Monthly Report IR Demo FEL Upgrade and Commissioning Project

June 1998


Management

June 1998 was the eleventh month for the $3.7M IR Demo Upgrade and Commissioning project. Cost and schedule performance are described in the accompanying Performance Assessment report by Gordon Smith. Highlights for the month include: attainment of "first light" from the FEL on June 15, 1998 and attainment of an average power record for FELs of 155 watts, just two days later on June 17, 1998.

CA 221: Scaleable Optical Cavity

June saw the completion of the commissioning of the FEL systems when first lasing was produced on June 15 at 20:25. Initial lasing was in pulsed mode which indicated that operation was strong and insensitive to alignments, etc. This was confirmed in subsequent runs the following days when first 50 then 155 W of CW lasing power at 5 microns was produced using the 98% outcoupler designed for 10 W operation. This output is more than 15 times the previous record for any FEL.

Mirror coating measurements by China Lake had set an upper bound on mirror absorption of 0.001 Our measurements suggest that it is roughly 5 times lower than that, truly excellent performance for the 5 micron band. We are in the process of comparing FEL performance to our models. If anything, early data suggests the laser is operating better than our model predicts.

We have taken spectral data at various cavity lengths and have effectively increased outcoupling by operating at lower linac repetition rates than the cavity round trip time. Lasing with more than 16% outcoupling has been observed. Diagnostics commissioned include the monochrometer with both a boxcar and a lock-in amplifier interface, the pyroelectric camera, and the power meters. Harmonic radiation was observed by eye and camera out to the 11th harmonic in the yellow/green.

Work in the coming month will be to install the high power mirrors and see what level of power can be produced and also to install and align an array of user equipment in preparation for the first user experiments.

CA 321: Upgrade Cryomodule System

The second set of four cavities were vertically tested. As a result of additional processing cycles, all cavities for the upgrade cryomodule have been pushed above 12 MV/M (vs. 8 MV/M specifications). The dog leg coupler window test stands were fabricated and leaked checked. The first two windows have been placed on the test stands and are ready for testing for cryogenic losses.

HOM ceramics were received and the fabrication of all the loads have been completed. Testing of these loads will be accomplished next month.

CA 421: Commissioning Preparations

This account has been closed to further obligations since October.

CA 521: FEL COMMISSIONING

We worked through the first half of the month to obtain the electron-beam quality required for lasing. On 13 Jun 98, a Saturday, we installed the wiggler. On Monday afternoon, 15 Jun 98, we turned on the machine and began lasing at low power just five hours later. We then lased at tens of watts on Tuesday, and on Wednesday at 1250 we achieved 100 W cw at 4.95 µm. Ultimately that same day we achieved 155 W cw briefly and 150 W cw stably, running at the latter power level for a time approaching an hour. The whole machine ran stably. By week's end, we were delivering well over 100 watts cw stably into the Optical Control Room located upstairs in the FEL Facility.

Encouraged by the success, we resolved to try for kilowatt lasing this summer. In turn, we needed to finish all remaining details on the machine for high power operations. To take full advantage of the availability of people, we did not run electron beam during the remainder of the month. Instead, we used the time to complete numerous installation activities, foremost of which was the entire vacuum system of the machine. Part of the vacuum activities was to replace eight problematic valves. Another activity centered on attempting to rejuvenate the photocathode in situ by way of high-voltage processing and heat cleaning. At month's end, the cathode's photoresponse appeared to be marginal, and plans were being made toward another rejuvenation attempt.

We began planning how to attempt kilowatt operation this summer while interleaving the associated commissioning activities with a nominal effort to support user experiments. A considerable amount of progress was made toward developing procedures that support recirculation and energy recovery, including particularly the "Lase with Energy Recovery Metaprocedure" and "RF Stability during Energy Recovery".

Replacing eight beamline valves because of concerns about their reliability; modifying the beamline leading to the injector dump to suppress scraping at our highest average currents (4-5 mA); and placing the entire machine under vacuum for the first time.

Upgrading the drive-laser pulse controller to permit operation at 37.4 MHz in support of kW-level lasing, as well as rejuvenating the photocathode.

Installing a synchrotron radiation monitor and limit switches on the associated viewers in both of the 180-degree dipole magnets, four additional DF trim dipoles, two DG and four DC trim dipoles in the recirculation arcs, and the last remaining skew quadrupole in the injector.

Changing the viewer flag for one of the wiggler viewers from graphite to beryllium; installing both of the Happek interferometric bunch-length monitors; and installing all cabling for the beam-loss monitors in the recirculation loop.

Testing additional ceramic windows with the 50 kW klystron system; the tests were successful.

Completing instrumentation of the Optical Control Room, to include its Laser Safety System (LSS); certifying the LSS configuration for the user laboratories; and progressing with the setup of both the Polymer Lab and the Metals Lab in the FEL Facility.