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The effect of sheared E × B flow on the blob dynamics in the scrape-off layer (SOL) of HL-2A tokamak has been studied during the plasma current ramp-up in ohmically heated deuterium plasmas by the combination of poloidal and radial Langmuir probe arrays. The experimental results indicate that the SOL sheared E × B flow is substantially enhanced as the plasma current exceeds a certain value and the strong sheared E × B flow has the ability to slow the blob radial motion via stretching its poloidal correlation length. The locally accumulated blobs are suggested to be responsible for the increase of plasma density just outside the Last Closed Flux Surface (LCFS) observed in this experiment. The results presented here reveal the significant role played by the strong sheared E × B flow on the blob dynamics, which provides a potential method to control the SOL width by modifying the sheared E × B flow in future tokamak plasmas.

Recent observations in HL-2A tokamak give new experimental evidences of energetic particle mode (EPM) avalanche. In a strong EPM burst, the mode structure propagates radially outward within two hundred Alfvén time, while the frequency of the dominant mode changes self-consistently to maximize wave-particle power exchange and mode growth. This suggests that significant energetic particle transport occurs in this avalanche phase, in agreement with theoretical framework of EPM convective amplification. A simplified relay runner model yields satisfactory interpretations of the measurements. The results can help understanding the nonlinear dynamics of energetic particle driven modes in future burning plasmas, such as ITER.

Mitigation of long-lived mode (LLM) by lower hybrid wave (LHW) is recently achieved on the HL-2A tokamak. The LLM changes from a typical steady-state to a fishbone-like frequency-chirping characteristic, and its higher poloidal harmonics disappear when LHW is injected into toroidal plasma. It is found that density fluctuation declines during this process while the total neutron count increases gradually. Those evidences indicate there is a mitigation effect of LHW on LLM, and the underlying mechanism can be explained as follows. On one hand, high power LHW firstly causes a drop in toroidal rotation and then results in decline of E × B shear, which is unfavorable for the maintenance of the internal transport barrier. The resulting relaxation of ion temperature gradient enhances thermal transport and leads to a drop of ion temperature at the core region. Thus, the plasma pressure becomes flattened and finally contributes to the mitigation of highly saturated internal mode. On the other hand, hybrid simulation by M3D-K suggests that the off-axis LHW can also reduce the grower rate of LLM via changing safety factor and magnetic shear.

The effect of isotope mass on the interaction between turbulence and geodesic acoustic mode (GAM) zonal flows has been investigated in HL-2A ohmically heated deuterium (D) and hydrogen (H) plasmas using a double-step Langmuir probe array. The experimental results indicate that the level of GAM zonal flows and the turbulence eddy size together with the eddy tilting angle are all increased in the edge region in D plasmas compared to those in H plasmas under similar discharge parameters involving plasma current, magnetic field and line-averaged density. Evidence shows that in D plasmas, the nonlinear energy transfer is the main cause of the stronger excitation of GAM zonal flows, which extract more energy from ambient turbulence and, consequently, lead to lower turbulent transport and better confinement in D plasmas. The experimental findings may contribute to the understanding of the isotopic physics and associated turbulent transport in tokamak plasmas.

The effect of impurity ions on the coupling between geodesic acoustic mode (GAM) zonal flow and local turbulent transport has been studied using a Langmuir probe array in HL-2A ohmically heated deuterium plasmas. The experimental results illustrate that both the frequency and amplitude level of the GAM zonal flow significantly reduce with increase in the carbon ion concentration, which is qualitatively consistent with theoretical predictions (Xie et al 2018 Plasma Phys. Control. Fusion 60 025015). Meanwhile less energy is transferred from turbulence to GAM zonal flow due to the reduction in tilting and stretching of the turbulent vortex. Consequently, the impurity ions enhance the turbulence and turbulent transport owing to the reduced GAM zonal flow, as demonstrated by experiment. The experimental results presented here therefore reveal the dual roles played by impurity ions in the dynamics of GAM zonal flow, which could contribute to the understanding of inherent mechanisms governing turbulent transport in the presence of impurity ions.

