SLAC, Menlo Park, California, USA
Duke ECE, Durham, North Carolina, USA
Plasma wakefield studies are normally conducted as single-shot experiments. Here, single-shot means that the plasma returns to its original state before the next bunch passes through the plasma. The time scale for the plasma to return to equilibrium is 10-100 ns, which is comparable to the bunch separation in proposed linear colliders. The SLAC linac typically delivers beam at a rate of 10 Hz to FACET but can be operated in a manner that delivers two electron bunches per RF pulse. We explore operation modes with beam separations as small 5.6 ns so that high repetition rate plasma wakefield acceleration can be studied at FACET.
WEOBA1
SLAC, Menlo Park, California, USA
The X-Band Test Area (XTA) at SLAC is an all X-Band compact RF photoinjector that can produce short, high current electron bunches. Computations have shown that the peak bunch brightness should exceed that from S-Band RF photoinjectors by a factor of four. This improved performance principally comes from the high (200 MV/m) peak fields that can be sustained on the gun cathode. During the first three months of XTA commissioning, 20 pC electron bunches have been routinely generated with the gun cathode operating at greater than 200 MV/m while the dark current levels have been low. The electron bunches are accelerated to 70 MeV in a one-meter long, travelling-wave, X-band structure after the gun (a newer version of this structure should allow acceleration to more than 100 MeV). This paper reviews progress to date including measurements of the bunch properties and the bunch-to-bunch stability. The lengths of the 20 pC bunches have been measured with a transverse X-Band deflection cavity to be 250 fs rms, as expected from simulations. Transverse emittance in the range of 0.9 mm-mrad have been measured. A path to reach expected low transverse emittance numbers is described.
