Spectral Analysis in EUV Range for Study of Core Impurity Behavior in HL-2A

Extreme ultraviolet(EUV) spectroscopy has been developed for impurity diagnostics in HL-2A tokamak. The EUV spectrometer consists of an entrance slit,a holographic varied-linespace(VLS) grating,a back-illuminated charge-coupled device(CCD) and a laser light source for optical alignment. Spectral lines in wavelength region of 20-500 A observed from HL-2A plasmas were analyzed to study the impurity behavior. Spectral and temporal resolutions used for the analysis were 0.19 A at CV(2×33.73 A) and 6 ms,respectively. It was found that carbon,oxygen and iron impurities were usually dominant in the HL-2A plasma. They almost disappeared when the siliconization was carried out. Although the EUV spectra were entirely replaced by the silicon emissions just after the siliconization,the emissions were considerably decreased with accumulation of discharges. Aluminum and neon were externally introduced into the HL-2A plasma based on laser blow-off(LBO) and supersonic molecular beam injection(SMBI) techniques for a trial of the impurity transport study,respectively. The preliminary result is presented for time behavior of EUV spectral lines.

Analysis Scheme for Density Modulation Experiments to Study Particle Confinements

Density modulation experiments are powerful experimental schemes for the studyof particle transport.The diffusion coefficients(D)and convection velocity(V),which cannot beevaluated from the particle balance in the equilibrium state,can be obtained separately.Further,the estimated values of D and V are determined independent of the absolute value of the particlesource rate,which is difficult to obtain experimentally.However,the sensitivities and interpreta-tion of D and V from the modulation experiments need to be considered.This paper describesnumerical techniques for solving the particle balance equation of the modulation components.Ex-amples of the analysis are shown regarding the data of LHD experiments,and the results of themodulation experiments are discussed.

Reference Design of ICRF Antenna for EAST

An antenna array suitable for plasma heating and current drive has been designed for the ion cyclotron resonance frequency range (ICRF) heating on the EAST superconducting tokamak. The ICRF heating is planned to operate in a frequency range of 30 MHz to 80 MHz and hence the antenna geometry is optimized for 55 MHz. The design is based on the conventional strap antenna element. The coupling properties of the antenna are calculated with a slab model of the plasma for the antenna simulation. The coupling code is extended for the analysis of the toroidal antenna array separated by septa.

Development of a Heavy Ion Bearn Probe for Measuring Electrostatic Potential Profile and Its Fluctuation in LHD

用一台 3-MV 双人脚踏车加速器的一根重离子横梁探针(HIBP ) 在大螺旋状的设备(LHD ) 上被安装了。在核心血浆的静电的潜力能在多达 3 T 的 toroidal 磁场力量下面被测量。由使用 HIBP，到离子根的从电子根的潜在的侧面的转变在核心血浆被观察在期间斜面起来电子密度。潜在的变化是也测量的电子回旋加速器电流开车(ECCD ) 。二种典型变化被观察。一个人是 reversed-shear-induced Alfv é n eigenmode (RSAE ) ，其频率在旋转变换侧面，和其它的进化期间变化，与经常的 geodeisc 声学的模式(鲸鱼群) 频率。

High Power RF Transmitters for ICRF Applications on EAST

An Ion Cyclotron Range of Frequency (ICRF) system with a radio frequency (RF) power of 4×1.5 MW was developed for the Experimental Advanced Superconducting Tokamak (EAST).High RF power transmitters were designed as a part of the research and development (R&D) for an ICRF system with long pulse operation at megawatt levels in a frequency range of 25 MHz to 70 MHz.Studies presented in this paper cover the following parts of the high power transmitter:the three staged high power amplifier,which is composed of a 5kW wideband solid state amplifier,a 100kW tetrode drive stage amplifier and a 1.5MW tetrode final stage amplifier,and the DC high voltage power supply (HVPS).Based on engineering design and static examinations,the RF transmitters were tested using a matched dummy load where an RF output power of 1.5MW was achieved.The transmitters provide 6MW RF power in primary phase and will reach a level up to 12MW after a later upgrade.The transmitters performed successfully in stable operations in EAST and HT-7 devices.Up to 1.8MW of RF power was injected into plasmas in EAST ICRF heating experiments during the 2010 autumn campaign and plasma performance was greatly improved.

