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.     

Simple Emission Model of Supersonic Molecular Beam

Recently some modes of supersonic molecular beam injection （SMBI）have been put forward. Among them there are electrostatic “double layer”-shielding, simple collective and optimized numerical models to explain the experiment phenomenon. The penetrated depth A and particle deposition were calculated theoretically. About 1/7 in- cident thermal electron flux was amputated and, A increased seven times. The previous simulation is not enough for the SMBI fueling mechanism research. Hence, further investigations, both in experiment and in theory should be developed. The phenomena of line emission due to supersonic molecular beam （SMB） are of particular importance.     

Observation of Non-Local Transport Phenomena with SMBI in HL-2A

The non-local transport phenomenon induced by supersonic molecular beam injection （SMBI） was first observed in the HL-2A tokomak. In comparison with the phenomena induced by other methods in various tokamaks, it has its own feature： the effect induced by SMBI in HL-2A lasts much longer than that induced by pellet injection in other similar size tokomaks. Both the bolometer radiation and He emission decrease when the non-local effect appears. This suggests that an electron transport barrier has been formed at the position just outside the q = 1 surface when the non-local effect appears.     

The first results of divertor discharge and supersonic molecular beam injection on the HL-2A tokamak

HL-2A tokamak is the first tokamak with divertors in China. The plasma boundary and the position of the striking point on the target plates of the HL-2A closed divertor were simulated by the current filament code and they were in agreement with the diagnostic results in the divertor. Supersonic molecular beam injection (SMBI) system was first installed and tested on the HL-2A tokamak in 2004. In the present experiment low pressure SMBI fuelling on the HL-2A closed divertor was carried out. The experimental results indicate that the divertor was operated in the `linear regime' and during the period of SMB pulse injection into the HL-2A plasma the power density convected at the target plate surfaces was 0.4 times of that before or after the beam injection. It is a useful fuelling method for decreasing the heat load on the neutralizer plates of the divertor.     

Role of Advance Refuelling and Heating on Edge Reynolds Stress—Induces Poloidal Flow in HL—1M

The radial profile of electrostatic Reynolds stress,plasma poloidal rotations,radial and poloidsal electric fields have been measured in the plasma boundary region of the HL-1M tokamak using a multiarray of Mach/Langmuir probes.In the experiments of ohmic discharge,lower hybrid current drive,supersoniuc molecular beam injection (SMBI)and multi-shot pellet injection,the correlation between the Reynolds stress and poloidal flow in the edge plasma is presented.The adial profile changes of the Reynolds stress and poloidal flow velocity Vpol with lower hybrid wave injection power and SMBI injection are obtained.The results indicate that the sheared poloidal flow can be generated in tokamak plasma due to the radially varying Reynolds stress.     

Experiments on High Pressure Supersonic Molecular Beam Injection in the HL-1M Tokamak

Supersonic molecular beam injection (SMBI) was first proposed and demonstrated on the HL-1 tokamak, was successfully developed and used on the HL-1M tokamak,and was then applied on the HT-7 superconducting tokamak, the Tore Supra tokamak and the WT-AS stellarator. With the new     

Heat Transport of Non-Local Effect with Modulated SMBI on HL-2A

Modulated supersonic molecular beam （SMB） injection is introduced to study transport features of non-local transport phenomenon on HL-2A. Repetitive non-local effect induced by modulated SMBI allows Fourier trans-formation of the temperature perturbation, yielding detailed investigation of the pulse propagation. Fourier analysis provides evidence for existence of internal transport barriers. Meanwhile, experimental progress of nonlocal effect was made in the HL-2A Tokamak in 200Z The core electron temperature Te rise increases from 18% to more than 40% and the duration of the Te rise could be prolonged by changing the conditions of SMB injection.     

The First Results of Supersonic Molecular Beam Injection in the HL-2A Tokamak

HL-2A tokamak, the first tokamak with divertor in China, has been constructed and put into operation in 2002. The main parameters are R=1.65 m, a=0.4 m, BT=2.8 T, Ip = 0. 48 MA. The divertor of HL-2A is unique, because it is characterized with a large closed divertor chamber. The device has double divertor chamber, but now it is operating with lower single null configuration to study the physics of divertor for the next step design of a divertor. Supersonic molecular beam injection （SMBI） system with LN2 cooling trap was first installed and demonstrated on the HL-2A tokamak in 2004. The first results of SMBI into HL-2A plasma are to demonstrate the function of the HL-2A divertor and to observe the cold pulse propagation during multi-pulse SMBI on HL-2A Tokamak.     

