Minutes of FEL Gun Committee Meeting

Thursday, 20 May 99
By: Charlie Sinclair

Addendum to the Minutes


Just a couple clarifications regarding the FEL Gun minutes.

First, regarding checking out the cesium flow from the new cesiator. I am sure Larry Phillips has a rate monitor which can in principle do the job. The industry standard is pretty much a quartz crystal which resonates about 6 MHz. The physical principle is simply that adding mass to the crystal lowers the resonant frequency. These systems, when supplied commercially, are designed to monitor thicknesses considerably greater than a monolayer, and thus do not normally have electronics which permits observation of single Hz frequency shifts. To test the cesiator, where a single monolayer is the relevant thickness to be monitored (about 100 ngm/cm**2), a full monolayer corresponds to about 10 Hz frequency drop. Given the anticipated rate of cesium delivery, the rate of frequency change will be at or below about 1 Hz/minute. It is easy to get frequency drifts larger than this due to thermal effects, electronic instability, etc., etc. We have made modified electronics for our crystal monitor to observe 1 Hz frequency shifts, though we have not used it at the level below 1 Hz/minute. Unless Larry has special electronics, his monitor probably won't do the job. There is certainly no problem doing the test(s) in a bell jar, which is what I suspect Larry has for a test chamber. I do not have a test chamber per se, but rather build or assemble from available parts a suitable chamber for a particular job, as the need arises. In the present case, it is necessary to mount the crystal thickness monitor with respect to the cesiator as it would be in the gun - i.e. the thickness monitor should be where the cathode is with respect to the cesiator. Perhaps this can be done easily in the (presumed) bell jar, perhaps not. If not, someone needs to look at the geometry and figure out what needs to be put together to get a meaningful test done. Of course, one could always just put the new cesiator in and assume it would work....... Not my style.

Also, regarding the titanium, I was suggesting buying a slug of it large enough to make a new ball, not a much smaller piece for testing in the ion implantation and/or coating test chamber (though the latter would surely be interesting also)

May 20, 1999 Minutes