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\2009 - 2-

RF FOIL (1) -- R&D PLANPhase 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 (X0 ≈ 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\2009 - 3-

(extras)

R. Mountain, Syracuse University VELO Update, 5 Nov\2009 - 4-

RF FOIL & RF BOXcross 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 mm2

• 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)

CURRENTDESIGN

FOIL

R. Mountain, Syracuse University VELO Update, 5 Nov\2009 - 5-

RF FOIL REQUIREMENTSPhysics:

– 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\2009 - 6-

Composite Mirror Applications Inc.Initial conversations very promising

– They are interested in this projectCMA 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\2009 - 7-

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”