Results 1 - 10 of 631
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[en] Properties of the geodesic acoustic mode (GAM) density fluctuations are studied using two toroidally separated Langmuir triple-probe arrays on the top of HT-7 tokamak. The GAM scenario is identified in the potential fluctuations with the toroidally symmetric structure (n = 0) and satisfying the temperature scaling of GAM mode frequency. Some theoretical predictions about the mode features of GAM density fluctuations are verified in our experiments: the toroidal mode number of GAM density fluctuations is n = 0; its amplitude is consistent with the theoretical prediction in a factor of 2; the density and potential fluctuations of GAM is in anti-phase at the top of plasma cross-section. Strong nonlinear interactions are found between GAM density fluctuations and ambient turbulence (AT). The results support the conclusions that the envelope modulation of potential fluctuations is dominantly caused by the direct regulation of GAM in the generation processing, and the envelope modulation of density fluctuation is due to the GAM shear effect.
[en] The 35-channel Hα (λ = 656.3 nm) line intensity and impurities behaviour of a 9-channel C III, 7-channel bremsstrahlung emission, single channel O II (λ = 441.5 nm) and O V (λ = 278.1 nm) diagnostics were investigated in ac discharges on the HT-7 tokamak. The data analysis identified that the intensity of multi-channel Hα emission and impurities emission of C III (λ = 464.7 nm), O II and O V for the negative current plasma are much lower than for the positive current plasma. Lower hybrid wave plays a different role for the co-driven and anti-driven directions during current transition in ac discharges. Therefore, the emission of C III, O II and Hα behaviours is very different when the current direction transits from positive to negative, and vice versa.
[en] The inner components of the HT-7 vacuum vessel, including the belt limiters, were upgraded before the 2008 spring campaign in order to improve the power exhaust capacity in the longer pulse discharge. The longest discharge duration had been extended from 306 s to over 399 s, which demonstrated that the upgrading in the HT-7 device was very successful. In addition, the maximum temperature on the surface of the high-field-side belt limiter in the long pulse operation was not more than 100 deg. C in the long pulse operation, while the relatively high temperature rise was about 50 deg. C. The simulation and the observation of the power deposition on the belt limiter have been carried out and these results showed that the power exhaust capacity of the belt limiter could afford the long operation. The heat flux pattern on the belt limiter needs further study.
[en] Movable liquid lithium limiter (LLL) experiments with both free-surface and capillary-pore system (CPS) configurations were successively utilized on HT-7 in 2009. In the campaign of 2011, experiments with a new lithium (Li) limiter, which used a CPS configuration with a pore size of about 100 μm and active liquid Li injection from outside of HT-7, were performed. It was found that liquid Li could flow freely driven by only gravity. Confinement of the liquid Li was improved by using the CPS configuration. It was also found that plasma performance was improved due to low recycling and significantly reduced impurity radiation. However, when the CPS LLL is employed as the primary limiter the plasma disruptivity rate increases from ∼15% to ∼90% possibly due to Li emission
[en] The Institute of Plasma Physics, Chinese Academy of Sciences (IPP/CAS or ASIPP) has EAST in shaped plasma configuration and HT-7 with circular cross-section. Both machines focus on the investigation of some critical issues relating to steady-state and high performance plasma operation. Significant progress in developing technologies for long pulse operation, including CW heating and current drive, plasma control, actively water cooled in-vessel components, PFC material, wall conditioning, etc. has been achieved both in EAST and HT-7. These technologies enable significant extension of both plasma pulse length and plasma performance. EAST will be equipped with sufficient heating and current drive power in next few years for steady-state high performance plasma research. It provides unique opportunity for development of key fusion technologies and materials. The progress and future plan of TBM research on EAST is also reported.
[en] Diagnostic neutral beam (DNB), combined with spectral diagnostics, is employed to measure the ion temperature in HT-7. The factors affecting the extracted beam are studied in the experiment for the high performance diagnostic neutral beam. A 6.5 A extracted hydrogen current at 43 keV of 100 ms was obtained after optimization. The extracted beam has a proton ratio as high as 40%, and can penetrate into the core plasma after neutralization to measure the ion temperature effectively.
[en] A moveable graphite limiter has been developed in order to investigate the influence of the horizontal plasma position on the density limit in the HT-7 tokamak. The local recycling and density limit behaviour has been studied in this Letter, which shows that if plasma is shifted outwards the recycling is low, for inwards shift is high. For these set of ohmic discharges a maximum Greenwald number, NGW>1.2, was achieved, when the plasma column was repositioned more than Δ//=+2.25 cm outwards. It is important that lower local recycling discharge leads lower radiation power and higher density
[en] In an integrated structure low resistance CICC joint, current is conducted by outer cable strands coming into touch with the conductive Cu sole. So it is an important condition for satisfying joint performance that each strand of the cable inside the joint is able to come to the outermost by transposition. The author presents analysis, calculation and figures for the strand transposition. According to the twist procedures of the superconducting cable, the author computed the actual pitch of each stage cable, consecutively computed the projection of each stage cable on the axis of the cable (z axis) and the corresponding twist angle as the z coordinate changes, which is then drawn by Auto CAD. From the results shown in the figures, the minimal cable length, which enables each strand to transpose almost equally to the outermost of the cable in such a length, can be determined as the optimal joint length
[en] A special winding machine with high accuracy has just been developed and applied to the construction of HT-7U Tokamak. It is one of the critical facilities for R and D of HT-7U construction. The machine mainly consists of five parts, including a CICC pay-off spool, a four-roller correcting assembly, a four-roller forming/bending assembly, a continuous winding structure and a CNC control system with three-axis AC servo motors. The facility is used for Cable in Conduit Conductor (CICC) magnet fabrication of HT-7U. The main requirements of the winding machine are: continuous winding to reduce joints inside the coils; pre-forming CICC conductor to avoid winding with tension; suitable for all TF and PF coils of various coil shapes and within the dimension limit; improving the configuration tolerance and the special flatness of the CICC conductor. The author emphasizes on the design and fabrication of the special winding machine for HT-7U. Some analyses and techniques in winding process for trial D-shape coil are also presented