201 mhz cavity studies derun li lawrence berkeley national laboratory mucool rf workshop (fermilab)...

201 MHz Cavity 201 MHz Cavity StudiesStudies

Derun LiDerun LiLawrence Berkeley National LaboratoryLawrence Berkeley National Laboratory

MuCool RF WorkshopMuCool RF Workshop(Fermilab)(Fermilab)

July 7 and 8, 2009

MuCool RF Workshop: 201-MHz RF Cavity Studies

Derun Li - Lawrence Berkeley National Lab – July 7, 2009

OutlineOutline• Brief review and progresses of the 201-MHz Brief review and progresses of the 201-MHz

test program test program – RF tests with flat Cu and curved thin Be windowsRF 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 magnetRF 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 Simulation study of RF cavity in strong magnetic fieldfield

• 201-MHz cavity fabrication for MICE201-MHz cavity fabrication for MICE



Primary GoalsPrimary Goals• Development of normal conducting 201-MHz cavity that Development of normal conducting 201-MHz cavity that

can operate at a gradient of can operate at a gradient of ~ 16 MV/m in a few Tesla ~ 16 MV/m in a few Tesla magnetic fieldsmagnetic fields environment environment– Prototype: exploring engineering solutions (challenges)Prototype: exploring engineering solutions (challenges)– RF conditioning and operation without and with RF conditioning and operation without and with BB fields fields

• Operating a NC RF cavity (with thin and curved Be Operating a NC RF cavity (with thin and curved Be windows) at ~ 16 MV/m in strong windows) at ~ 16 MV/m in strong B B fieldfield could be very could be very challenging, but to be confirmed experimentallychallenging, but to be confirmed experimentally– Test with stronger magnetic fieldsTest with stronger magnetic fields

• SC coupling coil for MUCOOL: being fabricated at ICST, Harbin



201-MHz Prototype Cavity201-MHz Prototype Cavity• The cavity design parameters The cavity design parameters

– Frequency: 201.25 MHzFrequency: 201.25 MHz– ββ = 0.87 = 0.87– Shunt impedance (Shunt impedance (VTVT22/P/P): ~ 22 ): ~ 22

MΩ/mMΩ/m– Quality factor (Quality factor (QQ00): ~ 53,500): ~ 53,500– Be window radius and thickness: Be window radius and thickness:

21-cm and 0.38-mm21-cm and 0.38-mm• Nominal parameters for cooling Nominal parameters for cooling

channels in a muon collider or a channels in a muon collider or a neutrino factoryneutrino factory – ~ 16 MV/m peak accelerating field~ 16 MV/m peak accelerating field– Peak input RF power ~ Peak input RF power ~ 4.6 MW4.6 MW per per

cavity (85% of Qcavity (85% of Q00, 3, 3 filling time) filling time)– Average power dissipation per Average power dissipation per

cavity ~ cavity ~ 8.4 kW8.4 kW– Average power dissipation per Be Average power dissipation per Be

window ~ window ~ 100 watts100 watts

The 201-MHz cavity at MTAThe 201-MHz cavity at MTA



Test Setup at MTA Test Setup at MTA The 805-MHz and 201-MHz cavities at MTA, FNAL for RF The 805-MHz and 201-MHz cavities at MTA, FNAL for RF

breakdown studies with external magnetic fields.breakdown studies with external magnetic fields.

805 MHz pillbox cavity805 MHz pillbox cavity

201 MHz cavity201 MHz cavity



RF Tests of curved thin Be RF Tests of curved thin Be WindowsWindows

• The cavity reached to ~ 19 MV/m The cavity reached to ~ 19 MV/m – Cavity frequency had to be retuned Cavity frequency had to be retuned

– Cavity frequency was Cavity frequency was stable stable during the operation, during the operation, however, we did observe frequency shift due to RF however, we did observe frequency shift due to RF heating on the windowsheating on the windows

• Frequency shift of ~ 125 kHz (from 0 to ~ 19 MV/m, 150-Frequency shift of ~ 125 kHz (from 0 to ~ 19 MV/m, 150-micro-second pulse, 10-Hz repetition rate) in ~ 10 minutes, micro-second pulse, 10-Hz repetition rate) in ~ 10 minutes, well within the tuning range ( ~ 110 kHz/mm, well within the tuning range ( ~ 110 kHz/mm, 4 mm range) 4 mm range)

• With low external magnetic fieldWith low external magnetic field– Cavity can be operated at ~ 19 MV/m with a few Cavity can be operated at ~ 19 MV/m with a few

hundred Gauss stray field from Lab-G magnethundred Gauss stray field from Lab-G magnet

• Tests with stronger external magnetic fieldsTests with stronger external magnetic fields– SC coupling coil for MuCoolSC coupling coil for MuCool



Tests with Magnetic FieldsTests with Magnetic Fields

The 100-cm long coaxial The 100-cm long coaxial section was replaced by section was replaced by 20-cm one20-cm one

