PAC09 - List of Authors (Gallardo, J.C.)

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Gallardo, J.C.

Paper	Title	Page
TU5PFP004	Effect of External Magnetic Fields on the Operation of RF Cavities	809
	D. Stratakis, J.S. Berg, J.C. Gallardo, R. B. Palmer BNL, Upton, Long Island, New York
	Funding: This work supported by the U.S. Department of Energy, contract no. DE-AC02-98CH10886. Beam cooling for a future neutrino factory or muon collider requires high gradient rf cavities in the presence of strong magnetic fields. Experimental measurements suggested that the maximum accelerating gradient drops as the axial magnetic field increases. Little is known about the explicit dependence of the gradient on the strength of the magnetic field. The experimental observation of dark currents arising from local regions with enhanced surface field intensities under external magnetic fields however, suggests a new possible mechanism of breakdown based on electron field emission. A model of magnetic field breakdown is proposed. We illustrate that the field emitted electrons are focused by the external fields into small spots on the other side of the cavity and estimate the energy density they deliver to the wall. We show that this energy increases with the magnetic field, and this may lead to melting of the cavity surface. The influence of local fields at the emitter side is discussed and the extent to which space-charge affects this process is investigated. Results of our model are compared with recent experimental data from the 201 MHz and 805 MHz cavities.

Paper

Title

Page

TU5PFP004

Effect of External Magnetic Fields on the Operation of RF Cavities

809

D. Stratakis, J.S. Berg, J.C. Gallardo, R. B. Palmer
BNL, Upton, Long Island, New York

Funding: This work supported by the U.S. Department of Energy, contract no. DE-AC02-98CH10886.

Beam cooling for a future neutrino factory or muon collider requires high gradient rf cavities in the presence of strong magnetic fields. Experimental measurements suggested that the maximum accelerating gradient drops as the axial magnetic field increases. Little is known about the explicit dependence of the gradient on the strength of the magnetic field. The experimental observation of dark currents arising from local regions with enhanced surface field intensities under external magnetic fields however, suggests a new possible mechanism of breakdown based on electron field emission. A model of magnetic field breakdown is proposed. We illustrate that the field emitted electrons are focused by the external fields into small spots on the other side of the cavity and estimate the energy density they deliver to the wall. We show that this energy increases with the magnetic field, and this may lead to melting of the cavity surface. The influence of local fields at the emitter side is discussed and the extent to which space-charge affects this process is investigated. Results of our model are compared with recent experimental data from the 201 MHz and 805 MHz cavities.