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201 MHz Cavity Status and Test Plans at MTA
MICE Collaboration Meeting at RAL, UKOctober 22 ~ 24, 2005
Derun Li
Center for Beam PhysicsLawrence Berkeley National Laboratory
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 2
Cavity Status @ Last Meeting
MICE Collaboration meeting last June at NuFact-2005 in Frascati
Cavity fabrication: in collaboration with J-Lab, University of Mississippi, Oxford UniversityCavity parts fabrication at Mississippi; e-beam welding, EP and
cleaning at J-Lab Power couplers: assembly and high power tests at SNSVacuum assembly and tests at J-Lab, … , shippingCurved Be windows: in collaboration with Oxford University
In MTA, FNALPreparation for accepting the cavity: installation, baking,
vacuum, RF transmission lines, …Cleaning room purchased and will allow us for in situ assembly
of Couplers Window replacement Inspection of cavity
Low power measurement: frequency and coupling
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 3
Cavity Progress Since Last MICE Meeting
• Cavity fabrication: in collaboration with J-Lab, University of Mississippi, Oxford University Cavity parts fabrication at Mississippi; e-beam welding, EPs
and cleaning at J-Lab Power couplers: assembly and high power tests at SNS Vacuum assembly and tests at J-Lab, … , shipping Curved Be windows: in collaboration with Oxford University:
three curved Be windows, one with Ti-N coating
Cavity shipped in early September, and now at MTA FNAL Strong supports and helps from FNAL: Preparation for accepting the
cavity: installation, baking, vacuum, RF transmission lines, … Cleaning room was ready for in situ assembly of
Couplers Window replacement Inspection of cavity
Cavity installation Vacuum leak tight Low power measurement: frequency and coupling
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 4
• Final interior buffing of cavity is performed to ensure the surfaces are ready for electropolishing
• Less buffing needed near equator where fields are lower
• An automated process of buffing was developed using a rotary buffing wheel and a cavity rotation fixture
• Some local hand work required to clean up some areas
• A series of pads with graduated coarseness was used
• Goal was scratch depth shallow enough for EP removal
Final Interior Buffing
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 5
• After buffing, cavity underwent a chemical cleaning process
• Test bars with various degrees of buffing were run through an electropolish process
• Cavity was rotated with a U-shaped electrode fixed in place
• Initial polish failed due to depletion of the solution, and rebuffing was required
• 2nd EP successfully removed scratches in high field regions
• Final process is a high pressure water rinse of cavity surface
Interior Surface Electropolish
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 6
• Coupling loops were fabricated using standard copper co-ax
• Most coupler parts were joined by torch brazing – vacuum leaks were found in two of the outer conductor joints
• Coupling loop contains an integrated cooling tube
• The coupler was designed to mate with an SNS style RF window manufactured by Toshiba
• High power conditioning performed at SNS (ORNL)
• The MICE coupler will require a bellows connection interface with the outer vacuum vessel ports
Cavity RF Couplers
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 7
Shipment to the MTA at FNAL
• System assembly included: tuner plates, port blank-offs, diagnostic spool, window cover plates, gate valve and window pump-out tubes
• Final leak check conducted prior to shipping
• Cavity was back-filled with nitrogen in its assembled state and packaged in a custom made crate for shipping to the MTA
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 8
Final Assembly at the MTA
• Cavity assembly was mounted on the support and couplers were installed in a portable clean room
• Dummy copper windows (flat) are used initially
• Couplers were set and frequency was measured
• Bakeout system hardware was installed
• System is now leak tight and ready for bake
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 9
Cavity Installation at MTA
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 10
Cavity Installation at MTA
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 11
Cavity InspectionIr
is A
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Cou
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rs
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 12
Last Low Power Measurements
E-beam welding Ports Water cooling lines • Couplers assembled first time (mid-April-2005)• First low power measurement
• frequency ~ 199.5 MHz• coupling ~ 5 (max)• Q ~ 5000
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 13
Low Power Measurements
f = 199.578 MHz
Q0 = 49,000 ~ 51,000Better than 90%of design value
Two couplers• balanced• coupling adjustments
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 14
Tuner Measurements
• Mechanical tuning plates at four locations
• Dial indicators to measure displacement between Al plates
• Tuning measurement in air– Equivalent to MICE cavity
under vacuum
• Adjusted up to 2-mm with 8 steps of 0.25-mm each
• Measured tuner sensitivity – ~ 78 kHz/mm
• Calculated tuner sensitivity– 115 kHz/mm– Disagreements may be due
to deflection of the Al plates
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 15
Curved Be windows
• Each cavity will require a pair of 0.38 mm thick pre-curved beryllium windows with Ti-N coating
• Double-curved shape prevents buckling caused by thermal expansion due to RF heating
• Thermally induced deflections are predictable
• A die is applied at high temperature to form window
• Copper frames are brazed to beryllium windows in a subsequent process
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 16
RF Power
Two couplers
Load Two Couplers ─ Critical coupling─ Ceramic windows are integrated in
the couplers─ Design and built at LBNL ─ Conditioning started using 805
MHz RF power at the SNS ─ Good vacuum ~ low 10-8 T─ Achieved 600 kW in TW mode
(matched load)─ Achieved 10 kW average power (~
9 kW average for nominal NF parameters)
─ Achieved 2.4 MW peak power in SW mode (at variable short positions)
─ Ceramic windows work fine during two weeks of the RF conditioning
─ Shipped to MTA for final assembly
Couplers Tests at SNS
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 17
Bake-out and Vacuum
• Hot water bake-out system installed at MTA– Safety– Control and operation
• Electric heating system• Two vacuum leaks found
before and after bake-out– Bottom port– Top port
• Vacuum leaks fixed and now cavity is leak tight– 3.3x10-8 Torr at latest
• Two RF probes calibrated– -55, -54 dB (at maximum)
0.00E+00
2.00E-08
4.00E-08
6.00E-08
8.00E-08
1.00E-07
1.20E-07
1.40E-07
0 20 40 60 80Pumping time (hours)
Vacuum (Torr)
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 18
High Power Test at MTA
Plans underway– Coordination among LBNL, FNAL, J-Lab and ANL
> Weekly video meetings> MUCOOL Friday meetings
– Diagnostics (RF probes, dark current, x-ray, vacuum, … )– Near term plan
> Purchase high power RF components– Power splitter (matched Tee) at 6” coaxial transmission line– Transitions to 4” coaxial lines with elbows to the couplers– Directional couplers
– High power test plans being developed> Expect to have RF power (up to ~ 5 MW) in 6 ~ 8 weeks> Test with Ti-N coated flat copper windows (installed) first
– Double check coupling balance and adjustment before high power– Double check calibration of RF probes
> Conditioning without magnetic field first– Combinations of short pulse and high RF powers
> Curved Be windows + magnetic fields later– Suggestions are always very welcome
MICE Collaboration Meeting at RALOctober 22 ~ 24, 2005
201 MHz Cavity Status Derun Li
Center for Beam Physics LBNL Page 19
Summary
• Cavity assembly at MTA, FNAL is complete– Cavity is vacuum leak tight, now at ~ 3.3x10-8 Torr– More RF components need to be ordered– Two couplers have been balanced and adjusted– Two RF probes calibrated
• Curved Be windows with Ti-N coatings (one is ready now, two are underway) will be ready for high power tests
• High power test plans being developed• Problems we had with cavity ports are not an issue for
MICE
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