Separation of the nearest Separation of the nearest curved Be window from curved Be window from the face of Lab-G magnet the face of Lab-G magnet is 10-cm (before was 110-is 10-cm (before was 110-cm)cm)

Maximum magnetic field Maximum magnetic field near the Be window ~ 1.5 near the Be window ~ 1.5 Tesla (5 Tesla in magnet)Tesla (5 Tesla in magnet)

The 201-MHz cavityThe 201-MHz cavity

Lab-G magnetLab-G magnet



Rad

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Cavity Gradient (MV/m)Cavity Gradient (MV/m)

Tests at external field Tests at external field B = 0 B = 0

Radiation data compared with a fitting with to Radiation data compared with a fitting with to gradient to ~ 14gradient to ~ 14thth power power



Rad

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Rad

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Cavity Gradient (MV/m)Cavity Gradient (MV/m)

Radiation at Radiation at B = 0.5-B = 0.5-T T FieldField

Radiation data compared with a fitting with to Radiation data compared with a fitting with to gradient to ~ 14gradient to ~ 14thth power power

0.5-T B field to the 0.5-T B field to the nearest Be windownearest Be window



Test Results We have so farTest Results We have so far Multi-pactoring was observed at the entire magnetic field Multi-pactoring was observed at the entire magnetic field

range up to 3.75-T (~ 1.1-T at nearest Be window)range up to 3.75-T (~ 1.1-T at nearest Be window) A strong correlationship exists between cavity vacuum and A strong correlationship exists between cavity vacuum and

radiation levelsradiation levels We have achieved ~ 14 MV/m at 2.5-T (~ 0.75-T to the nearest We have achieved ~ 14 MV/m at 2.5-T (~ 0.75-T to the nearest

curved thin Be window) curved thin Be window) ~ 19 MV/m without B~ 19 MV/m without B The test results are very encouragingThe 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 fieldeffects in the stray field Numerical studies with external Numerical studies with external magnetic fields and SC coupling coilmagnetic fields and SC coupling coil



Numerical Study with B Field (Bob’s Numerical Study with B Field (Bob’s Talk)Talk)

• Physics models and numerical simulations (BNL, Physics models and numerical simulations (BNL, SLAC, …)SLAC, …)– Cavity with flat windows: 5 MV/m on axis; 2-T uniform Cavity with flat windows: 5 MV/m on axis; 2-T uniform

external magnetic field; scan of a few points from one external magnetic field; scan of a few points from one cavity sidecavity side



201-MHz Cavity for MICE201-MHz Cavity for MICE• Eight 201-MHz cavities + with materials for two more Eight 201-MHz cavities + with materials for two more

spare cavities spare cavities • Baseline design: 201-MHz for MUCOOL, butBaseline design: 201-MHz for MUCOOL, but

– Cavity body profile has been modified Cavity body profile has been modified • Raise resonant frequencyRaise resonant frequency

– Port extrudingPort extruding• Port interface is different from the MUCOOL cavityPort interface is different from the MUCOOL cavity

– RF coupler and ceramic windowRF coupler and ceramic window• The same window as for the MUCOOL cavityThe same window as for the MUCOOL cavity

– Curved Beryllium windowsCurved Beryllium windows• Improved design to better control silver alloy flow during the Improved design to better control silver alloy flow during the

brazingbrazing– Tuners and interface with RFCC moduleTuners and interface with RFCC module– Post-processing: water cooling pipes, cleaning (EP & Post-processing: water cooling pipes, cleaning (EP &

water rinsing), low power measurement, tuning, water rinsing), low power measurement, tuning, assembly and shipping assembly and shipping



Four RF Cavities in each RFCC Four RF Cavities in each RFCC ModuleModule

SC coupling Coil

Cavity Couplers

Vacuum Pump201-MHz cavity201-MHz cavity

Curved Be window



Update on MICE RF Cavity Update on MICE RF Cavity DesignDesign

•3-Dimensional RF cavity parameterized 3-Dimensional RF cavity parameterized model to study frequency shifts from RF model to study frequency shifts from RF ports and curved Be windows and Eports and curved Be windows and Epeakpeak

•Frequencies variation between cavities Frequencies variation between cavities should be within should be within 100 kHz 100 kHz

•Fabrication Fabrication – Modification of the mold for prototype Modification of the mold for prototype

cavitycavity• Reduction in diameter to raise the

MICE cavity frequency

– Tune cavities close to design frequency Tune cavities close to design frequency by deformation of cavity body (if by deformation of cavity body (if needed)needed)

– Fine tuners operate in the push-and-Fine tuners operate in the push-and-pull mode pull mode 230 kHz 230 kHz



Visit to ACME Spinning in April Visit to ACME Spinning in April 2009 (1/2)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 profile Re-spun the two half spare shells to new profile • Measured frequency shifts before and after Measured frequency shifts before and after spinningspinning

