Real-Time Feed-backed Anode Power Supply for 170 GHz gyrotron in KSTAR

3.6 MW (66 kV/55 A) high voltage power supply system was developed for the 170 GHz ECH&CD system in KSTAR. It consists of the cathode power supply (CPS), anode power supply (APS), and body power supply (BPS).Currently, modulation frequency of APS was limited to less than 1 kHz due to the parasitic capacitance of Zener diode circuit including gyrotron. In order to solve these lacks of controllability and high frequency modulation of APS, the existing APS is replaced by a new type of APS and it is tested for KSTAR 170 GHz gyrotron system. This paper presents the new APS design and characteristics and the test results for 170GHz gyrotron in KSTAR ECH system.


Introduction
In A 3.6 MW (66 kV/55 A) high voltage power supply system was developed for the 170 GHz ECH&CD system in KSTAR.It consists of the cathode power supply (CPS), anode power supply (APS), and body power supply (BPS).
Currently, modulation frequency of APS was limited to less than 1 kHz due to the parasitic capacitance of Zener diode circuit including gyrotron.The APS consists of fixed resistors and many series connections of Zener diodes.Each Zener diode has the voltage holding of 200V.The input of APS is connected to the output of CPS with the reference of the ground potential.The cathode-anode voltage is not actively regulated following the fluctuation of the cathode voltage.In order to solve these lacks of controllability and high frequency modulation of APS, the existing APS is replaced by a new type of APS and it is tested for KSTAR 170 GHz gyrotron system.The new APS is composed of a Cap Charger Power Supply (CCPS), High Voltage Switch (HVS) Tank.The CCPS has specification of rated energy at maximum 35kJ/S and the control frequency at 20 kHz.The storage energy of the CCPS is supplied to cathode-anode of gyrotron pursuant to HVS tank.The HVS consists of a on/off switch and a discharging switch which are made by parallel and series connections of many MOSFET fast solid-state switch of which switching on-off time is less than 1 microsecond.
This configuration reduced significantly the total parasitic capacitance between cathode and anode in gyrotron.The developed new APS has specification of rated voltage at 0~50 kV, rated current at maximum 1 A. Also, the voltage output is regulated with stability of 0.3% and the modulation is possible to up to 10 kHz with the rising and falling time less than ten microseconds.The output of CCPS is rapidly feedback controlled by real time control board using analog comparator circuit.Since the CCPS reference (common to chassis) is connected to the CPS output, the cathode-anode voltage will be supplied with constant level.In addition, the active cathode-anode voltage control capability will be applicable for the active beam current control to overcome the beam emission cooling effect for the long pulse operation of the gyrotron This paper presents the new APS design and characteristics and the test results for 170GHz gyrotron in KSTAR ECH system

New APS power supply
The new Anode Power is composed of Capacitor Charger Power Supply, High Voltage Switch.Capacitor.Charger Power Supply characteristic is as follow : -

Simulation
The simulation was using PSIM.The new APS in ECH system is verified the system stability.The overall ECH system with the new APS is shown in Fig 6.

Simulation results
The new APS Simulation results are shown in Fig 7.

Conclusion
The new anode power supply has a large number of outstanding features :

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The output of CCPS is rapidly feedback controlled by real time control.

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The cathode-anode voltage will be supplied with constant level.

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The APS modulation is possible to up to 10kHz with the stability of ±0.3%.

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The rising and falling time less than ten microseconds.In conclusion, the new anode power supply was found to be suitable for gyrotron application.
Fig1 shows the cap.charger power supply and Fig2 shows the inside of high voltage swtich

Fig 8 .Fig 9 .
Fig 8. Rising and falling time of APS