[en] A new high-resolution tangential imaging X-ray crystal spectrometer (TXCS) is described for implementation on the Experimental Advanced Superconducting Tokamak (EAST) to provide spatially and temporally resolved data on the toroidal plasma rotation velocity and on the ion and the electron temperature. These data are derived from observations of the satellite spectra of helium like argon (Ar XVII). The TXCS will provide data for all experimental conditions, which include ohmically heated discharges as well as plasmas with radio-frequency (RF) waves and neutral-beam heating. The latest experimental results show that lower hybrid waves (LHW) induce a co-current change in a toroidal rotation of up to 4/s in the L-mode plasma core region. A modification of the toroidal rotation develops on the extended plasma region and a long time scale (≥1 s). The experimental setup and the initial experimental results are presented.

[en] Plasma rotation driven by RF waves such as lower hybrid current driven (LHCD) and ion cyclotron range of frequencies (ICRF) heating is considered to be able to provide the sufficient rotation for suppressing RWM instability on ITER. Substantial rotation has been recorded on major MCF devices without external momentum input. Recent experimental rotation observations of H-mode plasmas on EAST under LHCD and ICRF were presented in this paper. It was found that co-current core rotation increase was induced for H-mode discharges. For stationary type-III H-mode, core plasma rotation was constant. Type-I ELM decreases the rotation over each burst while ion temperatures remain unchanged. Rotation increase in H-mode plasmas scales proportionally to the increase in plasma stored energy normalized by the plasma current. (author)

[en] Experiments were performed on EAST and J-TEXT for ohmic plasmas with net counter- and co-current toroidal acceleration generated by density ramping-up and ramping-down. Core toroidal rotation is increasing with T_e/T_i increasing in observed region (r/a ≤ 0.3). There may be certain correlation between rotation variation and temporal change in density fluctuation intensity. Meanwhile, it is shown that core counter-current toroidal acceleration is gradually increased with the increase of ramp rate in electron density. Direction reversal from co- to counter-current of edge C"4"+ toroidal rotation is observed by ramp up in electron density. Additionally on EAST, net co-current toroidal acceleration was also formed by LHCD or ICRF. For the current experimental results, toroidal acceleration was between -50 km/s"2 in counter-current direction and 70 km/s"2 in co-current direction. E_φ may be one of the co-current toroidal forces, which may generate co-current toroidal acceleration, and acts on the plasma as a whole. On the other hand, electron-ion toroidal friction may be one of the counter-current toroidal forces, which may produce counter-current toroidal acceleration, because electrons move in counter-current direction in order to produce a toroidal plasma current. (author)

[en] Core plasma rotation of both L-mode and H-mode discharges with ion cyclotron range of frequency (ICRF) minority heating (MH) scheme were measured with a tangential X-ray imaging crystal spectrometer on EAST. Co-current central impurity toroidal rotation change was observed in ICRF-heated L- and H-mode plasmas. Rotation increment as high as 30 km/s was generated at ∼ 1.7 MW ICRF power. Scaling results showed similar trend as the Rice scaling but with significant scattering especially in L-mode plasmas. We varied plasma current, toroidal field and magnetic configuration separately to study their effect on L-mode plasma rotation, while keeping other major plasma parameters and heating unchanged during the scanning. It was found that larger plasma current could induce plasma rotation more efficiently. A scan of toroidal magnetic field indicated that the largest rotation was obtained for on-axis ICRF heating. The comparison between lower-single-null (LSN) than (double-null) DN configurations showed that LSN discharges rendered larger rotation change for the same power input and plasma parameters. (author)

[en] A quantitative evaluation of various deconvolution methods and their applications in processing plasma emitted spectra was performed. The iterative deconvolution algorithms evaluated here include Jansson's method, Richardson–Lucy's method, the maximum a posteriori method and Gold's method. The evaluation criteria include minimization of the sum of squared errors and the sum of squared relative error of parameters, and their rate of convergence. After comparing deconvolved results using these methods, it was concluded that Jansson's and Gold's methods were able to provide good profiles that are visually close to the original spectra. Additionally, Gold's method generally gives the best results when considering all the criteria above. The applications to the actual plasma spectra obtained from the EAST tokamak with these methods are also presented in this paper. The deconvolution results with Gold's and Jansson's methods show that the effects of instruments can be satisfactorily eliminated and clear spectra are recovered. (paper)

[en] Pressure gradient driven m = 1 internal kink mode destabilization that follows an L-H transition is observed in the operational region of the EAST tokamak, which manifests in periodic oscillations in soft x-ray (SXR) and Mirnov coil signals. Using tomography with the high resolution soft x-ray detection array, we find that the rotation direction of the 1/1 kink mode is in the ion diamagnetic drift direction in poloidal cross-section. A large displacement of the hot core is attributable to the shift of the 1/1 internal kink mode. In contrast to stationary oscillations with fixed frequency, various frequency chirping behavior is observed with this 1/1 kink mode. Furthermore, we also occasionally observe that a 2/1 neoclassical tearing mode (NTM) is triggered by a 1/1 internal kink mode via mode coupling in a high-performance plasma. The spatial structure of a 2/2 mode, which is the harmonic mode of the 1/1 kink mode, is also presented in this paper. Large amounts of medium-Z impurities accumulate in the central plasma region where the 1/1 kink mode instability bursts. Finally, we also find that the frequency beating associated with a 1/1 kink mode is a consequence of plasma rotation. Based on all of these observations, we propose that the plasma pressure gradient, the driving force in kink modes, is plausibly the product of an intense concentration of impurities, which are related to plasma rotation.