Beam Ion Transport from Neutron Emissivity Measurement in Deuterium Neutral Beam-Heated Deuterium Plasmas of the HL-2A Tokamak

An experiment at the HL-2A tokamak with a high-energy deuterium neutral beam （NB） injection （30 keV, about 0.6 MW） was performed. The emission of d-d fusion neutrons dominated by beam-plasmas reactions when the deuterium NB was injected into the deuterium target plasma was observed by means of a ^235U fission chamber. To obtain information on NB deposition and the slowing down of beam ions in HL-2A plasmas, a very short-pulse deuterium NB injection, or the so-called ＂blip＂ injection, was performed into MHD-quiescent Ohmic deuterium plasmas. Analysis of neutron decay following the NB ＂blip＂ injection indicates that tangentially injected beam ions are well confined, slowing down classically in the HL-2A. In contrast to the MHD-quiescent plasma, anomalous losses of beam ions were observed when tearing mode instabilities were present.     

Beam-loss driven injection optimization for CSNS/RCS

This paper summarizes the painting injection optimization for the Chinese Spallation Neutron Source （CSNS） ring. This optimization focuses on two main design goals： the lower beam loss and a spacecharge tune shift low enough to avoid strong resonances. Finally, the 3-D particle tracking is performed and we get some important results about the beam properties and beam loss.     

Particle confinement and density profile behaviour on HL-1M

In this paper the density profile behaviour and the particle confinement operation regime on HL-1M have been studied under the pellet injection (PI), supersonic molecular beam injection (SMBI), gas puffing (GP) and lower hybrid current drive experimental situations. The relationships between density profile, particle confinement time and edge safe factor have been explored. The density profile, which is measured by six-channel far-infrared ray laser interferometer has been analysed by using the peaking coefficient calculation code. Changes of the outward and inward diffusion velocities before and after the peaking of the central density profile have been calculated using the global particle balance equations. The particle confinement operation regimes have been discussed. The peaking density profile can be easily obtained under the condition of efficient fuelling. In ohmic discharges, confinement time increases as the peaking density profile factor rises, and is saturated at a critical value related to the fuelling efficiency. The particle confinement time of SMBI lies between the values of GP and PI, and its value is about 3-5 times of the energy confinement time.     

基于超声分子束和普通充气的聚变等离子体密度反馈实验研究

本文介绍了全超导托卡马克装置EAST实验中等离子体密度反馈的方法和结果. EAST密度反馈采用普通充气 (gas puffing) 和超声分子束 (supersonic molecule beam injection, SMBI) 在放电过程中反馈进气, 获得稳定、预期的等离子体密度. 典型的一天放电实验中, 每次放电的充气量和壁滞留的变化可分为两个阶段: 第一阶段为初始约20次放电, 该阶段充气量非常高且呈指数趋势下降, 粒子滞留率为80%–90%, 壁滞留迅速上升. 第二阶段为随后的约50次放电, 该阶段充气量较小且保持稳定, 粒子滞留率为50%–70%, 壁滞留缓慢上升. SMBI的加料效率为15%–30%, 延迟时间小于5 ms. 因此使用SMBI 进行密度反馈效果优于gas puffing反馈, 相同条件下前者充气量较后者减少了～ 30%, 壁滞留减少了～ 40%, 再循环系数也相应减少. gas puffing反馈时, 采用脉宽调制模式效果优于脉幅调制模式. SMBI密度反馈可以作为未来EAST长脉冲高参数放电的主要手段之一. 关键词： 密度反馈 超声分子束 再循环 壁滞留     

Investigation of Edge Fluctuation Characteristics on the HL-2A Tokamak

The edge plasma fluctuation characteristics are studied by the fast reciprocating scanning 6-probes in the boundary region. These probes can measure edge plasma temperature, density, poloidal electric field, radial electric field, Reynolds stress, and their profiles in once discharges. Measurement results are used to analyze plasma confinement, turbulent fluctuations and their correlation characteristics during multi-shot pellet injection （MPI） , supersonic molecular beam injection （SMB1） and electron cyclotron resonant heating （ ECRH ） discharges.     

