The drift source: A negative ion source module for direct current multiampere ion beams

The concept of a modular large size ion source is under investigation in ou r laboratory for the development of the very intense (tens of amperes) nega tive ion (D-) beams needed for neutral beam injection in thermonuclear fusi on research. The basic idea is to develop a compact small ion source produc ing the required ion flux (20-30 mA/cm(2)) over a total surface of about 20 0 cm(2) and designed in such a way that it can easily be juxtaposed with ot her identical modules. A large negative ion source of any size (up to sever al m(2)) and shape could be realized as a set of several modules. The antic ipated advantage of this concept is the minimization of the risk inherent i n a large extrapolation in size (e.g., approximate to 1.0 m(2) for an ignit ion device to test engineering concepts) of the present ion sources. In thi s context, we have developed and tested a source module, called the DRIFT s ource, whose main properties are presented in this article. The particular magnetic field configuration of this module ensures, in a simplified way, a very good plasma confinement allowing operation of the source at very low filling pressures. Up to now, a D- current of 1 A (20 mA/cm(2)) 50 keV ener gy, 1 s pulse length, was obtained with cesium vapor seeding at 0.15 Pa sou rce pressure with an arc power of 2.5 kW/l (12 kW). (C) 1999 American Insti tute of Physics. [S0034-6748(99)02712-4].