Design of 118 MHz twelfth harmonic cavity of APS PAR

Two radio frequency (RF) cavities are needed in the Positron Accumulator Ring (PAR) of the Advanced Photon Source. One is for the first harmonic frequency at 9.8 MHz, and the other is for the twelfth harmonic frequency at 118 MHz. This note reports on the design of the 118 MHz RF cavity. Computer models are used to find the mode frequencies, impedances, Q-factors, and field distributions in the cavity. The computer codes MAFIA, URMEL, and URMEL-T are useful tools which model and simulate the resonance characteristics of a cavity. These codes employ the finite difference method to solve Maxwell`s equations. MAFIA is a three-dimensional problem solver and uses square patches to approximate the inner surface of a cavity. URMEL and URMEL-T are two-dimensional problem solvers and use rectangular and triangular meshes, respectively. URMEL-T and MAFIA can handle problems with arbitrary dielectric materials located inside the boundary. The cavity employs a circularly cylindrical ceramic window to limit the vacuum to the beam pipe. The ceramic window used in the modeling will have a wall thickness of 0.9 cm. This wall thickness is not negligible in determining the resonant frequencies of the cavity. In the following, results of two- and three-dimensional modeling of the cavities using the URMEL-T and MAFIA codes are reported

Longitudinal multibunch instabilities in the Advanced Photon Source storage ring

A longitudinal coupled-bunch (CB) instability was encountered in the 7-GeV Advanced Photon Source (APS) positron storage ring whose threshold depends on the bunch fill pattern in a nontrivial way. The beam spectrum exhibited a coupled-bunch signature, which could be reproduced by an analytical model. The beam fluctuations were found to be correlated with the rf cavity temperatures, consistent with the measured temperature dependence of the higher-order mode (HOM) frequencies. Fast beam loss due to a multibunch effect was observed with other patterns of very long bunch trains. The nature of these instabilities has not yet been characterized. Multibunch instabilities had not been observed previously with electrons, although such patterns of long bunch trains were not studied systematically in this case

High peak power test of S-band waveguide switches

The injector and source of particles for the Advanced Photon Source (APS) is a 2856-MHz S-band electron-positron linear accelerator (linac) which produces electrons with energies up to 650 MeV or positrons with energies up to 450 MeV. To improve the linac rf system availability, an additional modulator-klystron subsystem is being constructed to provide a switchable hot spare unit for each of the five existing S-band transmitters. The switching of the transmitters will require the use of SF6-pressurized waveguide switches at a peak operating power of 35 MW. A test stand was set up at the Stanford Linear Accelerator Center (SLAC) Klystron-Microwave laboratory to conduct tests characterizing the power handling capability of these waveguide switches. Test results are presented

Feasibility studies of a compact mm-wave linac FEL

Short wavelength FELs impose stringent requirements on the quality of the electron beams. The key factor in obtaining a single-pass UV or x-ray FEL is the generation of small emittance electron beams with ultra-high brightness. The pioneering work at Los Alamos National Laboratory in the last decade has resulted in a dramatic improvement in the production of high electron beam brightness and small beam emittance using rf photocathode gun. The lower bound on the emittance of a 1-nC bunch without any emittance compensation is on the order of 3 {pi} mm-mrad. This is well within the emittance requirement being considered here. Although the original R&D work at Argonne, in collaboration with the University of Illinois at Chicago and University of Wisconsin-Madison, has produced encouraging results in the area of rf structure design, x-ray mask fabrication, and LIGA processing (Lithography, Electroforming, and Molding), the goal to prove feasibility has not yet been achieved. In this paper, we will present feasibility studies for a compact single-pass mm-linac FEL based on LIGA technology. This system will consist of a photocathode rf gun operated at 30 GHz, a 50-MeV superconducting constant gradient structure operated at 60 GHz, and a microundulator with 1-mm period

An overview of the APS 352-MHz rf systems

The Advanced Photon Source (APS) is a 7-GeV full energy positron storage ring for generating synchrotron radiation with an injector. The booster synchrotron rf system consists o a single 1-MW klystron which drives four five-cell cavities at 352 MHz. The storage ring cavities consist of four groups of four single cells powered by two 1-MW klystrons for 100-mA operation. An overview of the operation of the APS 352-MHz rf systems is presented

MM-wave cavity/klystron developments using deep x-ray lithography at the Advanced Photon Source.

Recent microfabrication technologies based on LIGA (German acronym for Li thographe, G alvanoformung, und A bformung) have been applied to build high-aspect-ratio, metallic or dielectric, planar structures suitable for high frequency rf cavity structures. The cavity structures would be used as parts of linear accelerators, microwave undulators, and mm-wave amplifiers. The microfabrication process includes manufacturing of precision x-ray masks, exposure of positive resist by x-rays through the mask, resist development, and electroforming of the final microstructure. Prototypes of a 32-cell, 108-GHz constant impedance cavity and a 66-cell, 94-GHz constant-gradient cavity were fabricated using the synchrotron radiation sources at APS. Preliminary design parameters for a 91- GHz modulator klystron along with an overview of the new technology are discussed

Quasielastic axial-vector mass from experiments on neutrino-nucleus scattering

We analyze available experimental data on the total and differential charged-current cross sections for quasielastic neutrino and antineutrino scattering off nucleons, measured with a variety of nuclear targets in the accelerator experiments at ANL, BNL, FNAL, CERN, and IHEP, dating from the end of sixties to the present day. The data are used to adjust the poorly known value of the axial-vector mass of the nucleon.Comment: 27 pages, 19 figures. Typos corrected; tables, figures and references added, discussion extended; matches published versio

The Aspun Project

A study of pulsed spallation neutron source, that could deliver fluxes in excess of 1 /times/ 10/sup 17/ N/cm/sup 2/-sec began at Argonne in 1981. A review of various accelerator concepts to act as an intense charged particle source to generate spallation neutrons resulted in the selection of a Fixed-Field Alternating-Gradient (FFAG) accelerator as the preferred devices. This paper describes the design and operation of the FFAG Accelerator. 10 refs., 6 figs

Analytical study of the generation and control of orbit errors in the ANL 4-GeV CW electron microtron design

The 4-GeV CW Electron Microtron (GEM) Design has 3 linac sections and 3 dispersive straight sections. Six 60/sup 0/ sector bending magnets separate the linac and dispersion straight sections. A magnetic optical system has been designed within the dispersive straight sections to contain the beam during the 36 or 37 return passes through the linacs. A major concern is the effect of small alignment or field errors on the equilibrium or desired orbit with a relatively strong focussing system. The results of an analytical study which shows the effect of small random errors on the orbit are presented. A study was also undertaken on the control of the orbit position by making error measurements in one dispersive section and making an angular adjustment with a small dipole in the preceding dispersive section. The analysis indicates that the orbit position can be adequately and easily controlled in the presence of random alignment and field errors