Mahzad - 8/9/2007 AAC Presentation 1 High Pressure RF Studies Mahzad BastaniNejad Muons, Inc., Old...

Mahzad - 8/9/2007Mahzad - 8/9/2007 AAC PresentationAAC Presentation 11

High Pressure RF StudiesHigh Pressure RF Studies

Mahzad BastaniNejadMahzad BastaniNejad

Muons, Inc., Muons, Inc.,

Old Dominion UniversityOld Dominion University

Muons, Inc.

OutlineOutline

HPRF Breakdown studiesHPRF Breakdown studies• Paschen Curve MeasurmentPaschen Curve Measurment• Metallic BreakdownMetallic Breakdown• Magnetic field dependenceMagnetic field dependence

Electrode Breakdown AnalysisElectrode Breakdown Analysis• Surface CharacterizationSurface Characterization• Fowler Nordheim behaviorFowler Nordheim behavior

Plans for beam testsPlans for beam tests• Mark II (old test cell)Mark II (old test cell)• Mark III Mark III

Muons, Inc.

Mahzad – 8/9/ 2007 AAC Presentation

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Pressurized High Gradient RF CavitiesPressurized High Gradient RF Cavities

Copper plated stainless-steel, with GH2 to 1600 psi & 77 K, Copper plated stainless-steel, with GH2 to 1600 psi & 77 K, Hemispherical 1” Electrodes, 800 MHz test cell in MTAHemispherical 1” Electrodes, 800 MHz test cell in MTA

Muons, Inc.


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5T Solenoid

Pressure barrier

Mark II Test Cell

MuCool Test Area (MTA)

Wave guide to coax adapter

Muons, Inc.


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HPRF Test Cell Measurements in MTAHPRF Test Cell Measurements in MTA

Electrode breakdown regionPaschen region

Electrode breakdown region

Muons, Inc.

• Paschen curve verified Paschen curve verified • Maximum gradient limited by breakdown of metal.Maximum gradient limited by breakdown of metal.• Cu and Be have same breakdown limits (~50 MV/m), Mo(~63MV/m), W(~75MV/m).Cu and Be have same breakdown limits (~50 MV/m), Mo(~63MV/m), W(~75MV/m).• Results show no B dependence, much different metallic breakdown than for vacuum Results show no B dependence, much different metallic breakdown than for vacuum cavities. cavities. Need beam tests to prove HPRF works.Need beam tests to prove HPRF works.


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Electrode Breakdown Analysis in High Pressure Cavities:Electrode Breakdown Analysis in High Pressure Cavities: Scanning Electron Microscope Images of ElectrodesScanning Electron Microscope Images of Electrodes

Beryllium Molybdenum Tungsten

Muons, Inc.

φ

Schematic of the mapped ElectrodeMahzad – 8/9/ 2007 AAC Presentation

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Breakdown Data AnalysisBreakdown Data Analysis

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Muons, Inc.

)E

Bexp(

)E(A)E(i

Surf

23FN

2SurfFN

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Electrons quantum mechanical tunnelling through a barrier in presence of electric field

W


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nE)E(i

Muons, Inc. 800 MHz Test Cell (MarkII) is not 800 MHz Test Cell (MarkII) is not

ideal for Beam testsideal for Beam tests

• Designed for gas and material breakdown studies not beam Designed for gas and material breakdown studies not beam studies.studies.

• Difficult to change frequency for any PressureDifficult to change frequency for any Pressure Need to disassemble TC to change shims under Need to disassemble TC to change shims under

electrodes to change capacitance.electrodes to change capacitance.

• Need to synchronize Linac and cavity frequency and phaseNeed to synchronize Linac and cavity frequency and phase Pressure changes frequency (by dielectric of hydrogen)Pressure changes frequency (by dielectric of hydrogen)

• Walls are thick, so the 400 MeV proton beam is degraded.Walls are thick, so the 400 MeV proton beam is degraded.


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Muons, Inc. Model of Beam in Old Test CellModel of Beam in Old Test Cell

Beam is degraded with 2” of Stainless Steel (Rakhno).

Half Test Cell


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HPRF in an Intense BeamHPRF in an Intense Beam

• The current Pressurized RF Test Cell will be used in the first The current Pressurized RF Test Cell will be used in the first beam test.beam test.

• We are studying ideas to mitigate the unwanted behavior of We are studying ideas to mitigate the unwanted behavior of the test cell. the test cell.

A new test cell design is under study:A new test cell design is under study: Designed for beam testing.Designed for beam testing. For testing ionization recombination models (A. T.)For testing ionization recombination models (A. T.) Allow clearing electrodes to be installed to prevent the Allow clearing electrodes to be installed to prevent the accumulation of charges.accumulation of charges. Another design implementation is to install grids to test the Another design implementation is to install grids to test the idea of gas-cooled RF windows for higher accelerating idea of gas-cooled RF windows for higher accelerating gradients.gradients.


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Muons, Inc.

800 MHz Pressurized RF Cavity with irises and clearing electrodes

Concept of the Next Test Cavity

B

Beam

Coax power feed

irises

Voltage pickup

+ and – clearing electrodes

Muons, Inc.

Conceptual schematic of a test cell design with irises and clearing electrodes:Conceptual schematic of a test cell design with irises and clearing electrodes:

• To mitigate the effects of electron and ion charge build up. To mitigate the effects of electron and ion charge build up. • The strong magnetic field will confine the protons and electrons from the ionized The strong magnetic field will confine the protons and electrons from the ionized hydrogen energy absorber to the central region of the cavity, away from the irises. hydrogen energy absorber to the central region of the cavity, away from the irises. • Electrons that do not recombine can be absorbed in the clearing electrodes.Electrons that do not recombine can be absorbed in the clearing electrodes.


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Another concept being developed to allow

remote tuning

HP 805MHz Cavity

RF Cavity

Pressure Vessel


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Muons, Inc.

HPRF Studies SummaryHPRF Studies Summary

• Paschen Curve behavior tested for 800 MHz for first time with Paschen Curve behavior tested for 800 MHz for first time with high density hydrogenhigh density hydrogen

• Dense gas suppresses dark currents and multipacting.Dense gas suppresses dark currents and multipacting. HPRF does not degrade in magnetic fieldsHPRF does not degrade in magnetic fields. .

Very fast conditioningVery fast conditioning

• New way to study RF breakdown discovered.New way to study RF breakdown discovered. Fowler-Nordheim (quantum mechanical) explanationFowler-Nordheim (quantum mechanical) explanation

• Development and Demonstration of HPRF in conditions for Development and Demonstration of HPRF in conditions for muon cooling under waymuon cooling under way

We really need the MTA beamline!We really need the MTA beamline!


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Muons, Inc.

Mahzad - 8/9/2007 AAC Presentation 1 High Pressure RF Studies Mahzad BastaniNejad Muons, Inc., Old...

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