Expected frequency shift ~ 1 MHzExpected frequency shift ~ 1 MHzMeasurements:Measurements: Shell #1:Shell #1:

197.275 MHz (before)197.275 MHz (before)198.180 MHz (after)198.180 MHz (after)



Visit to ACME Spinning in 04-2009 Visit to ACME Spinning in 04-2009 (2/2)(2/2)

•Spun and measured a new half shell (frequency: Spun and measured a new half shell (frequency: 198.415 MHz)198.415 MHz)

•Developed a fabrication procedureDeveloped a fabrication procedure• Pre-polishing copper sheetsPre-polishing copper sheets

• Inspecting the surface Inspecting the surface

• Polishing visible scratches locally if necessary (before and Polishing visible scratches locally if necessary (before and after)after)

• Handling and shippingHandling and shippingPolished surfacePolished surface

Local polishing to remove Local polishing to remove deeper scratches deeper scratches

Surface inspection during Surface inspection during the spinningthe spinning



Cavity Inspection at LBNL (1/2)Cavity Inspection at LBNL (1/2)• 12 spun half shells arrived LBNL in May 200912 spun half shells arrived LBNL in May 2009•CMM scans to pair best matches of two half shells in CMM scans to pair best matches of two half shells in

diameters, all of them have been measured diameters, all of them have been measured

Polished cavity Polished cavity surfacesurface

Center hole for Center hole for handling & spinninghandling & spinning

Labeling eachLabeling eachshell shell



Cavity Inspection at LBNL (2/2)Cavity Inspection at LBNL (2/2)• CMM scans to pair best matches of two half shells CMM scans to pair best matches of two half shells

(diameters) (diameters) • Over 1,500 points along the cavity perimeter Over 1,500 points along the cavity perimeter • Find the best match of average radii, radius Find the best match of average radii, radius

deviations and the location of the deviation angles 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



Fabrication Status at Applied Fusion Fabrication Status at Applied Fusion (1/3)(1/3)

•Fixtures used for the MuCool prototype shipped to Fixtures used for the MuCool prototype shipped to Applied FusionApplied Fusion

•Two re-spun half shells arrived Applied Fusion in early Two re-spun half shells arrived Applied Fusion in early May for fabrication test/practiceMay for fabrication test/practice

• E-beam welding testsE-beam welding tests• Stiffener ringsStiffener rings• Equator Equator

• Port extruding Port extruding • Water cooling pipes Water cooling pipes

E-beam welding of E-beam welding of the stiffener ringthe stiffener ring




E-beam strength testingE-beam strength testing

Port extruding and flange Port extruding and flange welding testingwelding testing



Applied FusionJune 9, 2009




Current Plan at Applied FusionCurrent Plan at Applied Fusion• June – September 2009:June – September 2009:

― Machine the shells and prep for EBMachine the shells and prep for EB

― EBW stiffener ringsEBW stiffener rings

― Equator weldingEquator welding

― Port extruding (4 in each cavity)Port extruding (4 in each cavity)

― Machine and weld port flangesMachine and weld port flanges

― Machine-finish and EBW of the nose ringsMachine-finish and EBW of the nose rings

― Machine-finish and EBW of the nose ringsMachine-finish and EBW of the nose rings

― Tig-weld water cooling pipes Tig-weld water cooling pipes

― Vacuum check of the cavity and water cooling pipesVacuum check of the cavity and water cooling pipes

Integration of cavities, coupling coils and other module Integration of cavities, coupling coils and other module components will take place at LBNLcomponents will take place at LBNL



Schedule Summary (Presented at CM23 & Schedule Summary (Presented at CM23 & 24)24)



SummarySummary

• 201-MHz RF cavity tests201-MHz RF cavity tests – MP was observed at the entire magnetic field range up MP was observed at the entire magnetic field range up

to 3.75-T (~ 1.1-T at nearest Be window)to 3.75-T (~ 1.1-T at nearest Be window)– A strong correlation exists between cavity vacuum and A strong correlation exists between cavity vacuum and

radiation levelsradiation levels– We have achieved ~ 14 MV/m at 2.5-T (~ 0.75-T to the We have achieved ~ 14 MV/m at 2.5-T (~ 0.75-T to the

nearest curved thin Be window) ~ 19 MV/m without Bnearest curved thin Be window) ~ 19 MV/m without B– More careful systematic RF conditioning studies More careful systematic RF conditioning studies – MuCool SC coupling coilMuCool SC coupling coil– Study of cavity frequency stability with thin Be window Study of cavity frequency stability with thin Be window

from 0 to high power (~ 5 MW) for a given duty factor from 0 to high power (~ 5 MW) for a given duty factor (information is important to MICE cavity tuner designs)(information is important to MICE cavity tuner designs)

– Study MP of the RF (co-axial) coupler with B fieldsStudy 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

201 mhz cavity studies derun li lawrence berkeley national laboratory mucool rf workshop (fermilab)...

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