In this work, the coupling among several MHD modes across different spatial regions, including the neoclassical tearing mode (NTM) and two branches of Alfvén eigenmode (AE) in the core and the edge localized mode (ELM), has been investigated in the HL-2A high beta H-mode plasmas. The NTMs induce a saturated m/n = 1/1 helical core (m and n are the poloidal and toroidal mode numbers, respectively) through the ‘magnetic-flux pumping’ effect. The ELM crash results in a rapid (

Since the last IAEA Fusion Energy Conference in 2018, significant progress of the experimental program of HL-2A has been achieved on developing advanced plasma physics, edge localized mode (ELM) control physics and technology. Optimization of plasma confinement has been performed. In particular, high-β N H-mode plasmas exhibiting an internal transport barrier have been obtained (normalized plasma pressure β N reached up to 3). Injection of impurity improved the plasma confinement. ELM control using resonance magnetic perturbation or impurity injection has been achieved in a wide parameter regime, including types I and III. In addition, impurity seeding with supersonic molecular beam injection or laser blow-off techniques has been successfully applied to actively control the plasma confinement and instabilities, as well as plasma disruption with the aid of disruption prediction. Disruption prediction algorithms based on deep learning are developed. A prediction accuracy of 96.8% can be reached by assembling a convolutional neural network. Furthermore, transport resulting from a wide variety of phenomena such as energetic particles and magnetic islands has been investigated. In parallel with the HL-2A experiments, the HL-2M mega-ampere class tokamak was commissioned in 2020 with its first plasma. Key features and capabilities of HL-2M are briefly presented.

A new cross-polarization scattering (CPS) diagnostic has been developed on HL-2A, which aims to measure the local magnetic fluctuation inside the plasma. It is based on the scattering of an incident microwave beam into the perpendicular polarization by magnetic fluctuations. The CPS diagnostic has been designed in the Q-band (33–50 GHz), which consists of the electronic system, quasi-optical, and polarization rejector. The ray-tracing code is used to simulate the propagation of the probe and scattered rays. To test the performance of the quasi-optical system, a 3D test platform is built and detailed test results are shown. Two methods are developed for polarization rejector on HL-2A: wire grid polarizer and dual-polarized horn antenna (DPHA). The laboratory test result shows that the polarization rejection of both methods is better than 30 dB, which meets the needs for magnetic fluctuation detection. In the future, the CPS diagnosis will be used to study the electromagnetic turbulence behavior in the high-performance plasma of the HL-2A tokamak.

Collective Thomson Scattering (CTS) diagnostic technique has great potential in measuring velocity distribution of fast ions in magnetically confined fusion devices. Here we present design and development of a 105 GHz fast ion CTS system on HL-2A tokamak. The gyrotron with high power transmission/antenna is used to generate a probe beam. To better focus the scattering beam and effectively avoid the stray contamination, a W-band Cassegrain antenna is utilized to receive the scattering beam from the central chord. The scattering signal is estimated at 10–30 eV and the frequency broadening is less than 2 GHz for typical HL-2A plasmas. To pick out the weak signals, a multi-channel receiver system with working frequency of 103–107 GHz is developed. The steerable direction of probe beam enables that the scattering volume can move from core to edge, with which the spatial resolution range varies from 70 mm at low field side to 260 mm at high field side.

An ion cyclotron emission (ICE) diagnostic, which is based on a B-dot probe, has been recently designed and installed on HL-2A tokamak. The diagnostic is used to study various high-frequency magnetic field fluctuations which can be excited by energetic ions and runaway electrons in the plasma. The ICE diagnostic on HL-2A includes a high-frequency B-dot probe, direct current (DC) block, radio frequency splitters, filter bank and power detectors. The filter bank is composed of 16 channels filters, with the center frequency covering from 10 to 160 MHz, 10 MHz step length and 8 MHz bandwidth. The log detectors with a large dynamic range (from −80 dBm to −20 dBm) are used to detect the bandpass power. Test results of the B-dot probe, filters and power detectors are shown. The signals can also be sampled with a fast analog-to-digital converter with a 14-bit depth, 100 MHz bandwidth and 250 MSample/s sampling rate.

