Fully Implicit Iterative Solving Method for the Fokker-Planck Equation in Tokamak Plasmas

A three dimensional bounce-averaged Fokker-Planck （FP） numerical code has been newly developed based on fully implicit iterative solving method, and relativistic effect is also included in the code. The code has been tested against various benchmark cases： Ohmic con ductivity in the presence of weak Ohmic electric field, runaway losses of electrons in the presence of strong Ohmic electric field, lower hybrid current drive and electron cyclotron current drive via two- or three-dimensional simulation. All the test cases run fast and correctly during calculations. As a result, the code provides a set of powerful tools for studying radio frequency wave heating and current drive in tokamak plasmas.

Line identification of extreme ultraviolet (EUV) spectra from low-Z impurity ions in EAST tokamak plasmas

Extreme ultraviolet(EUV) spectra emitted from low-Z impurity ions in the wavelength range of10–500Å were observed in Experimental Advanced Superconducting Tokamak(EAST)discharges. Several spectral lines from K-and L-shell partially ionized ions were successfully observed with sufficient spectral intensities and resolutions for helium, lithium, boron, carbon,oxygen, neon, silicon and argon using two fast-time-response EUV spectrometers of which the spectral intensities are absolutely calibrated based on the intensity comparison method between visible and EUV bremsstrahlung continua. The wavelength is carefully calibrated using wellknown spectra. The lithium, boron and silicon are individually introduced for the wall coating of the EAST vacuum vessel to suppress mainly the hydrogen and oxygen influxes from the vacuum wall, while the carbon and oxygen intrinsically exist in the plasma. The helium is frequently used as the working gas as well as the deuterium. The neon and argon are also often used for the radiation cooling of edge plasma to reduce the heat flux onto the divertor plate. The measured spectra were analyzed mainly based on the database of National Institute of Standards and Technology. As a result, spectral lines of He Ⅱ, Li Ⅱ–Ⅲ, B Ⅳ–Ⅴ, C Ⅲ–Ⅵ, O Ⅲ–Ⅷ, Ne Ⅱ–Ⅹ,Si Ⅴ–Ⅻ, and Ar Ⅹ–XVI are identified in EAST plasmas of which the central electron temperature and chord-averaged electron density range in Te0=0.6–2.8 keV and ne=(0.5–6.0)×1019 m-3, respectively. The wavelengths and transitions of EUV lines identified here are summarized and listed in a table for each impurity species as the database for EUV spectroscopy using fusion plasmas.

Poloidal rotation induced by injecting lower hybrid waves in tokamak plasma edge

The poloidal rotation of the magnetized edge plasma in tokamak driven by the ponderomotive force which is generated by injecting lower hybrid wave(LHW) electric field has been studied. The LHW is launched from a waveguide in the plasma edge, and by Brambilla's grill theory, analytic expressions for the wave electric field in the slab model of an inhomogeneous cold plasma have been derived. It is shown that a strong wave electric field will be generated in the plasma edge by injecting LH wave of the power in MW magnitude, and this electric field will induce a poloidal rotation with a sheared poloidal velocity.

Hot Vertical-Displacement-Event Process due to Internal Energy Perturbations for HL-2M Tokamak Plasma

During the tokamak operation, variation of the stored energy can cause internal perturbations of the plasma. These perturbations may develop into large-scale vertical movement of the whole column for the vertically elon- gated tokamak, eventually generating the hot vertical displacement event （VIDE,）. It will cause considerable damage to the machine. In this work, the hot VDE process due to stored energy perturbations is investigated by a mature non-linear time-evolution code DINA. The influence on the vertical instability, the displacement direction and the electromagnetic loads on in-vessel components during the hot VDE are analyzed. It is shown that a larger perturbation leads to faster development of the vertical instability. Meanwhile the variation of the Shafranov shift, due to the energy change, is related to the VDE direction. The vertical electromagnetic force on the vacuum vessel and the halo current flowing in the divertor baffle become larger in the case of VDE moving towards the X point.

