Negative hydrogen ion ECR source

To find optimum conditions for the generation of negatively charged hydrogen ions, an ECR source has been investigated. The source consists of a cylindrical cavity placed between Sm-Co disk-type magnetic poles, and microwave and extraction systems. The way in which the negative ions are produced is by the capture of low-energy electrons by vibrationally excited molecules as a result of which the dissociative attachment of negatively charged molecules takes place. Molecules are excited in the plasma volume. The low-energy electrons emerge due to bombardment of the first electrode of the extraction system by the ECR-heated electrons. The intensity of the extracted negative hydrogen ion beam appears to be sensitive not only to pressure, microwave power, and extraction voltage, but also depends on the shape of the ECR surface. Experiments indicate that the hyperboloid of one sheet-type resonance surface is the most effective. Measurements carried out with microwave of 600 W at 2.45 GHz, and at a pressure of 0.3 mTorr show that the negative ion yield attains 1.2 mA through a 0.3-cm-diam extractor hole.