cold cavity bpm r&d for the ilc
DESCRIPTION
Cold Cavity BPM R&D for the ILC. Manfred Wendt Fermilab. The International Linear Collider. ILC Beam Parameters (nominal):. ILC Beam Instrumentation. ~ 2000 Button/stripline BPM’s ~ 1800 Cavity BPM’s (warm) 770 Cavity BPM’s (cold, part of the cryostat) 21 LASER Wirescanners - PowerPoint PPT PresentationTRANSCRIPT
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November 30, 2006 CARE Workshop Global Design Effort 1
Cold Cavity BPM R&Dfor the ILC
Manfred Wendt
Fermilab
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November 30, 2006 CARE Workshop Global Design Effort 2
The International Linear Collider
beam energy = 2 x 250 GeV
luminosity L = 2 x 1034
rep. frequency frep = 5 Hz
macro pulse length tpulse = 800 µs
# of bunches per pulse = 2820
bunch spacing Δtb = 308 ns
bunch charge = 3.2 nC
bunch length σz ≈ 300 µm
vert. emittance γ εy* = 0.04 mm mrad
RMS energy spread = 0.1 %
βx* (IP) = 21 mm
βy* (IP) = 0.4 mm
hor. beamsize (IP) σx = 500 nm
vert. beamsize (IP) σy = 5 nm
ILC Beam Parameters (nominal):
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ILC Beam Instrumentation
• ~ 2000 Button/stripline BPM’s• ~ 1800 Cavity BPM’s (warm)• 770 Cavity BPM’s (cold, part of the cryostat)• 21 LASER Wirescanners• 20 Wirescanners (traditional)• 15 Deflecting Mode Cavities (bunchlenght)• ~ 1600 BLM’s• Many other beam monitors, including toroids, beam
phase monitors, wall current monitors, faraday cups, OTR & other screen monitors, sync light monitors, streak cameras, feedback systems, etc.
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Cold BPM Requirements• BPM location in the cryostat, at the SC-quad• Every 3rd cryostat is equipped with a BPM/quad:
650x cold BPM’s total.– Real estate: ~ 170 mm length, 78 mm beam pipe
diameter (???).– Cryogenic environment (~ 4 K)– Cleanroom class 100 certification (SC-cavities nearby!)– UHV certification
• < 1 µm single bunch resolution, i.e. measurement (integration) time < 300 ns.
• < 200 µm error between electrical BPM center and magnetic center of the quad.
• Related issues:– RF signal feedthroughs.– Cabling in the cryostat– Read-out System
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November 30, 2006 CARE Workshop Global Design Effort 5
Possible Cold BPM Solutions
• Dedicated, high resolution BPM (baseline design):
Cavity BPM, based on the characterization of beam excited dipole eigenmodes, also requires the measurement of the monopole modes for normalization and evt. sign of the beam displacement.
• Combination of dedicated, lower resolution BPM’s and HOM coupler signal BPM’s (alternative design):– Simple, button style BPM’s (~ 50 µm resolution) for
machine tune-up and single bunch orbit measurements.– HOM coupler BPM signal processor as high resolution
BPM
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Cavity BPM PrincipleProblems with simple“Pill-Box” Cavity BPM’s• TM010 monopole
common mode (CM)• Cross-talk (xy-axes,
polarization)• Transient response
(single-bunch measurements)
• Wake-potential (heat-load, BBU)
• Cryogenic and cleanroom requirements
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CM-free Cavity BPM• uses waveguide ports to
suppress the monopole mode (no hybrid-junction required)
+ very high resolution potential (~ 20 nm)!
– complicated mechanics, i.e. cleanroom and cryogenic issues
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November 30, 2006 CARE Workshop Global Design Effort 8
KEK ATF nanoBPM CollaborationBINP cavity BPM:• C-Band (6426 MHz)• 20 mm aperture• Selective dipole-
mode waveguide couplers
• 3 BPM’s in a LLBL hexapod spaceframe (6 degrees of freedom for alignment)
• Dual-downconversion electronics (476 & 25 MHz)
• 14-bit, 100 MSPS digitizer
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November 30, 2006 CARE Workshop Global Design Effort 9
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Cavity BPM Resolution at ATF• 10 minute run• 800 samples• σ ≈ 24 nm
Move BPM in 1 µm steps
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November 30, 2006 CARE Workshop Global Design Effort 11
SLAC Cavity BPM
+ S-Band design for 35 mm beam-pipe aperture
+ Waveguide cut to beam-pipe (better cleaning)
+ Successful beam measurements at SLAC-ESA (~ 0.8 µm resolution)
– No cryogenic temperature tests so far.
