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

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IR Demo Project Weekly Report, April 26 - May 1, 1998

Date: May 1, 1998

FEL Management

This week was again devoted to commissioning activities except for one shift of scheduled maintenance on Tuesday and a shift on Friday with controlled access to the accelerator vault to allow adjustments of the Beam Positioning Monitors (BPMs). The basic highlight of the week was establishing a baseline machine setup for which the electron beam is centered through all of the beam-transport magnets. This setup constitutes the starting point from which the electron beam will be fine-tuned for lasing. A summary of the process currently envisioned is given in the Commissioning section below.

On Tuesday, April 22, a contingent of accelerator physicists, materials scientists and RF engineers from the Advanced Photon Source (ANL) visited the Laboratory to tour the FEL Facility and the Test Lab and to discuss the application of SRF linear accelerators to FELs. Final preparations were made this week for the May 4th Dedication of the Applied Research Center (ARC) building on the Jefferson Lab campus. The Director's Office and the FEL management organized a large poster session which will be displayed on the ARC building during the month of May to highlight research and development activities to be performed in the building by Jefferson Lab technical staff and the faculty and students from the ARC University Consortium. Much of the equipment which will be installed in the ARC building over the next year will benefit FEL users.

May 1 is the deadline for submission of abstracts to the FEL 1998 Symposium which will be hosted by the Lab during August. Nine abstracts have been submitted by members of the FEL team.

Installation Activities

The DG and DF µ-metal corrector magnets are measured, signed off, and ready for installation next week.

The last DY 180° bend magnet was measured and signed off. It is ready for final assembly with its vacuum chamber. Installation will be later as the operating schedule allows.

The DC µ metal corrector magnets were measured and found to be out of specifications. They will be modeled to resolve the problems.

A good 3-D model of the SC sextupole magnet with a special pole tip has been verified by measurements. Work continues to lower harmonics.

Due to space limitations, the remaining 3 SQ skew quads will be individually fabricated.

In mirror can 6, the mirror was replaced and 1 picomotor was installed. A Convectron was hooked to the FEL transport line and the line was pumped down.

The insertable mirror and all FEL diagnostic beam lines in optics control were installed. In the optical cavity, the mirror gimbals were locked.

The installation of a CARM for the wiggler area was completed and the unit is being calibrated.

Commissioning

This week was devoted principally to fine-tuning the electron beam as part of preparing for lasing, and to miscellaneous measurements of beam quality, with cw runs interspersed to exercise the machine and gather more data on cathode lifetime. At week's end, we had a machine setup for which the electron beam is centered through all of the beam-transport magnets. There is considerable horizontal-vertical coupling out of the cryomodule, and so we need to install skew quadrupoles at both ends of the cryomodule to cancel out the coupling. A consequence of the coupling is that the beam rotates through the wiggler region so that there is scraping on the narrow wiggler vacuum chamber of a magnitude that prohibits cw runs with this setup. Once the skew quads are in, this should no longer be a problem. They are already in fabrication and are slated to be installed Tuesday, 5 May, which is the next maintenance day. On the positive side, results of difference-orbit measurements taken this week are entirely consistent with model predictions. Thus far the machine settings generally remain stable as long as its hardware is not modified. To do the cw runs we used the machine settings from late last week. They permit high average current but are not well suited to be used as baseline settings for lasing.

Multislit #2, located at the input to the cryomodule, was found to be rotationally misaligned. Its alignment was corrected, and one can now see a small number of slits in both the horizontal and vertical directions. An earnest attempt to take data with Multislit #2 has not yet been made due to a bug in the user-interface code that is in process of being corrected. The beam at Multislit #1, located at the exit of the cryounit, tends to be too small to submit to accurate measurements of emittance. Indications now are that the machine setup we are fine-tuning provides emittances at Multislit #1 in the range 4-6 mm-mrad, versus the PARMELA prediction of 3.5 mm-mrad. We need to devise a procedure that involves an off-nominal setting of the quadrupole magnet immediately preceding the diagnostic.

The zero-phasing technique to measure bunch length was further refined this week, and at week's end was limited by scraping at the low-energy edge of the bunch during transport of the beam through the machine to the energy-recovery dump that is used as part of the measurement, a circumstance that needs to be rectified. The quad/viewer measurement of emittance at the wiggler location was also further refined but still needs more work. Presently multimonitor data suggest, at the wiggler, an emittance of 7.0±3.5 mm-mrad in the horizontal direction, with the vertical direction still uncertain. We are trying for <8.7 mm-mrad for first light. This initial data is rough and in need of refinement before it can be taken seriously, but it is nonetheless encouraging.

The much-awaited visit of Prof. Uwe Happek and crew from the University of Georgia to install and commission their interferometric bunch-length monitors is now scheduled for 7-13 May 98.

Next week the basic program is to do orbit optimization during day shifts and beam diagnostics/beam quality measurements during swing and owl shifts. The following week is devoted to continued beam optimization during day shifts, with cw running during swing shifts and beam-quality measurements during owl shifts. The goal is to be able to insert the wiggler in mid-to-late May and try to lase. It is an optimistic goal, but one that seems to be within reach.