Since the first performance of the HCOOH laser Polarimeter-Interferometer (PIer) in 2015 HL-2A experimental campaign, several optical technologies have been applied to improve the PIer system, including: (1) Optical alignment of the HCOOH laser at the long distance was implemented by the optical setup integrated by a lens and a high-sensitivity Pyroelectric Array Camera. (2) Due to application of the orthogonal waves transmission in the PIer system, some spurious intermediate frequency (IF) might be generated in the interferometry beat signal. For this problem, an effective optical adjustment method based on the single-polarization response characteristic of the Schottky diode detector was summarized in practice. (3) For double-passing type Faraday-effect polarimeter, analysis indicated that the severe oscillation disturbance in Faraday rotation angle was mainly caused by the stray lights or the feedback lights. Experimental results on HL-2A successfully validated that the unwanted feedback lights mainly came from the detector surface and was able to be effectively suppressed by the optic-isolator which was composed of a polarizer and a quarter-wave plate.

In this article we present the design of a phase contrast imaging (PCI) system on the HL-2A tokamak. This diagnostic is developed to infer line integrated plasma density fluctuations by measuring the phase shift of an expanded CO2 laser beam passing through magnetically confined high temperature plasmas. This system is designed to diagnose plasma density fluctuations with the maximum wavenumber of 15 cm−1. The designed wavenumber resolution is 2 cm−1, and the time resolution can reach 2 μs. The broad kρs ranging from 0.2 to 3 makes it suitable for turbulence measurement.

The impact of a low frequency MHD mode crash on triggering the H-mode has been studied in detail on the HL-2A tokamak. The mode manifests fishbone characteristics with a precession frequency f ≈ 14 – 19 kHz . The abrupt mode crash evokes substantial energy release from the core to the plasma boundary and hence increases the edge pressure gradient and E r × B flow shear, which further suppresses turbulence and leads to confinement improvement into the H-mode. Under the same NBI heating (∼1 MW), the I-phase plasma transits into H-mode with a rapid MHD mode crash while it returns to the L-mode without the presence of the mode in the I-phase. With increasing heating power by the ECRH added to the NBI, the MHD mode disappears. The statistical result shows that with the MHD mode crash the heating power for accessing the H-mode is significantly lower than that without the mode crash. All these facts reveal that the MHD mode crash in the I-phase plays a critical role in trigging the I → H transition at marginal heating power. In addition, it has been found that with the same NBI power heating, the magnitude of the mode (crash) increases with increasing plasma density, implying larger energy release being needed to access the H-mode for higher density plasmas.

Perturbative particle transport experiment has been performed in the HL-2A tokamak by using supersonic molecular beam injection (SMBI) as an external particle source. The spatiotemporal evolution of edge density perturbation is traced and the particle source and the flux-gradient relation are obtained experimentally. The flux-gradient relation is found to be far from the diffusive model and three different transport processes are revealed, including pinch-dominant process, diffusion-pinch process and intermittent decays., Nuclear physics, Plasma physics, Tokamak, Plasma, Particle transport, Supersonic molecular beam injection

The impact of supersonic molecular beam injection (SMBI) fuelling on plasma turbulence and shear flows, which forms a self-consistent state, has been studied in the HL-2A tokamak. The SMBI flattens the shear layer by collisional flow damping and increases the turbulence intensity. It is found that the SMBI can enhance the nonlinear regulation dynamics and acts as an external tool for turbulence quench via stimulating two dynamic processes. The SMBI-stimulated nonlinear interactions facilitate the L-H transition at the marginal heating power for accessing the H-mode. The effective reduction of the H-mode power threshold by SMBI is demonstrated. The result suggests that the SMBI could be a general tool for realization of controllable L-H transition via reducing the H-mode power threshold in future devices.

