Cold cavity bpm r d for the ilc
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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

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Cold Cavity BPM R&D for the ILC

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Cold cavity bpm r d for the ilc

Cold Cavity BPM R&Dfor the ILC

Manfred Wendt

Fermilab

Global Design Effort


The international linear collider

The International Linear Collider

ILC Beam Parameters (nominal):

Global Design Effort


Ilc beam instrumentation

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.

Global Design Effort


Cold bpm requirements

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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Possible cold bpm solutions

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

Global Design Effort


Cavity bpm principle

Cavity BPM Principle

Problems 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

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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Kek atf nanobpm collaboration

KEK ATF nanoBPM Collaboration

BINP 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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Cold cavity bpm r d for the ilc

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Cavity bpm resolution at atf

Cavity BPM Resolution at ATF

  • 10 minute run

  • 800 samples

  • σ ≈ 24 nm

Move BPM in 1 µm steps

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Slac cavity bpm

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)

Global Design Effort


Cold cavity bpm r d for the ilc

Global Design Effort


Cold cavity bpm r d for the ilc

Global Design Effort


Cold cavity bpm r d for the ilc

Global Design Effort


Cold cavity bpm r d for the ilc

Global Design Effort


Cold l band cavity bpm design

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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Scaling of the slac cavity bpm

Scaling of the SLAC Cavity BPM

Discrete port (current)

x=10 mm

y=30 mm

Excitation signal

Ports

General view

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Slac bpm scaled eigen modes

SLAC BPM (scaled): Eigen Modes

  • Mode Frequency

  • 1.017 – Parasitic E11-like

  • 1.023 – Parasitic E21-like

  • 1.121 – Monopole E01

  • 1.198 - Waveguide

  • 1.465 - Dipole E11

  • 1.627

Dipole

Parasitic mode. Coupling through

horizontal slots is clearly seen

Parasitic mode

Ez distribution

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Pillbox with wg slot coupling

Pillbox with WG Slot Coupling

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Optimization of the slot dimensions

Optimization of the Slot Dimensions

  • EM: Eigen-mode solver

  • FD: Frequency-domain solver

  • Slot-L = 55 mm & Slot-W = 5 mm Qload = 678

Global Design Effort


Ceramic windows in the coupling slots

Ceramic Windows in the Coupling Slots

Window –

Ceramic brick of alumina 96%

er≈ 9.4

Size: the same as slot

N type receptacle,

50 Ohm,

D=9.75 mm

d=3.05 mm

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Matched wg to coaxial transition

Matched WG-to-Coaxial Transition

11.13 mm

8.9 mm

47.03.mm

1

2

Diam. 4.46 mm

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Dipole mode sensitivity resolution

Dipole Mode Sensitivity (Resolution)

with:

with:

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Monopole mode investigation

Monopole-Mode Investigation

Monopole mode damping

using simple pin-antennas

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Unmatched transmission line combiner

Unmatched Transmission-line Combiner

  • 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)

In-phase signal combining for the monopole-mode signal

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Combiner induced frequency shift

Combiner-induced Frequency-shift

Appropriate length of combiner – reasonable length and non-resonant

Interaction with dipole mode

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Test model for n 2 temperature cycles

Test Model for N2 Temperature Cycles

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Cold cavity bpm r d for the ilc

Global Design Effort


Cold cavity bpm r d for the ilc

Global Design Effort


Cold cavity bpm r d for the ilc

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Cold cavity bpm r d for the ilc

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L band cavity assembly

L-Band Cavity Assembly

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Next steps

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!

Global Design Effort


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