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.