D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008 805-MHz Cavity Refurbishment and suggestions on future tests Derun Li and Robert Rimmer* Lawrence

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


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.


The 805-MHz Cavity The 805-MHz Cavity with RF Buttonwith RF Button

Cavity modified tohouse buttons


Surface Damage: windows, Surface Damage: windows, RF buttonRF button

WindowsWindows Button holderButton holder

Cu buttonCu button


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


Cavity Repair Setup


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


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?


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


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


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


New Ideas for 201-MHz RF New Ideas for 201-MHz RF Programs?Programs?


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


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?


Multipacting Simulation for Muon Collider Cavity

Lixin Ge and Zenghai LiAdvanced Computations DepartmentStanford Linear Accelerator Center

August 21, 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


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


SEY > 1 for copper

w/ 2T B field at 10 degreew/ 2T transverse B field

Multipacting w/ External Transverse Magnetic Field


SEY > 1 for copper

2T 2T


• Between upper and lower irises

• Between upper and lower cavity walls

Slight MP activities observed above 6 MV/m


• One-point impacts at upper wall

• Two-point impacts at beampipe

MP activities observed above 1.6 MV/m


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



Multipacting without External Magnetic FieldMultipacting without External Magnetic Field

Resonant trajectory at 5MV/m

High impact energy (heating?)

E magnitude field B magnitude field


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


Multipacting with External Transverse Multipacting with External Transverse Magnetic FieldMagnetic Field


2T

Resonant Trajectory at 50 MV/m with 2T external magnetic field(10 deg angle)

Documents

D. Li and R. Rimmer, RF Workshop, Fermilab, 10-15-2008 805-MHz Cavity Refurbishment and suggestions on future tests Derun Li and Robert Rimmer* Lawrence