A Possible New RF FOIL
for the VELO UPGRADE
Ray Mountain, Sheldon Stone
Syracuse University
CURRENT
DESIGN
RF FOIL & RF BOX
cross section
~1mm
• Separate modules from beam vacuum
• Foil is 300 um AlMg3, coated with
insulator and getter
• Foil shape set by overlapping sensors
and beam clearance
• Large area: 200 x 1000 mm2
• Maximum allowed pressure differential:
5 mbar (=> 10 kg = 22 lb)
• Shield against beam-induced EMI
• Wakefield suppressors to adapt beam
pipe geometry
• Was a huge engineering effort (NIKHEF)
FOIL
INSIDE VIEW OF RF-BOX MOUNTED IN VACUUM VESSEL
R. Mountain, Syracuse University
SU HEP Group Meeting, 1 Apr 2009 -2-
CURRENT
DESIGN
BEAM’S-EYE VIEW
van Beuzekom – RD07
R. Mountain, Syracuse University
SU HEP Group Meeting, 1 Apr 2009 -3-
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]
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)
R. Mountain, Syracuse University
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
• plus ???
SU HEP Group Meeting, 1 Apr 2009 -4-
IDEAS FOR UPGRADE DESIGN
(1) Consider having NO RF shield
– Variation of BTEV idea of having
sensors in primary vacuum, using wires
or strips to guide the beam (mirror)
current and local cryo-pumping to
remove outgassing
– A major re-think would be needed,
since no place for wires with overlaps
and many opportunities to despoil
primary vacuum
(2) Use existing technology, make foil
thinner by better fabrication method
– This is being pursued by NIKHEF, for
the current AlMg3 alloy
– Also Totem (@LHC) idea of using 150
um Inconel (Ni-Cr) foil at a distance of
1 mm from beam
R. Mountain, Syracuse University
(3) Use carbon fiber composite
substrate and replication technology
– Like that used in RICH-1 mirrors
(orig. BTEV RICH)
(4) Some other (crazy) idea
– Adapt RF cloth
– Adapt RF laminates
– …
SU HEP Group Meeting, 1 Apr 2009 -5-
Composite Mirror Applications Inc.
Initial conversations very promising
– They are interested in this project
CMA has experience producing
– Spherical mirrors for LHCb RICH-1
– Prototypes for BTEV RICH mirrors
– Many space-based mirrors and structures
for NASA
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
– Have good control of thickness variations
– Have solved adhesion problem in vacuum
• 18 years experience in high strength
Aluminum adhesion to polymers
R. Mountain, Syracuse University
SU HEP Group Meeting, 1 Apr 2009 -6-
FIRST ORDER DESIGN (1)
“straw man”
Keep same design as current foil
– 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)
FOIL
FLANGE
BOX
Produce foil + box + flange as an
integrated unit
– Avoids welding and other sealing
problems
– No seams, better for vacuum tightness
R. Mountain, Syracuse University
SU HEP Group Meeting, 1 Apr 2009 -7-
FIRST ORDER DESIGN (2)
Material
– Use same material as RICH1 mirrors
– M46J Carbon fibers + EX-1515 resin
• Large modulus fibers
• Low density
• Resin has “high” radiation
resistance and low outgassing
• Resin resists microcracking
– Layup: 4 ply thick ~ 0.4 mm
– Aluminum: 10 um thick (can do
thicker but introduces complications)
Radiation length
R. Mountain, Syracuse University
SU HEP Group Meeting, 1 Apr 2009 -8-
FIRST ORDER DESIGN (3)
S kin De pth as a fun ction of fre qu e ncy
RF shielding
– Aluminum has skin depth 13 um @
40 MHz (18 @ 20)
– But CF is conductive, so can get
reflection from it also
– (will calculate when get
conductivity info from CMA)
1 10
3
_Al( f )
m
100
_Cu( f )
m
_SS( f )
m
10
Mechanical stability under vacuum
– Simple plate approximation
– Min thickness required for 1 mm
max deflection with load 10 mbar
• AlMg3: 310 um (0.36%RL)
• CFRP: 250 um (0.11%RL)
1
1
10
100
f
MHz
Min im u m th ickn etmin
ss re qu ire d for 1 m m m ax de fle ction at give n DP = 1 0 m bar
3
2.5
(not too stupid: early FEA with
real foil design showed 0.35
mm deflection for 0.25 mm
thick Al under 15 mbar)
– If stiffer can make inner radius
smaller (maybe)
2
tm in( 1 m m E)
mm
1.5
1
0.5
0
0.1
1
10
100
1 10
3
E
GP a
R. Mountain, Syracuse University
SU HEP Group Meeting, 1 Apr 2009 -9-
OUTLOOK
Looks promising !
– No obvious show-stoppers met (yet)
PRACTICAL:
Manufacturing
– Prototype foil (+ box) can proceed as soon
as can provide CMA with a design
– They can handle some of the metrology
and testing for this
WORK YET TO DO:
Mechanical / Thermal
– Need real deflection calculations (FEA,
trying LISA) for mech, thermal effects
Vacuum
– Can CF hold required vacuum at this
thickness? May be a permeability issue
– Must test it to find out
– Need to bake out at some high temperature
Beam
– Calculate wakefield effects (MAFIA)
– Acceptable heat dissipation in VELO
– Eventual measurements of shielding and
power transfer
– Dynamic vacuum effects
– Radiation damage effects on CFRP
R. Mountain, Syracuse University
SU HEP Group Meeting, 1 Apr 2009 -10-