Low emittance foil diode studies for the recirculating linear accelerator (rla)

In recent RLA experiments, a foil diode was utilized followed by a 1.2-m-long 60-mTorr Argon gas cell or lower pressure classical IFR transport region. In order to improve the beam capture and transport efficiency, a number of diode configurations were studied both experimentally and numerically using JASON and the latest version of MAGIC code. In particular, a conical shank diode was investigated in detail. A study of the beam current was undertaken using apertures of gradually increasing I.D. steps of 6.4 mm. An excellent agreement between experiment and simulations was observed. MAGIC predicted the exact total diode current, the current through most of the apertures, and the beam envelope radius. An optimized diode geometry gave at the anode foil a very cold beam of 1.4 MV, 22.5 kA with an rms beam radius r = 1.5 cm and a geometric emittance /spl epsiv/ = 0.04 rad.cm. The foil and gas transport region lead always to an increase of beam emittance. A similar design for a 4 MV, 10 kA diode is also presented.