Drift-wave fluctuation in an inviscid tokamak plasma

In order to describe the characterization of resistive drift-wave nuctuauon in a [OKalnaK plasma, a coup^e~a lllVlbt;IU two-dimensional Hasegawa-Wakatani model is investigated. Two groups of new analytic solutions with and without phase shift between the fluctuant density and the ftuctuant potential are obtained by using the special function transformation method. It is demonstrated that the fluctuant potential shares similar spatio-temporal variations with the density. It is found from the solutions without phase shift that the effect of the diffusion and adiabaticity on the fluctuant density is quite complex, and that the fuctuation may be controlled through the adiabaticity and diffusion. By using the typical parameters in the quasi-adiabatic regime in the solutions with phase contours become dense toward the plasma edge and the distribution in the tokamak edge. shift, it is shown that the density gradient becomes larger as the contours have irregular structures, which reveal the nonuniform

Effect of shear equilibrium flow in Tokamak plasma on resistive wall modes

A code named LARWM with non-ideal magnetohydrodynamic equations in cylindrical model is used to describe the instability in Tokamak plasma surrounded by a conducting wall with finite resistivity. We mainly take three factors related to the shear equilibrium plasma flow into consideration to study the stabilizing effect of the shear flow on the resistive wall modes （RWMs）. The three factors are the velocity amplitude of flow, the shear rate of flow on plasma surface, and the inertial energy of equilibrium plasma flow. In addition, a local shear plasma flow is also calculated by the LARWM code. Consequently, it is found that the inertial energy of the shear equilibrium plasma flow has an important role in the stabilization of the RWMs.

GTC Simulation of Ideal Ballooning Mode in Tokamak Plasmas

In the present paper,we first derive the eigenmode equation of the ideal ballooning mode in tokamak plasmas using a gyrokinetic equation.It is shown that the gyrokinetic eigenmode equation can be reduced to the magnetohydrodynamic（MHD） form in the long wavelength limit when kinetic effects are ignored.Then,the global gyrokinetic toroidal code（GTC） is applied for simulations of the edge-localized ideal ballooning modes.The obtained mode structures are compared with the results of ideal MHD simulations.The observed scaling of the linear growth rate with the toroidal mode number is consistent with the ideal MHD theory.The simulation results verify the GTC capability of simulating MHD processes in toroidal plasmas.

PTC: Full and Drift Particle Orbit Tracing Code for α Particles in Tokamak Plasmas

Fusion born α particle confinement is one of the most important issues in burning plasmas,such as ITER and CFETR.However,it is extremely complex due to the nonequilibrium characteristics,and multiple temporal and spatial scales coupling with background plasma.A numerical code using particle orbit tracing method(PTC)has been developed to study energetic particle confinement in tokamak plasmas.Both full orbit and drift orbit solvers are implemented to analyze the Larmor radius effects on α particle confinement.The elastic collisions between alpha particles and thermal plasma are calculated by a Monte Carlo method.A triangle mesh in poloidal section is generated for electromagnetic fields expression.Benchmark between PTC and ORBIT has been accomplished for verification.For CFETR burning plasmas,PTC code is used for α particle source and slowing down process calculation in 2D equilibrium.In future work,3D field like toroidal field ripples,Alfven and magnetohydrodynamics instabilities perturbation inducing α particle transport will be analyzed.

A synthetic diagnostics platform for microwave imaging diagnostics in tokamaks

Interpreting experimental diagnostics data in tokamaks,while considering non-ideal effects,is challenging due to the complexity of plasmas.To address this challenge,a general synthetic diagnostics(GSD)platform has been established that facilitates microwave imaging reflectometry and electron cyclotron emission imaging.This platform utilizes plasma profiles as input and incorporates the finite-difference time domain,ray tracing and the radiative transfer equation to calculate the propagation of plasma spontaneous radiation and the external electromagnetic field in plasmas.Benchmark tests for classical cases have been conducted to verify the accuracy of every core module in the GSD platform.Finally,2D imaging of a typical electron temperature distribution is reproduced by this platform and the results are consistent with the given real experimental data.This platform also has the potential to be extended to 3D electromagnetic field simulations and other microwave diagnostics such as cross-polarization scattering.

