| Paper | Title | Page |
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| TU5PFP001 | Modeling RF Breakdown Arcs | 800 |
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Funding: DOE. OHEP We are modeling breakdown arcs in rf structures with Particle in Cell, (OOPIC Pro and VORPAL), Molecular Dynamics (HyDyn, LAMMPS), and an integrated radiation-magnetohyrodynamic package (HEIGHTS) to evaluate the basic parameters and mechanisms of rf discharges. We are evaluating the size, density, species temperature, radiation levels and other properties, to determine how the breakdown trigger works, what the growth times of the discharge are, effects of strong magnetic fields and what happens to both the arc and cavity energy. The goal is to have a complete picture of the plasma and its interaction with the wall. While we expect that these calculations will help guide further experimental studies, we have recently benchmarked model predictions against available experimental data on rise times of x ray pulses, and found a reasonable agreement. |
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| TU5PFP002 | Atomic Layer Deposition for SRF Cavities | 803 |
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Funding: DOE/OHEP We have begun using Atomic Layer Deposition (ALD) to synthesize a variety of surface coatings on coupons and cavities as part of an effort to produce rf structures with significantly better performance and yield than those obtained from bulk niobium, The ALD process offers the possibility of conformally coating complex cavity shapes with precise layered structures with tightly constrained morphology and chemical properties. Our program looks both at the metallurgy and superconducting properties of these coatings, and also their performance in working structures. Initial results include: 1) evidence from point contact tunneling showing magnetic oxides can be a significant limitation to high gradient operation, 2) experimental results showing the production sharp niobium/oxide interfaces from a high temperature bake of ALD coated Al2O3 on niobium surfaces, 3) results from ALD coated structures. |
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| TU5PFP032 | RF Studies at Fermilab MuCool Test Area | 888 |
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Funding: The United States Department of Energy The accelerating gradient in a RF cavity is limited by many factors such as the surface material properties, RF frequency, the external magnetic field and the gas pressure inside the cavity. In the MuCool Program, RF cavities are studied with the aim of understanding these basic mechanisms and improving their maximum stable accelerating gradient. These cavities are being developed for muon ionization cooling channel for a Neutrino Factory or Muon Collider. We report studies using the 805 MHz and 201 MHz RF cavities in the MuCool Test Area (MTA) at Fermilab. New results include data from buttons of different materials mounted in the 805 MHz cavity, study of the accelerating gradient in the 201 MHz cavity and X-ray background radiation from the cavities due to Bremsstrahlung. The 201 MHz cavity has been shown to be stable at 19 MV/m at zero magnetic field, well in excess of its 16 MV/m design gradient. We will also discuss results from the 201 MHz cavity study in magnetic field and introduce the test of E × B effects with the 805 MHz box cavity. |