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

Outline HPRF Breakdown studies HPRF Breakdown studies Paschen Curve MeasurmentPaschen Curve Measurment Metallic BreakdownMetallic Breakdown Magnetic field dependenceMagnetic field dependence Electrode Breakdown Analysis Electrode Breakdown Analysis Surface CharacterizationSurface Characterization Fowler Nordheim behaviorFowler Nordheim behavior Plans for beam tests Plans for beam tests Mark II (old test cell)Mark II (old test cell) Mark IIIMark III Muons, Inc. Mahzad – 8/9/ 2007 AAC Presentation 2

Pressurized High Gradient RF Cavities Copper plated stainless-steel, with GH2 to 1600 psi & 77 K, Hemispherical 1” Electrodes, 800 MHz test cell in MTA Muons, Inc. Mahzad – 8/9/ 2007 AAC Presentation 3

5T Solenoid Pressure barrier Mark II Test Cell MuCool Test Area (MTA) Wave guide to coax adapter Muons, Inc. Mahzad – 8/9/ 2007 AAC Presentation 4

HPRF Test Cell Measurements in MTA Electrode breakdown region Paschen 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. Need beam tests to prove HPRF works. cavities. Need beam tests to prove HPRF works. Mahzad – 8/9/ 2007 AAC Presentation 5

Electrode Breakdown Analysis in High Pressure Cavities: Scanning Electron Microscope Images of Electrodes Beryllium MolybdenumTungsten Muons, Inc. φ Schematic of the mapped Electrode Mahzad – 8/9/ 2007 AAC Presentation 6

Breakdown Data Analysis Be Mo Muons, Inc. Electrons quantum mechanical tunnelling through a barrier in presence of electric field W Mahzad – 8/9/ 2007 AAC Presentation 7

Muons, Inc. 800 MHz Test Cell (MarkII) is not ideal for Beam tests Designed for gas and material breakdown studies not beam studies.Designed for gas and material breakdown studies not beam studies. Difficult to change frequency for any PressureDifficult to change frequency for any Pressure  Need to disassemble TC to change shims under 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) Walls are thick, so the 400 MeV proton beam is degraded.Walls are thick, so the 400 MeV proton beam is degraded. Mahzad – 8/9/ 2007 AAC Presentation 8

Muons, Inc. Model of Beam in Old Test Cell Beam is degraded with 2” of Stainless Steel (Rakhno). Half Test Cell Mahzad – 8/9/ 2007 AAC Presentation 9

HPRF in an Intense Beam The current Pressurized RF Test Cell will be used in the first beam test.The current Pressurized RF Test Cell will be used in the first beam test. We are studying ideas to mitigate the unwanted behavior of the test cell.We are studying ideas to mitigate the unwanted behavior of the test cell. A new test cell design is under study:  Designed for beam testing.  For testing ionization recombination models (A. T.)  Allow clearing electrodes to be installed to prevent the accumulation of charges.  Another design implementation is to install grids to test the idea of gas-cooled RF windows for higher accelerating gradients. Mahzad – 8/9/ 2007 AAC Presentation 10 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: 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. Mahzad – 8/9/ 2007 AAC Presentation 11

Another concept being developed to allow remote tuning Mahzad – 8/9/ 2007 AAC Presentation 12 Muons, Inc.

HPRF Studies Summary Paschen Curve behavior tested for 800 MHz for first time with high density hydrogenPaschen Curve behavior tested for 800 MHz for first time with high density hydrogen Dense gas suppresses dark currents and multipacting.Dense gas suppresses dark currents and multipacting.  HPRF does not degrade in magnetic fields.  Very fast conditioning New way to study RF breakdown discovered.New way to study RF breakdown discovered.  Fowler-Nordheim (quantum mechanical) explanation Development and Demonstration of HPRF in conditions for muon cooling under wayDevelopment and Demonstration of HPRF in conditions for muon cooling under way  We really need the MTA beamline! Mahzad – 8/9/ 2007 AAC Presentation 13 Muons, Inc.