Author: Schwarz, T.A.
Paper Title Page
TUPFI064 Beam Induced Plasma Dynamics in a High Pressure Gas-Filled RF Test Cell for use in a Muon Cooling Channel 1496
  • B.T. Freemire, P.M. Hanlet, Y. Torun
    IIT, Chicago, Illinois, USA
  • M. Chung, M.R. Jana, M.A. Leonova, A. Moretti, T.A. Schwarz, A.V. Tollestrup, K. Yonehara
    Fermilab, Batavia, USA
  • M.G. Collura
    Politecnico di Torino, Torino, Italy
  • R.P. Johnson
    Muons. Inc., USA
  Filling an RF cavity with a high pressure gas prevents breakdown when the cavity is place in a multi-Tesla external magnetic field. The choice of hydrogen gas provides the additional benefit of cooling a beam of muons. A beam of particles traversing the cavity, be it muons or protons, ionizes the gas, creating an electron-ion plasma which absorbs energy from the cavity. The ionization rate can be calculated from a beam intensity measurement. Energy loss measurements indicate the loading per RF cycle per electron-ion pair range from 10-18 to 10-16 Joules in pure hydrogen, and 10-20 to 10-18 Joules when hydrogen is doped with dry air. The addition of an electronegative gas (oxygen) has been observed to reduce the lifetime of ionization electrons in the cavity to below 1 nanosecond. Additionally, the recombination rate of electrons and hydrogen ions has been measured to be on the order of 10-6 cubic centimeters per second. The recombination mechanism and hydrogen ion species, along with the three-body attachment process of electrons to oxygen, will be discussed.