For the first time supersonic molecular beam injection (SMBI) and cluster jet injection (CJI) were applied to mitigate edge-localized modes (ELMs) in HL-2A successfully. The ELM frequency increased by a factor of 2–3 and the heat flux on the divertor target plates decreased by 50% on average after SMBI or CJI. Energetic particle induced modes were observed in different frequency ranges with high-power electron cyclotron resonance heating (ECRH). The high frequency (200–350 kHz) of the modes with a relatively small amplitude was close to the gap frequency of the toroidicity-induced Alfven eigenmode. The coexistent multi-mode magnetic structures in the high-temperature and low-collision plasma could affect the plasma transport dramatically. Long-lived saturated ideal magnetohydrodynamic instabilities during strong neutral beam injection heating could be suppressed by high-power ECRH. The absolute rate of nonlinear energy transfer between turbulence and zonal flows was measured and the secondary mode competition between low-frequency (LF) zonal flows (ZFs) and geodesic acoustic modes (GAMs) was identified, which demonstrated that ZFs played an important role in the L–H transition. The spontaneously generated E × B shear flow was identified to be responsible for the generation of a large-scale coherent structure (LSCS), which provided unambiguous experimental evidence for the LSCS generation mechanism. New meso-scale electric potential fluctuations (MSEFs) at frequency f ∼ 10.5 kHz with two components of n = 0 and m/n = 6/2 were also identified in the edge plasmas for the first time. The MSEFs coexisted and interacted with magnetic islands of m/n = 6/2, turbulence and LF ZFs.

Author(s): Xu, M; Duan, XR; Liu, Y; Song, XM; Liu, DQ; Wang, YQ; Lu, B; Yang, QW; Zheng, GY; Ding, XT; Dong, JQ; Hao, GZ; Zhong, WL; Shi, ZB; Yan, LW; Zou, XL; Liu, YQ; Chen, W; Xiao, GL; Zhang, YP; Jiang, M; Hou, YM; Cheng, J; Liang, AS; Bai, XY; Cao, JY; Cao, Z; Chen, HT; Cui, CH; Cui, ZY; Delpech, L; Diamond, PH; Ekedahl, A; Feng, BB; Giruzzi, G; Gong, SB; He, HM; Hoang, T; Huang, M; Huang, Y; Ida, K; Inagaki, S; Isobe, M; Itoh, K; Itoh, SI; Ji, XQ; Ke, R; Kobayashi, M; Lei, GJ; Li, B; Li, GS; Li, HJ; Li, JQ; Li, Q; Li, Q; Li, XD; Li, YG; Li, Y; Mao, WC; Mazon, D; McKee, GR; Morita, S; Nie, L; Peng, JF; Peysson, Y; Rao, J; Ren, Y; Tynan, GR; Wang, HX; Wang, QM; Wei, HL; Xia, F; Xiao, XP; Xuan, WM; Yan, Z; Yao, K; Yu, LM; Yu, Y; Yu, DL; Yuan, BD; Yuan, BS; Zhang, JH; Zhou, Y; Liu, Y | Abstract: The mission of HL-2A is to explore the key physical topics relevant to ITER and to the advanced tokamak operation (e.g. the operation of future HL-2M), such as the access of H-mode, energetic particle physics, edge-localized mode (ELM) mitigation/suppression and disruption mitigation. Since the 2016 Fusion Energy Conference, the HL-2A team has focused on the investigations on the following areas: (i) pedestal dynamics and L-H transition, (ii) techniques of ELM control, (iii) turbulence and transport, (iv) energetic particle physics. The HL-2A results demonstrated that the increase of mean shear flow plays a key role in triggering L-I and I-H transitions, while the change of flow is mainly induced by the ion pressure gradient. Both mitigation and suppression of ELMs were realized by laser blow-off seeded impurity (Al, Fe, W). The 30% Ne mixture supersonic molecular beam injection seeding also robustly induced ELM mitigation. The ELMs were mitigated by low-hybrid current drive. The stabilization of m/n = 1/1 ion fishbone activities by electron cyclotron resonance heating was found on the HL-2A. A new m/n = 2/1 ion fishbone activity was observed recently, and the modelling indicated that passing fast ions dominantly contribute to the driving of 2/1 fishbone. The non-linear coupling between the toroidal Alfven eigenmode and tearing mode (TM) led to the generation of a high frequency mode with the toroidal mode number n = 0. The turbulence was modulated by TM when the island width exceeds a threshold and the modulation is localized merely in the inner area of the islands. Meanwhile, turbulence radial spread took place across the island region.

