| Paper | Title | Page |
|---|
| WEP76 | Performance of RF amplifiers for ISAC-II medium beta linac operation | 685 |
| | - A. K. Mitra, K. Fong, R. E. Laxdal, J. Lu, R. Shanks
TRIUMF
| |
| | A heavy ion superconducting linac at TRIUMF to
increase the final energy of radioactive beams from the
existing room temperature ISAC accelerator is now
operational. The linac consists of twenty quarter wave
cavities operating at 106 MHz to produce an accelerating
voltage gain of 20 MV. This paper describes the
operational experience of the 106 MHz rf tube amplifiers
which were installed and commissioned for the medium
beta linac in October 2005. Total rf power installed is 16
kW where one quarter power is used for regular linac
operation. During the initial commissioning of the
amplifiers, only one power tube was found to be noisy
and was replaced. The first major tube failure occurred in
April 2007 after 9000 operating filament hours. Soon
thereafter five more tubes showed signs of loss of gain. It
was evident that most of the tubes reached their tube life
by this time and all were replaced with new tubes. The
extension of tube life, and prediction of tube failure are
the main concerns of these tube amplifiers. Efforts are
being made to incorporate reduced filament power
operation in order to get longer tube life. Systematic
check of the amplifier performance during scheduled
maintenance and shutdown period is undertaken.
Reduction of tube emission and hence gain degradation
from their nominal value causes excessive drive power
from the rf control system to keep the cavity voltage
constant under closed loop. Hence monitoring the drive
power is useful to predict early tube failure. Input drive
power and gain of all the 20 amplifiers are available at the
EPICS data archive which can be monitored and plotted.
This will allow early warning of tube failure so that tubes
can be replaced before they actually fail. The failure
modes of the tubes and diagnostics to predict tube failure
will be described. | |