Upgrades to the LLNL flash x-ray induction linear accelerator (FXR) Page: 3 of 10
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UPGRADES TO THE LLNL FLASH X-RAY INDUCTION LINEAR
ACCELERATOR (FXR)
Raymond D. Scarpetti
Norman L. Back
John K. Boyd
Gregory G. Earley
Kenneth L. Griffin
Roderick G. Kerr
Ronald Kihara
Mike M. Ong
Jan-Mark Zentler
Lawrence Livermore National Laboratory
Livermore, CA
Abstract
The FXR is an induction linear accelerator used for flash radiography at the Lawrence
Livermore National Laboratory's Site 300 Test Facility. The FXR was originally
completed in 1982 and has been in continuous use as a radiographic tool. At that time the
FXR produced a 17 MeV, 2.2 kA burst of electrons for a duration of 65 ns.
An upgrade of the FXR was recently completed. The purpose of this upgrade was to
improve the performance of the FXR by increasing the energy of the electron injector
from 1.2 MeV to 2.5 MeV and the beam current from 2.2 kA to 3 kA, improving the
magnetic transport system by redesigning the solenoidal transport focus coils, reducing
the rf coupling of the electron beam to the accelerator cells, and by adding additional
beam diagnostics.
We will describe the injector upgrades and performance, as well as our efforts to tune the
accelerator by minimizing beam corkscrew motion and the impact of Beam Breakup
Instability on beam centroid motion throughout the beam line as the current is increased to
3 kA.
Introduction
The FXR1,2 is an induction linear accelerator used for flash radiography. It is the principle
diagnostic tool at the Building 801 hydrodiagnostics test bunker at the Lawrence Livermore
National Laboratory's Site 300 Test Facility. The accelerator is housed in a reinforced concrete
bunker and has an overall length of 42 meters (see Figure 1). It consists of eleven blocks of 4
accelerator cells each. The 44 accelerator cells each imparts an energy of from 300 to 350 keV to
the electron beam (see Figure 2). A 2.5 MV Injector generates a 65 ns, 2 to 3 kilo amperes of
electron beam current which is accelerated through the 44 accelerator cells to a final energy of 16-
18 MeV. This electron beam is focused onto a 1 mm thick tantalum target to produce an x-ray
fluence (flux) of 320-400 R, one meter from the target. The result is a single radiograph of the
device under test, with the x-ray film protected in a blast-proof cassette located behind the device.
The FXR was designed and built at the Lawrence Livermore National Laboratory beginning in
1978 at a cost of approximately $13 Million. It was activated in 1982 and since then, has been
available for flash radiography. The FXR Beam Upgrade effort began in 1991 to enhance the
performance of the FXR induction accelerator by, first, improving the electron beam quality by1
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Scarpetti, R. D., LLNL. Upgrades to the LLNL flash x-ray induction linear accelerator (FXR), article, June 30, 1997; (https://digital.library.unt.edu/ark:/67531/metadc625775/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.