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Register a new userSpin resonance strengths due to rf solenoids and dipoles for stored deuteron beams
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This submission was withdrawn because of an unresolved dispute between the authors [arXiv admin 2009-4-13].
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We recently used an rf solenoid to study the widths of rf spin resonances with both unbunched and bunched beams of 2.1 GeV_c polarized protons stored in the COSY synchrotron. A map, with unbunched beam at different fixed rf-solenoid frequencies, showed a very shallow possible depolarization dip at the resonance. Next we made frequency sweeps of 400Hz, centered at similar frequencies, which greatly enhanced the dip. But, with a bunched proton beam, both the fixed-frequency and frequency-sweep techniques produced similar maps, and both bunched maps showed full beam depolarization over a wide region. Moreover, both were more than twice as wide as the unbunched dip. This widening of the proton resonance due to bunching is exactly opposite to the recently observed narrowing of deuteron resonances due to bunching.
The Pulsed RF Heating (PRFH) is the well known effect in the development of high gradient accelerating cavities. There is a lot of research dedicated to the tolerable strength of electromagnetic field and the corresponding temperature rise leading to the surface degradation and cavity performance violation. To provide high quality of electron bunches, RF gun cavities operate in electron sources with high electric, and hence, magnetic RF fields. Being at the safe side with respect to cavity surface degradation, related to the PRFH result for S band in essentially transient thermal deformations, leading to the cavity frequency shift and quality factor change even within a few microseconds in the RF pulse. Thermo-elastic deformations consist of slow heat propagation from the cavity surface and fast elastic wave propagation from the very thin heated surface layer inside the cavity body with different in five orders typical velocities. For simulations of PRFH effects for more or less practical cavity design we can get results only in direct numerical simulations with certified software like ANSYS. The critical issue for such direct simulations is to combine in a single model the possibility of correct description for such qualitatively different process and to prove the reasonable precision of simulations. This report describes the procedure for simulation of PRFH related transient thermo-elastic deformations in S band cavities. The results of test simulations are presented to show the relative precision of simulations.
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.
Kinetics of the polarization buildup at the interaction of stored protons (antiprotons) with a polarized target is considered. It is demonstrated that for small scattering angles, when a projectile remains in the beam, the polarization buildup is completely due to the spin-flip transitions. The corresponding cross sections turn out to be negligibly small for a hydrogen gas target as well as for a pure electron target. For the latter, the filtering mechanism also does not provide a noticeable beam polarization.
CW photoinjectors operating at high accelerating gradients promise to revolutionize many areas of science and applications. They can establish the basis for a new generation of monochromatic X-ray free electron lasers, high brightness hadron beams, or a new generation of microchip production. In this letter we report on the record-performing superconducting RF electron gun with $textrm{CsK}_{2}textrm{Sb}$ photocathode. The gun is generating high charge electron bunches (up to 10 nC/bunch) and low transverse emittances, while operating for months with a single photocathode. This achievement opens a new era in generating high-power beams with a very high average brightness.
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