Linear Gyro-Kinetic Response Function for Zonal Flows

A linear response function for zonal flows is obtained by solving the gyro-kineticequation. This is an extension of a previous work which adopted the method of 'integrating alongparticle orbit' to solve the drift kinetic equation. The formula derived in this paper is used tocalculate the dispersion relation of geodesic acoustic mode, which is then compared with that ofthe gyro-kinetic analytic formula.

Asphericalizing the Light Collection Mirror for the 200-Point Thomson Scattering Diagnostic Installed on the Large Helical Device

Shown is a possibility to make the image of a laser beam over a distance of 2.5 m,formed by the spherical multi-segment mirror installed in LHD,twice sharper by suitably adjustingthe inclination of each segment mirror,which is equivalent to making the mirror surface aspherical.This will further enhance the attractiveness of a mirror-based Thomson scattering system.

Measurement of the Electron Bernstein Wave Emission with One of the Power Transmission Lines for ECH in LHD

Possibility of the measurement of radiated waves derived from the thermally emittedelectron Bernstein wave(EBW)is numerically investigated based on the assumption of the superdense core(SDC)plasma generated in LHD.EBW that is thermally emitted in the electroncyclotron resonance(ECR)layer may couple with the electromagnetic wave and be emitted to thevacuum via the EBW-extraordinary-ordinary(B-X-O)mode conversion process.We consider theuse of one of the transmission lines for electron cyclotron heating(ECH)in LHD as a receivingsystem of the emission.It is derived that the waves in the fundamental cyclotron frequency rangeare emitted as the EBW near their upper hybrid resonance(UHR)layer outside the last close fluxsurface(LCFS).On the other hand,waves in the second harmonics cyclotron frequency range areemitted in the core region.It means that successful measurement of waves of the second harmonicfrequency range emitted from extremely high dense core plasma with setting an aim angle forreceiving indicates a possibility of the second harmonic ECH by EBW in the core region withsetting the same aim angle and the same polarization for launching.

High Density Plasma Heating by EC-Waves Injected from the High-Field Side for Mode Conversion to Electron Bernstein Waves in LHD

To realize an excitation of electron Bernstein waves (EBW) via mode conversion from X-mode waves injected from the high magnetic field side (HFS), new inner-vessel mirrors were installed close to a helical coil in the large helical device (LHD). 77 GHz electron cyclotron (EC) wave beams injected from an existing EC-wave injection system toward the new mirror are reflected on the mirror so that the beams are injected to plasmas from HFS. Evident increases in the electron temperature at the plasma core region and the plasma stored energy were observed by the HFS beam injection to the plasmas with the line-average electron density of 7.5×10 19 m 3 , which is slightly higher than the plasma cut-off density of 77 GHz EC-waves, 7.35×10 19 m 3 . The heating efficiency evaluated from the changes in the time derivative of the plasma stored energy reached ～70%. Although so far it is not clear which is the main cause of the heating effect, the mode-converted EBW or the X-mode wave itself injected from the HFS, an effective heating of high-density plasma over the plasma cut-off of EC-wave was successfully demonstrated.

