Richard D'Arcy

Abstract:

This work represents the first long-term (µs+) simulations of capillary discharge devices, made feasible by the computationally inexpensive QUEST algorithm [4]. We have demonstrated that QUEST gives comparable results to full plasma fluid simulations both during and long after the discharge has terminated. Using QUEST, the heat flow through the plasma-wall interface was simulated for discharge current conditions relevant to the FLASHForward experiment [2], operated at kHz-MHz repetition rates. The model showed that 1 kHz and 10 kHz repetition rates could be sustained indefinitely, but that 100 kHz and MHz rates quickly exceeded the sapphire capillary melting point. By reducing the pulse length and amplitude, MHz repetition rates can feasibly be sustained while providing plasma conditions suitable for accelerator applications.

Abstract:

Electron beams to be accelerated in beam-driven plasma wakes are commonly formed by a photocathode and externally injected into the wakefield of a preceding bunch. Alternatively, using the plasma itself as a cathode offers the possibility of generating ultrashort, low-emittance beams by trapping and accelerating electrons from the ambient plasma background. Here, we present a beam-driven plasma cathode realized via laser-triggered density-downramp injection, showing stable beam formation over more than a thousand consecutive events with an injection probability of 95%. The plasma cathode is highly tunable, resulting in the injection of electron bunches of tens of pC of charge, energies of up to 79 MeV, and relative energy spreads as low as a few percent. The stability of the injected beams was sufficiently high to experimentally determine their normalized emittance of 9.3 μm rms with a multishot method.