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A new experimental facility named GISMO (Gasdynamic Ion Source for Multipurpose Operation) was constructed at the IAP RAS to continue investigations in the field of gasdynamic ion sources. The source utilizes 28 GHz/10 kW gyrotron radiation for heating magnetically confined plasma. Magnetic field configuration provided by a fully permanent magnet system is much like a simple mirror trap. The GISMO source is aimed at the production of bright ion beams with hundreds of milliamperes current. The facility has been tested for continuous-wave (CW) operation with 2 kW of heating power to check durability of a microwave injection system and the plasma chamber. A 2-electrode extraction system with an integrated Einzel lens was designed for a formation of CW high current beam with up to 100 kV accelerating voltage. The first results on ion beam production at GISMO are presented together with the general progress status of the facility.

The high efficiency of a new ion beam extraction system with a strongly inhomogeneous electric field has been experimentally demonstrated. Previously, this approach was proposed and analysed numerically by the authors. The experiment was carried out using a pulsed high-current electron-cyclotron resonance (ECR) ion source SMIS 37 with high frequency (37.5 GHz) and high power (100 kW) microwave plasma heating. The accelerating field strength is increased (when compared to a flat or a quasi-pierced geometry) in the plasma meniscus region due to its inhomogeneity. It allows for the increase of the ion acceleration rate and for expansion of the available range of current densities with effective ion beam formation. The experiment demonstrated the main advantages of this approach, such as: a significant decrease in the optimal accelerating voltage for certain values of current density; a possibility of ion beam formation with previously inaccessible current densities; a significant decrease in the ion flux to the puller in non-optimal modes of ion beam formation. Proton beams with a current density of up to 1.1 A cm-2 were obtained for the first time with an ECR ion source.

We consider a flow of completely ionized magnetized plasma streaming along divergent magnetic field lines from an open magnetic trap. An analytical model is proposed that takes into account a transition from a collisional (fluid) regime to a collisionless kinetic regime as the flow expands. This allows for study of the formation of a plasma potential along the magnetic field and the acceleration of ions in a self-consistent way. We show that ion acceleration may influence the potential profile; in particular, it significantly reduces the potential gap inside the Debye sheath near the plasma collector. This positive effect predicts low arcing in plasma absorbing units, which is important for all large-scale fusion-aimed experiments in mirror machines. Applications of the theory to smaller table-top machines are also considered.