Optimization of the extracted current density from the high energy diagnostic neutral beam injector of TdeV

Development of a high energy (40 kV, 1 A) neutral beam injector for diagnostic applications on TdeV is in progress. The injector operates with its source at ground potential and the neutralizer canal at ⩽−40 kV. The electrons in the neutralizer canal are retained by an electrostatic trap. The residual ions are collected near ground potential. Several diagnostics, including calorimetry, spectroscopy and a scanning multipin open probe array, are used to study the beam characteristics on its test stand. Hall probes and voltage dividers coupled with fiber optic links are used to optimize the efficiency of the extraction system, the electron trap, and the residual ion collection units. In its first stage of development, the injector has been optimized for operation with a single hydrogen beamlet. A beamlet divergence of less than 0.5 degrees was obtained. Up to 75 mA of ion current at 35 kV was extracted. The addition of another six extraction holes boosted the total extracted current to more than 600 mA at 36 kV.