Technology demonstration for the DARHT Linear Induction Accelerators
The Dual-Axis Radiographic Hydrodynamics Test (DARHT) facility will employ two 16-MeV, 3-kA Linear Induction Accelerators to produce intense, bremsstrahlung x-ray pulses for flash radiography. Technology demonstration of the key accelerator sub-systems is underway at the DARHT Integrated Test Stand (ITS), which will produce a 6-MeV, 3-kA, 60-ns flattop electron beam. We will summarize measurements of ITS injector, pulsed-power, and accelerator cell performance. Time-resolved measurements of the electron beam parameters will also be presented. These measurements indicate that the DARHT accelerator design is sufficiently advanced to provide the high quality electron beams required for radiography with sub-millimeter spatial resolution.
Design and Characterization of a High-Power Induction Module at Burst Double-Pulse Mode
The special design for a unique high-power double-pulse induction module is presented. By changing the length of one of the transmission lines between the cell and the Blumlein pulse forming line (PFL), the single pulse produced by the PFL can excite the induction cell twice and generate a second high-voltage pulse in the induction gap of the cell. An experiment has been conducted to investigate the differences between the first and second main pulses in rise time and voltage amplitude. The differences can be caused by the power loss of the transmission line, the nonlinear characterization of the cell's magnetic cores, and the pulse disturbances after the main pulses. The performance of the double-pulse module is also presented in this paper.
Beam-breakup calculations for the DARHT accelerator
An induction line that will accelerate a 4-MeV, 3-kA beam of electrons to 16- to 20-MeV in 64 gaps is modeled. To suppress beam-breakup (BBU) instabilities induced by excitation of RF deflecting modes, the growth factor Gamma must be kept sufficiently small (e.g. <3). On prototype DARHT cavities, RF measurements have shown that the normally degenerate TM modes are split in frequency by the asymmetry that the two pulsed-power drive rods present to the cavity. If half the cavities had vertical and half had horizontal drive-rod orientations, the effective number of gaps would be reduced by half if there were no coupling between the modes by the solenoid focusing and if the split modes had no overlap. The LLNL (Lawrence Livermore National Laboratory) code BREAKUP was used to study BBU growth for drive rod alternation patterns of blocks of 1, 2, 4, 8, 16, 24, 32, or 64 (no alternation) for both constant and alternating polarity solenoids.<<ETX>>