Operation of the new KVI ECR ion source at 10 GHz

The new KVI ECR ion source (ECR2) has been designed to be operated at 14 GHz. This choice was obtained as a compromise between expected better performance at higher frequencies as compared to e.g. the KVI Minimafios (10 GHz), in operation since 1982, and higher investment and expected running costs at even higher frequencies. For practical reasons, however, operation at 14 GHz has not started yet; instead during a few periods of several months experiments have been performed at 10 GHz. A schematic layout is shown in a figure. Three sets of coils, all with inner diameter 250 mm, produce the axial field; with yoke plates and yoke bars a maximum field of 0.78 T at the extraction side can be obtained with icoil = 1,000 A. The hexapole magnet was constructed in a closed configuration, as described earlier using NdFeB material (KOERDYM), put together by the manufacturer. The pole to pole distance is 82 mm, the length 300 mm. Measurements show that (within the vacuum chamber with r = 36 mm) the radial field scales like Br = 5.13 x 10-4 r2 (T, r in mm). More explicitly: at r = 36 Br = 0.665 T and Br ≥ 0.72 T measured 2.9 mm from the pole tip (r = 38.1). The first stage vacuum chamber is pretty large such that various future modifications (e.g. for production of metal ions) can be made; also this stage was equipped with a separate RF input and a movable plasma stage