Plasma-Wakefield Accelerator Group

Abstract:

The H- ion source and beam-line at FETS will require the beam current and beam position to be continually monitored. Current transformer toroids will measure the beam current and beam position monitors (BPMs) will determine the beam position. The ion source delivers pulses at a rate of 50 Hz with a current up to 60 mA, each pulse is 2 ms long, and a 324 MHz micro-bunch structure imposed by the radio frequency quadrupole (RFQ) accelerating structure. The toroid outputs will be acquired on a fast oscilloscope. Two BPM designs are under consideration (shorted strip-line or button type) but the processing for both types is similar and has been designed, with simulated measurements made. Each BPM uses four pickups, at a frequency of 324 MHz, which are mixed using RF electronics to an intermediate frequency of 10.125 MHz. The resulting signals are then digitized at 40.500 MHz and processed in an FPGA to produce the position and phase of the beam at each BPM location, with a precision of better than 100 μm and 0.05 rad. The measurements from the toroids and BPMs will be available via EPICS servers at every pulse.

Abstract:

We describe a scheme for controlling electron injection into the quasilinear wakefield driven by a guided drive pulse via ionization of a dopant species by a collinear injection laser pulse with a short Rayleigh range. The scheme is analyzed by particle-in-cell simulations which show controlled injection and acceleration of electrons to an energy of 370 MeV, a relative energy spread of 2%, and a normalized transverse emittance of 2.0 μm.