Towards efficient integration of cusp and dipole filter magnets in a compact H- source

4 Sep 2018, 15:30
2h 30m
Board: 33
Poster H– and D– sources for fusion, accelerators and other applications Poster Session #2

Speaker

Dr Carlo Baltador (LNL - INFN)

Description

The RF compact negative ion source NIO1 installed at Consorzio RFX, in collaboration with INFN-LNL, allows to test several magnetic filter configuration inside the ion source and their relation with the fringe field of the electrons suppression magnets embedded into the extraction grid (by convention z is the extraction axis, while extraction grid magnets deflects electrons along y direction). NIO1 has been designed to produce 9 H- beamlets (in a 3x3 pattern), each with current below 2 mA and 20 kV acceleration voltage in this first phase without source cesiation and up to 15 mA and 60 kV after careful cesiation. Since no cesium has been used yet in NIO1, the negative ion production relies on the volume process only. The most important role in order to improve the efficiency of this process is played by the magnetic filter field inside the source (of course, when NIO1 cesium operation will begin, filter effect will be mixed with cesium effect and acceleration voltage holding). The original source filter had an intensity up to Bx= 3 mT and it was provided by current I circulating in the plasma electrode, with source performance improving with Bx. To increase filter strength, further current increase is impractical. Therefore, we need to develop hybrid systems, where part of the filter is provided by permanent magnets (PMF) and another part may be tuned by current (CDF). The several possible configurations are here fully described and simulated with Opera3D. In particular, the cusp field, which confines NIO1 plasma can be partly altered, to provided also a dipole field. A simple PMF concept, giving By = 15 mT was designed and tested with no particular success, which can be explained by excessive value or by field orientation: simulations proving detrimental effect of filter and deflection interference are shown. More elaborate concepts, providing Bx > 4 mT up to 12 mT (depending on PMF sizes) are here described. The aim of this contribution is to show the studies of an innovative configuration for cusp magnets, together with an innovative technique to shape permanent magnets, in order to produce a filter field parallel (PMF) to the one generated by mean of electric current (CDF), retrieving also the possibility of field tuning by changing the current in the circuit. The finite element code OPERA 3D is used for this investigation and to study the effect of different solutions on beamlet optics. This work was set up with partial financial support of F4E/EUROfusion.

Primary author

Dr Carlo Baltador (LNL - INFN)

Co-authors

Dr Marco Cavenago (LNL - INFN) team LNL - INFN (LNL - INFN)

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