AWECS:A Linear Gyrokinetic df Particle-in-Cell Simulation Code for the Study of Alfvenic Instabilities in High-β Tokamak Plasmas

A 1-Dlinear gyrokinetic code called AWECS is developed to study the kinetic excitation of Alfvenic instabilities in a high-β tokamak plasma,with β being the ratio of thermal to magnetic pressure.It is designed to describe physics associated with a broad range of frequencies and wavelengths.For example,AWECS is capable of simulating kinetic ballooning modes,Alfvenic ion-temperature-gradient-driven modes,as well as Alfven instabilities due to energetic particles.In addition,AWECS may be used to study drift-Alfven instabilities in the low-β regime.Here,the layout of the code and the numerical methods used are described.AWECS is benchmarked against other codes and a convergence study is carried out.

Improved plasma position detection method in EAST Tokamak using fast CCD camera

To control the steady-state operation of Tokamak plasma, it is crucial to accurately obtain its shape and position. This paper presents a method for use in rapidly detecting plasma configuration during discharge of the Experimental Advanced Superconducting Tokamak device. First, a visible/infrared integrated endoscopy diagnostic system with a large field of view is introduced,and the PCO.edge5.5 camera in this system is used to acquire a plasma discharge image. Based on the analysis of various traditional edge detection algorithms, an improved wavelet edge detection algorithm is then introduced to identify the edge of the plasma. In this method, the local maximum of the modulus of wavelet transform is searched along four gradient directions, and the adaptive threshold is adopted. Finally, the detected boundary is fitted using the least square iterative method to accurately obtain the position of the plasma. Experimental results obtained using the EAST device show that the method presented in this paper can realize expected goals and produce ideal effects;this method thus has significant potential for application in further feedback control of plasma.

Plasma Electron Density Measuring and Processing on the J-TEXT Tokamak

Plasma electron density is one of the most fundamental parameters in the study of tokamak plasma physics.The method of plasma electron density measuring and processing on the Joint Texas Experimental Tokamak(J-TEXT) was presented in this paper.The principle of the plasma electron density measuring by hydrogen cyanide(HCN) laser interferometer was introduced.Room temperature triglycine sulface(TGS) detector was used to obtain the beat signal of HCN,and phase difference was measured by high-speed acquisition card DAQ2010.Based on the signal characteristics,a specific HCN processing algorithm was designed to eliminate the baseline offset accurately and process overturns of HCN signals effectively.As a result,plasma electron density with high accuracy and low noise has been obtained during the J-TEXT tokamak experiment.

Sawtooth Activity in Ohmically Heated Plasma on HT-7 Tokamak

Sawtooth activity on HT-7 tokamak has been investigated experimentally mainly by using soft x-ray diode array and magnetic probes. Their behaviors and occurrences are correlated closely to the discharge conditions: the electron density Ne, the electron temperature Te, the safety factor qa on plasma boundary and wall condition etc. When central line-averaged electron density Ne(0) is over 2.0×1013cm-3 , major sawtooth activity emerges with a period of up to 6.5 ms and a fluctuation amplitude of up to 2-30 % of SXR radiation signal. In some cases such as the safety factor between 4.2-4.7 and Zeff=3.0-6.0, a monster sawtooth activity often emerges without apparent deterioration of plasma confinement and without major disruption. During these events, abundant MHD phenomena are observed including partial sawtooth oscillations. In this paper, the observed sawtooth behaviors and their dependence on the and their dependence density Ne and wall condition in ohmically heated plasma are introduced, the results are discussed and presented.

