  A positive ion source with RF discharge in solenoidal magnetic field is
described. In this paper we present an overview of positive ion production in
saddle antenna (helicon discharge) radio frequency (SA RF) ion sources. The
efficiency of H+ ion production in recently developed RF sources with
solenoidal antennas was improved to 2.9 mA/kW. About 24 kW of RF power is
typically needed for 70 mA beam current production from a 7 mm emission
aperture. This efficiency is relatively low because in the RF discharge with a
solenoidal antenna, the plasma is generated near the coil and diffuses to the
axis creating a nearly uniform plasma density distribution in all cross
sections of the discharge chamber, when the plasma flow is necessary only near
an emission aperture. The efficiency of the extracted ion generation was
improved significantly by using a saddle antenna with solenoidal magnetic
field. In the RF discharge with the saddle antenna the plasma is generated near
the axis and the magnetic field suppress the plasma diffusion from the axis,
creating a peaked plasma density distribution on the emission aperture. With
the SA the efficiency of positive ion generation in the plasma has been
improved up to ~100 mA/cm2 per kW of RF power at 13.56 MHz. Continuous wave
(CW) operation of the RF source has been tested on the small ORNL SNS test
stand. The general design of the CW RF source is based on the pulsed version. A
compact design of ion source is presented. Some modifications were made to
improve the cooling and to simplify the design. Features of SA RF discharges
and ion generation are discussed.