Two different directions of scale-to-scale energy transfer that corresponds to forward and inverse energy cascades, respectively, were clarified in toroidal plasma turbulence by means of experimental analysis. In the present work we first report the evidence that the turbulence dominated by broad wavenumber spectrum was developed under the action of forward (direct) energy cascade in a reversed field pinch (RFP) plasma, while the generation of GAM zonal flow (ZF) was related with the energy concentrating into low frequency region from higher frequency region due to inverse energy cascade in a tokamak plasma. The two evidences are compared. The results indicate a modulation mechanism in turbulence which is relative to the generation or development of specific turbulent flows. This hints a correlation between energy transfer and the development of toroidal plasma turbulence.

Neutral beam (NB) attenuation and beam emission are important aspects for Beam Emission Spectroscopy diagnostic on magnetic confinement devices. In this article, we present the simulation of beam attenuation and beam emission in typical HL-2A discharge scenarios, i.e. Low mode (L-mode) and High mode (H-mode) discharges. Not only the NB attenuation, but also the plasma density and electron temperature determine the beam emission intensity. The pronounced beam emission peak ranges from ρ =r/a=0.7 to 0.9 in H-mode discharge, while it has a much lower and broader peak in L-mode discharge. 16 BES channels have been developed on HL-2A tokamak and the experimentally diagnosed data fit well with the simulation, showing not only the validation of this simulation but also the high performance of developed BES channels. And it provides a reference for the upgrading of a 64-channel BES system.

Isotope effects on instabilities driven by ion temperature gradient (ITG) and impurities in tokamak plasmas in the presence of tungsten ions are numerically studied. It is revealed that the tungsten ions significantly modify the isotope scaling of the maximum growth rates of the instabilities with respect to the main or effective ion mass number or M eff [=(1 − f z )M i + f z M z ] with (=Zn z /n e ) being impurity charge concentration. The most reasonable scaling is deduced as with , for ITG driven modes, whilst holds with , for tungsten impurity modes, in significant contrast with the case of light or intermediate impurities where the scaling is and for ITG and impurity modes, respectively. These results suggest that existence of tungsten impurity would enhance (weaken) the isotope effect of instability driven by ITG (tungsten impurity ions), which is beneficial (harmful) for improvement of confinement when hydrogen isotopes are used in plasmas. The results might also provide hints on studies of particle and energy transports and discharge performance, particularly, in ITER-like wall machines.

In HL-2A, an inverse sawtooth oscillation is observed with a long-lasting m/n = 1/1 mode during ECRH phase with power deposition inside sawtooth inversion radius (inner-deposited ECRH), while a normal sawtooth instead appears when the ECRH power is deposited outside sawtooth inversion radius (outer-deposited ECRH). Aluminum is then injected as a trace impurity with laser blow-off (LBO) method into the inner- and outer-deposited ECRH phases of HL-2A discharges to investigate the effect of ECRH on impurity transport. Temporal behavior of soft x-ray (SXR) array signals is analyzed with a 1D impurity transport code, and radial structures of impurity transport coefficients are obtained. The result shows that the radial transport of Al ions is strongly enhanced during the inner-deposited ECRH phase. In particular, an outward convection velocity is developed with positive values of 0 ≤ V(ρ) ≤ 3.8 m s−1 in ρ ≤ 0.5, while the convection velocity is inward in ρ ≥ 0.6. In the outer-deposited ECRH discharge, on the other hand, the convection velocity takes a big negative value in ρ ≤ 0.4 and close to zero at ρ ~ 0.6. In ohmic discharges, an inward V(ρ) always appears in the whole plasma radii and gradually increases toward the plasma edge (−3.2 m s−1 at ρ = 1). The simulation result also indicates that centrally-peaked Al ion density profiles presented in the outer-deposited ECRH discharge can be flattened by the inner-deposited ECRH. Modification of impurity transport is discussed in the presence of long-lasting m/n = 1/1 MHD mode.

