day we achieved 155 W cw briefly and 150 W cw stably, running at the latter power level for a time approaching an hour. The whole machine ran stably. We probably broke the 100 W milestone Tuesday, but as we later discovered, we fried the first mirror in the optical transport system that sees the light coming out of the optical cavity, and therefore we couldn't get all the power upstairs. So, Wednesday morning we put the power head directly in the mirror can so we could measure the power coming out of the optical cavity. New, better mirrors are on order and scheduled to be received here on Monday, 22 Jun 98. We of course ensured the Laser Safety Operating Procedure for the FEL Optical Control Room, as well as its Laser Safety System, were completed to let us lase safely. [Addendum added at 1520, 19 Jun 98:The power head was removed from the mirror can and taken back upstairs. The damaged mirror was rotated, but a significant area of damage still remains in the laser beam path. Notwithstanding the crummy mirror, at 1510 we had 116 W cw upstairs in the Optical Control Room(!), and the cw run was continuing.]

The machine is amazing. It is hard not to lase, especially once lasing has started, and it is easy to turn on the lasing process. We lase easily even with 2 Hz pulsed beam, and this means we will be able to insert viewers all around the machine and look at the beam profile anywhere with lasing turned on. One benefit, for example, is that we can visually stuff beam through the apertures of the recirculation loop as we commission it, and we can look at the decelerated beam in the energy- recovery dump line. This should make commissioning the full machine much easier than we had thought. We can provide both pulsed and cw beam to users as they desire. We also clearly see lasing harmonics as high as the 11th harmonic. There is so much to learn. We collected a wealth of spectral data yesterday (18 Jun 98), and of course more measurements of the lasing process will be forthcoming as we optimize the FEL. The potential of the machine is not yet known. Every indication is that the wiggler coupling efficiency is enormous, possibly of order 1.5% as compared to the anticipated 0.5%. The quality of both the wiggler and the electron beam is impeccable. We will know more (and with more accuracy) in due time.

Having achieved our key milestone, the commissioning philosophy now shifts. Summer plans fall into the following categories:
-understand and optimize the FEL,
-set up and conduct the first set of user experiments,
-take beam through the first recirculation arc [for coherent synchrotron radiation (CSR) measurements] and beyond.

Regarding the latter, to do parametric studies of CSR, we need all arc magnets installed except the sextupoles. What are missing are the air-core correctors. They are on site but need to be characterized and installed, tasks that should be complete by 15 Jul 98.

We formulated a list of near-term tasks, and they are as follows:
-measure x-ray production from Thompson back-scattering,
-do electron-beam energy scans while lasing,