Management

Highlights for the week include the use of the FEL for several user tests involving research collaborations with the Northrop-Grumman Corp. and the College of William & Mary.

The preliminary program for the next Laser Processing Consortium (LPC) workshop was distributed this week to FEL program's e-mail distribution list in addition to posting on the Web at http://www.jlab.org/intralab/calendar/wkshp.html?news. The LPC Workshop will be held 17-18 Jun 99 at Jefferson Lab. The program includes presentations from many of the existing collaborations and several new proposals for use of the FEL for both basic and applied R&D.

The final report from the Navy contract close-out review held on 26-27 Apr 99 was distributed this week from the Navy High Energy Laser Office at NRL. We thank Joung Cook and John Albertine for co-chairing the Review and for their complimentary and useful report.

As of midnight this evening (28 May 99) the FEL will be shutting down until mid-July because of scheduled site-wide maintenance activities on the Central Helium Liquifier, AC power and computer systems. These site-wide systems are expected to be available by July 5. Given the present limited resources in the FEL program, near-term operations of the FEL will be limited to activities which support machine physics data needed for the design of the FEL Upgrade and for high return users tests which support on-going user proposal development. The next operational

period scheduled to meet these objectives is presently 12 Jul 99 to 13 Aug 99.

These weekly reports have been generated every week for the last three years during the period of the joint Navy-DOE IR FEL construction and commissioning project. We will take a hiatus until the restart of operations in mid-July and wish all our readers a healthy and productive summer.
 
 

FEL Installation/Maintenance Activities

The gun's high-voltage power supply failed last Friday afternoon. The failure manifested itself first in arc-damaged connectors and feedthroughs that connect the supply to the stacks in the high-voltage tank. These components were replaced Monday, after which it becameclear there was also a problem with the supply itself. Fortunately we had a spare supply that we swapped with the damaged one, which ultimately enabled us to resume running Tuesday afternoon. The calibration of the spare supply is different from the original and will need to be firmly established. In the meantime, we used the eagle-eye method for determining the calibration: we adjusted the gun voltage until the viewer images of the electron beam looked right. Parts for the damaged supply are on order from the vendor; it will be repaired during the June down.
 
 

FEL Commissioning Activities

The principal activities of the week centered on electron-beam diagnostics and lasing studies in User Lab 1.

Regarding the former, we managed to get signals from both interferometric bunch-length monitors. We put the monitor that had been in the injection line ("Happek #1", from which we had never registered a signal) just downstream of the wiggler (the location of "Happek #2").

We put Happek #2 at the entrance of the first recirculation arc to support coherent-synchrotron- radiation studies. They are now both registering, but it became clear, for reasons still unknown, that the sensitivity of Happek #1 is less than that of Happek #2. Other diagnostic activities were devoted to checking the electron-beam setup as an aid to lasing, to doing a short exploratory study of injector properties versus cryounit cavity phase, and to emittance measurements.

The emittance measurements were impeded by too much camera sensitivity to ghost pulses on the viewer (which we partially corrected using filters), and a key viewer foil being wrinkled, thereby generating a warped beam spot. The foil will be replaced during the June down.
 
 

During FEL operations several tests were done to characterize the laser and perform initial testing of user systems. A measurement of the optical mode size while CW lasing in the user lab was performed using a scanning knife edge. We are in the process of comparing that data to pyrocam images taken in the optical control room. An initial set of tests were performed at

3.27 microns to determine the ablation threshold of Kapton for collaborators from Northrop Grumman and the College of William and mary. There is a potential NASA application for this in making perforated solar sails. Preliminary indications are that the threshold is near theoritical

predictions. We also performed some ablation testing on cobalt for PLD and looked for absorption effects on and off molecular resonances near 3 mircons, again for collaborators from Willliam and Mary. A single pulse capability was added to the laser and a remotely controllable stage in Lab 1 to enhance the ease of performing these tests.