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High-Pressure GH₂ RF Cavity Testing for Efficient Muon Beam Cooling at Fermilab

This study focuses on the beam test of a high-pressure GH₂-filled RF cavity conducted at Fermilab, aimed at improving muon beam cooling efficiency for Muon Colliders (MC) or neutrino factories (NF). By leveraging low-Z ionization energy-loss absorbers alongside RF technology, this research explores innovative solutions to optimize space utilization in muon beam systems. Collaborative efforts are made with Muons, Inc. to enhance the performance of muon cooling mechanisms that are crucial for future particle physics experiments.

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High-Pressure GH₂ RF Cavity Testing for Efficient Muon Beam Cooling at Fermilab

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  1. Beam Test of a High-Pressure GH2-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 All Experimenters Meeting, K. Yonehara
  2. m Muons, Inc. 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 All Experimenters Meeting, K. Yonehara
  3. m Muons, Inc. Series of talk in past AEM 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 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 All Experimenters Meeting, K. Yonehara
  4. Problem: B field effect on RF cavity Review A. Bross, MC’11 Data were taken in an 805 MHz vacuum pillbox cavity Required E in cooling channel X Gradient in MV/m >2X Reduction @ required field Peak Magnetic Field in T at the Window All Experimenters Meeting, K. Yonehara
  5. Review 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? All Experimenters Meeting, K. Yonehara
  6. 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 MTA exp. hall Entrance of MTA exp. hall 200 MHz cavity Compressor + refrigerator rooms SC magnet 400 MeV H- beam transport line Workstation All Experimenters Meeting, K. Yonehara
  7. High Pressure RF cavity & Beam parameters RF cavity HP GH2 Air RF inlet RF power inlet beam Gas inlet Gas inlet Hemisphere electrodes (to concentrate field strength at the middle of cavity) RF cavity + collimator in SC magnet 400 MeV H- beam line 400 MeV H- beam Beam pulse length 7.5 μs 5 ns bunch gap 109 H-/bunch 18 % of transmission in collimator system 1.8 108 protons/bunch passes through the cavity All Experimenters Meeting, K. Yonehara
  8. Study interaction of intense beam with dense H2 in high gradient RF field ν= 802 MHz Gas pressure = 950 psi Beam intensity = 2 108 /bunch Plasma loading in pure H2 gas RF power is lost due to plasma loading Equilibrium condition Electron production rate = Recombination rate RF power is recovered when beam is off RF pulse length (80 μs) Beam signal (7.5 μs) Ionization process p + H2 → p + H2+ + e- 1,800 e- are generated by incident p @ K = 400 MeV Huge RF power lost due to electrons’ power consumption But, it is not a breakdown!! All Experimenters Meeting, K. Yonehara
  9. Study electronegative gas effect ν= 802 MHz H2 + SF6 (0.01 % condensation) Gas pressure = 950 psi Beam intensity = 2 108 /bunch H2+SF6 (0.01%) gas RF pickup voltage Beam signal (7.5 μs) SF6 removes a residual electron Great improvement! All Experimenters Meeting, K. Yonehara
  10. 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 ν= 802 MHz Pure H2 gas Gas pressure = 950 psi Beam intensity = 2 108 /bunch Joule @ E = 20 MV/m electrons@ t = 200 ns Hence, energy consumption by one electron is (including with initial beam intensity change) Joule At this gas pressure, Muon collider: ne per one beam pulse = 1013μ × 103e = 1016 electrons → 0.6 Joule Neutrino Factory: ne per one beam pulse = 1012μ × 103e = 1015 electrons → 0.06 Joule 200 MHz RF pillbox cavity stores 8 Joule RF power >> plasma loading effect May need some improvement on 400 MHz and 800 MHz cavities All Experimenters Meeting, K. Yonehara
  11. 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 All Experimenters Meeting, K. Yonehara
  12. Casts All Experimenters Meeting, K. Yonehara
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