In this paper, we report an experimental study of the effect of a m/n=−2/−1 (m, n being poloidal and toroidal mode number, separately) classical tearing mode on (intermediate, small)scale microturbulence (see the definition in section 1) in the core of an EAST L mode plasma discharge. The microturbulence at different scales k ⊥ =10, 18 and 26 cm −1 (i.e., r k 2 i , 3.6 and 5.2, respectively. Here, r i is the ion gyroradius and k ⊥ is the perpendicular wavenumber) were measured simultaneously by the EAST multi-channel tangential CO 2 laser collective scattering diagnostics. Experimental results confirm that the decrease of microturbulent Doppler shift ( p = f kv 2 t t Doppler), inversely correlated to the increase of microturbulent mean frequency (defined in equation (1)), is due to the 2/1 tearing mode. Temporal evolution of frequencyintegrated spectral power S tot of microturbulence, found to be correlated with the width of 2/1 magnetic island, suggests the modulation effect on microturbulence by the tearing mode beyond Doppler shift effect. Modulation effects on microturbulence by the tearing mode are further demonstrated by the correlation between microturbulent envelope and magnetic fluctuations.

The first plasma discharges were successfully achieved on the experimental advanced superconducting tokamak (EAST) in 2006. The sawteeth behaviours were observed by means of soft x-ray diagnostics and ECE signals in the EAST. The displacement and radius of the q = 1 surface was studied and compared with the result of equilibrium calculation. The density sawtooth oscillation was also observed by the HCN laser interferometer diagnostics. The structure of the EAST operational region was studied in detail. Plasma performance was obviously improved by the boronization and wall conditioning. It was observed that lower q a and a wider stable operating region is extended by the GDC boronization.

Schottky junctions, formed by high work function metals and semiconductors, are important devices in electronics and optoelectronics. The metal deposition in traditional Schottky interfaces usually damages the semiconductor surface and causes defect states, which reduces the Schottky barrier height and device performance. This can be avoided in the atomically smooth interface formed by two-dimensional (2D) metals and semiconductors. For better interface tailoring engineering, it is particularly important to understand various interface effects in such 2D Schottky devices under critical or boundary conditions. Here we report the fabrication and testing of three types of MoS2 devices, i.e., using PtTe2, Cr and Au as contact materials. While the Cr/MoS2 contact is an ohmic contact, the other two are Schottky contacts. The van-der-Waals interface of PtTe2-MoS2 results in a well-defined OFF state and a significant rectification ratio of 104. This parameter, together with an ideality factor 2.1, outperforms the device based on evaporated Au. Moreover, a device in the intermediate condition is also presented. An abrupt increase in the reverse current is observed and understood based on the enhanced tunneling current. Our work manifests the essential role of doping concentration and provides another example for 2D Schottky interface design.

In the HT-7 superconducting tokamak, the onset of a multifaceted asymmetric radiation from the edge (MARFE) usually occurs in the early ohmic discharges of each experimental campaign before wall conditioning. The occurrence and location of a MARFE is identified by different diagnostic systems. An improved confinement mode plasma which was induced by the MARFE is observed, and the global particle confinement time increases 1.9 times. The relaxation time between the MARFE event trigger and the L-H transition is about 1.4 ms, the following L-H transition time is 1.9 ms, and the improved confinement mode phase is maintained for about 40 ms. The MARFE cools the plasma edge, and the electron density profile is observed to become more narrow and peaked. The occurrence of a MARFE is strongly correlated with Z eff but not with the density, and it always occurs at Z eff = 3-8 ohmic discharges. In the case of a good wall condition (Z eff = 1-2), the onset of MARFEs has not been observed before reaching the Greenwald density limit.

Electron density fluctuations were measured by a CO2 laser collective scattering diagnostic system on the HT-7 tokamak. The relationship between electron density fluctuations and magnetohydrodynamics has been studied under three ohmic plasma discharge conditions (kθ = 12 cm−1): (i) only Mirnov activities, (ii) only big sawtooth activities and (iii) Mirnov activities, sawtooth activities and slight disruptions coexisting. It has been shown that electron density fluctuations obviously increase during sawtooth activities or Mirnov activities. A periodic burst in the frequency spectrum of electron density fluctuations has been observed during case (iii); detailed investigations suggest magnetic energy, the equilibrium current gradient and the heat pulse may supply sources of free energy to micro-turbulence, leading to the micro-turbulence growing rapidly and significantly.

An electromagnetic wave coherent scattering system has poor longitudinal spatial localization. However, considering the spatial variation of magnetic field lines and the perpendicularity of the short-scale turbulence to these magnetic field lines, we may be able to obtain spatially localized turbulence measurements. In this paper, we first describe the method and simulation results for localized turbulence measurements by a laser () collective scattering diagnostic on the HT-7. Second, we study the performance of electron density fluctuations between channel 1 ( ) and channel 2 ( ) during sawtooth activities. After a sawtooth crash, the signals of channel 1 change considerably and the signals of channel 2 remain nearly the same; cross-correlations between the two channels are very low (≈0.1). These experimental results verify that our laser collective scattering diagnostic does have some spatial resolution on HT-7.

The erosion loss of cathode is essential for the lifetime of magnetoplasmadynamic thruster (MPDT). In this work, an endurance test system for MPDT cathodes was designed and developed, and the erosion characteristics, erosion rate and erosion mechanism of the cathode were studied using the system under vacuum condition. The WCe20 hollow cathode was selected to carry out the long-term erosion of 540 h with the argon propellant supply flow rate of 40 ml/min, the input current of 25 A, and the central magnetic field intensity of 96 Gs. In order to predict the theoretical service life of cathode, a steady state erosion numerical model was established. The calculation results show that the total erosion rate of sputtering and evaporation is 11.58 mg/h, which is slightly smaller than the test data of the average cathode corrosion rate of 12.70 mg/h in the experiment, because the experimental value includes start-up erosion rate.