D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
805-MHz Cavity 805-MHz Cavity Refurbishment and Refurbishment and
suggestions on future testssuggestions on future tests
Derun Li and Robert Rimmer*Derun Li and Robert Rimmer*
Lawrence Berkeley National LaboratoryLawrence Berkeley National Laboratory*Jefferson Laboratory*Jefferson Laboratory
RF Workshop at FermilabRF Workshop at FermilabOctober 15, 2008October 15, 2008
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
The 805-MHz CavityThe 805-MHz Cavity
Pillbox cavity
Be (or Cu) windows
Waveguide + window
Coupler
Thermo-couples or view ports
Three more view ports on the equator
Superconducting magnet
Thin Cuwindowand end-plate
film
RF Power
Up to three RF probes
The cavity has been tested for over six years.The cavity has been tested for over six years.
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
The 805-MHz Cavity The 805-MHz Cavity with RF Buttonwith RF Button
Cavity modified tohouse buttons
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Surface Damage: windows, Surface Damage: windows, RF buttonRF button
WindowsWindows Button holderButton holder
Cu buttonCu button
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Inspection of the Damaged Inspection of the Damaged Cavity SurfaceCavity Surface
The cavity is at JLab now.The cavity is at JLab now.
Damage found at the Kidney-Damage found at the Kidney-shape RF coupler and cavity shape RF coupler and cavity surface that faces the couplersurface that faces the coupler
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Cavity Repair Setup
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Cleaning of the Damaged Cleaning of the Damaged Cavity SurfaceCavity Surface
The cavity body surface has been The cavity body surface has been cleanedcleanedThe outer edge of the kidney-shape The outer edge of the kidney-shape coupler has been rounded by 2-mmcoupler has been rounded by 2-mmInside edge is being polished byInside edge is being polished byhands hands
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Cavity Repair StatusCavity Repair Status
• The cavity surface has been cleaned very wellThe cavity surface has been cleaned very well– Should be as good as it was, Should be as good as it was,
• Will condition well without magnetic fieldsWill condition well without magnetic fields• With magnetic fields? With magnetic fields?
– Do we want to do EP?Do we want to do EP?• Help prevent from field emissionHelp prevent from field emission• Can be done at JLab, time to set up + chemicalsCan be done at JLab, time to set up + chemicals• Possible problem?Possible problem?
– Trapped chemicals due to the cavity history Trapped chemicals due to the cavity history – Cleaning Cleaning
– Damaged button holderDamaged button holder• Exam with microscope to measure pit sizes per R. Palmer’s Exam with microscope to measure pit sizes per R. Palmer’s
requestrequest• Should we make a new button holder? Should we make a new button holder?
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Tests with ButtonsTests with Buttons
• More tests using the repaired cavity with More tests using the repaired cavity with buttons buttons – Previous test results or gradient limits might be Previous test results or gradient limits might be
limited by damaged surface, not peak fields on limited by damaged surface, not peak fields on buttonsbuttons
– How about a double button configuration?How about a double button configuration?• Two buttons for each material or coating Two buttons for each material or coating • SUPERFISH simulations show SUPERFISH simulations show ff = 805.89-MHz = 805.89-MHz• Inspect surface damage for each button experimentInspect surface damage for each button experiment
buttonbutton
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Do We Need A New Do We Need A New Cavity?Cavity?
• IF the repaired cavity does not work well as we IF the repaired cavity does not work well as we expected, we should consider to build a new cavity at expected, we should consider to build a new cavity at 805-MHz cavity. If the answer is yes,805-MHz cavity. If the answer is yes,– What’s kind of cavity?What’s kind of cavity?– Would be nice to have a cavity that can be rotated inside Lab-G Would be nice to have a cavity that can be rotated inside Lab-G
magnet to study ExB effects:magnet to study ExB effects:• Coupler designCoupler design
– In fact, we may learn from any angle configurations, with help In fact, we may learn from any angle configurations, with help from powerful simulation tools from powerful simulation tools
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
The 201-MHz Cavity The 201-MHz Cavity
Electric field distribution on axisElectric field distribution on axis(two curved windows)(two curved windows)
The MUCOOL prototype cavity (3-D model)The MUCOOL prototype cavity (3-D model)ff = 199.927 MHz = 199.927 MHz
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
New Ideas for 201-MHz RF New Ideas for 201-MHz RF Programs?Programs?