Observation of Magnetic Dipole Forbidden Transitions in LHD and Its Application to Burning Plasma Diagnostics

Magnetic dipole forbidden (M1) transition was studied in large helical device (LHD)and F-, Si- and Ti-like M1 transitions are successfully observed for highly ionized Ar, Kr, Mo andXe ions. The wavelengths measured in visible range for the heavy elements, which are carefullydetermined with extremely small uncertainties of 0.02～0.05 A as a standard wavelength of usualelectric dipole (E1) plasma emissions, are compared with theoretical predictions. The result showsa good agreement with recent Hatree-Fock calculation including semi-empirical adjustment. TheM1 intensity for the F-like ions is examined by analyzing the intensity ratio of M1 to E1. Densitydependence of the ratio is experimentally verified by comparing with collisional- radiative modelcalculation on level population. The M1/E1 line ratio for the F-like ions is applied to the(He^(2+)) particle diagnostics in ITER, in which a steady-state operation of burning plasmas basedon D-T fusion reaction is expected with α particle heating. Unfortunately, the present estimationsuggests a negative result for the α particle measurement because the ratio is largely enhanced bythe collisional excitation with bulk ions due to high ion temperature of ITER of 10 keV as assumedand the resultant effect of the collisional excitation with α particles becomes less. Meanwhile, theM1 transition, in particular, Ti-like WLⅢ (W^(52+)) transition (3627 A) emitted in visible range,is very useful for diagnostics of the impurity behavior and the core plasma parameters in ITER.

Design of High Power DC Break For ICRH Of EAST

1.5MW Ion Cyclotron Wave Heating system was developed, the transmitter and the antenna both have their ground loops, which will severely perturb the system's normal operation. To avoid perturbation, a DC break was designed. The S parameter and the VSWR (voltage standing wave ratio) of incident port were calculated; the thermal effect caused by conductor loss and dielectric loss was analyzed.

Investigation of Experimental Con6guration for Electron Bernstein Wave Heating on LHD

为在 LHD 上由使用加热的存在电子回旋加速器(ECH ) 加热天线的电子伯恩斯坦波浪(EBW ) 的试验性的配置的调查被执行。由使用在更低的港口安装的一条天线，指导倾斜的发射非凡(X---) 从高磁场方面(HFS ) 的模式是可得到的。自从折射索引的平行部件(因为磁场的不同类， N ||) 在繁殖期间变化，当发射 X 模式穿过甚至 N || 是的基本电子回旋加速器回声(ECR ) 层时， N || 能是零中午零开始。处于如此的一个条件，如果电子密度在某个水平上面，没有外面被抑制并且能对在 Doppler 被吸收的 EBW 变换模式，倾斜地发射的 X 模式能传递基本 ECR 层转移 ECR 层。由使用在水平港口安装的一条天线，向在稠密上的血浆的从更低的磁场方面(LFS ) 的倾斜的发射是可得到的。经由平常的模式(O) 的模式变换过程的 EBW 的刺激非凡的模式(X) 电子伯恩斯坦波浪(B) 被期望， O 模式向一个适当方向发射。O-X-B 模式变换率和力量免职的区域被改变磁场力量和发射方向调查。调查的结果建议在核心区域的有效加热由使用存在天线是困难的。发射天线的最后的镜子的重新整理可以被需要。

Refueling for Steady-State Plasma by Repetitive Pellet Injection in Large Helical Device

A repetitive pellet injector has been developed for investigation of refueling issues towards the steady-state operation in Large Helical Device (LHD). Continuous operation of more than 10000 pellet launching at 10 Hz has been demonstrated. The maximum repeating rate is 11 Hz. No technical constraint for longer operation has been found. The reliability of pellet launch has exceeded 99.9%. The initial application to the NBI-heated plasmas has been successful in the last experimental campaign of LHD. Although the pulse length is limited by the operational constraint of NBI, the plasma with a density of 8×10^19 m^-3 has been sustained for 2 s by the pellet injection at 10 Hz. A prospect for the future experiment is discussed on the basis of the initial result.

