Edge Structure of Reynolds Stress and Poloidal Flow on the HL-1M Tokamak

The measurement on radial profile of electrostatic Reynolds stress, plasma poloidal rotations, radial and poloidal electric field have been performed in the plasma boundary region of the HL-IM Tokamak using a multi-array of Mach/Langmuir probes. In the experiments of Lower Hybrid Current Drive (LHCD), Supersonic Molecular Beam injection (SMBI), Multi-shot Pellet Injection (MPI) and Neutral Beam injection (NBI), the correlation between the Reynolds stress and poloidal flow in the edge plasma is presented. The results indicate that a sheared poloidal flow can be generated in Tokamak plasma due to radially varying Reynolds stress.

Experiments and Studies of Edge Plasma Radial Transport and Confinement Property on the HL-1M Tokamak

This paper describes a Mach/Langmuir probe array with five pins and six pins, which can measure not only parallel flows and the flow perpendicular to the magnetic field but also the radial and the poloidal electric field E. arid E as well. Experimental measurements of the edge fluctuations, velocities of the toroidal, the poloidal flow and electric field have been carried out on both of SOL and the boundary region of HL-1M for Ohmic, biased H-mode, Lower Hybrid Current Drive (LHCD), Supersonic Molecular Beam Injection (MBI), Multi-shot Pellet Injection (MPI), Neutral Beam Injection (NBI), Ion Cyclotron Resonance Heating (ICRH) and Electric Cyclotron Resonance Heating (ECRH) discharges. The results show that the suppressions of the fluctuations are related to poloidal rotations produced by different discharge modes in the improved particle confinement property, simultaneously the change of the radial and poloidal electric field is generated and becomes more negative at the Tokamak plasma edge, and the sheared poloidal flow is related to the reduction in fluctuation level, and the poloidal velocity is mainly dominated by the E × B drift.

Velocity Measurement and Freezing Technology of Multi-shot Pellet on HL-1M Tokamak

A measuring system for high-speed hydrogen ice pellet was introduced in this paper and the photographing of flying pellet taken therein. With the system, a pellet (minimum size of φ 0.3 mm) velocity (ranging from 50 m/s to 2500 m/s) can be measured in the HL-1M tokamak fueling experiments. By analyzing photographs and the conditions of frozen pellets (including gas supply, gas replenishment, temperature controlling etc), the pellet-freezing technology is summarized in the paper.

Fuelling and Diagnostics with Pellet Injection in the HL-1M Tokamak

The pellet injection experiments for fuelling and diagnostics have been carried out on the HL-1M tokamak. The eight-pellet injector was installed on HL-1M. A reliable monitordetector and camera system was set up to take initial pellet photographs and measure the initial pellet speed and size. High fuelling efficiency of 60 % - 100 % and a density profile with a peaking factor of 1.8 - 2.0 were obtained. The maximum density close to 10^14/cm^3 in HL-1M was achieved with newly optimized combined fuelling techniques. Two typical models of pellet ablation have been utilized for simulative calculation of the ablation rates in HL-1M. In comparison with the distribution of the measured Hα emission intensity from the digital data of the CCD camera, the experimental result seems more optimistic for core fuelling than theoretical predictions by the two models. The safety factor profile q（r） has been extracted from the information provided by the CCD camera during the pellet injection. The reliability of the measured results depends mainly on the calibration of the imaging space position. Based on the calibration, the measured q-profile becomes more reasonable than those published previously for the same shot number and same photograph.

Ohmic Density Limit on HL-1M Tokamak

Investigations on density limit have been performed under a variety of discharge conditions on HL-1M, which include hydrogen isotope, siliconlzed wall coating and a variety of fuelling methods (gas puff, pellet and supersonic molecular beam (SMB) injection). Detailed analysis shows that the HL-1M density limit is a disruptive limit and related to first wall recirculating and fuelling methods. The destruction of the balance between radiation and input power is the main reason for the density disruption.

Observation of Electron Temperature Profile in HL-1M Tokamak

In this paper, the principle and method of the electron temperature measurement by means of electron cyclotron emission (ECE) have been discribed. Several results under different conditions on HL-IM tokamak have been given. The hollow profile of electron temperature appears in some stages, such as current rising, pellet injection and impurity concentration in the plasma centre. When the bias voltage is applied, the electron temperature profile become steeper. All of the phenomena are related with the transport in plasma centre.

