201 MHz Cavity Studies Derun Li Lawrence Berkeley National Laboratory MuCool RF Workshop (Fermilab) July 7 and 8, 2009

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 2Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Outline Brief review and progresses of the 201-MHz test programBrief review and progresses of the 201-MHz test program –RF tests with flat Cu and curved thin Be windows Curved Be windows installedCurved Be windows installed Cavity retuned to 200-MHzCavity retuned to 200-MHz Tested up to ~ 19 MV/mTested up to ~ 19 MV/m –RF tests with stray magnetic fields of Lab-G magnet Move the cavity next to Lab-G magnetMove the cavity next to Lab-G magnet New transmission lineNew transmission line New Vacuum pumpNew Vacuum pump Preliminary test resultsPreliminary test results –Simulation study of RF cavity in strong magnetic field 201-MHz cavity fabrication for MICE201-MHz cavity fabrication for MICE

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 3Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Primary Goals Development of normal conducting 201-MHz cavity that can operate at a gradient of ~ 16 MV/m in a few Tesla magnetic fields environmentDevelopment of normal conducting 201-MHz cavity that can operate at a gradient of ~ 16 MV/m in a few Tesla magnetic fields environment –Prototype: exploring engineering solutions (challenges) –RF conditioning and operation without and with B fields Operating a NC RF cavity (with thin and curved Be windows) at ~ 16 MV/m in strong B field could be very challenging, but to be confirmed experimentallyOperating a NC RF cavity (with thin and curved Be windows) at ~ 16 MV/m in strong B field could be very challenging, but to be confirmed experimentally –Test with stronger magnetic fields SC coupling coil for MUCOOL: being fabricated at ICST, Harbin

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 4Derun Li - Lawrence Berkeley National Lab – July 7, MHz Prototype Cavity 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 radius and thickness: 21- cm and 0.38-mm Nominal parameters for cooling channels in a muon collider or a neutrino factoryNominal parameters for cooling channels in a muon collider or a neutrino factory –~ 16 MV/m peak accelerating field –Peak input RF power ~ 4.6 MW per cavity (85% of Q 0, 3  filling time) –Average power dissipation per cavity ~ 8.4 kW –Average power dissipation per Be window ~ 100 watts The 201-MHz cavity at MTA The 201-MHz cavity at MTA

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 5Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Test Setup at MTA The 805-MHz and 201-MHz cavities at MTA, FNAL for RF breakdown studies with external magnetic fields. 805 MHz pillbox cavity 201 MHz cavity

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 6Derun Li - Lawrence Berkeley National Lab – July 7, 2009 RF Tests of curved thin Be Windows The cavity reached to ~ 19 MV/mThe cavity reached to ~ 19 MV/m –Cavity frequency had to be retuned –Cavity frequency was stable during the operation, however, we did observe frequency shift due to RF heating on the windows Frequency shift of ~ 125 kHz (from 0 to ~ 19 MV/m, 150-micro-second pulse, 10-Hz repetition rate) in ~ 10 minutes, well within the tuning range ( ~ 110 kHz/mm,  4 mm range)Frequency shift of ~ 125 kHz (from 0 to ~ 19 MV/m, 150-micro-second pulse, 10-Hz repetition rate) in ~ 10 minutes, well within the tuning range ( ~ 110 kHz/mm,  4 mm range) With low external magnetic fieldWith low external magnetic field –Cavity can be operated at ~ 19 MV/m with a few hundred Gauss stray field from Lab-G magnet Tests with stronger external magnetic fieldsTests with stronger external magnetic fields –SC coupling coil for MuCool

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 7Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Tests with Magnetic Fields The 100-cm long coaxial section was replaced by 20-cm one Separation of the nearest curved Be window from the face of Lab-G magnet is 10-cm (before was 110- cm) Maximum magnetic field near the Be window ~ 1.5 Tesla (5 Tesla in magnet) The 201-MHz cavity Lab-G magnet

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 8Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Radiation (mRem/hr) Cavity Gradient (MV/m) Tests at external field B = 0 Radiation data compared with a fitting with to gradient to ~ 14 th power

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 9Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Radiation (mRem/hr) Cavity Gradient (MV/m) Radiation at B = 0.5-T Field Radiation data compared with a fitting with to gradient to ~ 14 th power 0.5-T B field to the nearest Be window

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 10Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Test Results We have so far Multi-pactoring was observed at the entire magnetic field range up to 3.75-T (~ 1.1-T at nearest Be window) Multi-pactoring was observed at the entire magnetic field range up to 3.75-T (~ 1.1-T at nearest Be window) A strong correlationship exists between cavity vacuum and radiation levels A strong correlationship exists between cavity vacuum and radiation levels We have achieved ~ 14 MV/m at 2.5-T (~ 0.75-T to the nearest curved thin Be window) {~ 19 MV/m without B} We have achieved ~ 14 MV/m at 2.5-T (~ 0.75-T to the nearest curved thin Be window) {~ 19 MV/m without B} The test results are very encouraging The test results are very encouraging We may need to commission (condition) We may need to commission (condition) the 201-MHz cavity longer to reduce the the 201-MHz cavity longer to reduce the multi-pactoring before we can properly multi-pactoring before we can properly measure and study the magnetic field measure and study the magnetic field effects in the stray field effects in the stray field Numerical studies with external Numerical studies with external magnetic fields and SC coupling coil magnetic fields and SC coupling coil

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 11Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Numerical Study with B Field (Bob’s Talk) Physics models and numerical simulations (BNL, SLAC, … )Physics models and numerical simulations (BNL, SLAC, … ) –Cavity with flat windows: 5 MV/m on axis; 2-T uniform external magnetic field; scan of a few points from one cavity side

