To: J. Cook, D. Helms, W. Skinner

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IR Demo Project Weekly Report, February 9-13, 1998

Date: February 13, 1998

Management

Highlights for the week include: (1) notice of DOE support for CSR experiments on the IR Demo, (2) The "opportunity" to learn more about the surface physics of the IR Demo photogun by dis-assembling the gun stack for a careful examination and (3) good progress made on the alignment of the optical cavity components.

Preparations were made this week for next week's Navy program meeting which is scheduled for February 17 - 18. Representatives from the Navy program office at NRL and our colleagues from the Naval Post Graduate School are expected to attend the meeting.

On Thursday, February 12, we received notice from the DOE BES chemical science program office that Jefferson Lab would be receiving $200k of FY98 funds for performing CSR measurements and modelling. This work is an integral part of our current commissioning effort; moreover CSR effects are of interest to BES for the design of the 4th generation light sources.

FEL Installation Activities

Measurements of the first 180-degree dipole magnet were completed. Our Machine Shop modified its return-leg pieces to make proper assembly more reliable. This work does not affect the characteristics of the magnet. Plans are to install this magnet in the FEL Facility next week.

Installation of an independent Laser Safety System (LSS) for User Lab Room 6 is planned for early next week. It will use a smart card to control access to the room. Since the FEL laser is not presently operating, this LSS will not be tied into the FEL system.

Installation of the Machine Protection System continues and is scheduled to be completed next week.

The mirror mounts for the optical cavity were reworked and reinstalled. The upstream pellicle was tested, reworked, and will be reinstalled today.

Installation was completed to provide low-conductivity-water cooling for the insertable dumps. The stand for the insertable dump located at the end of the second recirculation arc was installed. The RF higher-order-mode filters were tested this week. Additional testing is scheduled for next week to measure the cavity quality factors in the cryomodule and Miram curves for all of its klystrons.

FEL Commissioning Activities

After refurbishment of the gun, commissioning resumed Monday, 9 Feb. 98. Unfortunately, it was short-lived because the gun field-emitted copiously down the beam pipe, a most unwelcome and unexpected circumstance. We terminated commissioning and began an autopsy of the gun. At this writing (1400 Friday, 13 Feb. 98), we know that the cathode has global particulates and a few localized splotches. Spectroscopy results obtained in-house indicate the presence of copper and iron, as well as several other elements. There is no evidence of pitting; the observations suggest arcing and/or sputtering occurred. The cathode will now be sent to William and Mary for auger analysis. Today we began opening the gun to examine the ball, tube, and anode plate and thereby acquire additional information for diagnosing the cause of the problem. Our present best estimate is that we will resume commissioning with beam on 2 Mar 98. We will be able to use the intervening time productively by doing more installation, RF and SRF commissioning, and training people on the FEL control system so that they will be better prepared for, and more efficient during, commissioning.

By way of simulations (PARMELA) we now have optimized machine settings for both 60 pC and 135 pC bunches. The 135 pC settings should "work" at 60 pC, and using them would eventually save time by circumventing the need to commission "twice", once for each bunch charge. However, the peak current for first light would be significantly higher if the optimal 60 pC settings were used. Correspondingly, the FEL gain would also be significantly higher, lending more confidence in successful lasing. On the other hand, there would not be as much flexibility a priori for CSR experiments were the settings "limited" to 60 pC. Because we wish to do everything within reason to assure success and efficiency in achieving first light, we will likely use the 60 pC optimal settings, and we will look at implications for CSR experiments by way of simulations. We hope next week to adopt baseline settings and freeze them so everyone can be clear and aligned on the precise program for near-term commissioning.