Influence of Superathermal Electrons oll Central Plasma Relaxation Oscillations during Localized Electron Cyclotron Heating on the HL-1M Tokamak

During initial studies of ECRH in the HL-1M tokamak, non-standard central MHD activities,such as saturated sawtooth, partially saturated sawtooth, double sawtooth, and the strong m = 1 bursts have been observed while changing the heating location, the ECRH power, the plasma density. Complete suppression of sawtooth is achieved for the duration of the ECRH, when the heating power is applied on the high-field side of low-density plasma, and exceeds a threshold value of power. The m = 1 bursts riding on the ramp phase of sawtooth can only be excited when the ECRH location is near the q = 1 surface on the high field side. The conditions under which the various relaxation activities are produced or suppressed are described. Experimental results imply that the energetic electrons generated during ECRH are responsible for the modification/or stabilization/or excitation of the instability. Near the q = 1 surface, the passing electrons play the role of reducing the shear and tending to stabilize the sawtooth activity, while the barely-trapped electrons play the role of enhancing or driving an internal kink instability.

Photographing of a Multi-Pellet Ablation Process in HL-1M Tokamak with CCD Camera

The 2D CCD camera has been used to take photos during hydrogen multi-pellet injection in HL-1M tokamak. The hydrogen multi-pellet (2 × 1.0 mm, 3× 1.2 mm, 3×1.2 ~ 1.3 mm) is horizontally injected into plasma. The observation is performed above the injection path at a sight angle 13.4°，As the shape of cloud ablation varies so quickly, the key points of the experiment have to be the high temporal resolution of CCD and the determination of pellet radial location in plasma. A series of improvements have been made with the experiment setup, including camera parameter, control (NA, ROI) and trigger mode, so as to satisfy the experiment requirements. Thus very nice photos along with the satisfying experimental results are obtained such as: (1) single exposure time reduced to 100 us (2) multi-frame in one discharge (FPS≥ 40) (3)multi-exposure for one pellet so that further observation of the temporal process of pellet ablation may be possible. Through the data analysis on the spatial distibution of pellet ablation clouds in photos taken, the pellet dimensions, trajectory of the cloud and pellet velocity are obtained, and the physical mechanism of pellet-plasma interactions also analyzed. In particular, it is possible to provide an effective means for measuring q-profile of HL-1M plasma.

Mechanisms of Extending Operation Region in the HL-1M Tokamak

Stable operating region in the HL-1M tokamak has been extended by means of wall conditioning, core fuelling and current control techniques. The mechanisms of the extension are analyzed in this paper. Lithiumization diminishes the impurities and hydrogen recycling to the lowest level. After lithiumization a high density up to 7×1019 m-3 was obtained easily by strong gas puffing with ordinary ohmic discharge alone. More attractively we found that metal Li-coating exhibited the effects of wall stabilization. The low qα limit with higher density was extended by a factor of 1.5-2 in comparison with that for boronization, and 1.2 for siliconization. Siliconization not only extended stable operating region significantly by itself, but also provided a good target plasma for other experiments of raising density limit. Core fuelling schemes are favourable especially for siliconized wall with a higher level of medium-Z impurity (Z = 14). After siliconization the maximum density near to 1020 m-3 was achieved by a combination of supersonic molecule beam injection and multipellet injection. The new defined slope of Hugill limit illustrating more clearly the situation under low qα and high ne discharges was created to indicate the new region extended by combining IP ramp-up with core fuelling. The slope with a large Murakami coefficient increased by a factor of 50-60 %.

POTENTIAL SAFE TERMINATION BY LASER ABLATION OF HIGH Z IMPURITY IN THE HL-1M TOKAMAK

A preliminary experiment for triggering a plasma current quench by high Z impurities has been performed on the HL1M tokamak.Using injection of impurity with the higher charge of the nuclei allows us to increase the radiation cooling.It can be a simple and potential approach for decreasing significantly the plasma thermal energy before a disruption and for safe termination of the plasma.

