[en] After a brief review of the relevant He II-flow equations, the authors report results of their investigations of He II counterflow in the presence of net liquid flow, using a narrow-plane parallel slit. Measurements of the liquid temperature inside the flow channel indicate that, with counterflow, there is always some supercomponent vorticity present at least along a part of the channel. With higher velocities, a transition from laminar to turbulent normal-component flow was observed

[en] Full text: Fast plasma current ramp down have been used to create different high l_i target plasmas at a rate of -(0.6 - 1)MA/s in HT-7. The LHW pulse was applied before or just before the plasma current is ramped down. The IBW heating was applied to further increase the plasma beta and improve the plasma confinement. With such a scenario, the steady state value of l_i > 1.5 was obtained for a duration of several current diffusion times, which is nearly quasi steady state. The global electron heating was observed, but the electron temperature profile was strongly peaked. Highest central electron temperature up to 4.5 keV at line-averaged density of 2.2 x 10¹⁹m^-3 has been obtained by applying the 400 kW LHW at N_parallel = 2.3 and 200 kW just before Ip is ramped down from 200 kA to a 120 kA plateau at a rate of -0.8MA/s. The ion temperature in such discharge was 1.5 keV. The fraction of the non- inductive current was about 80% of Ip. A stationary improved confinement has been observed in such a high l_i plasma. No impurity accumulation was observed during the improved confinement phase. The global confinement time at lower PLHW and lower density is close to the ITER-89P scaling, but higher than the ITER-89P scaling at higher PLHW and density. The energy confinement time is increased to the level above the ITER-89P scaling when IBW was applied. The current profile effect on the global confinement has been investigated through changed of the plasma internal inductance, l_i. An increase of the energy confinement time with l_i in the range of 1.2-1.7 is observed at the constant line averaged electron density and the injected power. No MHD activity was detected in the stationary phase, and small sawteeth only existed during the ramp down phase. The high l_i mode provides an alternative operational scenario for the high performance plasma under steady state condition.(author)

[en] As a complex physics system, Tokamak plasma is strongly coupled with external poloidal field. For iron core devices, the transformer magnetization properties play the most important role. Under reasonable magnetizing current filament model, the magnetization curve was derived from external magnetic experimental data detected by flux loops and small pick-up coils. To solve the inverse problem, singular value decomposition (SVD) scheme and iterative procedures were used and proved to be effective. This paves the way for plasma current profile reconstruction, and provides a possible practical solution for in situ transformers' characteristics determination

[en] LHCD experiments have been successfully carried out in tokamaks since 1980's. In IPP Hefei there is a LHCD project including a 100 kw power level experiment on HT-6B tokamak, a 500 kW experiment on HT-6M tokamak and a 1 MW Program on the HT-7 tokamak which is a superconductive machine under construction. The experiment on HT-6B has been carried on for a year. The microwave source consists of a magnetron with 100 kW output power, 2.45 GHz frequency and pulse length 100 mSec and a multijunction antenna composed by 8 subwaveguides. LHCD experiment has been performed under the conditions of with or without inductive DC electrical field. The dependence of the coupling between the launcher and the plasma to the operation parameters, such as B_t, N_e, plasma displacement, was obtained. The driven fast electrons were measured. The efficiency of LHCD was obtained. The MHD instabilities including sawtooth oscillations changed during LHCD and the amplification or suppression of the modes depended on the conditions of LHCD. 3 refs, 12 figs

No abstract available

[en] In this paper H_α line shape in front of the limiter in HT-6M tokamak is analyzed by multi-Gaussian fitting. The energy distribution of neutral hydrogen atoms reveals that H_α radiation is contributed by Frank-Condon (FC) atoms, atoms reflected at the limiter surface and charge exchange. Dissociation of hydrogen molecules and reflection of particles at the limiter surface are dominant in edge recycling. To lower particle reflection at the limiter surface is an important issue for controlling edge recycling. The measured profiles of neutral hydrogen atom density are reproduced by particle continue equation and a simplified one-dimension Monte-Carlo simulation code. (author)

