P.K. Sharma

Lower hybrid current drive at high density on Tore Supra

Lower hybrid current drive (LHCD) experiments with line-averaged density varying between 1.5 x 1019 and 6 x 10(19) m(-3) are performed on the Tore Supra tokamak under quasi-steady-state conditions with respect to the fast electron dynamics. The LHCD efficiency is analysed from the fast electron bremsstrahlung (FEB) and electron cyclotron emission (ECE). The effect of plasma equilibrium and particle fuelling is documented. It is concluded that the fast decay of FEB with plasma density could be consistent with simple scaling of the current drive efficiency and FEB. Plasma edge measurements are presented looking for the effect on fast electron emission. In a specific case of particle fuelling, an anomalous decay of the hard x-ray and ECE signals suggests deleterious interaction of the wave with edge plasma.

Comparative modelling of lower hybrid current drive with two launcher designs in the Tore Supra tokamak

Fully non-inductive operation with lower hybrid current drive (LHCD) in the Tore Supra tokamak is achieved using either a fully active multijunction (FAM) launcher or a more recent ITER-relevant passive active multijunction (PAM) launcher, or both launchers simultaneously. While both antennas show comparable experimental efficiencies, the analysis of stability properties in long discharges suggest different current profiles. We present comparative modelling of LHCD with the two different launchers to characterize the effect of the respective antenna spectra on the driven current profile. The interpretative modelling of LHCD is carried out using a chain of codes calculating, respectively, the global discharge evolution (tokamak simulator METIS), the spectrum at the antenna mouth (LH coupling code ALOHA), the LH wave propagation (ray-tracing code C3PO), and the distribution function (3D Fokker-Planck code LUKE). Essential aspects of the fast electron dynamics in time, space and energy are obtained from hard x-ray measurements of fast electron bremsstrahlung emission using a dedicated tomographic system. LHCD simulations are validated by systematic comparisons between these experimental measurements and the reconstructed signal calculated by the code R5X2 from the LUKE electron distribution. An excellent agreement is obtained in the presence of strong Landau damping (found under low density and high-power conditions in Tore Supra) for which the ray-tracing model is valid for modelling the LH wave propagation. Two aspects of the antenna spectra are found to have a significant effect on LHCD. First, the driven current is found to be proportional to the directivity, which depends upon the respective weight of the main positive and main negative lobes and is particularly sensitive to the density in front of the antenna. Second, the position of the main negative lobe in the spectrum is different for the two launchers. As this lobe drives a counter-current, the resulting driven current profile is also different for the FAM and PAM launchers.

Regulated High-Voltage Power Supply (RHVPS): Integration, Operation, and Test Results With LHCD System of SST-1

A regulated high-voltage power supply (RHVPS) and its results are presented for its initial integration and operation with lower hybrid current drive (LHCD) system. Experimental results are shown to show the ability of RHVPS as a practical source of electrical power for LHCD. Klystron is operated at 3.7 GHz. with a continuous wave RF power level of 500 kW with various subsystems. RHVPS has proven its capability for feeding power to klystron with a safe and good level of required quality. Up to 65 kV and a load current in excess of 18 A was imparted to klystron with a trapezoidal pulse of voltage. Repeatability of operation is shown by successive shot results. RHVPS is explained with its scheme and control system. Basic parameters are fulfilled with a dummy load testing of RHVPS. Test results are illustrated for basic parameters with resistive dummy load. LHCD system operation parameters and experimental parameters of RHVPS for its operation are discussed. A regulation on flat top level of voltage is as per the requirement of LHCD system. Initial integration of RHVPS has been successful and future plans are mentioned for full-fledged SST-1 operation.

High Power CW Testing of 3.7-GHz Klystron for SST1 LHCD System

A 3.7-GHz lower hybrid current drive (LHCD) system has been designed and installed for driving noninductive plasma current for steady-state operation of steady-state super-conducting tokamak-1 machine. Currently, its capability has been enhanced up to 2 MW by adding two additional klystrons, each capable of providing 500 kW, continuous wave (CW) power, to LHCD system. After performing factory acceptance test of these klystrons, they are installed and commissioned at site, at rated power, for more than 1000 s, before connecting them to main LHCD system. The auxiliary systems like supporting power supply system (magnet, filament, ion pump, etc.), active heat management system, protection system, transmission line pressurization system, low power RF drive system, and so on are interconnected with klystron system through versa module europa (VME)-based data acquisition and control system for remote CW operation of klystron at rated power. The klystron is protected by fast interlock protection in an event of arc or an electrical parameters excursion beyond a set window. The slow interlock is invoked in case of cooling failures, pressurization of waveguides, and so on. The klystron has two output arms and a recombiner is used to recombine power coming out from both the arms. The output power from the recombiner of the klystron is split into two arms, employing 3-dB power divider. This reduces the high power requirement of water dummy loads (DLs) to 250-kW CW. A directional coupler is included in both the arms for measuring forward and reflected power. The reflected power signal is fed to low power RF drive control, which removes the RF drive once reflected power beyond a threshold power is detected within 5 μs. The forward power signal is used for monitoring RF power being dumped into the water loads. The calorimetric measurements, employing Pt-100 sensors, are also carried out on water dummy loads. Our measurements suggest that the maximum RF power ( ~500-kW CW) extracted from klystron is dissipated on water cooled DLs. The unspent dc power ( ~800-kW CW) is dissipated in the collector that is heavily cooled with water flowing at ~1300 L/min. The power loss in the klystron body remained within 15 kW. The cavity temperature, measured using J-type thermocouple, remained below 150 °C. The output RF power, sampled through directional couplers and measured by RF detectors shows good agreement with calorimetric measurements. A detailed description of the klystron test setup and the test results obtained during its commissioning is presented in this paper.

Design data for quick development of Folded E plane Tee

Most of the microwave communication systems have requirement of power dividers that are essential for power splitting and combining operations. This paper presents a structure and methodology for designing a rectangular waveguide Folded E plane Tee. The structure proposed has the advantage of less area consumption as compared to a conventional waveguide Tee. The paper also presents design equations using which one can design a Folded E plane Tee at any desired frequency. The designs thus obtained at some random frequencies from the equations have been simulated in COMSOL Multiphysics and the scattering parameters obtained have been presented.

Initial integration of “regulated high voltage power supply” (RHVPS) with LHCD system of SST-1

A Regulated High Voltage Power Supply (RHVPS) and its results are presented for its initial integration and operation with LHCD system. Experimental results are shown to show the ability of RHVPS as a practical source of electrical power for LHCD. Klystron is operated at 3.7 GHz. with a continuous wave (CW) RF power level of 500 kW with various subsystems. RHVPS has proven its capability for feeding power to klystron with a safe and good level of required quality. Up to 65 kV and a load current in excess of 18 A was imparted to klystron with a trapezoidal pulse of voltage. Repeatability of operation is shown by successive shot results. RHVPS is explained with its scheme and control system. Basic parameters are fulfilled with a dummy load testing of RHVPS. Test results are illustrated for basic parameters with resistive dummy load. LHCD system operation parameters and experimental parameters of RHVPS for its operation are discussed. A regulation on flat top level of voltage is as per the requirement of LHCD system. Initial integration of RHVPS has been successful and future plans are mentioned for full-fledged SST-1 operation.