Experimental results of 40 kW, 1 MHz solid state high frequency power supply with inductively coupled plasma

A solid state High Frequency (HF) 1 MHz, 40 kW source is intended for plasma formation in a neutral beam source by inductive coupling of RF power. An important design feature of such an HF source is its ability to sustain large transient swings of load (due to impedance transition on microsecond time scales). A 40 kW High Frequency Power Supply (HFPS) has been configured with multiple Class-D H-bridge inverters modules by using latest generation switching semiconductors. Each module is capable of delivering 3 kW of power, then magnetic combiners and an LC tuning network provides a 1 MHz sinusoidal output to a 50 Ω standard load. The developed prototype power supply has been coupled to a single-driver RF ion source test bed ROBIN in IPR to characterize the system with actual load conditions. In a recent experimental campaign, tuning of matching network parameters helped to strike and sustain plasma over the pressure range of 1 Pa to 0.42 Pa with forward power of 37 kW to 22 kW. An additional impedance matching network was implemented to map the power supply impedance (50 Ω) with the impedance offered from the source (>90 Ω seen at PS end). A configurable frequency with resolution (∼1 kHz) helped to achieve a power factor close to unity. Experiments helped to study the behavior of the power supply in scenarios of dynamic (plasma) impedance. Auto-tunable frequency for matching the varying load is being implemented in the HF power supply.