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Test B-Field EffectsTest B-Field Effects
• Needs the SC coupling coilNeeds the SC coupling coil– Field map is not the same as in the cooling channelField map is not the same as in the cooling channel– How about a coaxial quarter wave cavity?How about a coaxial quarter wave cavity?
• Test 0, 90, and other anglesTest 0, 90, and other angles
Mechanical stabilityMechanical stabilityWater coolingWater cooling
A folded quarter-waveA folded quarter-wavecavity: more stored energycavity: more stored energy
Coaxial quarter-Coaxial quarter-wave cavitywave cavity
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Coaxial Coupler in BCoaxial Coupler in B
• Coaxial loop couplers for MICE 201-MHz cavities are close to SC coupling coil magnet– Potential RF breakdown in external magnetic fields– May need Ti-N coating?– What tests can be done?– Any suggestions?
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Multipacting Simulation for Muon Collider Cavity
Lixin Ge and Zenghai LiAdvanced Computations DepartmentStanford Linear Accelerator Center
August 21, 2008
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Numerical Study with B FieldNumerical Study with B Field
• Preliminary studies, in collaboration SLAC using Omega-3P and Track-3P codes– Cavity with flat windows: 5 MV/m on axis; 2-T uniform external
magnetic field; scan of a few points from one cavity side
E field contourE field contourTrajectories without Trajectories without
external B fieldexternal B fieldTrajectories with Trajectories with
external B = 2-T fieldexternal B = 2-T field
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
High impact energy (heating?)
Impact energy too low for MP
Impact energy of resonant particles vs. field levelImpact energy of resonant particles vs. field level
w/o external B field w/ 2T external axial B field
2 types of resonant trajectories:
• Between 2 walls – particles with high impact energies and thus no MP
• Around iris – MP activities observed below 1 MV/m
SEY > 1 for copper
2T
Multipacting w/ & w/o External Axial Magnetic Field
SEY > 1 for copper
Resonant trajectory
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
SEY > 1 for copper
w/ 2T B field at 10 degreew/ 2T transverse B field
Multipacting w/ External Transverse Magnetic Field
Impact energy of resonant particles vs. field levelImpact energy of resonant particles vs. field level
SEY > 1 for copper
2T 2T
2 types of resonant trajectories:
• Between upper and lower irises
• Between upper and lower cavity walls
Slight MP activities observed above 6 MV/m
2 types of resonant trajectories:
• One-point impacts at upper wall
• Two-point impacts at beampipe
MP activities observed above 1.6 MV/m
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Simulation ConditionSimulation Condition• Geometry: Pure pill box
– Radius: 0.1425m– Length: 0.1m
• Field: – 0 mode– Frequency: 805MHz
• Multipacting Simulation Condition:– Average Field Level Scan: 0-60MV/m, interval: 0.5MV/m – External Magnetic Field: 2T– Scan Angle: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 deg– Time step: 0.001 period to resolve external magnetic field– Total Particles: 164x1000x11x61x2=220,088,000– Each field level running 30 periods
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Impact energy of resonant particles vs. field levelImpact energy of resonant particles vs. field level
Multipacting without External Magnetic FieldMultipacting without External Magnetic Field
Resonant trajectory at 5MV/m
High impact energy (heating?)
E magnitude field B magnitude field
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
With External Transverse Magnetic FieldWith External Transverse Magnetic Field
No resonant trajectory when angle < 7 deg
2T
Single Impact Energy vs. field level for 4 deg
D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008
Multipacting with External Transverse Multipacting with External Transverse Magnetic FieldMagnetic Field
Impact energy of resonant particles vs. field levelImpact energy of resonant particles vs. field level
2T
Resonant Trajectory at 50 MV/m with 2T external magnetic field(10 deg angle)