Spectroscopic Measurements of Impurity Spectra on the EAST Tokamak

Ultraviolet (UV) and visible impurity spectra (200～750 nm) are commonly used to study plasma and wall interactions in magnetic fusion plasmas. Two optical multi-channel analysis (OMA) systems have been installed for the UV-visible spectrum measurement on EAST. These two OMA systems are both equipped with the Czerny-Turner (C-T) type spectrometer. The upper vacuum vessel and inner divertor baffle can be viewed simultaneously through two optical lenses. The OMA1 system is mainly used for multi-impurity lines radiation measurement. A 280 nm wavelength range can be covered by a 300 mm focal length spectrometer equipped with a 300 grooves/mm grating. The Dα/Hα line shapes can be resolved by the OMA2 system. The focal length is 750 mm. The spectral resolution can be up to 0.01 nm using a 1800 grooves/mm grating. The impurity behaviour and hydrogen ratio evolution after boroniztion, lithium coating, and siliconization are compared. Lithium coating has shown beneficial effects on the reduction of edge recycling and low Z impurity (C,O) influx. The impurity expelling effect of the divertor configuration is also briefly discussed through multi-channels observation of OMA1 system.     

Characterization of the Soft X-Ray Emission from the APF Plasma Focus Device Operated in Neon

Experimental results related to soft X-ray (SXR) properties of Neon plasma on the APF plasma focus device is presented. The experiments were carried on over wide range of neon pressure and at voltages 11, 12 and 13 kV six filtered photo PIN diodes and pin-hole camera. For the charging voltages of 11–13 kV with 2.17–3.04 kJ stored energy, the optimum operating pressure in neon is found to be in the range of 3.5–5 torr. The behavior of SXR intensities was registered by different filters and found out that Al-Mylar 6 μm and Cu 10 μm has the highest and lowest amount of X-ray transmission, respectively.     

DIVIMP Modeling of Impurity Transport in EAST

Simulations of carbon impurity transport in SOL/divertor plasmas with Ohmic heating on EAST tokamak were performed using the two-dimensional（2D）Monte Carlo impurity transport code DIVIMP.The background plasmas for DIVIMP simulations were externally taken from B2.5/Eirene calculation.Besides the basic output of DIVIMP,the 2D density distributions of the carbon impurity with different ionization states and neutral carbon atoms were obtained,the2D distributions of CII and CIII emissivities from C＋1and C＋2radiation respectively were also calculated.Comparison between the measured and calculated CIII emissivities showed favorable agreement,indicating that the impurity physics transport models,as implemented in the DIVIMP code,are suitable for the EAST tokamak plasma condition.     

Comprehensive Study on Soft X-Ray Emission from Admixtures of Nitrogen and Neon Gases in the APF Plasma Focus Device

The present work is an investigation on the effect of working gas composition as well as applied voltage and operating pressure on the behavior of SXR emitted from the APF device. Three volumetric ratios(90:10), (75:25), and (50:50) of nitrogen:neon (N₂:Ne) admixture were used with operating conditions at applied voltages of 11, 12, and 13 kV and operating pressures of 1.5, 2, 2.5, 3, 3.5, 4, 4.5, and 5 torr. Using (N₂:Ne) gas mixture ratios of (90:10) and (75:25) and at applied voltage of 11 kV, the optimum pressure for maximum intensity of SXR was 3.5 torr. However, for the percentage of (50:50), it shifts to higher pressure of 4 torr. At higher applied voltages of 12 and 13 kV, the optimum pressures shift to higher values, 4 torr for both volumetric ratios (90:10) and (75:25), and 4.5 torr for the ratio of (50:50). It was found that the intensity of SXR increases with the increase of neon (Ne) percentage in the admixture of (N₂:Ne) and applied voltage. The highest intensity was for the volumetric ratio of (50:50) operating at the voltage of 13 kV. Our results illustrated that mixing neon (Ne) with nitrogen (N₂) as the working gas in the PF is a power source of SXR emission.     

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-line- space （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 0.19A at CV （2×33.73 ,h,） 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.     

Soft X-Ray Emission Optimization Study with Nitrogen Gas in a 1.2 kJ Plasma Focus

Measurement of soft x-ray emission from a low-energy plasma focus operated with nitrogen within the pressure range of 0.1–1.0 mbar is presented. The x-rays are detected by using an assembly of Quantrad Si PIN-diodes with differential filtering and with a multipinhole camera. In the 1.0–1.3 keV and 1.0–1.5 keV windows, the x-ray yield in 4 geometry is 1.03 J and 14.0 J, respectively, at a filling pressure of 0.25 mbar and the corresponding efficiencies are 0.04% and 1.22%. The total x-ray emission in 4 geometry is estimated at 21.8 J, which corresponds to the system efficiency of about 1.9%. The soft x-ray emission is found dominantly as a result of electron beam activity on the anode tip, which is confirmed by the images recorded by a pinhole camera.     

