LET: Meetings: Minutes for 2005 June 7

Attending: Representatives from LEPP, FNAL, and SLAC

Peter Tenenbaum and Mark Woodley of SLAC reported on a possible design for a vertical arc which would allow construction of a "piecewise straight" LET (a compromise between a completely straight LET, which is easy to tune for emittance preservation, and a continually-curved LET, which would preserve a constant depth below the surface). Their talk is here. The impact of the pre-BDS arc on the performance of the laser wire system was discussed, especially important since the emitted SR power would be almost 10 kW for the 1 TeV CM ILC. Key to this issue, and also the issue of component activation, is the critical energy of the SR spectrum: applications such as food processing, medical equipment sterilization, etc., are limited by regulation to 6 MeV critical energy because higher photon energies can release neutrons from nucleii, resulting in activation. (UPDATE: the critical energy of the outer bends of the system shown is 3.8 MeV, but that of the central bends is 7.6 MeV, above the 6 MeV threshold). Andrei Seryi of SLAC presented an alternative configuration, in which the 5 straight segments of the ILC are closer to equal lengths; his presentation is here. Because the arc is far from the BDS the SR backgrounds for laser wires are much lower, the critical energy and SR emittance growth are reduced, and the maximum variation in tunnel depth below grade is actually slightly reduced as well (although the variation of the central segment is increased, but it is still no larger than the variation in the outlying segments). Finally, this arrangement leaves room for the BDS and/or the last vertical arc to get longer if needed for CM energies above 1 TeV (presumably supplied by a high-gradient CLIC-style linac).

Reports from the Laboratories:

LEPP: Jeff Smith found and fixed a bug in his wakefield code, leading to smaller emittance growths for some of his linac studies; he'll present his new results in 2 weeks. Lawrence Gibbons and Andy Wolski are working with a grad student and an undergraduate on bunch compressor simulations, with a goal of reproducing the existing studies and especially verifying (or not!) the transverse emittance portions of the previous studies by Snowmass.
FNAL: Kirti Ranjan is continuing to study DFS performance as a function of quad spacing in the main linac.
SLAC: Marc Ross will launch the Machine Protection System study this week, and seeks to make a list of errors which can cause mayhem within a single bunch train. Glen White will begin looking at the alignment and static tuning of the BDS. Progress is being made on the "scarecrow" set of decks, a first release of the linac decks may happen soon.

Old Business: No items of old business.

New Business: No items of new business.

Next Meeting: Tuesday, 21 June 2005, 12:30 / 11:30 / 9:30.