Design of the SSC linac
The preliminary design of the 600-MeV H/sup -/ linac for the Superconducting Super Collider (SSC) injector is described. The linac must provide a 25-mA beam during 7-35 mu s macropulses at 10 Hz within injection bursts. Normalized transverse emittances of less than 0.4 pi mm-mrad (RMS) are required for injection into the low Energy Booster (LEB) synchrotron. Cost, ease of commissioning, and operational reliability are important considerations. The linac will consist of an H/sup -/ source with electrostatic low-energy beam transport (LEBT), a 2.5-MeV radiofrequency quadrupole (RFQ) accelerator, a 70-MeV drift-tube linac (DTL), and 530 MeV of coupled-cavity linac (CCL). The RFQ and DTL operate at 428 MHz and the CCL operates at 1284 MHz. A modest total length of 143 m results from the tradeoff between cost optimization and reliability.<<ETX>>
Optimization of H− production from a small multicusp ion source
A small multicusp source has been developed to generate volume‐produced H− ion beams in pulsed operation. To obtain high H− current densities (J−>250 mA/cm2), this source requires relatively high gas pressure and high discharge power. Experiments have been conducted to improve the arc and gas efficiencies, the beam pulse shape, and the H− to electron ratio in the extracted beam by optimizing the filter magnetic field, the thickness and axial position of the extraction aperture in the plasma electrode, and by mixing xenon or other elements with hydrogen in the discharge. The biggest improvement is achieved by adding cesium to the source, resulting in a fivefold increase in the extractable H− current and a substantial drop in the e/H− ratio. In order to improve the lifetime of the cathode, both filament and coaxial type LaB6 cathodes have been developed and have been operated successfully in this H− source.
Production of H− ions with addition of cesium or xenon to a hydrogen discharge in a small multicusp ion source
The effect on H− ion production by adding cesium or xenon to a hydrogen discharge, in a small magnetically filtered multicusp ion source, has been investigated. Addition of cesium vapor to the hydrogen discharge resulted in a factor of 16 increase in H− output relative to the uncesiated discharge for the same operating parameters. Likewise, the addition of xenon gas to a hydrogen discharge resulted in a factor of 2.7 increase in H− output over pure hydrogen operation at optimum H2 source pressure, while maintaining the same arc parameters. Operation of the source with the plasma electrode at optimum bias voltage was essential to obtain this result.