Effects of injection beam parameters and foil scattering for CSNS/RCS

The China Spallation Neutron Source (CSNS) uses H- stripping and phase space painting method to fill a large ring acceptance with a small emittance linac beam. The dependence of the painting beam on the injection beam parameters was studied for the Rapid Cycling Synchrotron (RCS). The simulation study was done for injection with different momentum spreads, different rms emittances of the injection beam, and different matching conditions. Then, the beam loss, 99% and rms emittances were obtained, and the optimized injection beam parameters were given. The interaction between H- beam and stripping foil was studied, and the effect of foil scattering was simulated. The stripping efficiency was calculated and the suitable thickness of stripping foil was obtained. In addition, the energy deposition on the foil and the beam loss due to the foil scattering were also studied.     

Progress in the Secondary Heating System for the HL-2A Tokamak

In 2006, the following work on secondary heating systems for HL-2A tokamak have been done： the development of an electron cyclotron resonance heating （ECRH） system, the improvement of lower hybrid resonance heating （LHCD） system and the fabrication on neutral beam injection （NBI） system.     

A Particle-in-cell scheme of the RFQ in the SSC-Linac

A 52 MHz Radio Frequency Quadrupole （RFQ） linear accelerator （linac） is designed to serve as an initial structure for the SSC-Linac system （injector into Separated Sector Cyclotron）.The designed injection and output energy are 3.5 keV/u and 143 keV/u,respectively.The beam dynamics in this RFQ have been studied using a three-dimensional Particle-In-Cell （PIC） code BEAMPATH.Simulation results show that this RFQ structure is characterized by stable values of beam transmission effciency （at least 95%） for both zerocurrent mode and the space charge dominated regime.The beam accelerated in the RFQ has good quality in both transverse and longitudinal directions,and could easily be accepted by Drift Tube Linac （DTL）.The effect of the vane error and that of the space charge on the beam parameters have been studied as well to define the engineering tolerance for RFQ vane machining and alignment.     

Investigation of impurity transport using supersonic molecular beam injected neon in HL-2A ECRH plasma

In this paper, we describe the behavior of impurity transport in the HL-2A electron cyclotron resonance heating （ECRH） L-mode plasma. The neon as a trace impurity is injected by the supersonic molecular beam injection （SMBI） technique, which is used for the first time to study the impurity transport in HL-2A. The progression of neon ions is monitored by the soft X-ray camera and bolometer arrays with good temporal and spatial resolutions. The convection and diffusion process of the neon ions are investigated with the one-dimensional impurity transport code STRAHL. The results show that the diffusion coefficient D of neon ions is a factor of four larger than the neoclassical value in the central region. The value of D is larger in the outer region of the plasma （ρ 〉 0.6） than in the central region of the plasma （ρ 〈 0.6）. The convective velocity directs inwards with a value of ～-1.0 m/s in the Ohmic discharge, but it reverses to direct outwards with a value of ～ 8.0 m/s in the outer region of the plasma when ECRH is applied. The result indicates that the impurity transport is strongly enhanced with ECRH.     

A New Doppler Shift Spectroscopy for Measurement of Neutral Beam Profile

A new diagnostic based on Doppler shift is designed to measure the power profile of a hydrogen or deuterium neutral beam on the magnetic confined fusion machines. The interference filters and multi-channel photon detector array （PDA） are the main components of this diagnosis. The multi-channel PDA measures the line integrated Doppler Ha signal emitted by the neutral beam at one section in two directions. The local intensity of neutral beam can be obtained with the tomography technique. Compared to the conventional calorimeter diagnoses, this diagnosis can provide the beam profile without blocking the injection of neutral beam.     

BEPCII Injector Linac Upgrade and Beam Instabilities

The upgrade project of the Beijing Electron Positron Collider （BEPCII） and its injector linac is working well. The linac upgrade aims at a higher injection rate of 5OmA/min into the storage ring, which requires an injected beam with low emittance, low energy spread and high beam orbit and energy stabilities. This goal is finally reached recently by upgrading the linac components and by dealing with rich and practical beam physics, which are described in this study.     

Optimization of the beam quality in ionization injection by a tailoring gas profile

A new scheme is proposed to improve the electron beam quality of ionization-induced injection by tailoring gas profile in laser wakefield acceleration. Two-dimensional particle-in-cell simulations show that the ionization-induced injection mainly occurs in high-density stage and automatically truncates in low-density stage due to the decrease of the wakefield potential difference. The beam loading can be compensated by the elongated beam resulting from the density transition stage. The beam quality can be improved by shorter injection distance and beam loading effect. A quasi-monoenergetic electron beam with a central energy of 258 Me V and an energy spread of 5.1% is obtained under certain laser–plasma conditions.