Management

August 1998 was the thirteenth 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: (1) successful operation of the linac in the recirculation mode with cw currents up to 0.6 mA. (2) demonstration of cw lasing with energy recovery at low power (6W) and (3) hosting of the 20th International FEL Conference and FEL Users Workshop in Williamsburg.

CA 221: Scaleable Optical Cavity

Work continued to finalize the mounting of the high power 3 micron optics. By month's end the mirrors had been successfully brazed into their holders with additional stresses and resulting distortion within tolerances. The mirrors were then packed and sent to China Lake for final confirmation that they meet all specs. Assuming this is true, the high power 3 micron optics are now ready for installation in the FEL. Results of the testing will be available in September. In optical modeling, J. Foley, our visiting scientist was able to get the GLAD optics code operational with an upgraded version of the software running on a PC under Windows NT. He successfully set up a first test of the display capability with parabolic mirrors in a rooftop configuration which might be useful for 1 micron operation at high power. The goal of this effort will be to determine the tolerances associated with using a system of this kind as well as the rejection capability of higher order cavity modes. In the User Labs mounting of the mirror cans was completed in Lab 3 in preparation for alignment of the scanning systems for the metal processing system built by the LPC Metals Working Group.

CA 321: Upgrade Cryomodule System

Cavities IA017, IA018, IA074 and IA076 were subjected to a series of three 2K RF tests to determine if they did have increased amounts of hydrogen from rework procedures. This hydrogen can precipitate out during cooldown and increase the cavities surface losses and increase the heat load to the cryogenic bath. Cooldown rates in the FEL will be slower then that of the typical vertical test rate and can cause this hydrogen precipitation (Q-disease) to occur. This series of tests showed that two of the four cavities were sensitive to Q-disease at 50K/hr cooldown rates. These two cavities were produced from the same material (same niobium vendor). We suspect that this material which is in four of the eight cavities slated for the second module assembly will all behave the same and all four will need vacuum baking to 900°C for 4 hours. The furnace is being prepared for cavity treatments and the cavities are being mechanically measured for preparation.

A teststand dedicated for FEL pair testing was cleaned, baked and vacuum leak checked for the start of the assembly process. Plans are to start assembly of the first cavity pair that was not sensitive to Q-disease (IA074 and IA076) as soon as the cleanroom comes back on line from upgrade construction.

HOM loads for all eight cavities were fabricated, tested and assembled. Helium vessel modifications are underway to accept the FEL style HOM loads.

We inspected all shield assemblies. Minor repair was required as a result of shipping damage. This repair will be done in house. HOM loads were qualified for first cavity pair.

CA 421: Commissioning Preparations

This account has been closed to further obligations since October.

CA 431: IR FEL Commissioning

The month began with a deteriorated photocathode. Efforts to resuscitate the cathode via a combination of high-voltage processing and heat treatment ultimately resulted in a cathode suitable for operation at 330 kV, and subsequent commissioning involved operating the gun at this nominal voltage, as opposed to the usual 350 kV.

Commissioning efforts focused on recirculation, energy recovery, and lasing with energy recovery as we set out to achieve as much as possible prior to the FEL Conference that we hosted in Williamsburg, VA during 16-21 Aug. 98. We began by restoring lasing at low duty cycle with complete recirculation and energy recovery. While in the energy recovery mode, we doubled the drive laser operating frequency to 37 MHz and lased in the pulsed mode with a macropulse current (2 mA) that was twice the supplied current limit in the non-recovered mode (1 mA). We continued by running electron beam in the recirculation mode with the goal of improving beam transmission and beam quality through the recirculation and energy recovery hardware. Ultimately we achieved a maximum cw current in the energy recovery mode of 0.6 mA, and we had several periods of testing cw lasing at low laser power (6 W cw maximum).

Operations ceased on the evening of 13 Aug. 98 when an arc occurred in the gun during high voltage processing. The arc caused a vacuum leak which was subsequently localized to a flange in the high-voltage stack. Consequently we began implementing a plan for refurbishing the gun that will enable resumption of FEL commissioning in mid-September.

During the down-time, the FEL Operations and Safety Procedures, an annually updated document, was rewritten and coordinated through the cognizant individuals in the Accelerator Division.

FEL INSTALLATION

Installation and maintenance highlights in August included:

With regard to the gun refurbishment: removal of the cathode ball and anode plate for minor repolishing of blemishes due to arcing damage; completion of new, higher conductance getter shields; replacement of getter and ion pumps, and commencement of numerous minor modifications to external hardware.

Completion of hook-up and check-out of the sextupole magnets; all the magnetic elements are now installed in the FEL. Installation and leak check of the beam scraper.

Completion of the 3 µm high-power optics; they subsequently were sent to China Lake where the figure and optical loss will be measured.

Commencement of installation of the Analog Monitoring System (AMS); software control of the AMS oscilloscopes was used during this month's operations.

Installation and alignment of mirror cassettes in User Labs 4, 5 and 6; initial testing of DuPont-donated equipment for polymer processing was started.