Beam Test of a High-Pressure GH 2 -Filled RF Cavity (for efficient muon beam cooling for a MC or NF, since the low-Z ionization energy-loss absorber and RF occupy the same real estate ) K. Yonehara APC, Fermilab 8/22/111All Experimenters Meeting, K. Yonehara

Collaboration C. Ankenbrandt, A. Bross, M. Chung, G. Collura, G. Flanagan, B. Freemire, P. Hanlet, R. P. Johnson, D. Kaplan, G. Kazakevitch, A. Kurup, A. Moretti, J. Mukti, M. Neubauer, D. Neuffer, M. Notani, G. Pauletta, M. Popovic, A. Tollestrup, Y. Torun, R. Sah, T. Schwarz, + AD external beam division + AD mechanical design + Machine shop + Rad/Hydrogen safety committees + Director/Division Heads + Operators & Technicians Supported for many years by the DOE HEP SBIR-STTR program 8/22/112All Experimenters Meeting, K. Yonehara Muons, Inc.

Series of talk in past AEM MTA and Muons Inc. Experiments - Pierrick Hanlet, May 9, 2005 MTA and Muons Inc. Experiments - Pierrick Hanlet, May 9, 2005 High Pressure MuCool RF Cavities in B Field - Pierrick Hanlet, May 22, 2006 High Pressure MuCool RF Cavities in B Field - Pierrick Hanlet, May 22, 2006 High Pressure rf Cavities - Alvin Tollestrup, June 28, 2010 Beam-Induced Electron Loading Effects in High Pressure rf Cavities - Moses Chung, July 19, 2010 Muon Collider Cavity Breakdown Processes - Katsuya Yonehara, August 23, 2010 Muon Collider Cavity Breakdown Processes - Katsuya Yonehara, August 23, /22/113All Experimenters Meeting, K. Yonehara Muons, Inc.

Problem: B field effect on RF cavity Gradient in MV/m Peak Magnetic Field in T at the Window >2X required field X A. Bross, MC’11 Required E in cooling channel Data were taken in an 805 MHz vacuum pillbox cavity Review 8/22/114All Experimenters Meeting, K. Yonehara

One possible solution Dark current is focused by B field Higher breakdown probability due to denser dark current Rolland Johnson and Dan Kaplan pointed out that dense hydrogen would absorb dark currents The model works perfectly in strong B fields (reference P. Hanlet’s talk) Now question is Can the gas filled cavity work with intense beam? Review 8/22/115All Experimenters Meeting, K. Yonehara

Mucool Test Area (MTA) & work space Multi task work space to study RF cavity under strong magnetic fields & by using intense H - beams from Linac Compressor + refrigerator rooms Entrance of MTA exp. hall MTA exp. hall SC magnet 200 MHz cavity Workstation 400 MeV H - beam transport line 8/22/116All Experimenters Meeting, K. Yonehara

High Pressure RF cavity & Beam parameters beam Gas inlet RF inlet 400 MeV H - beam Beam pulse length 7.5 μs 5 ns bunch gap 10 9 H - /bunch 18 % of transmission in collimator system protons/bunch passes through the cavity RF power inlet Gas inlet RF cavity + collimator in SC magnet 400 MeV H - beam line 8/22/117All Experimenters Meeting, K. Yonehara Hemisphere electrodes (to concentrate field strength at the middle of cavity) HP GH2Air

Study interaction of intense beam with dense H2 in high gradient RF field Beam signal (7.5 μs) RF power is lost due to plasma loading RF power is recovered when beam is off RF pulse length (80 μs) p + H 2 → p + H e - Ionization process 1,800 e - are generated by incident K = 400 MeV Huge RF power lost due to electrons’ power consumption But, it is not a breakdown!! ν= 802 MHz Gas pressure = 950 psi Beam intensity = /bunch 8/22/118All Experimenters Meeting, K. Yonehara Plasma loading in pure H2 gas Equilibrium condition Electron production rate = Recombination rate

Study electronegative gas effect H2+SF6 (0.01%) gas SF6 removes a residual electron Great improvement! Beam signal (7.5 μs) ν= 802 MHz H2 + SF6 (0.01 % condensation) Gas pressure = 950 psi Beam intensity = /bunch RF pickup voltage 8/22/119All Experimenters Meeting, K. Yonehara

Preliminary estimation of plasma loading effect in HPRF cavity for cooling channel From RF amplitude reduction rate, RF power consumption by plasma can be estimated E = 20 MV/m Hence, energy consumption by one electron is (including with initial beam intensity change) Joule t = 200 ns At this gas pressure, Muon collider: n e per one beam pulse = μ × 10 3 e = electrons → 0.6 Joule Neutrino Factory: n e per one beam pulse = μ × 10 3 e = electrons → 0.06 Joule ν= 802 MHz Pure H 2 gas Gas pressure = 950 psi Beam intensity = /bunch 200 MHz RF pillbox cavity stores 8 Joule RF power >> plasma loading effect May need some improvement on 400 MHz and 800 MHz cavities 8/22/1110All Experimenters Meeting, K. Yonehara

Summary 400 MeV H - beam is available at MTA First beam test in gas filled cavity has been done No breakdown occurred Observed plasma loading in the cavity Demonstrated mitigation of plasma loading with SF6 dopant Plan next beam test 8/22/1111All Experimenters Meeting, K. Yonehara

Casts 8/22/1112All Experimenters Meeting, K. Yonehara