A simple, convenient rf discharge source for the production of an intense beam of hydrogen atoms is described. The design and operation is such that the discharge tube can be operated over a period of several thousand hours, producing an intense beam with dissociation ∼95%.
An ion source consisting of a duoplasmatron feeding a PIG discharge system has been built and is named a duoPIGatron. The extraction electrodes, located at the end of the PIG discharge opposite the duoplasmatron, are accel-decel with a 5 cm diam and multiapertures. The source is simple, flexible, and efficient. 1 A beams are extracted in steady-state operation with ion energies from 1.5 to 5 keV. 4 A beams are extracted with 0.1 sec pulses and a 10% duty cycle at ion energies of 20 to 40 keV. At 30 to 40 keV, about 60% of the ion beam is within a half-angular divergence of 1.2° with no magnetic lens. Using a hydrogen gas cell this system produces 2.6 A (equivalent) of 17.5 and 35 keV H0 particles within a half-angular divergence of 1.2°. One of the present limitations in scaling the source to larger beams is the current capabilities of the power supplies. As larger supplies are available attempts will be made to scale this system to the 10 A beam modules needed for future fusion research.
Extending the encouraging confinement results in Tokarnak devices and further establishing scaling laws makes it essential to attain ion temperatures corresponding to the collisionless regime, where reactors will operate. Ohmic heating used in the present devices is self-limiting since the plasma resistance drops as the temperature increases. Neutral-beam injection heating is not only a supplemental heating scheme that is efficient and not self-limiting but is also a developed technology ready for application. Injection heaters have been developed at ORNL for ORMAK which are capable of supplying 60 kW to the plasma per injector with up to four units usable. These systems use 4 A of H+ and ions at 35-40 keV from a duoPIGatron ion source. These heaters are capable of increasing the ion temperatures in the 8 × 105 cm3 ORMAK plasma volume to several keV at densities of ≈ 3-6×1013cm−3.
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