High power continuous wave microwave system at 3.7 GHz

Abstract

The lower hybrid current drive ͑LHCD͒ system is an important system in superconducting steady state tokamak ͑SST-1͒. It is used to drive and maintain the plasma current for 1000 s with a duty cycle of 17%. The LHCD system is being designed to launch 1 MW of radio frequency ͑rf͒ power at 3.7 GHz. The rf source is comprised of two high power klystron amplifiers, each capable of delivering 500 kW rf power. In this article, the results obtained during installation and commissioning of these klystrons are presented. Two klystrons ͑model TH2103D͒ have been successfully installed and commissioned on dummy loads, delivering ϳ200 kW power for more than 1000 s. The maximum output power that could be obtained is limited due to the available direct current ͑dc͒ power supply. The test system is comprised of a TH2103D klystron, a low power rf ͑3.7 GHz/25 W͒ source, two high power four port circulators, two high power dual directional couplers, two arc detector systems, and two dummy water loads. To avoid rf breakdown in the rf components of the transmission line, the system has been pressurized with dry air to 3 bar. To energize and operate the klystron, a high voltage dc power supply, a magnet power supply, an ion pump power supply, a Ϫ65 kV floating anode modulator power supply, and a filament power supply are used. An arc detector unit has been installed to detect and initiate action within a few microseconds to protect the klystron, waveguides, and other rf passive components during arcing. To protect the klystron in the event of an arc, a fast responding ͑Ͻ10 s͒, rail gap based pressurized crowbar unit has been used. The entire system is water cooled to avoid excess temperature rise during high power continuous wave operation of the klystron and other rf components. The tube requires initial conditioning. Thereafter, the output rf power is studied as a function of beam parameters such as cathode voltage and beam current.

Design criteria and current status of LHCD system on SST1 machine

“…These switches would determine the flow of power either into the plasma load or into the water dummy loads. The installation and testing of these tubes have been already reported [21]. The entire transmission line is pressurized with dry nitrogen gas up to 3 bars.…”

“…This section is centered on two klystrons from Thales (TH 2103 D), each of which could deliver 500 kW, CW power at 3.7 GHz [21]. Each klystron provides output from two arms (250 kW in each arm).…”

Design and performance of high voltage power supply with crowbar protection for 3-Φ high power rf amplifier system of cyclotron

“…The anode power supply (rated at 20 kV, 22 A) feeds dc power to the anodes of all the three tetrode tubes. It uses two forced air cooled transformers and each transformer has delta connected primary at 415 V, 3-phase, 50 Hz, 250 kVA power and two secondary windings, one of which in star and 2016 JINST 11 T07004 secondary windings from both the transformers are connected to their respective 3-phase full wave bridge rectifier assembly giving 5 kV dc each after rectification [4] and then these are connected in series to provide 20 kV dc at 600 Hz ripple frequency, as shown in figure 2. The rectifier assembly consists of 12 avalanche diodes (each rated at 1.6 kV, 40 A) connected in series in each limb.…”

Characteristics of electron cyclotron resonance plasma formed by lower hybrid current drive grill antenna

“…The main parameters of the ADITYA tokamak and LHCD system are shown in table 1. The RF power generated by the klystron [25,26] was injected into the ADITYA vacuum vessel from the LHCD antenna, which is originally designed to launch lower hybrid waves to drive plasma current non-inductively. A photograph of grill antenna is shown in figure 1.…”