THE GVM (Generating Volt Meter)

Generating Voltmeter -- This is a windmill type instrument that mechanically chops the electric field to generate a signal exactly proportional to the accelerator's terminal voltage. This is a critical system responsible for precisely controlling electron beam energy.

2 MV Accelerator

photo of 2MV gvm[gif 90K] [png 82k][jpeg 19K] photo - 17-Aug-95
The accuracy of the GVM's measurement will eventually set limits on single frequency lasing stability. Therefore, an entirely new system was designed and built with the goal of <100 parts-per-million accuracy and wide bandwidth. A precision 4 blade chopper is driven at 10,000 RPM by a regulated brushless servo motor. The signal is integrated and demodulated in such a way that phase and frequency noise are cancelled.

6 MV Accelerator

photo of 6MV gvmphoto - 22-Jan-98 [jpg 25K][png 98k][gif 117K]

As part of upgrades to the 6 MV accelerator, a new GVM based on the above 2 MV system has been built. Its chopper uses eight blades to achieve a bandwidth of 900 Hz.

updated 1-Mar-97 - GR -