MEMORANDUM

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

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IRFEL Weekly Report Oct. 21-25 1996

Date: October 25, 1996

Management

The September 1996 monthly report was finalized and distributed.

Interim milestones for the IRFEL Program were finalized this week. They are serving as a communication aid in phasing the Accelerator Division resources that will be needed for installation, alignment, and checkout of the various subsystems.

The WBS managers began preparing for an informal review of the status of the IRFEL Program by the Navy which is scheduled to take place next Tuesday, 29 October.

A draft agenda was prepared for the first meeting of the SURA Maritime Technical Advisory Committee on December 17-18.

Injector Test Stand

Regarding operation of the 250 keV gun:

We ran the gun for a 6-hour period at 1 mA average current, during which the quantum efficiency (QE) dropped from 4.8% to 3.5%, with the bulk of the change occurring in the first 45 minutes. The data show an e-folding time of about 40 hours. The area of the cathode used was 6 mm off center. It had an initial QE about 30% higher than the center of the cathode which was used for previous tests. After the run, the relative QE of the center of the cathode was remeasured and, within the accuracy of the measurement, found to be unchanged. The effect of the solenoid on the emittance of the beam exiting off-axis is still unknown, so we don't yet know whether this additional current from the cathode is usable for the FEL.

We continue to have problems with electro-optical modulators (EOMs). Of the four in-hand, two have failed hard, and two do not meet the specification but might be usable. Consequently, no thesis-quality transverse-emittance data have been taken. We are working with the vendor to remedy the situation and expect replacements sometime next week. Meanwhile, a schedule to cover multiple-shift operation has been posted in anticipation of laser availability. Presently plans are to explore gun stability via additional cw runs while laser operation is worked.

Regarding fabrication of the new high-voltage stack:

The first ceramic was coated with the high resistance coating at HiTemp. Unfortunately, the final layer of plating (nickel) on the metalized ends evaporated and spoiled the coating properties because of the high firing temperature. Processing a second ceramic was started by removing the nickel down to the moly-manganese base metalization and preparing for the high resistance coating. The original ceramic will have its metallization and coating ground away and be remetalized and coated again. The process is being monitored by a Jefferson Lab employee detailed to HiTemp.

The new mid voltage ring for the stack is being polished on two shifts.

A taper in the bores of the flimsy kovar rings for the new ceramics prevented complete fit-up on the metalized ends. The rings were rebored by our shop and sent back to HiTemp.

The rotisserie for ion implantation was pumped down and tested for rotation and its shipping crate made up. We will have to mount a more powerful alternate motor to drive it, but in all other respects, it is ready to ship. The test body made from the original ceramic material was prepared for the full scale ion implantation test at Lawrence Berkeley Lab.

We have decided that the anti-field-emission coated cathode support tube would be installed later, after we try the new stack of ceramics at the higher voltage gradients. It is more prudent to make changes "one at a time" and experience shows that we could recover from a leak in a ceramic if they exhibit the same characteristic punctures. Polishing has stopped at 9 micron diamond grit on cathode support tube.

The first anti-field-emission coated sample electrodes were received from FM Technologies. They will undergo effectiveness tests at the College of William and Mary next week.

Regarding testing of the injector cryounit:

The cavity quality factor for the second cavity in the unit was measured to be 5.5 e9 at 4 MV/m. This agrees with measurements in the Vertical Test Assembly done prior to installation of the cavities into the cryostat. Today (Friday, 25 Oct) and Monday we will make measurements at higher gradients. All acceptance tests should be complete by close of business Tuesday.

Tests were done of the magnetostrictive tuner to generate 1 A and 5 A direct-current hysteresis loops. We are evaluating the results.

The static heat load of the cryostat is about 6 W, which concurs with the design value.

Regarding other ITS progress:

The chopper cavity, which will be needed for measurements of bunch length aspart of the reconfiguration for 350 keV operation, is now undergoing rf testing.

Acceptance tests of the ITS BPM were successfully completed.

Accelerator Systems

A simulation of the IRFEL injector with first-light beam was run this week. It indicates that we can compress 33 pC bunches down to rms bunch lengths of about 0.5 ps by the time they reach the entrance of the linac. Based on this finding, we project that, with the additional bunching provided by the optical chicane preceding the wiggler, we should be able to get rms bunch lengths of about 0.25 ps at the wiggler if the linac is phased correctly. This is substantially shorter than the nominal 1 ps requirement for first light. Our projection still needs to be confirmed via simulations of the beam all the way to the wiggler, and they are currently underway.

The saddle coil for the modified prototype dipole magnet was received and installed. The prototype magnet was then characterized. The saddle-coil configuration provided a substantial improvement in the magnitude of the fringe fields, taking them all the way down to the default levels that had been used in the original linear-optics design of the transport lattice. It also cut down how far the fringe fields extend from the magnet aperture, although they still extend further than we would comfortably like. Therefore we are going to machine a prototype field clamp and can probably install it and test the modified magnet by the end of next week.

The Northrop-Grumman magnet designer visited us this week, and we coordinated the above developments with him. He plans to adjust his dipole-magnet designs to accommodate the saddle-coil configuration. We expect to be able to place the optical-chicane dipoles in procurement in about 3 weeks. The remaining dipoles will follow after finalizing their respective designs.

The procurement package for the weak quadrupole magnets was reduced because a decision was made to remove 10 quadrupole magnets from the nuclear-physics accelerator for use in the IRFEL. It also was modified to include a 2-month window for ordering the additional weak quads that would be needed for upgrading the design to include a second cryomodule. The package was then sent to Procurement early this week.

Detailed requirements were identified for the beamline leading into the straight-ahead dump that will be used in generating first light. Based on these requirements, this beamline was designed, and the necessary beam-rastering magnets were specified. A similar design was also completed for the beamline leading into the injector dump, again in order to specify the necessary beam-rastering magnets. A similar analysis is underway for the beamline leading to the energy-recovery dump.

FEL System

Wiggler

STI Optronics has signed off the top-level assembly drawing and has sent us both the hardcopy and an electronic copy of the drawing. This will be integrated into the assembly drawings for the wiggler girder. The conceptual design for the wiggler girder is complete, and details are now being engineered. A review was held with V. Christina from Northrop-Grumman to go over the conceptual design of the vacuum chamber.

Optics

Layouts for the optical transport lines for both the FEL and for the photoinjector in the new FEL Facility were initiated. Many of the existing components in the ITS optical transport line can be reused. Procurements of components for the optical cavity continue.

Operations/Commissioning

Considerable progress was made in delineating the control interfaces that are implicit in the design of the IRFEL. This has enabled us to get better organized with respect to identifying the required control software and generating the software that isn't already available.

As mentioned above, detailed requirements were identified for the beamline leading into the straight-ahead dump that will be used in generating first light.

Facility

Due to rain last week, plans were shuffled for the concrete pour that would finalize the ceiling of the enclosure and the truck ramp base. Wall forms for the shielding level were placed and most of the forms for the second pour for the entrance labyrinth were positioned. The pour is now scheduled for next Tuesday, and it will include many of these areas. The overall schedule is unaffected.

We started the procurement process for a new drive-laser clean room for the FEL Facility. It will lead to a schedule improvement because it will be ready as soon as the ITS is shut down.

We held an internal design review for the high-voltage power supply to be installed in the FEL Facility for powering the gun there. We plan to get a bid package out for the pressure vessel by late November.