A program of upgrades to the 6 MV accelerator is being carried out as part of a National Science Foundation
Instrumentation Grant. The goals are:
Increase repetition rate from 1 to 10 Hz
Improve terminal voltage stabilization
These goals are being accomplished by installing:
A new high-performance Generating Voltmeter (GVM) system
Voltage grading resistors along the accelerator tubes and columns
A new high current charge induction system
A charge modulator system
12-Jul-98 - The new GVM has been in operation now for two months and works very well. A larger motor was installed
and speed reduced from 10 to 8 thousand RPM. This reduces bandwidth from 900 Hz to 700 Hz but is still sufficient
for our goal of 10 pps operation. System gain and response time have been increased by a factor of seven over the old
system and will be increased further as the bandwidth of other elements, particularly the optical link, is increased.
The terminal now comes fully into regulation at 4 pps rate, but under some conditions, running at this rate seems to
induce arcing. The cause of this effect is under investigation.
28-Feb-98 - Modifications are complete and the tank is closed. The accelerator and FELs run fine. The new GVM has
a problem with excessive loading of its motor due to viscous drag from the SF6 gas. A stronger motor
has been ordered.
31-Jan-98 - Generating voltmeter is complete and installed. Resistor installation is about half complete. Induction
system components are awaiting installation. Development of the modulator is deferred pending further testing of the
charging system and regulation with the new components.