Supression of Upstream Field Emission in RF Accelerators

Conference · Mon Nov 30 23:00:00 EST 2015

OSTI ID:1645115

Marhauser, Frank ^[1]; Benson, Stephen V. ^[1]; Douglas, David R. ^[1]; Ament, L.J.P. ^[2]

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1. Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
2. ASML US Inc., Wilton, CT, USA

So-called elec­tron load­ing is the pri­mary cause for cav­ity per­for­mance lim­i­ta­tions in mod­ern RF ac­cel­er­at­ing cav­i­ties. In su­per­con­duct­ing RF cav­i­ties in par­tic­u­lar, the onset of par­a­sitic elec­tron ef­fects may start at field lev­els as low as a few MV/m. Elec­tron load­ing can be at­trib­uted to mainly three phe­nom­ena: field emis­sion, mul­ti­ple im­pact elec­tron am­pli­fi­ca­tion, and RF elec­tri­cal break­down. Field emis­sion has been a per­sis­tent issue de­spite ad­vances in SRF tech­nol­ogy, whereas RF elec­tri­cal break­down and mul­ti­pact­ing can be con­trolled by ap­pro­pri­ate cav­ity de­sign choices. Field emis­sion be­comes a major con­cern when the elec­trons emit­ted are cap­tured by the ac­cel­er­at­ing RF field and di­rected along the beam axis through a se­ries of cav­i­ties or even en­tire cry­omod­ules. Con­se­quently, elec­trons can ac­cu­mu­late en­ergy com­pa­ra­ble to that of the main beam over sim­i­lar dis­tances. This can rep­re­sent a con­sid­er­able dark cur­rent, which can travel down­stream or up­stream de­pend­ing on the field-emit­ting site of ori­gin. In this paper, a method is pre­sented that can sig­nif­i­cantly sup­press the up­stream field emis­sion by de­sign.

• Research Organization: Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 1645115
• Report Number(s): JLAB-ACC-15-2191; DOE/OR/23177-3617
• Country of Publication: United States
• Language: English