HL-1M Tokamak Research Articles

Measurement of the Plasma Rotation Velocity by Using Visible Spectrum on HL-1M Tokamak

The plasma rotation velocity were measured in HL-1M with Doppler shifts of C III, C II, O II and Hα line by a SKD high resolution spectrometer. The effects of density, hydrogen pellet injection and carbon impurities injected by laser-blow-off on toroidal (Vφ) and poloidal (Vθ) rotation velocity have been observed. The Vθ measured from Hα line is only half of that from C II impurity line.

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 qa 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 qa 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%.

Diagnosis for the Interaction of Supersonic Molecular Beam with Plasma

Supersonic Molecular Beam Injection (SMBI) is a new fuelling method for Tokamaks and has recently been improved to enhance the flux of the beam and to make a survey of the cluster effect within the beam. There are a series of new phenomena, which implicate the interaction of the beam (including clusters) with the toroidal plasma of HL-1M Tokamak. The Hα signals from the edge show a regular variation around the torus. Around the injection port, the edge Hα signals are positive rectangular wave, which is consistent with that of the injection beam pulses. The edge electron temperature, measured with movable Langmuir probes, decreases by an order of magnitude and the density increases by an order of magnitude. Hα emission at the beam injection port, measured with CCD camera at an angle of 13.4 degrees to the SMBI line, shows many separate peaks within the contour plot. These peaks may show the strong emission produced by the interaction of the hydrogen clusters with the plasma. Hydrogen clusters may be produced in the beam according to the empirical scaling (Hagena) law of clustering onset, Γ* = kd0.85P0/T02.29. Here d is the nozzle diameter in μm, P0 the stagnation pressure in mbar, T0 the source temperature in K, and k is a constant related to the gas species. If Γ* > 100, clusters will be formed. In present experiment Γ* is about 127.

High Density Experiments in the HL-1M Tokamak

The plasma performance of high density has been investigated in the HL-1M Tokamak. Different density limits are given for three fueling methods i.e. gas puffing, pellet injection and molecular beam injection (MBI). The maximum Murakami constant is CM = 3.4 × 1019 m-2T-1 for Ohmic discharge. A maximum line-averaged density of 8.2 × 1019 m-3 has been achieved for Ohmic discharge at qa = 4.4. A 1.4 times of the Greenwald limit is obtained at Ip = 120 kA. The rising rates and peak factors of density are discussed. The plasma confinement of high density is analyzed, including the behavior of density limit disruption.

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, siliconized 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.

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 Er and Eθ 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.

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-1M 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.

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 × ϕ 1.0 mm, 3 × ϕ 1.2 mm, 3 × ϕ 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 ns (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 distribution 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.

Investigation of Edge Plasma Features in the HL-1M Tokamak

Edge plasma features in typical HL-1M discharges were presented. Particle confinement and plasma rotation have been investigated in the discharges with lower hybrid current drive (LHCD), molecular beam injection (MBI) and pellet fuelling. LHCD can make particle confinement increase a factor of 2-3 for low-density discharge. Particle confinement time and poloidal rotation can be at least doubled after pellet injection, while MBI can make confinement time increase about one order of magnitude with higher performance.

In situ silicon and lithium coating and its removal in the HL-1M tokamak

Siliconization and lithium coating of the wall in the HL-1M tokamak were performed by means of DC glow discharges with a mixture of SiH 4 and He and lithium evaporation in a He glow discharge, respectively. With the wall conditioning, impurities and radiation power losses are generally lower than those with boronization, and strong wall pumping and low hydrogen recycling occur in these tokamak discharges. The excellent wall conditions lead to great progresses in such experiments as the multi-shot pellet injection, LHCD and long pulse discharges. Removal of these coatings by DC glow discharges with H 2 and He was demonstrated.

Fast multichannel plasma radiation losses measuring system

Abstract Fast Multichannel Radiation Losses Measuring System (MRLMS) has been developed for T-11M (Troitsk, Russia) and HL-1M (Chengdu, China) tokamak plasma diagnostics applications. Its main advantages are improved signal-to-noise ratio and fast response time achieved by utilization of silicon photodiode linear array manufactured by International Radiation Detectors Inc. (IRD, Torrance, CA, USA) for absolute radiometry applications in the vacuum ultraviolet, extreme ultraviolet and soft X-ray spectral regions.