DEVELOPMENT OF A NEUTRAL PARTICLE ANALYZER FOR THE HL-1M TOKAMAK

A neutral particle energy analyzer (NPA) has been developed to investigate the energy spectra of neutral particles emitted from the HL1M tokamak plasma. The NPA consists of a pair of 45o parallel electrostatic plates, a gas stripping cell, a column of channeltrons for recording ions,and the relevant instrumentation and software. There are eight energy channels in the NPA with energy ratio of 8 between the lowest energy channel and the highest one. Calibration experiment is the key issue for the development of NPA. Calibrations of energy, energy resolution and registration efficiency have been carried out. The scattering of neutrals through the stripping gas impingement, which is severe for the particle energy we concerned, has also been measured to calibrate the registration efficiency accurately. With the NPA, the heating effects of lower hybrid wave on the plasma ions in the HL1M tokamak for different plasma parameters, especially for different plasma density, have been investigated.

Disruption Mitigation Using Laser Ablation of High-Z Impurities in HL-1M Tokamak

Major plasma disruptions are considered to be a serious problem for development of tokamak fusion reactors. The preliminary experiment results in HL-1M presented here describe the methods of amelioration of plasma current quench in major disruptions using laser ablation of high-Z impurities, which support the design of next generation large tokomaks like ITER. Using injection of impurity with higher electric charge can produce resistive highly radiating plasma and increase the radiation cooling of plasma to make a safe termination of the disruption. It can be possibly a simple and potential approach to decrease significantly the plasma thermal energy and magnetic energy before a disruption then obtain a safe plasma termination. The magnetic energy can be dissipated by impurity radiation .

Recent Experimental Results of HL-1M Tokamak and Progress of HL-2A Project

Recent experimental results of HL-1M tokamak and progress of HL-2A project are presented. Strong fishbone instability was observed during off-axis ECRH. This is first observation of the fishbone instability purely driven by energetic electrons produced by ECRH. The MBI was first proposed and demonstrated on HL-1M. Recently new results of MBI experiment were obtained by increasing the pressure of gas. A stair-shape density increment was obtained with high-pressure multi-pulse MBI just like the density evolution behavior during the multipellet injection. It is

Scaling Properties of Runaway Electrons in HL-1M Tokamak

1 Introduction Runaway electrons in tokamaks have been widely studied theoretically and experimentally. Runaway electrons have received lately a great attention due to several reasons： a） the possibility to study electromagnetic turbulence by measuring the runaway flux fluctuations and its energy spectra, and b） the runaway electrons are powerful diagnostics capable of yielding valuable information on the actual distribution function of fusion experiments.

Snake Perturbations during Pellet Injection in the HL-1M Tokamak

Pellet injection experiments have been widely carried out with various toroidal plasmas, peaked density profile and improved con finement are frequently observed, and some interesting phenomena have also been found.One of them is the long-lived m=1/n=1 oscillation observed on soft X-ray emission and other diagnostics (notably the microwave interferometers and the ECE systems) after pellet injection in JET, JT-60,

The Effect of Recycling in the HL-1M Tokamak

It is often stated that even clean tokamak discharges disrupt at high density. One possibility is that such disruption result from the energy loss arising from hydrogen recycling at the edge of the plasma.this energy loss could lead to a contraction of the current channel and the production of a disruptively unstable configuration.

Studies of Electron Heat Transport in HL-1M Tokamak ECRH Plasma

Anomalous transport is one of the most important subjects for the tokamak research.Experiments have confirmed that anomalous transport is caused by turbulences driven by temperature and density gradient in plasma. The experiments show that ion diffusion can be reduced to neoclassical level in high parameter plasma with internal transport barrier.

The Spatio-Temporal Characteristics of Sawtooth Instabilities in the HL-1M Tokamak

The MHD instabilities in the plasma centre can be observed with pinhole cameras to record soft X-ray (SXR) emission along many chords with high speatial resolution. The soft X-ray system in the HL-1M tokamak consists of three pinhole cameras with 60 chords. The method of singular value decomposition(SVD) can split such signals into orthogonal spatial and temporal vectors. By this means,

Particle Confinement Improvement by Current Ramp on the HL-1M Tokamak

The scaling laws of energy confinement are very significant for confinement improvement. A typical scaling law of ohmic heating with low effective charge and radiation power is given by

Pellet and Supersonic Molecular Beam Injection Fuelling on the HL-1M Tokamak

An eight-shots pellet injection (PI) and a supersonic molecular beam injection (SMBI) system have proposed and developed on the HL-1M tokamak for advanced fuelling experiments. The peaked density profile and improved confinement are typical feature of PI and SMBI discharge. It strongly depends on the wall recycling conditions of the HL-1M tokamak and injection parameters.