Thermionic Gun
Fast Pulser – The pulser design is described in:
M.J. Browne et al., “A Multi-Channel Pulser for the SLC Thermionic Electron Source,” IEEE Trans. Nucl. Sci. 32 (1985) 1829; the preprint is available as SLAC-PUB-3546 (PDF, 446 KB).
The pulser connector has 3 concentric sets of finger stock that are used to make electrical contact with the filament, cathode, and ground plane respectively of the installed EIMAC Y-796 cathode-grid assembly.
The grid of the Y796 is connected to the ground plane, which is the high voltage electrode of the gun.
In normal operation, a dc voltage biases the cathode positive with respect to the grid. A fast negative pulse is applied to the cathode so that momentarily the cathode is negative with respect to the grid. If the cathode is sufficiently hot, it will emit electrons when it has a negative potential with respect to the grid.
After installation in the gun, but before the high voltage is turned on, the monitor output can be connected to a fast scope to check the pulser performance without electron emission. The filament can be on during this test if desired.
The pulser can be tested on the bench before installation in the gun using a dummy load. The SLAC dummy load consists of a pair of Cu sheets secured to each side of a roughly 1-mm thick phenolic sheet. Soldered to the Cu sheet facing the pulser are two concentric Cu sleeves that connect to the outer and middle finger stock of the pulser. In addition, the center of each sheet has a hole ~25 mm in diameter in the center of which is a large allen screw bolted to the phenolic. The screw connects to the innermost (filament) finger stock of the pulser. To provide a resistive load of ~12 Ω, 8´100 Ω resistors, symmetrically arranged, are soldered in parallel between the Cu plates around their outer edge.
Photos of the pulser and dummy load.
Return to Sources Group Home Page
This page maintained
by Jym Clendenin and was last updated