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RF Photocathode Guns

The AWA facility maintains the world’s two highest-charge RF photocathode guns, both capable of 100 nC per bunch.

The L-band drive RF photocathode gun produces both single-electron bunches as well as trains of electron bunches spaced at 1.3 GHz.

In single-bunch operation, the drive gun produces a wide variety of bunches from 10 pC to 100 nC, a dynamic range of four orders of magnitude.

In bunch-train operation, the drive gun produces trains of variable pulse length, from one to 32 bunces, with total charge of 600 nC. The L-band witness RF photocathode gun produces single bunches of electrons from 10 pC to 10 nC.

Drive and Witness RF Guns

The 1.3 GHz Drive and Witness RF guns have identical geometries but use different photocathodes, Cs2Te and Mg, respectively. The RF gun is a 1.5 cell SW cavity operating at 1.3 GHz. Each gun has been conditioned up to 14 MW which corresponds to 88 MV/m on the cathode.

The RF power available to guns in operation is limited since the two guns and one accelerating cavity share the power from Klystron 1. When both guns are operated simultaneously (e.g., during two-beam acceleration operation), the drive gun is typically operated at 80 MV/m and the witness gun at 50 MV/m due to power limitations.

However, the two beamlines are fully independent and can be operated separately at full-field strength of 80 MV/m, where the beam energy at the exit of the drive gun is 8 MeV.