Kilpatrick limit

In particle accelerators, a common mechanism for accelerating a charged particle beam is via copper resonant cavities in which electric and magnetic fields form a standing wave, the mode of which is designed so that the E field points along the axis of the accelerator, producing forward acceleration of the particles when in the correct phase.

The maximum electric field E achievable is limited by a process known as RF breakdown. The reliable limits for various RF frequencies f were tested experimentally in the 1950s by W. D. Kilpatrick.

An approximate relation by least-square optimization of the data yields

f = 1.64 M H z ⋅ ( E E 0 ) 2 ⋅ exp ⁡ ( − 8.5 E 0 E ) , with E 0 = 1 M V m (megavolts per metre).

This relation is known as the Kilpatrick Limit.