Applications of the constant-current variable-voltage dc accelerator

Variable beam energy at constant current is useful for industrial applications such as surface hardening and passivation or semiconductor processing. We discuss a dc accelerator, under development for the DOE magnetic fusion energy program, which uses electrostatic quadrupole (ESQ) focusing to maintain constant current while the voltage is variable over a wide range. The use of ESQs also allows a conservative design that alleviates known causes of dc voltage breakdown. The beam is accelerated by a series of 100 kV ESQ modules, stackable to a megavolt or more. The energy is tunable to as low as 20 keV without reduction in current. Single-beam and multiple-beam systems have been designed, capable of accelerating typically 50 mA of N+ or O+ per beam. (orig.)