Main Linac Issues for RDR 1/20/2006 Area group H. Hayano From Linac Area discussion posted on the web:

Power source Modulator and klystron power Should we use more high power klystron, modulator? 10MW klystron drives 24 TESLA cavities, considering 7% WG loss and 11% overhead for 35MV/m operation. 0.21%/m WG loss (7% loss=33m), split/combine loss, circulator loss, attenuator loss in each branch, input coupler matching. --> Need detail of WG configuration and loss estimation. Klystron performance Currently available tubes are enough robust? It appears there are problems with tubes of Thales, CPI and Toshiba. --> should update BCD to reflect this, should strengthen R&D to solve them. RF distribution Need detail configuration design to maximize average gradient. Three way distribution system with attenuator in each cryomodule feed as an possible scheme. --> Need detail of WG configuration and loss estimation, again. Need performance simulation with cavity gradient variation for attenuator requirement.

Cryomodule(1) Cryo-plant spacing What is a reasonable value of overhead? TESLA TDR : 1.5, CERN philosophy : 1.7. The largest available cryoplant and the full allowable pressure drops in cryomodule piping determine the spacing. Overhead factor makes spacing more closer than present 5.3km. --> Need decision of overhead factor. Cavity package Lutz will mention this, later. --> Chris’s presentation. Cavity spacing TDR 283mm iris-to-iris spacing reasonable? There would be discussion at CERN cryomodule meeting. --> Chris’s presentation. HF absorber between cryomodules Need to determine specs/size of the higher frequency absorber. absorbing power, location, size would be discussed at CERN cryomodule meeting. --> Chris’s presentation. Spoilers MPS people may want to put spoilers in every cryomodule to avoid direct beam hit of cavities. beam hit to spoiler may cause deposition of materials on the cavities. --> install them at warm side, and make protection valve system to isolate cold section.

Cryomodule(2) Quadrupole spacing One in every 32 cavities for lower cost, change it back to one in every 24. To make all RF unit the same distribution system, one quad in one RF unit would be good. --> send it to CCB. Quadrupole location Quad-package in center of module is harder to do movers, not directly supported. need to stress on keeping cleanness of BPM and quad beam pipe. Independent cryostat for quad-BPM package is worth discussing. --> continue discussion and R&D. Quad type and strength Should we consider superferric quads and smaller aperture? need several size of quad to cover energy variation(5-250GeV). How do we deal with TeV upgrade to cover GeV? Independent cryostat for quad-BPM package is worth discussing for moving its position in TeV upgrade. --> continue discussion and R&D. Correctors Should we make correctors isolated from quads? corrector windings on quads will induce persistent current on quad windings resulting residual dipole field. Move corrector far away from quad or install mover on the quad? --> continue discussion and R&D.

Cryomodule(3) BPM resolution What value of Linac BPM resolution should be? LET simulations suggest to be 5 ~10µm. Resolving beam jitter request 1/3 of sigma (say a few 100nm). Tune-up operation request enough resolution with 1/10 charge of beam. Within a similar cost, better resolution should be taken. --> continue discussion, R&D and cost estimation with/by instrumentation GG.

Over all Instrumentation sections Number of diagnostic region? Need to specify the number of diagnostic section. The spoilers for MPS should include in this region. --> ask instrumentation GG. Packing fraction We should define the packing fraction of Linac. need to specify the length of quad, corrector, BPM, HF absorber. --> Chris’s presentation. End of list