Wakefields Generated by Electron Beams Passing Through a Waveguide Loaded With an Active Medium

The wakefields of a relativistic electron beam passing through a waveguide loaded with an active medium with weak resonant dispersion have been considered. For the calculations in this paper the parameters of the medium are those of a solution of fullerene (C60) in a nematic liquid crystal that exhibits activity in the X-band. It was shown that several of the TM accelerating modes can be amplified for the geometries under consideration; structures in which higher order modes are amplified exhibit essential advantages as PASERs. In particular, the amplification of the highest mode occurs in a structure loaded with a rather thick active medium layer that maximizes the energy stored by the active medium.Comment: 7 pages, 6 figures, submitted to 2006 Advanced Accelerator Concept

Studies of Particle Acceleration by an Active Microwave Medium

The PASER is potentially a very attractive method for particle acceleration, in which energy from an active medium is transferred to a charged particle beam. The effect is similar to the action of a maser or laser with the stimulated emission of radiation being produced by the virtual photons in the electromagnetic field of the beam. We have been investigating the possibility of developing a demonstration PASER operating at X-band. The less restrictive beam transport and device dimensional tolerances required for working at X-band rather than optical frequencies as well as the widespread application of X-band hardware in accelerator technology all contribute to the attractiveness of performing a PASER demonstration experiment in this frequency range. Key to this approach is the availability of a new class of active materials that exhibit photoinduced electron spin polarization. We will report on the status of active material development and measurements, numerical simulations, and progress towards a planned microwave PASER acceleration experiment at the Argonne Wakefield Accelerator facility.Comment: 9 pages, 3 figures, submitted to Proceedings of the 2006 Advanced Accelerator Concepts Worksho

Radio-Frequency Measurements of Coherent Transition and Cherenkov Radiation: Implications for High-Energy Neutrino Detection

We report on measurements of 11-18 cm wavelength radio emission from interactions of 15.2 MeV pulsed electron bunches at the Argonne Wakefield Accelerator. The electrons were observed both in a configuration where they produced primarily transition radiation from an aluminum foil, and in a configuration designed for the electrons to produce Cherenkov radiation in a silica sand target. Our aim was to emulate the large electron excess expected to develop during an electromagnetic cascade initiated by an ultra high-energy particle. Such charge asymmetries are predicted to produce strong coherent radio pulses, which are the basis for several experiments to detect high-energy neutrinos from the showers they induce in Antarctic ice and in the lunar regolith. We detected coherent emission which we attribute both to transition and possibly Cherenkov radiation at different levels depending on the experimental conditions. We discuss implications for experiments relying on radio emission for detection of electromagnetic cascades produced by ultra high-energy neutrinos.Comment: updated figure 10; fixed typo in equation 2.2; accepted by PR

Observation of the Askaryan Effect: Coherent Microwave Cherenkov Emission from Charge Asymmetry in High Energy Particle Cascades

We present the first direct experimental evidence for the charge excess in high energy particle showers predicted nearly 40 years ago by Askaryan. We directed bremsstrahlung photons from picosecond pulses of 28.5 GeV electrons at the SLAC Final Focus Test Beam facility into a 3.5 ton silica sand target, producing electromagnetic showers several meters long. A series of antennas spanning 0.3 to 6 GHz were used to detect strong, sub-nanosecond radio frequency pulses produced whenever a shower was present. The measured electric field strengths are consistent with a completely coherent radiation process. The pulses show 100% linear polarization, consistent with the expectations of Cherenkov radiation. The field strength versus depth closely follows the expected particle number density profile of the cascade, consistent with emission from excess charge distributed along the shower. These measurements therefore provide strong support for experiments designed to detect high energy cosmic rays and neutrinos via coherent radio emission from their cascades.Comment: 10 pages, 4 figures. Submitted to Phys. Rev. Let

Strange quark suppression in 225 GEV/C pi-minus beryllium interactions

The Chicago Cyclotron Magnet Spectrometer at Fermi1ab was used to study the production of W (783) and rp (1020) mesons in 225 GeV/c pi--Be interactions via their decays into pi+pi- ratio, the strange quark suppression factor.A was determined to be 0.31 ± 0.05, in good agreement with a world average of about 0.29.U of I OnlyThesi

Strange Quark Suppression in 225 Gev/c Negative Pion Beryllium Interactions

129 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.The Chicago Cyclotron Magnet Spectrometer at Fermilab was used to study the production of (omega)(783) and (phi)(1020) mesons in 225 GeV/c (pi)('-) Be interactions via their decays into (mu)('+)(mu)('-). Based on the observed (phi)/(omega) production ratio, the strange quark suppression factor (lamda) was determined to be 0.31 (+OR-) 0.05, in good agreement with a world average of about 0.29.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Strange Quark Suppression in 225 Gev/c Negative Pion Beryllium Interactions

129 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.The Chicago Cyclotron Magnet Spectrometer at Fermilab was used to study the production of (omega)(783) and (phi)(1020) mesons in 225 GeV/c (pi)('-) Be interactions via their decays into (mu)('+)(mu)('-). Based on the observed (phi)/(omega) production ratio, the strange quark suppression factor (lamda) was determined to be 0.31 (+OR-) 0.05, in good agreement with a world average of about 0.29.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Dielectric Collimators for Linear Collider Beam Delivery System

In this paper, dielectric collimator concepts for the linear collider are described. Cylindrical and planar dielectric collimator designs for CLIC and ILC parameters are presented, and results of simulations to minimize the beam impedance are discussed. The prototype collimator system is planned to be fabricated and experimentally tested at Facilities for Accelerator Science and Experimental Test Beams (FACET) at SLA

Wakefields generated by electron beams passing through a waveguide loaded with a slightly dispersive active medium

The wakefields of a relativistic electron beam passing through a waveguide loaded with an active medium with weak resonant dispersion are considered. For the calculations in this paper, the parameters of the medium are those of a solution of fullerene (C_{60}) in a nematic liquid crystal that exhibits activity in the X-band. It is shown that several of the TM accelerating modes can be amplified for the geometries under consideration; structures in which higher order modes are amplified exhibit essential advantages as PASERs. In particular, the amplification of the highest mode occurs in a structure loaded with a rather thick active medium layer that maximizes the energy stored by the active medium