Secondary-electron-enhanced Plasma as an Alternative to Double/variable-frequency Heating in Ecris

“Double Frequency Heating” (DFH) now has become the method of choice to optimize the output from the newest generation ECRIS installations. It was a challenge to compare this method with the comparatively cheap method of “metal dielectric” (MD) structure introduced into the plasma chamber, which has also proven to strongly enrich the plasma with electrons that are effectively trapped and heated. At the 14GHz ECRIS installation at Frankfurt, we have carried out a series of experiments using the two available RF-transmitters to launch two different frequencies into the IKF ECRIS. Due to restriction in the available frequency difference, the source could not be operated in real DFH-mode but was operated in “Frequency Tuning Mode” (FTM), for which also positive results are reported in literature. It turned out that the double RF-injection does not change the source performance substantially. The measured effects are in the order of 20% to 30% as reported elsewhere. In contrast to this, the enhancement gained by the MD method is much higher. The measured enhancement ratios even surpass those, reported for real double frequency heating.