Although the deuterium and helium have almost the same mass,a Penning Optical Gas Analyzer(POGA) system on the basis of the spectroscopic method and Penning discharging has been designed on EAST,since 2014.The POGA system was developed successfully in 2015,it was the first time that EAST could detect helium partial pressure in deuterium plasma(wall conditioning and plasma operation scenario).With dedicated calibration and proper adjustment of the parameters,the minimum concentration of helium in deuterium gas can be measured as about 0.5% instead of 1% on the other tokamak devices.Moreover,the He and D_2 partial pressures are measured simultaneously.At present,the measurable range of deuterium partial pressure is 1?×?10^(-7)mbar to 1?×?10^(-5)mbar,meanwhile the range of helium is 1?×?10^(-8) mbar to 1?×?10^(-5)mbar.The measurable range can be modified by means of the adjustment of POGA system's parameters.It is possible to detect the interesting part of the gas with a time resolution of less than 5 ms(the 200 ms because of conductance of transfer pipe at present).The POGA system was routinely employed to wall conditioning and helium enrichment investigation in2015.Last but not the least,the low temperature plasma of POGA is generated by normal penning gauge Pfeiffer IKR gauge instead of Alcatel CF2 P,which has been suspended for a few years and was used for almost all the POGA systems in the world.
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.
The ion saturation current is very important in probe theory, which can be used to measure the electron temperature and the floating potential. In this work, the effects of energetic ions on the ion saturation current are studied via particle-in-cell simulations. It is found that the energetic ions and background ions can be treated separately as different species, and they satisfy their individual Bohm criterion at the sheath edge. It is shown that the energetic ions can significantly affect the ion saturation current if their concentration is greater than T_e/(γi2 T_(i2))^(1/2), where Te is the electron temperature, and γ_(i2) and T_(i2) represent the polytropic coefficient and temperature of energetic ions, respectively. As a result, the floating potential and the I V characteristic profile are strongly influenced by the energetic ions. When the energetic ion current dominates the ion saturation current, an analysis of the ion saturation current will yield the energetic ion temperature rather than the electron temperature.
The parametric decay instabilities(PDIs)of ion Bernstein wave with different input power levels are investigated via particie-in-cell simulation.It is found that the number of decay channels increases with the input power.Resonant mode-mode couplings dominate for a low input power.With increasing the input power,the nonresonant PDIs appear to dissipate the energy of the injected wave and give rise to edge ion heating.The generated child waves coupie with each other as well as the injected wave and/or act as a pump wave to excite new decay channels.As a result,the frequency spectrum is broadened with the increase of the input power.
Recent ion cyclotron resonance frequency(ICRF) coupling experiments for optimizing ICRF heating in high power discharge were performed on EAST. The coupling experiments were focus on antenna phasing and gas puffing, which were performed separately on two ports of the ion cyclotron resonance heating(ICRH) system of EAST. The antenna phasing was performed on the I-port antenna, which consists of four toroidally spaced radiating straps operating in multiple phasing cases; the coupling performance was better under low wave number ∣k_‖∣(ranging from 4.5 to 6.5). By fuelling the plasma from gas injectors, placed as uniformly spaced array from top to bottom at each side limiter of the B-port antenna, which works in dipole phasing, the coupling resistance of the B-port antenna increased obviously.Furthermore, the coupling resistance of the I-port antenna was insensitive to a smaller rate of gas puffing but when the gas injection rate was more than a certain value(>1021 s^(-1)), a sharp increase in the coupling resistance of the I-port antenna occurred, which was mainly caused by the toroidal asymmetric boundary density arising from gas puffing. A more specific analysis is given in the paper.
On the experimental advanced superconducting tokamak(EAST), a pair of voltage and current probes(V/I probes) is installed on the ion cyclotron radio frequency transmission lines to measure the antenna input impedance, and supplement the conventional measurement technique based on voltage probe arrays. The coupling coefficients of V/I probes are sensitive to their sizes and installing locations, thus they should be determined properly to match the measurement range of data acquisition card. The V/I probes are tested in a testing platform at low power with various artificial loads. The testing results show that the deviation of coupling resistance is small for loads RL?>?2.5 Ω, while the resistance deviations appear large for loads RL?
This paper reports for the first time an experimental study on the power deposition profile of the ion cyclotron range frequencies(ICRF)power depositing on electrons in HT-7.The fast Fourier transform(FFT)analysis and the break in slope(BIS)method are utilized to obtain the information of the power deposition.The results indicate that the electrons were heated directly,and the electrons absorbed around 20%of the input power of the discharge of interest.
