MICE RF Cavity Measurements Derun Li Center for Beam Physics Lawrence Berkeley National Laboratory March 26, 2010 University of California, Riverside, California

Summary What we have so far 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 Preliminary analysis Near term plans Near term plans 2 MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010

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

CMM Scans of MICE Cavity 4 MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010 Special probe to measure the inside profile of the cavity Special probe to measure the inside profile of the cavity Cavity interior profile being measured with special probe Cavity interior profile being measured with special probe (  1,800 points per scan) (  1,800 points per scan) The profile will be used to verify cavity RF models The profile will be used to verify cavity RF models

Preparation for RF measurements 5 MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010 Lifting fixtures Stand for RF measurements

RF measurements, Team Work! 6 MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010 Be window installation

RF Measurements, Results 7 MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010 S 11 measurements S 21 measurements

MICE Cavity Design Parameters 8 MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010 The cavity design parametersThe cavity design parameters –Frequency: MHz – β = 0.87 –Shunt impedance (VT 2 /P): ~ 22 MΩ/m –Quality factor (Q 0 ): ~ 53,500 –Be window diameter and thickness: 42-cm and 0.38-mm Nominal parameters for MICE and cooling channels in a neutrino factoryNominal 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 Two cavities have been measured in different window configurations using Be windows #1 and #2 MICE cavity #1: S 21 measurements (2 probes) with all ports shorted: Q  44,000 – 44, 600 (over 80% of the design Q) MICE cavity #1: S 21 measurements (2 probes) with all ports shorted: Q  44,000 – 44, 600 (over 80% of the design Q) MICE cavity #4: S 21 measurements (2 probes) with all ports shorted: Q  43,600 – 44, 000 (over 80% of the design Q) MICE cavity #4: S 21 measurements (2 probes) with all ports shorted: Q  43,600 – 44, 000 (over 80% of the design Q) 9 MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010 Window 1) 2) 1) (2 (1 (2 (2 (1 Frequency MHz MHz MHz Window 1) 2) 1) (2 (1 (2 Frequency MHz MHz MHz

Measurements and Analysis Measurements of frequency changes from RF ports Measurements of frequency changes from RF ports From open to short:  +11 kHz/port (S 11 measurements) From open to short:  +11 kHz/port (S 11 measurements) Preliminary analysis (S. Virostek) Preliminary analysis (S. Virostek) Assuming there is a cavity body frequency (equivalent to the iris terminated by flat metal sheet/window), f body Assuming there is a cavity body frequency (equivalent to the iris terminated by flat metal sheet/window), f body The curved Be window introduces frequency shifts of +Δf 1 (out) by window #1 and - Δf 2 (in) by window #2 if neglecting 2 nd order frequency shifts due to local field changes by the curved window, therefore: The curved Be window introduces frequency shifts of +Δf 1 (out) by window #1 and - Δf 2 (in) by window #2 if neglecting 2 nd order frequency shifts due to local field changes by the curved window, therefore: Measured frequency ≈ f body ± Δf 1 ± Δf 2 The “±” depends on Be window configurations The “±” depends on Be window configurations 10 MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010

Measurement Data Analysis 11 MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/ Δf 1 + Δf 2 Cavity body frequency: f body Window # 1 Window # 2

Data Analysis (cont’d) Three measurements should determine f body, Δf 1 and Δf 2 Three measurements should determine f body, Δf 1 and Δf 2 From MICE cavity #1 measurements: From MICE cavity #1 measurements: = f body – Δf 1 + Δf 2 f body = MHz = f body – Δf 1 – Δf 2 Δf 1 = MHz = f body + Δf 1 – Δf 2 Δf 2 = MHz From MICE cavity #4 measurements: From MICE cavity #4 measurements: = f body – Δf 1 + Δf 2 f body = MHz = f body – Δf 1 – Δf 2 Δf 1 = MHz = f body + Δf 1 – Δf 2 Δf 2 = MHz Conclusions: 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 knobs 12 MICE 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 Physical measurements of the first five MICE cavities and three Be windows CMM scans CMM scans RF measurements of the remaining three MICE cavities RF measurements of the remaining three MICE cavities Find center (average) frequency of all (10) MICE cavities Find center (average) frequency of all (10) MICE cavities Cavity tuning to the center frequency in combination with Be windows Cavity tuning to the center frequency in combination with Be windows Each cavity and Be window will be measured and labeled (identified) with f body and Δf Each cavity and Be window will be measured and labeled (identified) with f body and Δf Cavity coupler and tuner fabrication and tests Cavity coupler and tuner fabrication and tests (A. DeMello) (A. DeMello) 13 MICE RF Cavity Measurements, D. Li, Lawrence Berkeley National Lab, 3/26/2010