To: J. Cook, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IR Demo Project Weekly Report, January 25-29, 1999
Date: January 29, 1999
Management
Highlights for the week include the finishing of the planned installation/maintenance
activities and the start-up of gun conditioning.
We have confirmed that RADM Paul Gaffney will be visiting the
FEL project as a quest of the Commonwealth's Secretary of Technology
(Don Upson) on Feb. 16th.
Several papers were presented on the FEL program at this week's
SPIE High Power Laser Conference in San Jose.
FEL Installation/Maintenance Activities
The following installation/maintenance items were completed this
week:
The gun was high-voltage processed, and the cathode was heat-cleaned
and cesiated. The high- voltage power supply for the gun was
tested to 5 mA into a relatively low impedance load.
Twelve viewers were aligned and their gains checked. Three new
viewers were installed, two in the first recirculation arc, and
one in the energy-recovery dump line. Four beam-loss monitors
were installed as beam-scraping diagnostics. They are not linked
to the machine protection system. The two new beam-current monitors
were connected, and their electronics were tested.
The rf system, dipole-magnet power supplies, and beam-position
monitors were checked out.
A vacuum leak in the first recirculation arc developed and was
fixed.
The modified infrared detectors in the waveguides of the cryomodule
were tested under full- gradient conditions, and their trip levels
were reset.
FEL Commissioning Activities
The week was devoted principally to getting the machine ready
to run. It took a couple of days to chase down and fix vacuum
leaks stemming from installation of new diagnostics. Meanwhile,
final touches in rejuvenating the gun took place. After installation
of a new cathode wafer, the gun was high-voltage processed to
the point of quiet field emission at 430 kV. It was heat- treated
last night at 675 C for two hours to purge remanent impurities.
Early this afternoon the cathode was cesiated, and just before
this writing (1500 Friday, 29 Jan 99) its photoresponse was measured.
Unfortunately the white-light response was only 1.4 µA,
with a red-to-white ratio of 28-to-1. These numbers are nearly
identical to those of the last cathode at the beginning of its
run, and they indicate the cathode is dirty. We do not know why
this is happening, i.e., whether the "dirt" is coming
prior to installing the cathode in the gun, or in conjunction
with the high-voltage processing. Plans are to turn on the gun
Monday. If the current is satisfactory, commissioning will resume.
If not, then most likely we will do a protracted, lower-temperature
heat clean, recesiate, and try again.
System checks also took place throughout the week, including, for example, turning on the magnet and rf systems, as well as running the drive laser. In addition, the new "FEL Driver Recovery Procedure/Optimization Test Plan" was fleshed out.