V. Ivanov

X-BAND LINEAR COLLIDER R&D IN ACCELERATING STRUCTURES THROUGH ADVANCED COMPUTING ∗

This paper describes a major computational effort that addresses key design issues in the high gradient accelerating structures for the proposed X-band linear collider, GLC/NLC. Supported by the US DOE’s Accelerator Simulation Project, SLAC is developing a suite of parallel electromagnetic codes based on unstructured grids for modeling RF structures with higher accuracy and on a scale previously not possible. The new simulation tools have played an important role in the R&D of X-Band accelerating structures, in cell design, wakefield analysis and dark current studies.

Confined flow multiple beam guns for high power RF applications

In this paper, confined flow multiple beam guns for high power RF applications is presented. Here, the challenge is to develop electron guns and the associated magnetic circuit to confine and compress the electron beams and transport them through the separate beam tunnels to the spent beam collector. A solid model of 185 kV multiple beam gun (MBG) for an X-band klystron is presented in this paper.

A gridded electron gun for a sheet beam klystron

In this paper we propose a gridded electron gun(dispenser-cathode gun) for sheet beam devices. The current generation of accelerators typically use klystrons with a cylindrical beam generated by a pierce-type electron gun. The gun design were used to determine the starting point for the electrodes to produce the compression. The use of grid was chosen for short pulse formation. The result showed that a very quality beam could be achieved even in the presence of the shadow grid.Calabazas Creek Research Inc. (CCR) is developing rectangular, gridded, thermionic dispenser-cathode guns for sheet beam devices. The first application is expected to be klystrons for advanced particle accelerators and colliders. The current generation of accelerators typically use klystrons with a cylindrical beam generated by a Pierce-type electron gun. As RF power is pushed to higher levels, space charge forces in the electron beam limit the amount of current that can be transmitted at a given voltage. The options are to increase the beam voltage, leading to problems with X-ray shielding and modulator and power supply design, or to develop new techniques for lowering the space charge forces in the electron beam. The current development program addresses issues related to beam formation at the emitter surface, design and implementation of shadow and control grids in a rectangular geometry, and the high voltage insulator.

Development of Multiple Beam Guns for High Power RF Sources for Accelerators and Colliders

There is a need for high power RF sources for the next generation of accelerators and colliders. Sources that operate at reduced beam voltage allow solid state power supplies with significant cost reduction over conventional pulse modulators. Multiple beam RF sources provide reduced beam voltage by using a multiplicity of beamlets that traverse the RF circuit through individual beam tunnels, reducing the space charge forces that drive the voltage requirement. The current generation of multiple beam devices typically use Brillouin focusing, which limits high power operation. The devices reported here utilize confined flow focusing which allows much tighter control of the electron beamlets and consequently, higher power operation. Progress in the development of a 100 MW multiple beam electron gun with confined flow focusing is reported.

Design, fabrication, and test of an X-Band multiple beam klystron

Fabrication was completed on an X-Band multiple beam klystron (MBK) designed to produce 50 MW of RF power in microsecond pulses. The klystron incorporates a confined flow, multiple beam gun where the cathodes are located relatively far from the device axis. This required unique focusing structures to maintain beam quality. The MBK will be tested at Brookhaven National Laboratories.

Simulating accelerator structure operation at high power

The important limiting factors in high-gradient accelerator structure operation are dark current capture, RF breakdown and electron multipacting. These processes involve both primary and secondary electron field emission and produce plasma and X-rays. To better understand these phenomena, we have simulated dark current generation and transport in a linac structure and a square-bend waveguide, both high power tested at SLAC. For these simulations, we use the parallel, time-domain, unstructured-grid code Tau3P and the particle tracking module Track3P. In this paper, we present numerical results and their comparison with measurements on energy spectrum of electrons transmitted in a 30-cell structure and of X-rays emitted from the square-bend waveguide.

An electron gun for a sheet beam klystron

Calabazas Creek Research, Inc.(CCR) is developing a rectangular, gridded, thermionic, dispenser-cathode gun for sheet beam devices. We present the preliminary design of a 415 kV, 250 A gridded gun for a sheet beam klystron, giving results from 2D and 3D simulations.Calabazas Creek Research, Inc. is developing rectangular, gridded, thermionic, dispenser-cathode gun for sheet beam devices. The first application is expected to be klystrons for use in advanced particle accelerators and colliders. The current generation of accelerators typically use klystrons with a cylindrical beam generated by a Pierce-type electron gun. As RF power is pushed to higher levels, space charge forces in the electron beam limit the amount of current that can be transmitted at a given voltage. The options are to increase the beam voltage leading to problems with X-ray shielding and modulator and power supply design, or to develop new techniques for lowering the space charge forces in the electron beam. The current program addresses issues related to beam formation at the emitter surface, design and implementation of shadow and control grids in a rectangular geometry, and is directed toward a robust, cost-effective, and reliable mechanical design. A prototype device will be developed that will operate at 415 kV, 250 A and be designed for an 80 MW, X-Band, sheet-beam klystron. The cathode will have 100 cm/sup 2/ of cathode area with an average cathode current loading of 2.5 A/cm/sup 2/. For short pulse formation, the use of a grid was chosen. We will report the electrostatic and beam optics design in both 2- and 3-D as well as a thermal-mechanical analysis of the cathode region.