Aimed at high-confinement (H-mode) plasmas in the Experimental Advanced Superconducting Tokamak (EAST), the effect of local gas puffing from electron and ion sides of a lower hybrid wave (LHW) antenna on LHW–plasma coupling and high-density experiments with lower hybrid current drive (LHCD) are investigated in EAST. Experimental results show that gas puffing from the electron side is more favourable to improve coupling compared with gas puffing from the ion side. Investigations indicate that LHW–plasma coupling without gas puffing is affected by the density near the LHW grill (grill density), hence leading to multi-transition of low–high–low (L–H–L) confinement, with a correspondingly periodic characteristic behaviour in the plasma radiation. High-density experiments with LHCD suggest that strong lithiation gives a significant improvement on current drive efficiency in the higher density region than 2 × 1019 m−3. Studies indicate that the sharp decrease in current drive efficiency is mainly correlated with parametric decay instability. Using lithium coating and gas puffing from the electron side of the LHW antenna, an H-mode plasma is obtained by LHCD in a wide range of parameters, whether LHW is deposited inside the half-minor radius or not, implying that a central and large driven current is not a necessary condition for the H-mode plasma. H-mode is investigated with CRONOS.

A new technique for wall conditioning that will be especially useful for future larger superconducting tokamaks, such as ITER, has been successfully developed and encouraging results have been obtained. Solid carborane powder, which is non-toxic and non-explosive, was used. Pulsed RF plasma was produced by a non-Faraday shielding RF antenna with RF power of 10 kW. The ion temperature was about 2 keV with a toroidal magnetic field of 1.8 T and a pressure of 3 × 10-1 Pa. Energetic ions broke up the carborane molecules, and the resulting boron ions struck and were deposited on the first wall. In comparison with glow discharge cleaning boronization, the B/C coating film shows higher adhesion, more uniformity and longer lifetime during plasma discharges. The plasma performance was improved after ICRF boronization.

Oxidation experiments by ion cyclotron resonance discharge in a gas mix of oxygen and helium (He/O-ICR) have been performed in a HT-7 in the presence of a permanent magnetic field of 1.5-2.0 T at wall temperatures of 400 to 470 K. Two kinds of gas mixture ratios of 4 : 1 and 1 : 1 (helium to oxygen) were used. With the same filling rate of oxygen, a higher pressure of He in the He/O-ICR plasma is beneficial for removal of co-deposition and reduces oxygen retention. For the same filling pressure, both the oxygen retention rate and the removal rate of H and C atoms during the He/O-ICR experiment were lower than that in the pure O-ICR experiment. The influence of ICR power and filling pressure on hydrogen and carbon removal rates was analysed. The highest removal rates of H and C atoms up to 5.4 × 10 21 atoms/h and 7.2 × 10 21 atoms/h, respectively, were obtained in 40 kW He/O-ICR cleaning with a ratio of He/O of 4 : 1 at 9.8×10 −2 Pa. By He-ICR cleanings and baking in helium gas, most oxygen retained on the wall was sufficiently removed before the subsequent plasma discharge. High power and high pressure He-ICRF cleanings are effective in removing the oxygen retained in the walls. Plasma discharges could be recovered after a few tens of disruptive plasma discharges.

Electromagnetic cyclotron waves (ECWs) near the proton cyclotron frequency are common wave activities in the solar wind and have attracted much attention in recent years. This paper investigates 82,809 ECWs based on magnetic field data from the Solar Terrestrial Relations Observatory‐A mission between 2007 and 2013. Results show that ECWs may last for just a few seconds or incessantly for several tens of minutes. The time fraction of ECW storms among all solar wind is about 0.9%; the storms are obtained with the duration threshold of 10 min, amplitude criterion of 0.032 nT, and time separation limit of 3 min for combination of intermittent ECWs. Most of ECWs have their amplitudes less than 1 nT, while some ECWs have large amplitudes comparable to the ambient magnetic field. The distributions of the durations and amplitudes of these ECWs are characterized by power law spectra, respectively, with spectrum indexes around 4. Statistically, there seems to be a tendency that ECWs with a longer duration will have a larger amplitude. Observed ECW properties are time dependent, and the median frequency of left‐hand ECWs can be lower than that of right‐hand ECWs in some months in the spacecraft frame. The percentage of left‐hand ECWs varies in a large range with respect to months; it is much low (26%) in a month, though it frequently exceeds 50% in other months. Characteristics of ECWs with concurrent polarizations are also researched. The present study should be of importance for a more complete picture of ECWs in the solar wind.