M. Leonova

Pressurized rf cavities in ionizing beams

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

Chao Formalism & Kondratenko Crossing Tests

SF_6

Unexpected Enhancements and Reductions of RF Resonance Strengths

and

Status of the Michigan Ultra‐Cold Spin‐Polarized Hydrogen Jet

O_2

MICE CAVITY INSTALLATION AND COMMISSIONING/OPERATION AT MTA*

were measured.

RF breakdown of 805 MHz cavities in strong magnetic fields

We recently started testing Chao’s proposed new matrix formalism for describing the spin dynamics due to a single spin resonance; this seems to be the first generalization of the Froissart‐Stora equation since it was published in 1960. The Chao matrix formalism allows one to calculate analytically the polarization’s behavior inside a resonance, which is not possible using the Froissart‐Stora equation. We recently tested some Chao formalism predictions using a 1.85 GeV/c polarized deuteron beam stored in COSY. We swept an rf dipole’s frequency through 200 Hz while varying the distance from the sweep’s end frequency to an rf‐induced spin resonance’s central frequency. While the Froissart‐Stora formula can make no prediction in this case, the data seem to support the Chao formalism.We also started investigating the new Kondratenko method to preserve beam polarization during a spin resonance crossing; the method uses 3 rapid changes of the crossing rate near the resonance. With a proper choice of crossing par...

Operation of normal-conducting RF cavities in multi-tesla magnetic fields for muon ionization cooling: a feasibility demonstration.

We recently analyzed all available data on spin-flipping stored beams of polarized protons, electrons, and deuterons. Fitting the modified Froissart-Stora equation to the measured polarization data after crossing an rf-induced spin resonance, we found 10 ‐20-fold deviations from the depolarizing resonance strength equations used for many years. The polarization was typically manipulated by linearly sweeping the frequency of an rf dipole or rf solenoid through an rf-induced spin resonance; spin-flip efficiencies of up to 99:9% were obtained. The Lorentz invariance of an rf dipole’s transverse R Bdl and the weak energy dependence of its spin resonance strength E together imply that even a small rf dipole should allow efficient spin flipping in 100 GeV or even TeV storage rings; thus, it is important to understand these large deviations. Therefore, we recently studied the resonance strength deviations experimentally by varying the size and vertical betatron tune of a 2:1 GeV=c polarized proton beam stored in COSY. We found no dependence of E on beam size, but we did find almost 100-fold enhancements when the rf spin resonance was near an intrinsic spin resonance.

PLASMA CHEMISTRY IN A HIGH PRESSURE GAS FILLED RF TEST CELL FOR USE IN A MUON COOLING CHANNEL

Progress on the Michigan ultra‐cold proton‐spin‐polarized atomic‐hydrogen Jet target is presented. We describe the present status of the Jet and some beam test results.