Project Update: A Possible New RF FOIL for the VELO UPGRADE Ray Mountain, Sheldon Stone Syracuse University

R. Mountain, Syracuse University VELO Update, 5 Nov\ RF FOIL (1) -- R&D PLAN Phase I Objective: Produce a quarter-length RF Foil prototype, incorporating all difficult design features needed. –Collaboration with CMA, Inc. (compositemirrors.com) –Develop a new high performance material, likely a multi-function nanocomposite material. A candidate formulation has been identified (X 0 ≈ ½ AlMg3) –Develop processing procedures for the materials and structure shape –Optimize material and process parameters by series of coupon samples –Fabricate the ¼-length prototype, incorporating the foil surface, sides, and flange in one integrated piece (no sealing) –Test and evaluate performance characteristics, including metrology, thickness uniformity, vacuum permeability, etc. –Build “accelerator simulator” as RF shielding test chamber (at SU) Evaluation Phase: Evaluate viability of prototype material and structure. Perform radiation damage testing, involve CERN LHC experts for determination of its operation in primary vacuum, etc. Phase II Objective: Design and fabricate real RF Foil for LHCb upgrade. Plan to begin Phase I in December, but awaiting funding decision (expected soon)...

R. Mountain, Syracuse University VELO Update, 5 Nov\ (extras)

R. Mountain, Syracuse University VELO Update, 5 Nov\ RF FOIL & RF BOX cross section ~1mm INSIDE VIEW OF RF-BOX MOUNTED IN VACUUM VESSEL Separates modules from beam vacuum Foil is 300 um AlMg3, coated with insulator and getter Foil shape set by overlapping sensors and beam clearance and beam effects Large area: 200 x 1000 mm 2 Maximum allowed pressure differential: 5 mbar (=> 10 kg = 22 lb) Shields against beam-induced EMI Wakefield suppressors to adapt beam pipe geometry Was a huge engineering effort (NIKHEF) CURRENT DESIGN FOIL

R. Mountain, Syracuse University VELO Update, 5 Nov\ RF FOIL REQUIREMENTS Physics: –Must not allow excessive multiple scattering should have the smallest radiation length possible (e.g., low Z) in acceptance should minimize total material before first measured point [MFL,PC] –Must allow detectors to overlap, for reasons of tracking (i.e., no acceptance gaps) and alignment will have complicated corrugated shape –Must get as close as possible transversely to IP must allow approach to be < ~7.mm (original design goal was 5.mm, accelerator limit in 2001) –Must stand high radiation environment without degradation in mechanical or electrical properties must withstand ~500 Mrad dose [MA,PC] Mechanical: –Separate primary vacuum <1e-9 mbar (accelerator) from secondary vacuum ~1e-4 mbar (detector), and maintain this ultra-high vacuum level must have no pinholes or virtual leaks outgassing must be minimal –Must mechanically hold differential vacuum of ~5.mbar (transient) to ~1e-4 mbar (steady) without rupturing or even deflecting so as to touch sensors (1 mm clearance) must be strong (to this level of load) must be stiff must have low fatigue, for repeated pumpings must hold mechanical stability and accuracy (tolerances) Electrical: –Must shield against RF EMI pick-up effects from accelerator (noise in detectors) must provide enough RF skin depth thickness (T<10 -3 ) must be made at least partly of good conductor must reduce any surface/skin effects (?) [MFL] –Must not electrically short sensors if contact is made must have inner insulating surface or coating Thermal: –Must handle heating effects (electronics, beam wakefield) and cooling effects (modules, bb radiation) and not thermally deform so as to damage sensors must have sufficiently low CTE from about +40ºC down to -30ºC (? plus beam heating) wakefield power dissipation can be large (~kW) –Perhaps like it to help with cooling the electronics [pref not req’d] low emissivity surface (or coating), or actual cooling of foil (active/passive) [SB] would need then to bleed off heat away from sensors Beam (Electrodynamic): –Must suppress wakefield impact on beams need smooth geometry to reduce effects [MFL] need continuous electrical contact from one end to the other [MFL] should have a small beam aperture [PC] –Must be “dynamic”-vacuum-compatible (i.e., effects due to presence of beam, which means ion-induced desorption, synchrotron radiation, electron multipacting) [MFL] so need NEG coating on UHV side, which as low (ion-, photon-, electron-) desorption coefficient

R. Mountain, Syracuse University VELO Update, 5 Nov\ Composite Mirror Applications Inc. Initial conversations very promising –They are interested in this project CMA has experience producing: –Many space-based mirrors and structures for NASA –Spherical mirrors for LHCb RICH-1 –Prototype mirrors for BTEV RICH Manufacture technique –Compression molding replication Make forms (positive + negative) Lay up sheets of CF “cloth” and “uni” with resin Apply elevated pressure and temperature to forms, resin flows, squeezes layup to required thickness –Can replicate features down to 3 mm (or maybe smaller), as long as they are on the forming mandrel –Can make many types of structures, can make exact duplicates of structures as well –Have good control of thickness variations –Have solved adhesion problem in vacuum (delamination, so-called) 18 years experience in high strength Aluminum adhesion to polymers Used in many space (vacuum) applications Good corporate partner for R&D

R. Mountain, Syracuse University VELO Update, 5 Nov\ FIRST ORDER DESIGN (1) Keep same design as current foil –same geometric form of foil and box –as a basis for discussions, for now Replace AlMg3 by CFRP composite –plus Al deposition and NEG on accelerator side –plus insulator deposition on VELO side (n.b. CF is conductive) Produce foil + box + flange as a single integrated unit –Avoids welding foil to box, and other sealing problems –No seams, better for vacuum tightness Investigate the critical issues using this first-order design … FOIL BOX FLANGE “straw man”