Soft X-Ray Emission in the Water Window Region with Nitrogen Filling in a Low Energy Plasma Focus

For operation of the plasma focus in nitrogen, a focus pinch compression temperature range of 74–173 eV (0.86 × 10⁶–2 × 10⁶ K) is found to be suitable for good yield of nitrogen soft X-rays in the water window region. Using this temperature window, numerical experiments using five phase Lee model have been investigated on UNU/ICTP PFF and APF plasma focus devices with nitrogen filling gas. The Lee model was applied to characterize and optimize these two plasma focus devices. The optimum nitrogen soft X-ray yield was found to be Y_sxr = 2.73 J, with the corresponding efficiency of 0.13 % for UNU/ICTP PFF device, while for APF device it was Y_sxr = 4.84 J, with the corresponding efficiency of 0.19 % without changing the capacitor bank, merely by changing the electrode configuration and operating pressure. The Lee model code was also used to run numerical experiments for optimizing soft X-ray yield with reducing L₀, varying z₀ and ‘a’. From these numerical experiments we expect to increase the nitrogen soft X-ray yield of low energy plasma focus devices to maximum value of near 8 J, with the corresponding efficiency of 0.4 %, at an achievable L₀ = 10 nH.     

Electron Cyclotron Emission Imaging on the EAST Tokamak

An upgraded electron cyclotron emission imaging (ECEI) system consisting of new optics lenses with necessary electronics for receiving and processing signals for two dimension (2D) ECEI diagnostics was installed on EAST. Hyperboloid lens were adopted in the new system to optimize the spatial resolutions. The mixers array of sixteen elements measured the plasma electron cyclotron emission at eight frequencies simultaneously, and the profiles of the electron temperature and its fluctuation in an area of 20 cm (vertical) × 6 cm (horizontal) could then be analyzed. Eevolution of sawtooth precursor and crash in EAST was observed.     

Study of Carbon Impurity Transport at SOL in EAST

Transport of carbon in the edge plasma of EAST with 啊heating power Pin of 8 MW is studied using DIVIMP code. The background plasmas for DIVIMP are taken from the results by using B2.5-Eirene code. For different plasma densities at the core-SOL interface and the different divertor operational regimes, namely low recycling, high recycling and detachment, the simulated results show that the impurity density in SOL is higher for the high recycling regime than that for the low recycling regime, while impurity density in SOL is lower for the detachment regime than that for both the low and high recycling regimes.     

Spectral Efficiency of Extreme Ultraviolet Emission from CO2Laser-Produced Tin Plasma Using a Grazing Incidence Flat-Field Spectrograph

A grazing incidence flat-field spectrograph using a concave grating was constructed to measure extreme ultraviolet (EUV) emission from a CO 2 laser-produced tin plasma throughout the wavelength region of 5 nm to 20 nm for lithography. Spectral efficiency of the EUV emission around 13.5 nm from plate, cavity, and thin foil tin targets was studied. By translating the focusing lens along the laser axis, the dependence of EUV spectra on the amount of defocus was investigated. The results showed that the spectral efficiency was higher for the cavity target in comparison to the plate or foil target, while it decreased with an increase in the defocus distance. The source’s spectra and the EUV emission intensity normalized to the incident pulse energy at 45 from the target normal were characterized for the in-band (2% of bandwidth) region as a function of laser energy spanning from 46 mJ to 600 mJ for the pure tin plate target. The energy normalized EUV emission was found to increase with the increasing incident pulse energy. It reached the optimum value for the laser energy of around 343 mJ, after which it dropped rapidly.     

Impurity Effects on Transistor Behavior at Low Temperature

Unusual low temperature behavior has been observed in NPN silicon transistors when gallium is employed as the base dopant. The current gain exhibits a pronounced "hump" near 76°K in these devices, which enables them to be studied and utilized at this low temperature. Near the hump temperature, the tolerance of the gallium doped devices to fast neutrons is observed to be approximately a factor of five greater than at room temperature. The peak in transistor gain at low temperature has been explained in terms of the change in emitter injection efficiency with temperature as a result of the different rates of carrier freeze-out in the base and emitter regions. In the model proposed, the increased radiation tolerance results from a decrease in the recombination in the emitter space charge region at low temperatures.     

X-Ray and Corpuscular Emission from Hot-Spots in Plasma-Focus Discharges

A dense magnetized plasma, as produced by high-current discharges of the Plasma-Focus (PF) type, can form locally very small (tiny) regions-so called hotspots-characterized by extreme values of basic parameters. Within such hot-spots     

Present Status of the Electron Cyclotron Emission Measurements on HT-7 and EAST

Present status of the diagnostics for electron cyclotron emission measurements on both HT-7 and EAST is reported. A 16-channel heterodyne radiometer system and a 20-channel grating polychromator, have been installed on HT-7 and EAST. A 32-channel heterodyne ra- diometer system, with a wider frequency coverage and better spatial resolution, is being built. In order to provide a reliable electron temperature profi, an in-situ absolute calibration system is currently being built. With the ECE measurements, study on the electron heat transport and the anomalous Doppler resonance is conducted.     

