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Title: Scaling of induction-cell transverse impedance: effect on accelerator design

Abstract

The strength of the dangerous beam breakup (BBU) instability in linear induction accelerators (LIAs) is characterized by the transverse coupling impedance Z . This note addresses the dimensional scaling of Z , which is important when comparing new LIA designs to existing accelerators with known i BBU growth. Moreover, it is shown that the scaling of Z with the accelerating gap size relates BBU growth directly to high-voltage engineering considerations. It is proposed to firmly establish this scaling though a series of AMOS calculations.

Authors:
 [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1296655
Report Number(s):
LA-UR-16-26141
TRN: US1601768
DOE Contract Number:
AC52-06NA25396
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; SCALING LAWS; LINEAR ACCELERATORS; DESIGN; ELECTRIC IMPEDANCE; INDUCTION; COMPARATIVE EVALUATIONS; BEAM DYNAMICS; COUPLING; INSTABILITY; accelerators; electron beams; instability; high-voltage breakdown

Citation Formats

Ekdahl, Carl August. Scaling of induction-cell transverse impedance: effect on accelerator design. United States: N. p., 2016. Web. doi:10.2172/1296655.
Ekdahl, Carl August. Scaling of induction-cell transverse impedance: effect on accelerator design. United States. doi:10.2172/1296655.
Ekdahl, Carl August. 2016. "Scaling of induction-cell transverse impedance: effect on accelerator design". United States. doi:10.2172/1296655. https://www.osti.gov/servlets/purl/1296655.
@article{osti_1296655,
title = {Scaling of induction-cell transverse impedance: effect on accelerator design},
author = {Ekdahl, Carl August},
abstractNote = {The strength of the dangerous beam breakup (BBU) instability in linear induction accelerators (LIAs) is characterized by the transverse coupling impedance Z⊥. This note addresses the dimensional scaling of Z⊥, which is important when comparing new LIA designs to existing accelerators with known i BBU growth. Moreover, it is shown that the scaling of Z⊥ with the accelerating gap size relates BBU growth directly to high-voltage engineering considerations. It is proposed to firmly establish this scaling though a series of AMOS calculations.},
doi = {10.2172/1296655},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 8
}

Technical Report:

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  • This paper discusses the multi-year ''campaign'' to measure and reduce the transverse impedances of the original DARHT-2 accelerator cells in order to limit the beam-breakup instability (BBU) growth through the machine. A series of three prototype cells were designed, modeled, and measured. One of the most important methods for limiting the impedance was the introduction of ferrite absorbers in the oil region immediately upstream of the insulator. When properly tuned in terms of thickness, the effective Q's could be significantly reduced for both the 10 inch ''standard'' cells and the 14 inch ''injector'' cells. We also present a new experimentalmore » method (twin lead-loop) to measure the transverse impedance. This method has a number of important advantages over the well-known TSD approach, especially in the low Q regime. For the final prototype standard cell design, we found that Z-perp could be limited to <300 ohms/m with Q's ranging from 3 to 6. There was reasonable agreement between measurements and simulation results from the AMOS code (peak amplitudes within 25-30 percent) with the exception that the resonant mode around 200 MHz had a double-peaked structure that could not be reproduced by simulation.« less
  • A high-current, cyclic electron accelerator, capable of accelerating several kiloamperes of electron current is described. The accelerating elements of the device are linear induction modules which match well to high-current operation. A racetrack configuration is utilized to return the electrons to the induction modules, thereby providing electron acceleration to an energy given by the gap voltage multiplied by the number of electron transits during the total pulse duration of the induction modules.
  • The effect of beam-generated positive ions on the beam-breakup instability in linear electron accelerators is calculated using simple models. The strongly nonlinear dependence of the ion focusing force on radius makes a complete suppression of the mode growth possible, in contrast to solenoidal focusing. The predicted gas pressures for significant stabilization of the mode growth in a machine configuration like ATA is relatively low (10/sup -5/ to 10/sup -4/ torr), even for high-Q modes.
  • Several accelerator-based intense neutron sources have been constructed or designed by various laboratories around the world. All of these facilities have a common scheme of a linac and synchrotron or accumulator ring, and the system produces the proton energy of 500 to 1000 MeV. The average beam currents range from a few mA to a few hundred mA. The protons are then used to generate high-flux neutrons by spallation out of heavy-metal targets. In a synchrotron system, the protons are already bunched, and thus the pulse rate of the neutron beam is that of the repetition rate of the synchrotron.more » For an accumulator system, the pulse rate is determined by the extraction repetition rate of the accumulator. We have conceptually designed a new system that uses a linear-induction accelerator which can be operated for an average beam current up to a few mA with a repetition rate up to 100 Hz. The details of the design will be given.« less