Recent experiment results from the HL-2A tokamak are presented in this paper. Supersonic molecular beam injection (SMBI) with liquid nitrogen temperature propellant is used. Low temperature SMBI can form hydrogen clusters that penetrate into the plasma more deeply and efficiently. Particle diffusion coefficient and convection velocity (D = 0.5?1.5?m2?s?1 and Vconv < 40?m?s?1, respectively) are obtained at the plasma periphery using modulated SMBI. Multi-probe measurements reveal the m = 0?1, n = 0 symmetries of directly measured low frequency (7?9?kHz) electric potential and field are simultaneously observed for the first time. Impurity transport is determined with the laser blow-off system and transport code. A disruption predictor has been derived based on MHD activity observations and statistical analysis. Sawtooth characteristics during ECRH are investigated and coupling between m = 1 and m/n = 2/1 modes is studied. Detachment features of HL-2A divertor are numerically and experimentally studied using the code SOLPS5.0 and measured data. The long divertor legs and thin divertor throats in HL-2A pose MHD shaping problems resulting in momentum losses even at low densities and strongly enhanced main chamber losses.

With the rapidly development of civil aviation and a large number of introduction of new models and technologies, higher requirements are put forward to the number and quality of aircraft maintenance personnel. Following the construction of Tianjin's brand major-Electrical Engineering and Automation, combining with the Excellent engineer education and training programs of our school, research and exploration on experimental teaching reform for the course of Fly-By-Wire(FBW) of aircraft is done based on the concept of CDIO in this paper, which is guided by the demand for knowledge of engineering practice. It is enable students to develop engineering thinking patterns and aircraft maintenance awareness, increase the ability of learning, thinking and analytical problem reversely, so that to enhance their competitiveness of employability and adaptability of work. KEYWORD: Fly-By-Wire; engineering practice; aircraft maintenance; CDIO; teaching reform

We report an experimental result on the stabilization of the energetic–ion driven internal kink mode (ion fishbone) by electron cyclotron resonance heating (ECRH), observed for the first time in a toroidal plasma. The mode asserts itself a resistive branch close to the marginal stability point. The resulting fishbone mode depends not only on the injected power but also on the radial deposition location of ECRH, and the instability can be completely suppressed when the injected ECRH power exceeds certain threshold. Analysis by the fishbone dispersion relation, including the resistive effect, suggests that the magnetic Reynolds number plays a key role in the mode stabilization—it weakens the mode growth-rate and enhances the critical energetic–ion beta without changing the energetic–ion population. This ion fishbone stabilization mechanism can be important for future devices such as ITER, which has significant ECRH capability.

Multi-scale interactions have been observed recently in the HL-2A core NBI plasmas, including the synchronous coupling between kink mode and tearing mode, nonlinear couplings of TAE/BAE and TM near surface, AITG/KBM/BAE and kink mode near surface, and between kink mode and high-frequency turbulence. Experimental results suggest that several couplings can exist simultaneously, Alfvenic fluctuations have an important contribution to the high-frequency turbulence spectra, and the couplings reveal the electromagnetic character. Multi-scale interactions via the nonlinear modulation process maybe enhance plasma transport and trigger sawtooth-crash onset.

Two groups of frequency sweeping modes are observed and interpreted in the HL-2 A plasmas with qmin ~ 1. The tokamak simulation code calculations indicate the presence of a reversed shear q-profile during the existence of these modes. The mode frequencies lie in between TAE and BAE frequencies, i.e. ωBAE 1 and nqmin − m > 0, and another group of modes characterized by up-sweeping frequency with qmin drop, owing to qmin < 1 and nqmin − m < 0 before sawtooth crash. The kinetic Alfven eigenmode code analysis supports that the down-sweeping modes are kinetic reverse shear Alfven eigenmodes (KRSAEs), and the up-sweeping modes are RSAEs, which exist in the ideal or kinetic MHD limit. In addition, the down- and up-sweeping RSAEs both have fast nonlinear frequency behaviour in the process of slow frequency sweeping, i.e. producing pitch-fork phenomena. These studies provide valuable constraint conditions for the q-profile measurements.

