High electric fields in a superconducting RFQ structure

High surface electric fields have been obtained in the first tests of a superconducting RF quadrupole device. The RF quadrupole fields were generated between niobium vanes 6.5 cm in length, with an edge radius of 2 mm and a beam aperture of 6-mm diameter. In tests at 4.2 K, the 64-MHz device operated CW at peak surface electric fields of 128 MV/m. Virtually no electron loading was observed at fields below 100 MV/m. It was possible to operate at surface fields of 210 MV/m in pulses of 1-ms duration using a 2.5-kW RF source. For the vane geometry tested, more than 10 cm² of surface support a field greater than 90% of the peak field. The result indicates that electric fields greater than 100 MV/cm can be obtained over an appreciable area, sufficient for some accelerator applications. It also shows that superconducting RF technology may provide an extended range of options for RF quadrupole design