D. Bora

Cyclotron resonance heating systems for SST-1

RF systems in the ion cyclotron resonance frequency (ICRF) range and electron cyclotron resonance frequency (ECRF) range are in an advanced stage of commissioning, to carry out pre-ionization, breakdown, heating and current drive experiments on the steady-state superconducting tokamak SST-1. Initially the 1.5u2009MW continuous wave ICRF system would be used to heat the SST-1 plasma to 1.0u2009keV during a pulse length of 1000u2009s. For different heating scenarios at 1.5 and 3.0u2009T, a wide band of operating frequencies (20–92u2009MHz) is required. To meet this requirement two CW 1.5u2009MW rf generators are being developed in-house. A pressurized as well as vacuum transmission line and launcher for the SST-1–ICRF system has been commissioned and tested successfully. A gyrotron for the 82.6u2009GHz ECRF system has been tested for a 200u2009kW/1000u2009s operation on a water dummy load with 17% duty cycle. High power tests of the transmission line have been carried out and the burn pattern at the exit of transmission line shows a gaussian nature. Launchers used to focus and steer the microwave beam in plasma volume are characterized by a low power microwave source and tested for UHV compatibility. Long pulse operation has been made feasible by actively cooling both the systems. In this paper detailed test results and the present status of both the systems are reported.

42-GHz/500-kW Electron Cyclotron Resonance Heating System on Tokamak SST-1

The 42-GHz electron cyclotron resonance heating (ECRH) system on SST-1 is used to carry out ECRH-assisted preionization, breakdown, start-up, and heating experiments at 0.75-T (second harmonic) and 1.5-T (fundamental harmonic) operation. The gyrotron delivers 500-kW power at 42-GHz frequency at -50-kV beam voltage, 20-A beam current, and 19-kV anode voltage. The gyrotron has been commissioned successfully on dummy load for full parameters (500 kW/500 ms). The transmission line consists of matching optic unit, circular corrugated waveguide, miter bend with bidirectional coupler, waveguide switches, polarizer, bellows, dc breaks, and an uptaper. Approximately 20-m-long transmission line is used to launch the power from gyrotron to tokamak, and the burn pattern at the exit of line near the tokamak ensures a good Gaussian beam. A composite launcher [consisting of four mirrors (two profiled and two plane), two gate valves, and two vacuum barrier windows] is used to connect two ECRH systems (42 and 82.6 GHz). The 82.6-GHz/200-kW ECRH system is also planned for SST-1 to carry out experiments at 3-T magnetic field. The 42-GHz ECRH system has been commissioned with tokamak SST-1, ECRH power has been launched in tokamak, and successful ECRH-assisted breakdown is achieved at second harmonic.

Data Acquisition and Control System for ECRH Systems on SST-1

In steady-state superconducting tokamak-1, two electron cyclotron resonance heating systems have been installed to carry out breakdown and heating experiments. The 82.6-GHz gyrotron delivers 200-kW continuous wave power (1000 s), while the 42-GHz gyrotron delivers 500-kW power for a 500-ms duration. The gyrotron system consists of various auxiliary power supplies, the crowbar unit, and the water cooling system. The Versa Module Europe-based data acquisition and control system has been designed, developed, and implemented for safe and reliable operation of the gyrotron. The control and the monitoring softwares have been developed using the VxWorks real-time operating system and open source softwares like Tcl-Tk tool kit, MDSplus, and the GNU C compiler on Linux.

VME based data acquisition and control system for Gyrotron based ECRH system on SST-1

A Gyrotron capable of delivering 200kW power at 82.6 GHz has been installed for pre-ionization and heating experiments on SST1 tokamak. Gyrotron based Electron Cyclotron Resonance Heating (ECRH) system involves systematic operation of different auxiliary power supplies, crowbar unit and water cooling system. Versa Module Europe (VME) based Data Acquisition and Control (DAC) system has been designed and implemented for the gyrotron operation. Softwares have been developed using VxWorks RTOS and open source Tcl-Tk tool-kit, GNU C/C++ compiler on Linux.

High Voltage and Auxiliary Power Supply System for 200kW CW Generator

The 200 kW generator is designed and developed for ion cyclotron resonant heating (ICRH) experiments on Aditya Tokamak and 1.5 MW stage for SST-1 (steady-state super-conducting tokamak 1). The 200 kW stage uses 4CM 300,000GA tetrode. An existing DC power supply capable of delivering 30 kV, 20 A has successfully reconfigured with necessary protections and controls. This is being used for ICRH experiments in Aditya tokamak. screen grid power supply of 1 kVDC, 1 amp, filament power supply of 18 VAC, 430 Amp, have been developed in-house, while the control grid power supply is procured indigenously. High voltage power supplies for the pre-driver stage (2 kW), driver stage (20 kW) have been designed and commissioned along with necessary protections. All the high voltage and auxiliary power supplies can be operated and controlled in manual or remote mode through data acquisition and control (DAC) system. The existing 200 kW system would be augmented with the 1.5 MW stage for experiments on SST1 tokamak This paper presents the details of auxiliary and high voltage power supplies that are developed in house for 200 kW stage. The monitoring and arc protection circuits are described. Results of the wire-burn test are highlighted.