A High Resolution Position Sensitive Detector for Ultraviolet and X-Ray Photons

A new type of position sensitive detection system for ultraviolet and x-ray photons and for particles is described. A compact laboratory model with one-dimensional readout was constructed and tested. The full width at half maximum response to single x-rays was typically 0.13 mm, but the position determination accuracy was comparable to the channel center-to-center spacing of 0.053 mm. The detection system can be readily adapted to two-dimensional readout. Potential applications of this device for single-photon and flux counting in ultraviolet and x-ray astronomy are discussed.     

A Michelson Interferometer for Electron Cyclotron Emission Measurements on EAST

A Michelson interferometer, on loan from EFDA-JET(Culham, United Kingdom)has recently been commissioned on the experimental advanced superconducting tokamak(EAST,ASIPP, Hefei, China). Following a successful in-situ absolute calibration the instrument is able to measure the electron cyclotron emission(ECE) spectrum, from 80 GHz to 350 GHz in extraordinary mode(X-mode) polarization, with high accuracy. This allows the independent determination of the electron temperature profile from observation of the second harmonic ECE and the possible identification of non-Maxwellian features by comparing higher harmonic emission with numerical simulations. The in-situ calibration results are presented together with the initial measured temperature profiles. These measurements are then discussed and compared with other independent temperature profile measurements. This paper also describes the main hardware features of the diagnostic and the associated commissioning test results.     

Plasma Stability Evaluation Based on MHD Activity and Hard X-Ray Emission in the IR-T1 Tokamak

Determinations of the poloidal beta, internal inductance, plasma energy, plasma pressure, plasma temperature, plasma resistance, plasma effective atomic number, magneto-hydrodynamics (MHD) activity, Runaway electrons energy and energy confinement time are essential for tokamak experiments and optimized operation. Also some of the plasma information can be deduced from these parameters, such as plasma toroidal current profile, and MHD instabilities. In this contribution we investigated about measurements of some plasma parameters as well as MHD activity and Runaway electrons energy. For this purpose we used the magnetic diagnostics and a hard X-ray spectroscopy in IR-T1 tokamak. A hard X-ray emission is produced by collision of the Runaway electrons with the plasma particles or limiters. The mean energy was calculated from the slope of the energy spectrum of hard X-ray photons. In this paper in order to measure energy of the Runaway electrons, we obtained hard X-ray energy in every 5 ms intervals, from the beginning to the end of plasma. Results indicated mean energy of Runaway electrons is maximum during the 0–5 ms interval.     

Pinch Current and Soft X-Ray Yield Limitations by Numerical Experiments on Nitrogen Plasma Focus

The modified version of the Lee model code RADPF5-15a is used to run numerical experiments with nitrogen gas, for optimizing the nitrogen soft X-ray yield on PF-SY1. The static inductance L ₀ of the capacitor bank is progressively reduced to assess the effect on pinch current I _pinch. The experiments confirm the I _pinch, limitation effect in plasma focus, where there is an optimum L ₀ below which although the peak total current, I _peak, continues to increase progressively with progressively reduced inductance L ₀, the I _pinch and consequently the soft X-ray yield, Ysxr, of that plasma focus would not increase, but instead decreases. For the PF-SY1 with capacitance of 25 μF, the optimum L ₀ = 5 nH, at which I _pinch = 254 kA, Ysxr = 5 J; reducing L ₀ further increases neither I _pinch nor nitrogen Ysxr. The obtained results indicate that reducing the present L ₀ of the PF-SY1 device will increase the nitrogen soft X-ray yield.     

A Proportional Counter Spectrometer for the Study of the Solar Soft X-Ray Spectrum

An instrument, containing seven proportional counter detectors, has been designed for flight on the N.A.S.A. Orbiting Solar Observatory-D. The wavelength band 1 - 18? is divided into 24 energy intervals by means of pulse height analysis. Five detectors are employed in this wavelength range; two of them provide low sensitivity alternatives at the short wavelength end of the range. Low sensitivity detectors are selected automatically by the instrument in response to increased solar X-ray activity. Two additional detectors are employed for the 44 - 55? and 44 - 62? wavelength bands. A calibration system, employing radioactive sources, is used for "in flight" calibration of all the detectors and electronic systems. Detectors are connected sequentially to a single main amplifier and eight-channel pulse height analyser. A data compression system is employed to make economical use of the available telemetry words. High voltages for the detectors are derived from two inverter circuits which employ corona stabiliser tubes. Two redundant inverter circuits provide low voltage supplies for the instrument. A spectrum in the range 1 - 18? can be obtained every sixteen seconds.     

EAST离子回旋系统液态相移器的理论设计

对EAST离子回旋系统液态相移器的原理进行了理论分析和计算,结果表明:利用液态相移器可产生相位差,从而可用离子回旋波进行电流驱动。另外,液态相移器也可与单支节液态调配器结合使用,构成传输线阻抗匹配系统。