PAC07 - List of Authors (Newsham, D. J.)

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Newsham, D. J.

Paper	Title	Page
WEPMS071	EVIDENCE FOR FOWLER-NORDHEIM BEHAVIOR IN RF BREAKDOWN	2499
	M. BastaniNejad, A. A. Elmustafa Old Dominion University, Norfolk, Virginia M. Alsharo'a, P. M. Hanlet, R. P. Johnson, M. Kuchnir, D. J. Newsham Muons, Inc, Batavia C. M. Ankenbrandt, A. Moretti, M. Popovic, K. Yonehara Fermilab, Batavia, Illinois D. M. Kaplan Illinois Institute of Technology, Chicago, Illinois
	Funding: Supported in part by DOE STTR grant DE-FG02-05ER86252 Microscopic images of the surfaces of metallic electrodes used in high-pressure gas-filled 800 MHz RF cavity experiments are used to investigate the mechanism of RF breakdown. The images show evidence for melting and boiling in small regions of ~10 micron diameter on tungsten, molybdenum, and beryllium electrode surfaces. In these experiments, the dense hydrogen gas in the cavity prevents electrons or ions from being accelerated to high enough energy to participate in the breakdown process so that the only important variables are the fields and the metallic surfaces. The distributions of breakdown remnants on the electrode surfaces are compared to the maximum surface gradient E predicted by an ANSYS model of the cavity. The surface local density of spark remnants, presumably the probability of breakdown, shows a power law dependence on the maximum gradient, with E¹⁰ for tungsten and molybdenum and E⁷ for beryllium. This is reminiscent of Fowler-Nordheim behavior of electron emission from a cold cathode, which is explained by the quantum-mechanical penetration of a barrier that is characterized by the work function of the metal.
THPMN094	Simulations of Parametric-resonance Ionization Cooling	2927
	D. J. Newsham, R. P. Johnson, R. Sah Muons, Inc, Batavia S. A. Bogacz, Y.-C. Chao, Y. S. Derbenev Jefferson Lab, Newport News, Virginia
	Funding: Supported in part by DOE SBIR grant DE-FG02-04ER84016 Parametric-resonance ionization cooling (PIC) is a muon-cooling technique that is useful for low-emittance muon colliders. This method requires a well-tuned focusing channel that is free of chromatic and spherical aberrations. In order to be of practical use in a muon collider, it also necessary that the focusing channel be as short as possible to minimize muon loss due to decay. G4Beamline numerical simulations are presented of a compact PIC focusing channel in which spherical aberrations are minimized by using design symmetry.