[en] Characteristics of ion temperature measured with charge-exchange recombination spectroscopy (CXRS) were studied in Ohmic, lower-hybrid-wave (LHW) driven and ion-cyclotron-resonance-frequency (ICRF) heated plasmas in HT-7. The results indicate that the central ion temperature T_i0 follows the one-third power law in the product of central line-averaged density n-bar_e and plasma current I_p in Ohmic discharges and is therefore consistent with the Artsimovich scaling law T_i0 = K · (I_p · B_t · n-bar_e · R²)^1/3. It is shown that there is an appreciable increase of ion temperature during the operation with both LHW and ICRF and that the increment of ion temperature in those shots is mainly due to the energy transfer via collisions between ions and electrons rather that by direct heating of the ions.

[en] m/n = 1/1 pressure gradient driven impurity-related ideal internal kink mode locking is observed in EAST limit-cycle state H-mode plasmas. This 1/1 mode has a radial structure with no inversion around the resonance, which implies that the mode has an ideal internal kink structure. The rotation direction of the 1/1 internal kink mode, as obtained by tomography of a high-resolution multi-array soft x-ray system, is the ion diamagnetic drift velocity direction. Impurities accumulated in the central region play a vital role in mode excitation. Remarkable loss of the yield of neutron rate due to 1/1 mode is also observed. A notch at the location in the vicinity of q = 1 is also observed in the local toroidal rotation profile. Furthermore, the frequency chirping behavior of the 1/1 kink mode is related to the toroidal rotation velocity of the plasma. (brief communication)

[en] Highlights: • After the beamlines upgrade, the plasma temperature, especially the ions temperature is substantially improved and reaches 3.2keV in the simulations which is much higher than the experimental temperature in the past. • After upgrading, the neutral beam is injected in the same direction instead of the balanced-injection. The orbit loss drops sharply by 83% and the external charge exchange loss drops by 50% after the beamline upgrade. The maximum loss share is only the shine-through loss. • After the neutral beam is upgraded, the counter-IP beam is rarely seen in the later experiments (only when the plasma is changed to clockwise). The two beamlines in the same injection direction with the plasma current leads to a significant increase of the neutron rate. The neutron rate can be as high as 4.542x1014/s in the prediction. • Due to the absence of current cancellation during balanced-injection, NBCD is greatly improved after upgrade, and the NBCD can reach 100kA which greatly reduces the Ohmic current and provides an important condition for long pulse steady-state operation. The neutral beams(NB) on EAST are being upgraded according to the scheme that the beamline located on Port F will be moved to Port D and adjusted clockwise injection to counterclockwise injection(top view), while the beamline on Port A is unchanged with counterclockwise injection. The two beamlines are modified to counterclockwise injection consistent with the direction of plasma current (co-IP) instead of the primarily balanced-injection (co-IP and counter-IP). The two coming co-IP beamlines are expected to play important roles in plasma heating, neutron emission and current drive in EAST operating scenarios. The injection performances after the beam upgrade are predicted by the simulation codes ONETWO/NUBEAM and TRANSP/NUBEAM to model the discharges on EAST. After the beamlines are upgraded, the bulk ions are heated to a high temperature above 3.2 keV, which is much higher than that in the previous experiments. The orbit loss drops sharply by 83 % and the external charge exchange loss drops by 50 % after the beamline upgrade. The neutron rate induced by the upgraded beamline is greatly enhanced to the order of 10¹⁴/s with co-IP injection as opposed to the balanced-injection, and it is also heightened with the increases of plasma density and beam power. The simulation results show that it leads to a significant improvement of the beam-driven current and provides a practical condition for EAST to carry out long pulse and steady-state experiments. The assessment on the injection capabilities of the upgraded neutral beams is an important guiding reference to the subsequent EAST experiments.

[en] To increase the area of measurement, improve the temporal-spatial resolution, and enhance the stability of long time operation, poloidal X-ray crystal spectrometer (PXCS) has been upgraded in EAST. A new larger pixelated two-dimensional detector was used in poloidal system. With spatial calibration, more area of plasma can be measured. Water cooling system was deployed to keep the detector within working temperature in vacuum environment. EAST experimental results showed that high signal-noise ratio He-like argon ions spectra were successfully obtained by upgraded PXCS system. Argon ions temperature calculated by PXCS showed good agreement with results from toroidal X-ray crystal spectrometer (TXCS) for both temporal evolution and profiles. Also PXCS system has been proved to have capability to work consistently and steadily in long-pulse discharges. Upgrade of PXCS on EAST was successful. Results in EAST campaign validated the stability and reliability of the new PXCS system. (authors)