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Title: The Resistive-Wall Instability in Multipulse Linear Induction Accelerators

Abstract

The resistive-wall instability results from the Lorentz force on the beam due to the beam image charge and current. If the beam pipe is perfectly conducting, the electric force due to the image charge attracts the beam to the pipe wall, and the magnetic force due to the image current repels the beam from the wall. For a relativistic beam, these forces almost cancel, leaving a slight attractive force, which is easily overcome by external magnetic focusing. However, if the beam pipe is not perfectly conducting, the magnetic field due to the image current decays on a magnetic-diffusion time scale. If the beam pulse is longer than the magnetic diffusion time, the repulsion of the beam tail will be weaker than the repulsion of the beam head. In the absence of an external focusing force, this causes a head-to-tail sweep of the beam toward the wall. This instability is usually thought to be a concern only for long-pulse relativistic electron beams. However, with the advent of multipulse, high current linear induction accelerators, the possibility of pulse-to-pulse coupling of this instability should be investigated. Lastly, we have explored pulse-to-pulse coupling using the linear accelerator model for Dual Axis Radiography for Hydrodynamicmore » Testing beam dynamics code, and we present the results of this paper.« less

Authors:
ORCiD logo
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1352365
Report Number(s):
LA-UR-16-23759
Journal ID: ISSN 0093-3813
Grant/Contract Number:
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
IEEE Transactions on Plasma Science
Additional Journal Information:
Journal Volume: 45; Journal Issue: 5; Journal ID: ISSN 0093-3813
Publisher:
IEEE
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; electron beam instabilities; intense relativistic electron beams; linear induction accelerators (LIAs)

Citation Formats

Ekdahl, Carl. The Resistive-Wall Instability in Multipulse Linear Induction Accelerators. United States: N. p., 2017. Web. doi:10.1109/TPS.2017.2681040.
Ekdahl, Carl. The Resistive-Wall Instability in Multipulse Linear Induction Accelerators. United States. doi:10.1109/TPS.2017.2681040.
Ekdahl, Carl. Mon . "The Resistive-Wall Instability in Multipulse Linear Induction Accelerators". United States. doi:10.1109/TPS.2017.2681040. https://www.osti.gov/servlets/purl/1352365.
@article{osti_1352365,
title = {The Resistive-Wall Instability in Multipulse Linear Induction Accelerators},
author = {Ekdahl, Carl},
abstractNote = {The resistive-wall instability results from the Lorentz force on the beam due to the beam image charge and current. If the beam pipe is perfectly conducting, the electric force due to the image charge attracts the beam to the pipe wall, and the magnetic force due to the image current repels the beam from the wall. For a relativistic beam, these forces almost cancel, leaving a slight attractive force, which is easily overcome by external magnetic focusing. However, if the beam pipe is not perfectly conducting, the magnetic field due to the image current decays on a magnetic-diffusion time scale. If the beam pulse is longer than the magnetic diffusion time, the repulsion of the beam tail will be weaker than the repulsion of the beam head. In the absence of an external focusing force, this causes a head-to-tail sweep of the beam toward the wall. This instability is usually thought to be a concern only for long-pulse relativistic electron beams. However, with the advent of multipulse, high current linear induction accelerators, the possibility of pulse-to-pulse coupling of this instability should be investigated. Lastly, we have explored pulse-to-pulse coupling using the linear accelerator model for Dual Axis Radiography for Hydrodynamic Testing beam dynamics code, and we present the results of this paper.},
doi = {10.1109/TPS.2017.2681040},
journal = {IEEE Transactions on Plasma Science},
number = 5,
volume = 45,
place = {United States},
year = {Mon May 01 00:00:00 EDT 2017},
month = {Mon May 01 00:00:00 EDT 2017}
}

Journal Article:
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  • The electron beam in a linear induction accelerator is generally susceptible to growth of the transverse beam breakup instability. In this paper we analyze a new technique for reducing the transverse coupling between the beam and the accelerating cavities, thereby reducing beam breakup growth. The basic idea is that the most worrisome cavity modes can be cutoff by a short section of coaxial transmission line inserted between the cavity structure and the accelerating gap region. We have used the three-dimensional simulation code S-smcapsO-smcapsS-smcaps to analyze this problem. In brief, we find that the technique works, provided that the lowest TEmore » mode cutoff frequency in the coaxial line is greater than the frequency of the most worrisome TM mode of the accelerating cavity.« less
  • A general model for wakefield-generated instabilities in linear accelerators, originally developed for cumulative beam breakup [1], is applied to the resistive wall instability. The general solution for various bunch charge distributions and application to various accelerator configurations are presented.
  • Feedback stabilization of magnetohydrodynamic (MHD) modes in a tokamak is studied in a cylindrical model with a resistive wall, plasma resistivity, viscosity, and toroidal rotation. The control is based on a linear combination of the normal and tangential components of the magnetic field just inside the resistive wall. The feedback includes complex gain, for both the normal and for the tangential components, and it is known that the imaginary part of the feedback for the former is equivalent to plasma rotation [J. M. Finn and L. Chacon, Phys. Plasmas 11, 1866 (2004)]. The work includes (1) analysis with a reducedmore » resistive MHD model for a tokamak with finite β and with stepfunction current density and pressure profiles, and (2) computations with a full compressible visco-resistive MHD model with smooth decreasing profiles of current density and pressure. The equilibria are stable for β = 0 and the marginal stability values β{sub rp,rw} < β{sub rp,iw} < β{sub ip,rw} < β{sub ip,iw} (resistive plasma, resistive wall; resistive plasma, ideal wall; ideal plasma, resistive wall; and ideal plasma, ideal wall) are computed for both models. The main results are: (a) imaginary gain with normal sensors or plasma rotation stabilizes below β{sub rp,iw} because rotation suppresses the diffusion of flux from the plasma out through the wall and, more surprisingly, (b) rotation or imaginary gain with normal sensors destabilizes above β{sub rp,iw} because it prevents the feedback flux from entering the plasma through the resistive wall to form a virtual wall. A method of using complex gain G{sub i} to optimize in the presence of rotation in this regime with β > β{sub rp,iw} is presented. The effect of imaginary gain with tangential sensors is more complicated but essentially destabilizes above and below β{sub rp,iw}.« less