Revision 1

Accepted · first revision · record

Title: Microscopic mechanism that initiates vacuum RF breakdown on copper
Plain: Breakdowns start at small spots on a polished copper surface, but which process lights the spark (electrons pulled out by the field, crystal defects moving to the surface, local melting) is not agreed.
Precise: In Cu accelerating structures at 3-30 GHz, breakdown occurs at surface fields $eE_{s} \sim 2-3\,\mathrm{MeV}/\mathrm{cm}$, and Fowler-Nordheim fits of dark current give field-enhancement factors $\beta \sim 30-100$ although no protrusions of matching height are observed. Identify the sequence of processes (dislocation-driven surface roughening, field-emission heating of emitters, neutral evaporation, plasma ignition) that turns an intact surface into an arc, with a model that predicts the threshold field and its dependence on hardness and crystal structure of the metal.
Settled by: In-situ imaging of breakdown sites before and after the event together with a model that reproduces measured thresholds for at least two metals of different crystal structure.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: (empty)
Posed since: (empty)