity test was done at Lab G Demonstrated that GH 2 can absorb a dark current (energy) 2006: Demonstrated HPRF cavity under B field at MTA 2011: First beam test done at MTA Goal of RFOFO 25 MV/m at 3 T

3. Review scientific goal of Summer 2011 beam test RF field must be recovered in few nano seconds 1.DC to 800 MHz, Hydrogen breaks down at E/P = 14. It indicates we can use DC data as a framework to explain results. Need different frequency measurements to test frequency dependence 2.Electrons move with a velocity,. Current. Power dissipation due to electrons in phase with RF and dissipate energy through inelastic collisions = Measurements with beam verify mobility numbers and verify our loss calculation 3.Electrons recombine with positive ions and removed. If this is very fast they don’t load cavity, if slow cause trouble Beam measurement will give the recombination rate 4.Solution: use electronegative gas(es) to capture electrons and form negative ions Beam measurement will verify attachment rate 5.A+e →A - heavy negative ions. How long do these hang around and do they cause the breakdown voltage of the cavity to be lowered Beam measurement will give necessary answers From MAP Winter 2011 Done We’ve investigated item 2 to 5 from summer 2011 beam test 3/4/123MAP collaboration meeting 2012 Approved analytically No freq. dep. up to 800 MHz What we’ve learned?

4. MTA beam line & apparatus 400 MeV H - beam: Primary 1.5 × 10 12 H - /beam pulse Max. 20 % of beam penetrates through collimators 7.5 μs beam pulse length H - → H + at vacuum window & cavity wall (5 mm SS material at entrance) 3/4/124MAP collaboration meeting 2012 See Mukti’s poster RF field: 0, 10, 20, (25), 30 MV/m GH 2 pressure: 500, 800, 950 psi Beam int.: Full, 1/7, 1/10 N 2, H 2, H 2 /SF 6, H 2 /N 2

5. Compare 950 MeV/c proton (400 MeV proton) vs 200 MeV/c muon beams in HPRF cavity dE/dx[0.2 GeV/c] = 4.4 MeV/g cm 2 μ beam in GH 2 proton beam dE/dx[0.95 GeV/c] = 6.2 MeV/g cm 2 3/4/125MAP collaboration meeting 2012 dE/dx of 400 MeV proton from Fermilab LINAC is comparable with 200 MeV/c muon (nominal p in cooling channel) Same beam bunch structure But, different beam intensity (6.3 10 14 μ/pulse (MC) vs 3 10 11 p/pulse(LINAC)) and different beam pulse (60 ns/pulse (MC) vs 7.5 μs/pulse (LINAC)) Study of beam-induced plasma in high grad RF field is deliverable

6. Analysis model Equivalent circuit Envelop of RF PU Envelop of Toroid PU Beam on 3/4/126MAP collaboration meeting 2012 RF power loss in plasma Be aware!! This is NOT a real muon accelerator cavity It is a test cell that has a small stored energy Beam loaded 800 MHz high pressure RF cavity # of protons in cavity GH 2

7. Measure energy gain of single electron from RF field dw dw can be accurately determined at very small n e (βn e ∼ αn e ∼ 0) Preliminary Time [μs] 3/4/127MAP collaboration meeting 2012 if we know # of protons β: Recombination by H n + α: Electron capture by something else GH 2

8. Electronegative gas doped hydrogen Preliminary α becomes very large number with 0.01 % SF 6 Real electron density growth is shown on right-hand side plot Expected capture time (α -1 ) is 10 -9 ~ 10 -10 s from capture cross section The growth rate seems to be slower than constant α It indicates complicated SF 6 chemistry 3/4/128MAP collaboration meeting 2012 H 2 /SF 6 Blue solid line: α -1 = 12 10 -9 s Yellow solid line: α -1 = 9 10 -6 s

9. Expected electron capture rate in SF 6 doped H 2 gas 3/4/129MAP collaboration meeting 2012 Preliminary Estimated electron capture time from equilibrium RF field Real α -1 should be faster (τ ~ 10 -10 s)