Reconstruction of Current Profiles and q Profiles on the HL-1M Tokamak

The algorithm for reconstructing plasma current and safety factor profiles on a tokamak with an iron core transformer is given and applied to the analysis of experimental data. It is shown that a central negative magnetic shear region is realized througth ajusting the ramp-up rate of plasma current in ohmic discharges and through lower hybrid current drive on HL-1M tokamak.

A prototype switched Ethernet data acquisition system

A prototype switched Ethernet data acquisition system has been built up and successfully operated in HL-1M tokamak experiments. The system is based on a switched high bandwidth Ethernet network with which the CAMAC crates are directly interfaced. It takes the advanced features of LAN switch and Ethernet CAMAC controller (ECC 1365 MK III, HYTEC product) to avoid the rewriting of CAMAC driver for an individual computer system and to ensure high data transmission rate between CAMAC system and host computers on the network. It is a new approach to DAS system architecture and provides a solution for a well-known bottleneck problem in traditional distributed DAS system for fusion research. An average throughput of the test system reaches over 100 Mbps. The system features also an easy and low cost migration from traditional distributed DAS system. In the paper, the hardware configuration, software structure, performance of the system and the method of migrating from current DAS system are discussed in detail.

Improvement of plasma performance with wall conditioning in the HL-1M tokamak

Studies and selection of plasma facing materials continue to be a concern for future fusion devices, and ongoingefforts are being made in the HL-1M tokamak. The advanced methods of wall modification adopted on HL-1M are surveyed.Significant improvements in tokamak plasma performance have been obtained by using boron, silicon or lithium containingsubstances as a material for wall coatings. The siliconization technique is highlighted. Lithiumization, as the newesttechnique, will be investigated further.

Plasma behaviour with molecular beam injection in the HL-1M tokamak

A new method of gas fuelling has been introduced in the HL-1M tokamak. The method consists of a pulsed high speed molecular beam formed by a Laval type nozzle. The velocity of the well collimated hydrogen beam is about 500 m/s. About 6 × 1019 molecules pass through the nozzle and into the vacuum chamber in each pulse. A series of helium pulses was injected into the HL-1M low density (n̄e = 4 × 1018 m-3) hydrogen plasma. With penetration depth up to 12 cm, the ramp-up rate of the electron density, dn̄e/dt, was as high as 3.1 × 1020 m-3·s-1 at steady state, and the resulting plasma density reached n̄e = 5.6 × 1019 m-3. The profile peaking factor of the electron density, Qn = ne(0)/⟨ne⟩ of about 100 ms after helium molecular beam injection (MBI) reached a maximum value of more than 1.51. The energy confinement time τE measured by diamagnetism is 26 ms, which is over 30% longer than that of the gas puffing (GP) results under the same operational conditions. The improvement of τE and increase of Qn for MBI were comparable to those of small pellet injection (PI) in HL-1M, as well as those of slow PI in ASDEX (Kaufmann, M., et al., Nucl. Fusion 28 (1988) 827). It is argued that the peaked density profile induced by the deepened particle injection is a factor essential for the confinement improvement apart from the isotope effect of helium particles, because the density peaking factor Qn is normally less than 1.4 for GP plasma in HL-1M. The particle confinement time with MBI increased sixfold in comparison with that before injection.

The fluctuations and flow velocities measured with a Mach probe array on the HL-1M tokamak

The fluctuations and flow velocities measured with a Mach probe array on the HL-1M tokamak

The fluctuations and flow velocities measured with a Mach probe array on the HL-1M tokamak

This paper describes a Mach probe array with four pins which can measure not only parallel flows but the flow perpendicular to the magnetic field as well. Experimental measurements of the fluctuations and velocities of the toroidal and the poloidal flow have been carried out on both of SOL and the boundary region of HL-1M for ohmic, biased H-mode and LHCD discharges. The results show that the suppressions of the fluctuations are related to poloidal rotations produced by electrode biasing and LH waves injecting in the improved particle confinement modes.