HL-2A Experiments Scenarios for 2011


In the 2011 experimental campaign, significant improvement was made in the auxiliary heating, plasma control, wall conditioning, and diagnostics on HL-2A tokamak. The discharge parameters achieved in the past experimental campaigns are as follows: 2.74 T(toroidal magnetic field), 450 kA (plasma current), 6s (duration), 5keV (electron temperature), 2.8keV (ion temperature), 0.81020 m-3 (plasma density), 150 ms energy confinement time, and 78 kJplasma stored energy. Based on above progress and use of the newly developed auxiliary heating and current drive system of 5MW and a set of 30 different diagnostic system, a variety of experiments related to the H-mode physics have been carried out on HL-2A. After the realization of H-mode in the divertor configuration for the first time in China, extending the parameter space of ELMy H-mode discharges on HL-2A tokamak in terms of toroidal magnetic fieldBT2.5T, plasma current (Ip300kAwere realized in 2011 experimental campaign, creating  high performance plasmas on HL-2A tokamak. In the development of neutral beam system, a complementary gas puffing was applied to the neutralization cell so that the neutralization efficiency was improved up to 80% and the power reached 800kW. Furthermore, H-mode was realized with purely NBI in addition to the implementation of both NBI and ECRH, while the ECRH-aided startup experiment was carried out with a high auxiliary pre-ionization. 

Frontier physical researches were carried out in the H-mode plasma with the high parameters, including the studies on plasma transport, turbulence properties, SMBI, energetic particles physics, MHD and its control. A number of achievements were obtained in the researches on the mechanism of L-H transition, energetic particle physics, divertor physics, and mitigation and control of the edge localized mode using SMBI. So far the advances in experimental and theoretical studies were presented in the international conferences or published in academic journals, which are as follows:

1)  The ELM mitigation with SMBI or CJI fuelling technique was a success. It is a new achievement of SMBI technique, which is developed at SWIP first and has its own independent intellectual property right in the world. For the first time, the SMBI at low temperature and high voltage was applied in the HL-2A experiment, producing a large number of tiny cold particles in the deuterium beam and forming clusters in the plasma, so that the ELM was effectively mitigated. It is a promising new method for ELM control other than the pellet injection and the resonant magnetic perturbation (RMP). 

2)  Progress was made in the study on the filament turbulence structure (blob) of the edge plasma. Using probe array with high time and space resolution, we measured the filament potential and density fluctuation. The 3D spatial structures of plasma filaments are measured in the boundary plasma and large-scale structures along a magnetic field line analysed for the first time. The relationship between the density and the potential of blob was explored, and the experimental results agree well with the prediction of theoretical simulation. For the first time the two probe arrays separated toroidally were placed on the edge of the tokamak. This innovative approach proved to have small disturbance to the edge plasma while greatly extending the effective viewing area and providing more formation about the filament structure, which is useful in the research on the generation mechanism and fluid behavior of the filament structure as well as the ELM-filament in the H-mode. 

3)  The characteristics of the density fluctuation induced by GAM were studied by means of three 4-probes placed poloidally. It was found that the GAM induced fluctuation is about 1% of the electrostatic fluctuation, which agrees well with the theoretical prediction. In addition, it is observed that the burst of GAM can modulate the anomalous particle transport in the plasma edge. 

4)  In the non-local transport research, the core electron thermal transport reduction triggered by far off-axis ECRH switch-off is investigated. A reflectometer was used to measure the spectrum of density fluctuation when the high power ECRH was switch-off. For the first time, a decrease in the high frequency fluctuation was found inside the plasma when a non-local phenomenon appeared. It revealed that the non-local transport is closely linked to the turbulence in the plasma core. It provides us with a new insight of non-local transport and sheds an interesting light on the mechanism of non-local phenomenon. Such new findings has been presented in international conferences and published abroad, initiating an effort worldwide to explore the role of turbulence in the non-local transport.