Improvements in Synchronization of the PBFA-II Accelerator with Laser-Triggered Gas Switches

摘要

PBFA II is a 36-module ion accelerator built by Sandia National Laboratories for inertial confinement fusion studies. In the water-filled, pulse-forming section of the accelerator, each module is fitted with a 5.0-MV, SF sub 6 -filled gas switch located between an intermediate storage capacitor and the first pulse forming line. The intermediate storage capacitor is charged to 4.8-5.0 MV in approximately 950 ns by a Marx generator located in the oil section of the machine. The gas switch is required to close on command and transfer the stored capacitor energy to Line 1, a coaxial transmission line of 100 ns two-way electrical length. The switches are triggered by a single 3.0-J KrF laser located under the accelerator; a complex beam-splitting/distribution system is used to deliver 20-40 mJ, 35 ns FWHM beamlets to the individual switches. In order to properly drive the experimental load on PBFA II, equal-amplitude pulses must be produced by each pulse-forming line with a module-to-module first-to-last timing difference (spread) of less than 20 ns. The gas switch, the last command-triggered point in the module, is the major determinant of total machine synchrony. To compensate for the additional (<3 ns) rms jitter of three sets of self-breaking water switches downstream of the gas switches, first-to-last timing spread of the 36 gas switches must be less than 15 ns. 5 refs., 6 figs.