HL-2A Experiments Scenarios for 2010


In 2010 experimental campaign, the operational parameters of HL-2A were further improved by improving and controlling the plasma faced wall conditions, especially upgrading the high power heating systems of ECRH and NBI. The achieved parameters are as follows: 2.7T (toroidal magnetic field), 450kA (plasma current), 4.2s (duration), 5keV (electron temperature), 2keV (ion temperature), and 0.81020 m-3 (plasma density). Steady and repetitive H-mode discharges were realized in HL-2A tokamak, with the total auxiliary heating power of 5MW and the supersonic molecular beam injection (SMBI) and pellet injection techniques. Seven special research topics were devoted to improving the HL-2A plasmas confinement. The ECRH-assisted start-up experiment was carried out on HL-2A and expected results were obtained. A number of new results were achieved with the SMBI technique when the plasmas were highly confined with high operational parameters in the energetic fishbone physics, beta-induced Alfven eigenmodes driven by the energetic electrons, neoclassic tearing mode instability, edge zonal flow and blob, MHD instabilities, disruption and its alleviation and other areas. Innovative results were obtained in the studies of plasma zonal flow and sheared Alfven eigenmodes. The beta-induced Alfven eigenmodes excited by energetic electrons were observed for  the first time in the world, which was reported in the oral presentation in the 23th IAEA Conference. 

Turbulence and zonal flows: A number of peaked values of the low frequency zonal flows with finite radial wave number were observed in the power spectrum of the electric potential. Plus, the two dimensional transmission of the blob was measured with the probe in the radial direction. The blob was observed to be generated inside the last closed magnetic surface when the normalization density was n/nG0.7. This result is significant for a better understanding of the generation of the blob. The change of the pitch angle of the edge plasma during the current ramp-up was measured for the first time with a loop probe array. The prominent change of the modulation range of the turbulence caused by the zonal flows was reported in the oral presentation in the 23th IAEA Conference, too.

Energetic particle physics: Various kinds of frequency sweepping of the electron fishbone frequency were observed on HL-2A, including the upward, downward, and V-shaped changes of the frequency, and the frequency jump was observed for the first time. In particular, the beta –induced Alfven eigenmodes excited by the energetic electrons was observed for the first time.

Particle transport: The particle pump-out effect was investigated with the high power ECRH. Various fishbone instabilities were observed with the NBI heating system, including the ion fishbone instabilities of sawtooth mixed type, consecutive type and classic type, as well as the MHD activity when the long sustained loop module n=1. In the H-mode study, the width and height of the H-mode edge transport barrier was observed using the microwave reflectometer and the edge probe diagnostics. A preliminary research was devoted to the magnetic lag loop effect during the L-H transition. The characteristics of the edge localized mode and its relation to the plasma parameters were investigated. 

Key techniques of nuclear fusion, such as fueling techniques, diagnostic techniques and heating techniques for plasmas, and high-voltage power supply techniques, were developed to meet the needs of the HL-2A experiments.

The 25-tube extruded pellet injection and SMBI were developed, and corresponding components were also developed. The pellet vacuum system and the control system were further improved and applied to the experiments. The penetration of SMBI and CJI fuelling techniques on the tokamak were improved. For the first time the new pellet fuelling system operated on HL-2A, conducting particle transport study, comparison of the efficiencies of various felling methods, and other studies.

High temperature plasma diagnostics were investigated. Multi-channel bremsstrahlung measurement (spacial resolution 4cm, time resolution 0.01ms), the visible light imagery temporal and spatial profile measurement (CCD pixel 640480, time resolution 5ms) and impurity injection by the laser blow-off (automatic control of the focus, impurity injection rate and time sequence) were developed and applied to HL-2A experiments. Besides, many diagnostics were improved. The multi-spatial point measurement of the plasma parameters was enabled in the Thomson scattering system, and the edge TS system is being developed; Using the 8-channel HCN laser interferometer, a complete plasma density profile was obtained and the plasma current profile measurement was investigated in a primary way; The high frequency plasma turbulence signals were able to be obtained with the improved Mirnov coils; The edge transport barrier distribution was measured using a microwave reflectometer and a probe for the first time in China; The suprathermal electron radiation power spectrum was measured with the CdTe detector, providing the data for the further energetic physics analysis. A high speed camera system and a vacuum untraviolet spectrum diagnostic (EUV) with the space-time and spectrum resolution were developed. Various diagnostics were improved to provide reliable and stable data including the electron temperatures and densities of the plasmas for the 2010 experimental campaign on HL-2A.

The heating for the plasmas on HL-2A was investigated. 6 ECRH systems were built and the commissioning was done; The double puffing system to the NBI system was built, improving the efficiency of neutralizing the 30keV deuterium ion beams by 10-15%; The stable operation of the 3MW ECRH with the high power was realized, while the neutral beam system worked with above a power of 0.9 MW, which was 0.7MW in regular operations. The combination of ECRH and NBI has been made to be the regular auxiliary heating systems for HL-2A, providing a solid foundation for the steady experiments for the repetitive H-mode discharges.

The high voltage power supplies were investigated. The main circuit of the PSM power supplies was built, and the fully digital type control system was basically ready after the commissioning. Two high voltage modulators were added and put into operation in the ECRH experiments; 100 IGBT units of adjustable full solid high-voltage modulators were installed in series and the commissioning was done to the switches. With the output of 40KV/50A, an entire set of the full solid high-voltage modulators was basically built; the phaseshift trigger of the 125MVA unit excitation rectifying device was redesigned and developed into a digital one; the vibration measuring system of the generator was improved, and in particular, the measurement and analysis of the low frequency vibration value was improved.