MICE RF Cavity Measurements

Derun LiCenter for Beam Physics

Lawrence Berkeley National LaboratoryMarch 26, 2010

University of California, Riverside, California

Summary• What we have so far– The first five MICE RF cavity bodies arrived LBNL in

December 2009– Three completed Be windows at LBNL– CMM and low power RF measurements

– Design and construction for lifting fixture– Design and construction of stands for RF measurements– Extension for CMM measurements

– RF Measurement results of two MICE cavities• Preliminary analysis

• Near term plans

2MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010

The RF Cavity at LBNL

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CMM Scans of MICE Cavity

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• Special probe to measure the inside profile of the cavity• Cavity interior profile being

measured with special probe ( 1,800 points per scan)• The profile will be used to verify

cavity RF models

-650 -600 -550 -500 -450 -400 -350 -300 -250 -200 -150

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0

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100

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200

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Preparation for RF measurements

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Lifting fixtures

Stand for RF measurements

RF measurements, Team Work!

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Be window installation

RF Measurements, Results

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S11 measurements

S21 measurements

MICE Cavity Design Parameters

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• The cavity design parameters – Frequency: 201.25 MHz– β = 0.87– Shunt impedance (VT2/P): ~ 22 MΩ/m– Quality factor (Q0): ~ 53,500– Be window diameter and thickness: 42-cm and 0.38-mm

• Nominal parameters for MICE and cooling channels in a neutrino factory – 8 MV/m (~16 MV/m) peak accelerating field– Peak input RF power: 1 MW (~4.6 MW) per cavity – Average power dissipation per cavity: 1 kW (~8.4 kW)– Average power dissipation per Be window: 12 watts (~100 watts)

Measurement Results• Two cavities have been measured in different

window configurations using Be windows #1 and #2• MICE cavity #1: S21 measurements (2 probes) with all ports

shorted: Q 44,000 – 44, 600 (over 80% of the design Q)

• MICE cavity #4: S21 measurements (2 probes) with all ports

shorted: Q 43,600 – 44, 000 (over 80% of the design Q)

9MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010

Window 1) 2) 1) (2 (1 (2 (2 (1

Frequency 200.990 MHz 199.786 MHz 201.179 MHz 201.179 MHz

Window 1) 2) 1) (2 (1 (2

Frequency 200.642 MHz 199.454 MHz 200.839 MHz

Measurements and Analysis• Measurements of frequency changes from RF ports

• From open to short: +11 kHz/port (S11 measurements)

• Preliminary analysis (S. Virostek)• Assuming there is a cavity body frequency (equivalent to the iris

terminated by flat metal sheet/window), fbody

• The curved Be window introduces frequency shifts of +Δf1 (out) by

window #1 and - Δf2 (in) by window #2 if neglecting 2nd order

frequency shifts due to local field changes by the curved window, therefore:

Measured frequency ≈ fbody ± Δf1 ± Δf2

• The “±” depends on Be window configurations10MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010

Measurement Data Analysis

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- Δf1

+ Δf2

Cavity body frequency: fbody

Window # 1

Window # 2

Data Analysis (cont’d)• Three measurements should determine fbody, Δf1 and Δf2

• From MICE cavity #1 measurements:200.990 = fbody – Δf1 + Δf2 fbody = 201.084 MHz

199.786 = fbody – Δf1 – Δf2 Δf1 = 0.697 MHz

201.179 = fbody + Δf1 – Δf2 Δf2 = 0.602 MHz

• From MICE cavity #4 measurements:200.642 = fbody – Δf1 + Δf2 fbody = 200.741 MHz

199.454 = fbody – Δf1 – Δf2 Δf1 = 0.693 MHz

200.839 = fbody + Δf1 – Δf2 Δf2 = 0.594 MHz

• Conclusions:– Profiles of the two windows must be different ( 100 kHz)

– Cavity frequency variation within ± 400 kHz (prediction)

– Be windows can be used as additional tuning knobs12MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010

Near Term Plans• Physical measurements of the first five MICE cavities and

three Be windows• CMM scans

• RF measurements of the remaining three MICE cavities• Find center (average) frequency of all (10) MICE cavities • Cavity tuning to the center frequency in combination with Be

windows• Each cavity and Be window will be measured and labeled

(identified) with fbody and Δf • Cavity coupler and tuner fabrication and tests (A. DeMello)

13MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010