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Superconducting radio-frequency electron guns are viewed by many as the preferred technology for generating the high-quality, high-current beams needed for future high power free-electron lasers and energy recovery linacs. All previous guns of this type have employed elliptical cavities, but there are potential advantages associated with other geometries. Here we describe the design, commissioning, and initial results from a superconducting radio-frequency electron gun employing a quarter-wave resonator configuration, the first such device to be built and tested. In initial operation, the gun has generated beams with bunch charge in excess of 78 pC, energy of 469 keV, and normalized rms emittances of about 4:9 m. Currently, bunch charge is limited by the available drive laser energy, and beam energy is limited by x-ray production and the available rf power. No fundamental limits on beam charge or energy have been encountered, and no high-field quenching events have been observed.

Planar-channeled electrons radiate electromagnetic energy with sharp peaks in the emission spectrum. A model is developed to predict the locations of these peaks, which are shown to correlate well with experimental observations. A by-product of the model is that it provides a sensitive method for determining the interplanar potential energy function in a crystal.