February 1999
Management
Highlights for the month: FEL operations resumed early in the month of February after the January maintenance period. At month's end, the FEL power record had been raised to over 550 watts by recirculating over 3 mA of linac current. (Note: this record was raised to 710 watts on March 11 by recirculating 3.6 mA).
On Tuesday February 16th, Rear Admiral Paul Gaffney, Chief of Naval
Research, visited Jefferson Lab for a tour and briefing on the FEL project
and potential applications of interest to the Navy. Admiral Gaffney was
accompanied by two officials from the Office of Naval Research, Dr. Jim
DeCorpo and Dr. Eli Zimet, and the Commonwealth's Secretary of Technology,
Don Upson. The technical briefing included a status report on the current
FEL, the proposal to upgrade the FEL for 20 kW of IR power, and potential
IR applications of interest to the Navy and two of our industrial partners,
Northrop Grumman and Advanced Energy Systems. By all accounts, the visit
went well and we are expecting continued collaboration with the Navy.
CA 321: Upgrade Cryomodule System
Cavity pair work has been completed with the delivery of the fourth
cavity pair. Cryounit work completed includes completion and delivery of
the first cryounit. The second, third, and fourth units are 80, 40, and
20 % complete. Cryomodule assembly work has started with the delivery of
the first cryounit and preparations are underway to install the first beamline
thermal transition.
CA 521: FEL COMMISSIONING
On 10 Feb. 99 we decided to run with a 330 kV gun due to field-emission activity at 350 kV after cesiation. We quickly commissioned all of the new diagnostics installed during the January down and successfully ran at the new beam mode of 74.8 MHz repetition rate. We were limited by waveguide IR detector trips and by some beam scraping around the cryomodule exit, meaning the transverse properties of the recirculated beam needed further improvement.
By month's end we had run the FEL stably while lasing at >400 W with ~2.5 mA beam at 74.8 MHz, we had lased at cw power levels up to 553 W at 4.9 µm with slightly more than 3 mA average current, and we had stably recirculated cw currents up to 3.7 mA. We could quickly establish stable cw lasing at 470 W with ~3 mA current.
Measurements of electron-beam quality continued. A very nice set of data on transverse emittance versus cryomodule gang phase (related to bunch length) was taken at the exit of the first recirculation arc. It suggests the presence of coherent synchrotron radiation effects, but it is not definitive. A carefully controlled parametric study remains to be done, and part of the program for diagnostics is to establish a good machine setup to support the study. The machine setup for CSR studies and the machine setup for high-power lasing are not necessarily one and the same.
At month's end we had just begun commissioning the first "user test"
in User Lab 1.
FEL INSTALLATION/MAINTENANCE
During Feb. 99 we validated the Machine Protection System with the
new 74.8 MHz mode, we brought the electron gun on line at 330 kV, and we
installed a suite of diagnostics on one of the cryomodule waveguides for
use in ascertaining the cause of, and fix for, the IR detector trips. Several
relatively minor installation/maintenance tasks also took place, but for
the most part we ran the machine.