– No clean-room certification– Needs a reference cavity or
signal– Reduced beam-pipe
aperture (nominal: 78 mm)
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November 30, 2006 CARE Workshop Global Design Effort 12
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November 30, 2006 CARE Workshop Global Design Effort 13
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November 30, 2006 CARE Workshop Global Design Effort 14
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Cold L-Band Cavity BPM Design• Waveguide-loaded pillbox with slot coupling.• Dimensioning for f010 and f110 symmetric to fRF,
fRF = 1.3 GHz, f010 ≈ 1.1 GHz, f110 ≈ 1.5 GHz.• Dipole- and monopole ports, no reference cavity for
intensity signal normalization and signal phase (sign).• Qload ≈ 600 (~ 10 % cross-talk at 300 ns bunch-to-
bunch spacing).• Minimization of the X-Y cross-talk (dimple tuning).• Simple (cleanable) mechanics.• Iteration of EM-simulations for optimizing all
dimensions.• Vacuum/cryo tests of the ceramic slot window.• Copper model for bench measurements.
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November 30, 2006 CARE Workshop Global Design Effort 17
Scaling of the SLAC Cavity BPM
General viewPorts
Discrete port (current) x=10 mmy=30 mm
Excitation signal
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SLAC BPM (scaled): Eigen Modes
Mode Frequency
1 1.017 – Parasitic E11-like 2 1.023 – Parasitic E21-like3 1.121 – Monopole E01 4 1.198 - Waveguide5 1.465 - Dipole E11
6 1.627
Dipole
Parasitic mode. Coupling throughhorizontal slots is clearly seen
Parasitic modeEz distribution
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Pillbox with WG Slot Coupling
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Optimization of the Slot Dimensions
• EM: Eigen-mode solver• FD: Frequency-domain solver• Slot-L = 55 mm & Slot-W = 5 mm Qload = 678
Q external and Q loaded vs slot length
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
30 40 50 60 70 80
Slot length, mm
Q
Q ext EM
Q load EM
Q load FD
Qload (EM) vs Slot_W (Slot_L=55)
0
200
400
600
800
1000
1200
1400
1 2 3 4 5 6 7 8 9
Width, mm
Q
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Ceramic Windows in the Coupling Slots
Frequency, GHz 1.46
Loaded Q ~ 600
Beam pipe radius, mm 39
Cell radius, mm 114
Cell gap, mm 10
Waveguide, mm 122x110x25
Coupling slot, mm 47x5x3
Window –Ceramic brick of alumina 96%
r ≈ 9.4
Size: the same as slot
N type receptacle,50 Ohm,D=9.75 mmd=3.05 mm
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Matched WG-to-Coaxial Transition
47.03.mm
2
1
Diam. 4.46 mm
11.13 mm 8.9 mm
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Dipole Mode Sensitivity (Resolution)
x
q
Q
R
QQZfxxV
x
sh
11000110110
11)(
GHzxf 46.1)(110 500Z
600Q
141
110
mmx
sh
Q
R
20000 Q
nCq 1
with:
nCVxxV /10145.4)( 3110
mnCmVV /4110 VBWTkZV seThermalNoi 7.00
500Z
KJk /1038.1 23
KT 300
MHzQ
fBW 4.2
110
110
with:
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Monopole-Mode Investigation
Monopole mode damping using simple pin-antennas
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Unmatched Transmission-line Combiner
In-phase signal combining for the monopole-mode signal
• 180 degrees for dipole-mode. Standing wave with some frequency detuning.
• lTL~ 200 mm to avoid resonances around 1.46 GHz (SW eigenmodes for lTL~ 200 mm at: f3 ~1.1 GHz, f5 ~1.9 GHz)
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Combiner-induced Frequency-shift
BPM spectrum vs length of combiner (one leg)
0
0.5
1
1.5
2
2.5
3
0 50 100 150 200 250 300 350
mm
GH
z
Quadrupole
Dipole
Monopole
Appropriate length of combiner – reasonable length and non-resonantInteraction with dipole mode
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Test Model for N2 Temperature Cycles
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November 30, 2006 CARE Workshop Global Design Effort 30
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L-Band Cavity Assembly
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Next Steps…
• N2 temperature cycles with the test model.
• Drafting of the complete assembly.• EM modeling and fine tuning of the
dimensions.• Investigation of the tolerances.• Prototype manufacturing.• RF measurements and characterization.
Thanks for your patience!