The LANL/AES normal-conducting radio-frequency injector has been tested at cw cathode gradients up to 10 MV=m. Field-emission electrons from a roughened copper cathode are accelerated to beam energy as high as 2.5 MeV and impinge on a stainless steel target. The energies of the resulting bremsstrahlung photons are measured at varying levels of injector cavity rf power corresponding to different accelerating gradients. At low cavity power, the bremsstrahlung spectra exhibit well-defined endpoint energies at the positions where the number of single-photon events decreases to one (S=N ratio ¼ 1). Increasing the cavity power raises the probability of two-photon events in which two photons simultaneously arrive at the detector and register counts at twice the photon energy. The end-point energies at high cavity power are recorded at positions where the single-photon events transition to two-photon events. The measured end-point energies using this method are in excellent agreement with PARMELA calculations based on the cavity gradients deduced from the cavity rf power measurements.

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A radio-frequency quadrupole (RFQ) structure operating at low frequency has been developed for possible use in accelerators for heavy ion fusion or Tokamak plasma heating. The structure uses a series of shunt spiral inductors placed periodically along the electrodes of an electric quadrupole to achieve resonance at the desired frequency. A 1.2-m-long model has been constructed for low-power testing. The model resonates near 12 MHz and has radial dimensions that are reduced by a factor of 15 compared to the commonly used four-vane resonator.

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