Breakdown limit of RF cavities inside strong solenoid fields · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title
Breakdown limit of RF cavities inside strong solenoid fields
Plain
A muon collider needs accelerating cavities placed inside very strong magnets, and such cavities spark at lower fields than without the magnet.
Precise · changed · core
Revision 1: Vacuum normal-conducting cavities at $\sim 200\text{-}800\,\mathrm{MHz}$ in axial magnetic fields $B \sim 3e4\,\mathrm{G}$ show reduced maximum gradient, attributed to field-emitted electrons focused by B onto the walls, causing local heating. Establish the scaling of the safe gradient with B, frequency and wall material up to $B \sim 1e5\,\mathrm{G}$ and above, as required for 6D muon ionization cooling channels.
Revision 2: Vacuum normal-conducting cavities at $\sim 200\text{-}800\,\mathrm{MHz}$ in axial magnetic fields $B \sim 3 \times 10^{4}\,\mathrm{G}$ show reduced maximum gradient, attributed to field-emitted electrons focused by B onto the walls, causing local heating. Establish the scaling of the safe gradient with B, frequency and wall material up to $B \sim 10^{5}\,\mathrm{G}$ and above, as required for 6D muon ionization cooling channels.
Settled by
Gradient-limit measurements versus B up to the cooling-channel field for at least two wall materials and frequencies, compared with an electron-focusing heating model.
Kind
well-posed
Answer type
value
References
(empty)
Literature status
partially-resolved
Status note · changed
Revision 1: Beryllium-walled and high-pressure gas-filled cavities reached approximately $0.5\,\mathrm{MeV}/\mathrm{cm}$ in fields near $3e4\,\mathrm{G}$ at the Fermilab MuCool Test Area (reported around 2020); higher fields remain untested.
Revision 2: Beryllium-walled and high-pressure gas-filled cavities reached approximately $0.5\,\mathrm{MeV}/\mathrm{cm}$ in fields near $3 \times 10^{4}\,\mathrm{G}$ at the Fermilab MuCool Test Area (reported around 2020); higher fields remain untested.
Posed since
(empty)

Decisions