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 12Derun Li - Lawrence Berkeley National Lab – July 7, MHz Cavity for MICE Eight 201-MHz cavities + with materials for two more spare cavitiesEight 201-MHz cavities + with materials for two more spare cavities Baseline design: 201-MHz for MUCOOL, butBaseline design: 201-MHz for MUCOOL, but –Cavity body profile has been modified Raise resonant frequencyRaise resonant frequency –Port extruding Port interface is different from the MUCOOL cavityPort interface is different from the MUCOOL cavity –RF coupler and ceramic window The same window as for the MUCOOL cavityThe same window as for the MUCOOL cavity –Curved Beryllium windows Improved design to better control silver alloy flow during the brazingImproved design to better control silver alloy flow during the brazing –Tuners and interface with RFCC module –Post-processing: water cooling pipes, cleaning (EP & water rinsing), low power measurement, tuning, assembly and shipping

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 13Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Four RF Cavities in each RFCC Module SC coupling Coil Cavity Couplers Vacuum Pump 201-MHz cavity Curved Be window

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 14Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Update on MICE RF Cavity Design 3-Dimensional RF cavity parameterized model to study frequency shifts from RF ports and curved Be windows and E peak3-Dimensional RF cavity parameterized model to study frequency shifts from RF ports and curved Be windows and E peak Frequencies variation between cavities should be within  100 kHzFrequencies variation between cavities should be within  100 kHz FabricationFabrication –Modification of the mold for prototype cavity Reduction in diameter to raise the MICE cavity frequency –Tune cavities close to design frequency by deformation of cavity body (if needed) –Fine tuners operate in the push-and-pull mode  230 kHz

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 15Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Visit to ACME Spinning in April 2009 (1/2) Machined the MuCool mold to the new profileMachined the MuCool mold to the new profile Re-spun the two half spare shells to new profileRe-spun the two half spare shells to new profile Measured frequency shifts before and after spinning Measured frequency shifts before and after spinning Expected frequency shift ~ 1 MHz Measurements: Shell #1: Shell #1: MHz (before) MHz (after)

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 16Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Visit to ACME Spinning in (2/2) Spun and measured a new half shell (frequency: MHz)Spun and measured a new half shell (frequency: MHz) Developed a fabrication procedureDeveloped a fabrication procedure Pre-polishing copper sheetsPre-polishing copper sheets Inspecting the surfaceInspecting the surface Polishing visible scratches locally if necessary (before and after)Polishing visible scratches locally if necessary (before and after) Handling and shippingHandling and shipping Polished surface Local polishing to remove deeper scratches Surface inspection during the spinning

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 17Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Cavity Inspection at LBNL (1/2) 12 spun half shells arrived LBNL in May spun half shells arrived LBNL in May 2009 CMM scans to pair best matches of two half shells in diameters, all of them have been measuredCMM scans to pair best matches of two half shells in diameters, all of them have been measured Polished cavity surface Center hole for handling & spinning Labeling each shell

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 18Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Cavity Inspection at LBNL (2/2) CMM scans to pair best matches of two half shells (diameters) CMM scans to pair best matches of two half shells (diameters) Over 1,500 points along the cavity perimeterOver 1,500 points along the cavity perimeter Find the best match of average radii, radius deviations and the location of the deviation anglesFind the best match of average radii, radius deviations and the location of the deviation angles Examples of two shellsExamples of two shells Shell 4B (blue) and 6B (yellow) Radius deviations are magnified by a factor of 55 here

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 19Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Fabrication Status at Applied Fusion (1/3) Fixtures used for the MuCool prototype shipped to Applied FusionFixtures used for the MuCool prototype shipped to Applied Fusion Two re-spun half shells arrived Applied Fusion in early May for fabrication test/practiceTwo re-spun half shells arrived Applied Fusion in early May for fabrication test/practice E-beam welding testsE-beam welding tests Stiffener ringsStiffener rings EquatorEquator Port extrudingPort extruding Water cooling pipesWater cooling pipes E-beam welding of the stiffener ring

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 20Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Fabrication Status at Applied Fusion (2/3) E-beam strength testing Port extruding and flange welding testing

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 21Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Applied Fusion June 9, 2009 Fabrication Status at Applied Fusion (3/3)

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 22Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Current Plan at Applied Fusion June – September 2009: June – September 2009: ― Machine the shells and prep for EB ― EBW stiffener rings ― Equator welding ― Port extruding (4 in each cavity) ― Machine and weld port flanges ― Machine-finish and EBW of the nose rings ― Tig-weld water cooling pipes ― Vacuum check of the cavity and water cooling pipes Integration of cavities, coupling coils and other module components will take place at LBNL Integration of cavities, coupling coils and other module components will take place at LBNL

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 23Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Schedule Summary (Presented at CM23 & 24)

MuCool RF Workshop: 201-MHz RF Cavity Studies Page 24Derun Li - Lawrence Berkeley National Lab – July 7, 2009 Summary 201-MHz RF cavity tests201-MHz RF cavity tests –MP was observed at the entire magnetic field range up to T (~ 1.1-T at nearest Be window) –A strong correlation exists between cavity vacuum and radiation levels –We have achieved ~ 14 MV/m at 2.5-T (~ 0.75-T to the nearest curved thin Be window) {~ 19 MV/m without B} –More careful systematic RF conditioning studies –MuCool SC coupling coil –Study of cavity frequency stability with thin Be window from 0 to high power (~ 5 MW) for a given duty factor (information is important to MICE cavity tuner designs) –Study MP of the RF (co-axial) coupler with B fields MICE cavity fabrications: first 4 cavities by 2010MICE cavity fabrications: first 4 cavities by 2010