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A modified helix loaded cavity was developed. The design is a compromise between a rather simple construction, rigidity and small size on one hand and a reasonably good acceleration of low velocity ions on the other hand. It contains a tapered helix to reduce the ratio of peak electric to effective accelerating field to -7.1 at an optimum relative charged particle velocity of 6 = 0.092. Field measurements at room temperature have been performed as well as first measurements at 4.2 K. The rigidity of the helix was increased resulting in a typical frequency noise smaller ± 175HZpeak at the fundamental frequency of 142 MHz. The design accelerating field is 2.25 MV/m at a peak electric field of 16 MV/m leading to an optimum accelerating potential of 538 kV. In laboratory test measurements an effective accelerating field of 2.36 MV/m was achieved. This corresponds to an accelerating potential of 566 kV at a peak electric surface field of -17 MV/m.

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Pseudorandom timeofflight analysis with a timeofflight mass spectrometer Rev.The composition of a plasma jet and the velocity distribution of the different ions from an arc plasma source are investigated by a double time-of-flight method. The plasma source consists of a marine spark plug in coaxial configuration driven from a capacitor bank. The analysis of the plasma jet is performed by pulsed acceleration of plasma ions and measurement of their time of flight to a distant electron multiplier tube. Mainly oxygen and aluminum ions from the insulator are detected. The velocity of the highly ionized ions extends to 14 cm/ps. The lower ionized particles have lower initial velocities. The hydrogen ion content increases with increased time between shots. 3169