  Beginning in Fall 2018, the VERITAS high energy gamma-ray observatory (Amado,
AZ) was upgraded to enable Stellar Intensity Interferometry (SII) observations
during bright moon conditions. The system potentially allows VERITAS to
spatially characterize stellar objects at visible wavelengths with
sub-milliarcsecond angular resolution. This research project was on the
construction of a high voltage power supply for the photomultiplier tubes
(PMTs) used in the SII camera. The high voltage supply was designed to be
electrically isolated from all other electronics (except for the PMT) to reduce
noise pickup. The HV supply operates on a Li-Ion battery, and the high voltage
level is remotely programmed using a pulse width modulation (PWM) signal that
is generated by an Arduino Yun microcontroller and distributed through a fiber
optic cable. The electrical isolation of the fiber optic control system
suppresses the pickup of radio frequency interference through ground loops. A
separate fiber optic transceiver pair is used for the on-off control of the
high voltage power supply. Tests were performed that show the high voltage
level is reproducible to within one volt for a given duty cycle of the PWM
signal. Furthermore, the high voltage output level was shown to be stable with
respect to variations in the input battery voltage used to power the high
voltage supply. The high voltage system is currently being used in regular SII
observations at VERITAS. This poster will describe the detailed design and
performance of the system.
