Pressurized rf cavities in ionizing beams

Abstract

A muon collider or Higgs factory requires significant reduction of the six dimensional emittance of the beam prior to acceleration. One method to accomplish this involves building a cooling channel using high pressure gas filled radio frequency cavities. The performance of such a cavity when subjected to an intense particle beam must be investigated before this technology can be validated. To this end, a high pressure gas filled radio frequency (rf) test cell was built and placed in a 400 MeV beam line from the Fermilab linac to study the plasma evolution and its effect on the cavity. Hydrogen, deuterium, helium and nitrogen gases were studied. Additionally, sulfur hexafluoride and dry air were used as dopants to aid in the removal of plasma electrons. Measurements were made using a variety of beam intensities, gas pressures, dopant concentrations, and cavity rf electric fields, both with and without a 3 T external solenoidal magnetic field. Energy dissipation per electron-ion pair, electron-ion recombination rates, ion-ion recombination rates, and electron attachment times to $SF_6$ and $O_2$ were measured.Comment: 15 p

Simulation of plasma loading of high-pressure RF cavities

“…The RF field magnitude drops almost linearly during the beam time, and then continues to decrease slightly because of the energy stored in ions. The total decrease of the RF field magnitude is very small -less than 1 %, which is significantly different compared to large values due to plasma loading of HPRF cavities interacting with proton beams, observed in Fermilab MTF experiments [8] and simulations [11].…”

“…In our model, we use the following fit for the effective recombination rate, applicable to transient processes in the plasma, 6) where X = E/P is the ratio of electric field magnitude to the gas pressure. Values for the parameters a and b were obtained via comparison of HPRF simulations to various experimentally measured quantities, in particular, the plasma loading [8], and extrapolated to the range of parameters used in this work.…”

“…In simulations, the change of the RF field due to plasma loading can be approximated by an RLC resonant circuit formula [8]. In particular, the RF power dissipation can be described as…”

Gas Filled RF Resonator Hadron Beam Monitor for Intense Neutrino Beam Experiments

“…It is controlled by a gas pressure, RF gradient, and concentration of electronegative dopant in the cavity. Optimization of the RF parameter is done based on the past RF measurements [4,5]. Two operation modes are considered to diagnose the beam quality.…”

Muon colliders, neutrino factories, and results from the MICE experiment

“…The reverse occurs in "Final Cooling. "(Figure:Muons, Inc.) (top) HFOFO Snake lattice scheme, combining tilted solenoids with LiH-wedge and gaseous-hydrogen absorbers and RF cavities; (bottom) B z , beam positions, and dispersion vs. distance along beam axis[38] .…”