April 1998 was devoted principally to commissioning the FEL accelerator driver, with the goal of achieving the average current (1.1 mA) and energy (38 MeV) needed for first light. By month's end, we had achieved these goals and had begun the process of fine-tuning the electron beam to achieve the beam quality needed for lasing. A major part of these activities involved commissioning a wide variety of beam diagnostics, including a current-monitor cavity, transverse- emittance diagnostics (two multislits, quad/viewer, and multimonitor method), longitudinal phase- space diagnostics (zero-phasing technique for bunch length, two M_56 cavities, energy spread on viewers), and beam-position monitors. We have not yet finished commissioning the existing diagnostics, but we have a good start, and we still need to receive and install the University of Georgia interferometric bunch-length monitors. Regarding the beam-quality data taken to date, we are generally measuring six-dimensional phase-space parameters that are within factors of 2-3 of theoretical, a favorable situation given the short time we have been running the accelerator. In addition, cathode e-folding lifetime appears to be roughly 15-20 hours, and so preliminary indications are that the cathode will support a full 24-hour day period between recesiations when we attempt to lase, which is a favorable circumstance.

This month's cw runs were done with machine setups that permitted cw running butwere not well-suited as a baseline that eventually would permit lasing. Therefore we embarked on developing a suitable baseline setup. By month's end, we had developed a machine setup for which the electron beam is centered through all of the beam-transport magnets. With that setup, 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 slated to be installed Tuesday, 5 May 98, after which we hope to fine-tune the setup to achieve both the desired beam quality and "easy" mA-level cw running.

In short, based on where we stand now, our goal is to be able to insert the wiggler before the end of May and try to lase in June. It is an optimistic goal, but one that seems to be within reach. We will not install the wiggler until we establish sufficiently good beam quality.

FEL INSTALLATION

Installation highlights in April included:

Completion, debugging, and verification of the Machine Protection System (MPS). Testing and resetting the associated beam-loss monitors is an ongoing process, as is adjusting the MPS logic in keeping with the various commissioning activities that arise.