November 30, 2006 CARE Workshop Global Design Effort 1

Cold Cavity BPM R&Dfor the ILC

Manfred Wendt

Fermilab

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):

November 30, 2006 CARE Workshop Global Design Effort 3

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.

November 30, 2006 CARE Workshop Global Design Effort 4

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

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

November 30, 2006 CARE Workshop Global Design Effort 6

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

November 30, 2006 CARE Workshop Global Design Effort 7

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

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

November 30, 2006 CARE Workshop Global Design Effort 9

November 30, 2006 CARE Workshop Global Design Effort 10

Cavity BPM Resolution at ATF• 10 minute run• 800 samples• σ ≈ 24 nm

Move BPM in 1 µm steps

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)

November 30, 2006 CARE Workshop Global Design Effort 12

November 30, 2006 CARE Workshop Global Design Effort 13

November 30, 2006 CARE Workshop Global Design Effort 14

November 30, 2006 CARE Workshop Global Design Effort 15

November 30, 2006 CARE Workshop Global Design Effort 16

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.

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

November 30, 2006 CARE Workshop Global Design Effort 18

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

November 30, 2006 CARE Workshop Global Design Effort 19

Pillbox with WG Slot Coupling

November 30, 2006 CARE Workshop Global Design Effort 20

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

November 30, 2006 CARE Workshop Global Design Effort 21

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

November 30, 2006 CARE Workshop Global Design Effort 22

Matched WG-to-Coaxial Transition

47.03.mm

2

1

Diam. 4.46 mm

11.13 mm 8.9 mm

November 30, 2006 CARE Workshop Global Design Effort 23

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:

November 30, 2006 CARE Workshop Global Design Effort 24

Monopole-Mode Investigation

Monopole mode damping using simple pin-antennas

November 30, 2006 CARE Workshop Global Design Effort 25

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)

November 30, 2006 CARE Workshop Global Design Effort 26

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

November 30, 2006 CARE Workshop Global Design Effort 27

Test Model for N2 Temperature Cycles

November 30, 2006 CARE Workshop Global Design Effort 28

November 30, 2006 CARE Workshop Global Design Effort 29

November 30, 2006 CARE Workshop Global Design Effort 30

November 30, 2006 CARE Workshop Global Design Effort 31

November 30, 2006 CARE Workshop Global Design Effort 32

L-Band Cavity Assembly

November 30, 2006 CARE Workshop Global Design Effort 33

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!