10. Beam parameters in MC cooling channel Muon collider (L ≥ 10 34 cm -2 s -1 ) # of muons per second: 6.24 10 14* muons/sec Repetition rate of beam pulse: 15 ** Hz # of bunches: 12 bunches/beam pulse # of muons per bunch: 6.24 10 14 /15/12 = 3.5 10 12 Bunch gap: 5 ns (200 MHz) Total beam pulse length: 5 × 12 = 60 ns B field: 4 ~ 15 Tesla E field: 16 MV/m * 4 MW proton beam 0.2 μ/proton ** It is 60 Hz in SNS Baseline design 3/4/1210MAP collaboration meeting 2012

11. Evaluate RF power dissipation in MC cooling channel cavity For MC scheme (preliminary): GH 2 pressure = 180 atm Peak E = 16 MV/m RF frequency = 200 MHz τ capture -1 = α ≈ 0 s -1 β = 1.2 10 -8 cm 3 /s (past H 3 + recombination data) cf of dw = 0.2 (extrapolate from measurement, see slide 20) Beam size = 20 cm in radius RF power loss: dP loss = 9.6 J/m/beam bunch Total RF power loss: Ploss = 657 J/m/beam pulse It is twice larger than the stored energy of 200 MHz cavity (313 J/m). 3/4/1211MAP collaboration meeting 2012 See Ben’s poster for more detail 0.01 % SF 6 doped H 2 : τ capture = α -1 = 1.5 10 -9 s (from measurement) ⇒ dP loss = 10 J/m/beam bunch ⇒ Total loss = 120 J/m/beam pulse CAD drawing of helical cooling channel HPRF cavity Helical solenoid coil K. Yonehara et al., Proceedings of IPAC’10, MOPD076

12. RF power dissipation and E drop in MC cooling channel Pure H 2 (300 K) 3/4/1212MAP collaboration meeting 2012 preliminary RF dissipation in plasma RF field drop 200 MHz HCC β = 1.2 10 -8 cm 3 /s Pure H 2 (300 K) 200 MHz HCC β = 1.2 10 -8 cm 3 /s E/E0 goes negative Pure H 2 (77 K) preliminary 200 MHz HCC β = 1.2 10 -7 cm 3 /s Pure H 2 (77 K) 200 MHz HCC β = 1.2 10 -7 cm 3 /s Rep rate 60 Hz Rep rate 15 Hz preliminary

13. RF power dissipation and E drop in MC cooling channel H 2 /O 2 (0.1 %) (77 K) 3/4/1213MAP collaboration meeting 2012 preliminary RF dissipation in plasma RF field drop 200 MHz HCC β = 1.2 10 -7 cm 3 /s α -1 = 15 10 -9 s H 2 /O 2 (0.1 %) (77 K) 200 MHz HCC β = 1.2 10 -7 cm 3 /s α -1 = 15 10 -9 s Rep rate 60 Hz H 2 /SF 6 (0.01 %) (300 K) preliminary 200 MHz HCC β = 1.2 10 -7 cm 3 /s α -1 = 1.5 10 -9 s H 2 /SF 6 (0.01 %) (300 K) 200 MHz HCC β = 1.2 10 -8 cm 3 /s α -1 = 1.5 10 -9 s Rep rate 15 Hz

14. Application of HPRF cavity in NF Neutrino factory (n ν ≥ 10 13 s -1 ) # of muons per second: 6.24 10 14 muons/sec Repetition rate of beam pulse: 60 Hz # of bunches: 25 bunches/beam pulse # of muons per bunch: 6.24 10 14 /60/25 = 4.2 10 11 Bunch gap: 5 ns (200 MHz) Total beam pulse length: 5 × 25 = 125 ns B field: 3 Tesla E field: 16 MV/m cf of dw: 0.7 (from measurement, see slide 20) Beam size: 20 cm in radius 3/4/1214MAP collaboration meeting 2012 J.C. Gallardo & M.S. Zisman, Proceedings of IPAC’10, WEPE074 20 atm Pure GH 2 preliminary 200 MHz cooling channel β = 1.2 10 -8 cm 3 /s α -1 = 1.5 10 -9 s 200 MHz cooling channel β = 1.2 10 -8 cm 3 /s α -1 = 1.5 10 -9 s H 2 /SF 6 (0.01 %) 60 Hz rep rate