Predictions for EAST Divertor Performance

A detailed study of the divertor performance in EAST has been performed for bothits double null(DN)and single null(SN)configurations.The results of application of the SOLPS(B2-Eirene)code package to the analysis of the EAST divertor are summarized.In this work,we concentrate on the effects of increased geometrical closure and of magnetic topology variationon the scrape-off layer(SOL)and divertor plasma behavior.The results of numerical predictionsfor the EAST divertor operational window are also described in this paper.A simple Core-SOL-Divertor(C-S-D)model was applied to investigate the possibility of extending plasma operationalspace of low hybrid current drive(LHCD)experiments for EAST.

Soft x-ray tomographic reconstruction of Heliotron J plasma for the study of magnetohydrodynamic equilibrium and stability

The preparation for an experimental soft x-ray tomography study on the Heliotron J (H-J) machine is carried out,with the objectives of evaluating the capability of the current soft x-ray tomographic system in terms of the identification of different mode structures and their poloidal rotation,and the axis shift with different plasma and machine parameters,and fixing the physics goals for the experimental study.These preparations were carried out via a simulated soft x-ray data set arising from different plasma conditions,such as magnetic islands,low beta and high beta.Soft x-ray tomography (SXT) is performed by the discrete pixel method including singular value decomposition and Phillips-Tikhonov regularization,to obtain clear and smooth images.The H-J soft x-ray tomography results from simulated soft x-rays for the equilibrium H-J plasma sensed the magnetic axis shift clearly and an estimate was also achieved.Successful reconstruction for mode structure m =1/n =1 was obtained along with the realization of the poloidal rotation of the structure.The reconstruction for the m =2/n =1 mode was not very clear for the current soft x-ray diagnostic design.Effective mode identification was not possible due to the lack of measurements.The SXT from the current soft x-ray diagnostic on H-J,the magnetic axis shift can be estimated and the m =1/n =1 mode can be studied.Study of higher poloidal modes is difficult with the current design.

Formation of Edge Transport Barriers by L-H Transition and Large Reversed Plasma Current on LHD

On the Large Helical Device(LHD)where nested magnetic surfaces are surroundedby the ergodic field layer,edge transport barrier(ETB)was produced in neutral-beam-injection(NBI)heated plasmas through transition and non-transition processes.The former case is the ETBformation by L-H transition,where characteristics of L-H transition observed in a tokamak plasmaare clearly recognized.The confinement improvement is the modest(～10%),compared with theISS95 international stellarator scaling.The threshold power for the transition is comparable orslightly lower than the ITER scaling law established by tokamaks and compact tori.The ETBis formed inside the ergodic field layer of the vacuum field.The ETB formation destabilizes edgecoherent modes such as m/n=1/1,2/3 and 1/2,of which rational surfaces are in the magnetichill.The formed ETB is partially and transiently destroyed by these coherent edge MHD modesand edge localized modes(ELMs)typically observed in Hα signals.The latter ETB is observed ina plasma with large reversed NBI-driven current more than 100 kA at Bt = 1 T.In these plasmas,the edge magnetic shear is enhanced by the current and the rotational transform in the core regionis expected to be appreciably reduced.Thus reduced rotational transform in the plasma centralregion will enhance outward heat and particle fluxes toward ergodic edge layer.The ETB withsteep electron temperature gradient up to～5 keV/m is formed by blocking enhanced outwardheat flux.

Induced Charge of Spherical Dust Particle on Plasma-facing Wall in Non-uniform Electric Field

Induced charge of a spherical dust particle on a plasma-facing wall was investigatedanalytically,where non-uniform electric field was applied externally.The one-dimensional non-uniform electrostatic potential was approximated by the polynomial of the normal coordinatetoward the wall.The bipolar coordinate was introduced to solve the Laplace equation of the in-duced electrostatic potential.The boundary condition at the dust surface determines the unknowncoefficients of the general solution of the Laplace equation for the induced potential.From theobtained potential the surface induced charge can be calculated.This result allows estimating theeffect of the surrounding plasma,which shields the induced charge.