High-Power Test of Chemical Vapor Deposited Diamond Window for an ECRH System in SST-1

High-power tests on chemical vapor deposited (CVD) diamond window are carried out using 82.6-GHz Gyrotron. To test CVD diamond window with calorimetric dummy load, a matching optic unit is designed and fabricated with special profiled mirrors. The mirrors are fabricated by Gycom Russia and a mirror box assembly is fabricated at Institute for Plasma Research. The mirrors and mirror box are cooled with water. The mirror box consists of four arc detectors for the protection of window. The CVD diamond window is connected to a dummy load with this mirror box. The alignment of mirror is done during the testing of CVD window in pulsed condition. After achieving the desired Gaussian pattern at the exit of mirror box, system is connected to a dummy load for continuous wave test. The CVD window is tested maximum power up to 60 kW in pulse duration of 600 s.

A prototype experiment on remote steering antenna for ecrh system

In conventional electron cyclotron resonance heating systems, beam steering for current drive is achieved by rotating the mirrors of the launcher. Alternatively, it could be achieved remotely using a rectangular/square-corrugated waveguide (SCW). Symmetric beam steering is achieved at a length L (8a2/λ), where “a” is the width of the waveguide and “λ” is the wavelength of the microwave while at L/2 (4a2/λ) antisymmetric steering is seen. At a length of 2a2/λ, beam splitting into two equal lobes is observed. A low-power experiment on a remote steering antenna is carried out with an SCW at 2a2/λ and a plane fixed mirror at the exit of the SCW, which diverts the microwave beam in one direction. The microwave instrumentation consists of a Gunn oscillator (82.6 GHz/˜40 mW/TE10), an isolator, an attenuator, waveguides, and a mode converter (TE10 to HE11). The output of the mode converter is a 63.5-mm-diam corrugated waveguide, which couples the microwave beam to the SCW. The microwave power emerging from the waveguide is scanned in the far-field region using calibrated detectors. The power spectrum at the output of the SCW shows that the peak appears at the same angle input to the SCW. Effective steering is achieved for a smaller length of the waveguide at various input angles from 6 deg to 18 deg.

Design and Development of DC Power Supply System for 1.5MW, 40MHz, RF Amplifier

A 1.5 MW RF (ap40 MHz) amplifier using Eima tetrode 4CM2500KG is in the testing phase, here at Institute for Plasma Research (IPR). This amplifier is being developed for the ion cyclotron resonance heating (ICRH) system of Super Conducting Steady State Tokamak, SST1. This RF amplifier amplifies an input power of 200 kW to about 1.5 MW. Few DC power supplies are needed for the operation of this amplifier such as plate supply, screen supply, filament supply, and grid supply. We have a conventional HVDC power supply rated for 60 Kv@10 A for the preliminary testing of this RF amplifier. The required RHVPS (25 Kv@120 A) for this amplifier is under development, hence it is beyond the scope of this paper. This amplifier needs about 10 kW (15 V@650 A) of DC power for heating its filament. We have developed a DC power supply of 12kW (15 V@800 A) to feed the heater. Also, the amplifier needs about 4 kW (500 V@8 ADC) and 6 kW (1500 V@4 A) of DC power to feed its control grid and the screen grid, respectively. So, we have developed another two DC power supplies capable of delivering 6 kW (600 V@10 A) and 7.5 kW (1500 V@5 A) to bias the control grid and screen grid of this amplifier, respectively. These power supplies are to be remotely operated from a PC located at a distance of about 20 to 50 meters. Also, there are some interlocks needed among these power supplies and with the plate HVDC power supply, for the stable and safe operation of the amplifier. In this paper, the test results of all these power supplies on a dummy load will be presented

Commissioning of the 28-GHz Electron Cyclotron Resonance Heating System on ADITYA Tokamak

Abstract An electron cyclotron resonance heating system is commissioned on Aditya tokamak to carry out pre-ionization, start-up, and heating experiments. A high-power microwave source (gyrotron), capable of delivering 200-kW cw power at 28 ± 0.1 GHz, is commissioned successfully using a water dummy load for pulsed operation. The output mode of the gyrotron is TE02. The output power of the gyrotron is measured using microwave probe couplers, a spectrum analyzer, and calorimetric techniques. A hardwired interlock operates a rail-gap-based crowbar system in less than 10 μs under fault condition and protects the gyrotron. The rail-gap crowbar operation has been qualified with the high-voltage power supply by performing a 10-J wire-burn test prior to energizing the gyrotron. A transmission line consisting of matching optic units, dc break, polarizer, miter bend, and corrugated waveguides terminates with a boron nitride window. The total attenuation in the line is measured to be less than 1.1 dB. Based on quasi-optical theory, a beam launcher is designed, fabricated, and tested for ultrahigh-vacuum compatibility prior to commissioning on tokamak. After successful operation of the gyrotron on the dummy load, the gyrotron output has been coupled to the ADITYA tokamak, and successful breakdown of neutral gas is observed without assistance from an ohmic transformer.

Ion cyclotron resonance heating in SST-1 tokamak

Multimegawatt ion cyclotron resonance heating (ICRH) system is being developed for the steady state superconducting takamak SST-1 (1), which would form an important heating scheme during non-inductive steady state operation. 1.5 MW of RF power at different frequencies between 22-92 MHz is to be delivered to the plasma for pulse lengths of upto 1000 s. Water cooled antenna, interface and 9 inch Tx-line will ensure safe operation for long pulse operation. Three stages of matching would ensure maximum power coupling to the plasma. Power would be coupled to the plasma through two sets of antennae consisting of two strips in antenna box positioned 180 degree opposite to each other with capability of handling 0.8 MW/m2 heat load. Electromagnetic stress analysis of the antenna assembly shows that maximum 1.37 kNm torque would be exerted during plasma disruption operating at 3.0 T, 220 kA plasma current. Impurity generation by ICRH antennae is not so severe.