Investigation of Edge Plasma Features in the HL-IM 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.

Initial Plasma Startup Test on SUNIST Spherical Tokamak

The goal of the Sino-United Spherical Tokamak (SUNIST) at Tsinghua University is to extend the understanding of toroidal plasma physics at a low aspect ratio (R/a≈1.3) and to demonstrate a maintainable target plasma by non-inductive startup. The SUNIST device is designed to operate with up to 13 kA of ohmic heating field current, and to 0.15 T of toroidal field at 10 kA of discharge current. All of the poloidal fields can provide 30 mVs of Volt-seconds transformer. Experimental results of plasma startup show that SUNIST has remarkable characteristics of high ramp rate (dIp/dt≈50 MA/s ), high normalized current In of about 2.8 (In = Ip/αBt), and high-efficiency (Ip/Irod ≈0.4) production of plasma current while operating at a low toroidal field. Major disruption phenomena have not been observed from magnetic diagnostics of all testing shots. Initial discharges with 52 kA of plasma current (exceeding the designed value of 50 kA), 2 ms of pulse length and 50 MA/s of ramp rate have been achieved easily with pre-ionized filament.

Plasma equilibrium calculation in J-TEXT tokamak

Plasma equilibrium has been calculated using an analytical method. The plasma profiles of the current density, safety factor, pressure and magnetic surface function are obtained. The analytical solution of the Grad–Shafranov（GS） equation is obtained by the variable separation method and compared with the computed results of the equilibrium fitting code EFIT.

The Principle of Plasma Boundary Identification on HL-2A Tokamak

Plasma boundary identification is a basic task for studies on equilibrium and confinement in a divertor tokamak. With the progress on the experiments after engineering experiments, the boundary identification becomes an important issue for HL-2A. In order to satisfy the requirements of preciseness, simplified measurements and quickness, the filament current method instead of solving the equilibrium equations is used to identify plasma boundary on HL-2A. The involved principle, mathematics and the progresses, which have been made with this method, are given.

Exposure of W-TiC/Cu Functionally Graded Materials in the Edge Plasma of HT-7 Tokamak

Six-layered W-TiC/Cu functionally graded materials were fabricated by resistance sintering under ultra-high pressure and exposed in the edge plasma of HT-7 tokamak. Microstruc- ture morphologies show that the TiC particles distribute homogeneously in the W matrix, strength- ening the grain boundary, while gradient layers provide a good compositional transition from W- TiC to Cu. After about 360 shots in the HT-7 tokamak, clear surface modification can be observed after plasma exposure, and the addition of nano TiC particles is beneficial to the improvement of plasma loads resistance of W.

Radiation Losses in Ohmically Heated Plasma in the HT-7 Tokamak

Total radiation losses in ohmically heated plasma have been investigated in the HT-7 tokamak after different wall conditionings. Discharges after siliconization and boronization have been studied by using bolomitric measurements. Not only low-Z impurities but also high-Z impurities are reduced obviously after wall conditioning. The fraction of the total radiation loss to the ohmic input increases with increasing line-averaged central electron density. But it decreases with increasing the plasma current IP after wall conditionings. It is slightly lower for a boronized wall than that for a siliconized wall.

Approximate Methods for the Calculation of Plasma Internal Inductance for Circular Cross Section Tokamak

Calculation of Plasma internal inductance (li) is essential in Tokamak plasma research. Much more plasma parameters such as the plasma current density profile, magnetohydrodynamics instability, and plasma energy confinement time can be determined by using this parameter. Discrete poloidal magnetic probes along with the diamagnetic loop can be utilized in measurement of the Plasma internal inductance (li). In this paper Plasma internal inductance (li) is studied by theoretical and experimental approach for HT-7 Tokamak plasmas. The results of two methods are in good agreement with each other.