Enhanced Production of High-Charge-State Ions in ECRIS by Simultaneously Applied Special Wall Coating and Two-Frequency Heating

A study dedicated to enhance the performance of the volume effect in double-frequency heating (DFH) has been carried at the Frankfurt 14-GHz ECRIS of the Institut für Kernphysik, Goethe University Frankfurt, Germany. For this purpose, the electron density and temperature of the plasma have been enhanced by applying the established MD method developed by the authors. In addition to the standard RF frequency (14.3 GHz) injected from a klystron transmitter, a second RF frequency has been injected into the plasma chamber of the ECRIS via the second waveguide from a TWT transmitter, allowing variation of the injected frequency in the range between 13 and 15 GHz. A frequency gap of 800 MHz with almost overlapping resonance zones has been used in contrast to the minimum gap width of 1.5 GHz usually used in DFH. Applying the MD method permitted the increase in the intensity of the extracted Ar
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ion beam by a factor of 5 by adding a 150-W RF power from the TWT to the basic injection of 700 W from the klystron, a value that clearly exceeds enhancements that have been measured in earlier experiments with the DFH having two well separated resonance zones.