15. Summary First beam test done in summer 2011 Many hydrogen plasma physics were evaluated by comparing with experimental result – Pressure dependence on the energy gain of single electron – Larger recombination rate than what we expected (one order of magnitude) – Study electronegative gas effect Electron capture rate seems 10 times lower than what we expected Evaluated HPRF cavity for MC and NF applications – MC: It seems to work with electronegative gas – NF: It seems to works with electronegative gas 3/4/12MAP collaboration meeting 201215

16. Next beam test Take beam loading data with wider E/p range – E/p [V/cm/Torr] = 0.6 ~ 2.0 ~ 11.6 ~ 12.1 (red: new E/p range, black: original one) Take beam loading data with different doped gas – O 2 : Capture electrons – CO 2 : Slow down electron motion Precise measure beam intensity with new toroid system 3/4/12MAP collaboration meeting 201216

17. People who currently work on this analysis 3/4/12MAP collaboration meeting 201217 M. Chung 1, B. Freemire 2, M. Jana 1, L. Jenner 3, R.P. Johnson 4, M. Leonova 1, A. Moretti 1, D. Neuffer 1, M. Popovic 1, T. Schwarz 1, Y. Torun 2 1 Fermilab 2 Illinois Institute of Tech 3 Imperial college London 4 Muons, Inc

18. Extra slides 3/4/12MAP collaboration meeting 201218

19. RF cavity was fully recovered in 15 Hz operation RF PU at beam on RF PU at next RF pulse Beam pulse (1 pulse/min) RF pulse (15 Hz) 3/4/1219MAP collaboration meeting 2012 No plasma left over in next RF cycle

20. Drift velocity of electron in Hydrogen gas Green & Magenta: Experiment Red: Eye guide Blue: Heylen’s formula Heylen’s empirical formula (DC field): [cm/s] v drift is well reproduced at E/p < 14 V/cm/mmHg Range of HPRF cavity beam test 3/4/1220MAP collaboration meeting 2012

21. Correction factor for energy gain of single electron in HPRF cavity dw can be accurately determined from Bethe’s formula C correction factor Error bar: Fitting × 0.7 Small correction factor at low E/p → Less RF power loss (right direction) Preliminary We see the discrepancy between Heylen’s empirical drift velocity formula and our experiment Time [μs] E = 10 MV/m @ 950 psi E = 25 MV/m @ 500 psi 3/4/1221MAP collaboration meeting 2012

22. Past measurements of H 3 + recombination cross section There are many measurements and various results! It looks that the Hydrogen recombination community agreed that one recombination theory (Jahn-Teller) and one experimental (ISR, 2002) result are the most reliable Recombination rate from Jahn-Teller model But, the theory seems to valid at low energy region K < 0.1 eV. There is a structure at K > 0.1 eV. Our interesting K is above 0.1 eV. B. A. Tom et al, J. Chem. Phys. 130, 031101, 2009 Range of HPRF cavity beam test 3/4/1222MAP collaboration meeting 2012

23. Evaluate production of ionized electron term 2/1/12HPRF cavity Wednesday meeting23 C. J. Bakker and E. Segre, Phys. Rev. 81, 4, 489, 1951 Reliability of Bethe Bloch formula at low energy Bethe’s theory is rely on the Born approximation method Many theories mentioned that the Bethe’s theory is valid at the incident proton energy higher than 1 MeV J. W. Whopper et al, Phys. Rev. 121, 4, 1123, 1961

24. Pressure & temperature dependence on H n + recombination rate 2/1/12HPRF cavity Wednesday meeting24 We expect that the recombination rate will be improved in cold temperature & high pressure GH 2. J. Glosik et al, Phys. Rev. A79, 052707, 2009 A. Pysanenko et al, Czechoslovak. Jour. Phys, Vol.52, D681, 2002