[en] The H mode achieved by applying an edge ohmic heating pulse in HT-6M shows some new features. The floating potentials and their fluctuations at different radial positions are comparable to the ohmic phase levels before and during the L-H transition and increase after the H-L transition. The time-scale of the L-H transition is of the order of 1 ms, which is unusual. During the H confinement regime the plasma current becomes peaked. The MHD instabilities terminate the H mode or cause discharge disruption. Analyses show that edge current and relevant magnetic shear play a decisive role in establishing the transport barrier. The time-scales of the L-H transition and current penetration are governed by the resistive diffusion time. (author). 13 refs, 3 figs

[en] In this paper H_α line shape in front of the limiter in HT-6M tokamak: In this paper H_α line shape in front of the limiter in HT-6M tokamak is analyzed by multi-Gaussian fitting. The energy distribution of neutral hydrogen atoms reveals that H_α radiation is contributed by Frank-Condon (FC) atoms, atoms reflected at the limiter surface and charge exchange. Dissociation of hydrogen molecules and reflection of particles at the limiter surface are dominant in edge recycling. To lower particle reflection at the limiter surface is an important issue for controlling edge recycling. The measured profiles of neutral hydrogen atom density are reproduced by particle continue equation and a simplified one-dimension Monte-Carlo simulation code. 2) Current relaxation and its roles in improved confinement: Effective Low Hybrid wave Current Driving (LHCD) and improved confinement in higher electron density have been attained in HT-6M tokamak by combining with Low Hybrid wave Heating (LHH). Experiments and code simulation show that off-axis plasma current is driven and sustained by LHW in higher electron density and relax at the time scale of resistive diffusion. Sustaining of improved confinement is strongly governed by current density profile and its relaxation. Relevant issues are also discussed. (author)

[en] Lower hybrid wave (LHW) heating has been investigated in the HT-7 superconducting tokamak. It has been observed that the plasma performance is obviously enhanced by LHW heating. The ion temperature was increased by 0.4 keV and the electron temperature by 0.3 keV. Meanwhile the central line-averaged electron density was increased from 1x10¹⁹ to 2.6x10¹⁹ m^-3. The high-energy ion tail produced by the LHW was observed from the charge-exchange spectra measured by neutral particle analysis. An ion heating efficiency of (2-3)x10¹³ eV kW^-1 cm^-3 was obtained in the experiments. The evolution of the profiles of ion temperature shows clearly an off-axis ion heating by LHW, which is in agreement with code simulations. (author)

[en] Two sets of fast-scanning heterodyne radiometer receiver systems employing backward-wave oscillators (BWOs) in 78-118 and 118-178 GHz were developed and installed for electron cyclotron emission (ECE) measurements on HT-7 superconducting tokamak. The double sideband (DSB) radiometer in 78-118 GHz measures 16 ECE frequency points with a scanning time period of 0.65 ms. The other radiometer in 118-178 GHz consists of one independent channel of DSB heterodyne receiver with intermediate frequency (IF) of 100-500 MHz and two channels of single sideband (SSB) heterodyne receiver that are sensitive to upper sideband and lower sideband individually; the IF frequency of the SSB channels are 1.5 GHz around the local oscillator frequencies with 1 GHz bandwidth. By employing a novel design, this unique radiometer measures 3 ECE frequency points at each of the 16 local oscillator frequency points in 118-178 GHz, and the full band can be swept in 0.65 ms period, thus the radiometer measures 48 ECE frequency points in 0.65 ms in principle. Each of the local oscillators' frequency points can be preset by program to meet specific physics interests. Horizontal view of ECE was installed to measure electron temperature profiles; vertically viewing optics along a perpendicular chord was also installed to study nonthermal ECE spectra. Preliminary measurement results were presented during ohmic and pellet injection plasmas