Duoplasmatron Ion Source
Accelerator

The Duoplasmatron source (model HVEE-358) is a gas source mainly devoted for producing He and H.

In the Model 358 Duoplasmatron, a two-stage discharge is involved in the generation of the ion beam. The first discharge is sustained by the thermionic electron emission from a filament (cathode). An intermediate electrode acts as the anode for the first discharge and is equipped with an aperture in its center. The discharge is guided through the axial magnetic field in the aperture into the second discharge chamber. The second discharge is maintained between the intermediate electrode, which now acts as a cathode, and the main anode. The strong axial magnetic field generated in this region confines the plasma into a small volume, and is responsible for the high plasma density. The ions from the second discharge flow through the anode aperture into the extraction region.

Duoplasmatron source can be configured to produce both, negative and positive ions. H- can be directly obtained from the source, with currents of few tens of microamps.
However, the process is not so efficient for producing He-. Then, the source is operated in "positive mode", i.e. He+ ions are produced. After being extracted from the source, He+ ions are injected into a Lithium charge-exchange canal. Inside this canal, Li vapour exchange electrons with He beam, becoming this negative. Duoplasmatron source produces typically hundreds of microamps of He+. The efficiency of Lithium canal is around 2% giving as a result a few microamps of He- at the entrance of the accelerator.