Development of fast protection circuits for tube based high power RF amplifier

ITER-India has developed vacuum tube (Tetrode/Diacrode) based 1.5MW/36-60MHz high power RF amplifier for ITER. These vacuum tubes shall be protected against faults, like overcurrent, overvoltage, and short circuit that may occurs during RF operation. Auxiliary power supplies like Control Grid Power Supply (∼ 500V) & Screen Grid Power Supply (∼ 1500V) need external fast protection circuits to protect control grid & screen grid against negative current fault & arc/short circuit fault respectively considering stored energy limit criteria mentioned by the tube manufacturer. Negative current protection circuit for control grid & fast acting Series Switch unit for screen grid are designed, developed & tested to fulfil the requirement of protection during RF operation. Design, development, integration & testing results of external protection circuit will be presented in this paper. (author)