In our previous letter, the geodesic acoustic mode (GAM) induced by energetic particles (EGAMs) was reported in low density ohmic plasma on HL-2A (Chen et al 2013 Phys. Lett. A 377 387). We extend the experimental results of the EGAM mode in this paper. During strong tearing modes (TMs), the beta-induced Alfv?n eigenmodes (BAEs) and EGAM-induced density fluctuations are firstly measured by microwave Doppler reflectometers with different work frequencies. As predicted by theory, the measurements of magnetic probes and Doppler reflectometers suggest the EGAM magnetic oscillations have poloidal/toroidal mode numbers of m/n?=?2/0, and are localized in the core with a broad radial structure. The mode frequency is less than that of the conventional GAM (i.e. fEGAM/fGAM?1), and is constant in the radial direction. Our experimental results suggest that a density limit exists for the excitation of the EGAM in the ohmic plasma, and the density limit is improved with electron cyclotron resonance heating + neutral beam injection heating on HL-2A. The auto and cross squared bicoherences of magnetic and density fluctuations indicate that intense nonlinear interactions exist among EGAM, BAEs and strong TMs. These new observations will help us to understand the underlying physics mechanism for the excitation of fluctuations in the sub-Alfv?n frequency range.

Fishbone instability excited by energetic electrons during electron cyclotron resonant heating (ECRH) is identified on HL-2A. With high-power ECRH, periodic frequency jump phenomena are observed by soft x-ray arrays. Soft x-ray tomography shows that the poloidal and toroidal mode numbers are 1/1 and 2/2 with the frequency jump. There is an ECRH power threshold for the frequency jump phenomena, which is generally about 0.9 MW. The frequencies of the two modes increase with the ECRH power. Experiments show that trapped particles are dominant in the low-density high-power ECRH plasma. The precessional frequency of the energetic trapped electrons is calculated with different discharge parameters. The results indicate that the energy of resonant electrons is in agreement with the hard x-ray measurement.

The MHD instabilities driven by the energetic-particles are of particular importance for future burning plasma devices, where energetic particles will be abundantly produced by high power heating and fusion reaction. In this paper, some new phenomena induced by high power ECRH are presented. The high frequency (200kHz–350 kHz) instabilities have been observed during the high power ECRH or NBI. The frequencies of the modes are proportional to Alfvén velocity and very close to the TAE frequency in the plasma core. In the lower frequency range from 10 kHz to 35 kHz, the coexistence of multi-mode has also been found during the high power ECRH. The frequencies of the modes are proportional to Alfvén velocity, but much lower than it. Between the two frequency ranges, a new mode with the frequency from 50 kHz to 100 kHz has been observed with high power ECRH and NBI heating together. The modes have obvious frequency chirping within short time, which is the feature of the EPM like modes. The fishbone instability excited by energetic electrons during ECRH has been identified in HL-2A. It is interested to find the frequency jump phenomena in the high power ECRH. The frequency jumps between 8 kHz and 15 kHz within about 25ms periodically, when the power is 1.2MW. The new results are different from the phenomena on Tore-Supra, because the trapped particle dominates in this case.

The physics experiments on the HL-2A tokamak have been focused on confinement improvement, particle and thermal transport, zonal flow and turbulence, filament characteristics, energetic particle induced modes and plasma fuelling efficiency since 2008. ELMy H-mode discharges are achieved in a lower density regime using a combination of NBI heating with ECRH. The power threshold is found to increase with a decrease in density, almost independent of the launching order of the ECRH and NBI heating power. The pedestal density profiles in the H-mode discharges are measured. The particle outward convection is observed during the pump-out transient phase with ECRH. The negative density perturbation (pump-out) is observed to propagate much faster than the positive one caused by out-gassing. The core electron thermal transport reduction triggered by far off-axis ECRH switch-off is investigated. The coexistence of low frequency zonal flow (LFZF) and geodesic acoustic mode (GAM) is observed. The dependence of the intensities of LFZFs and GAMs on the safety factor and ECRH power is identified. The 3D spatial structures of plasma filaments are measured in the boundary plasma and large-scale structures along a magnetic field line analysed for the first time. The beta-induced Alfvén eigenmodes (BAEs), excited by large magnetic islands (m-BAE) and by energetic electrons (e-BAE), are observed. The results for the study of fuelling efficiency and penetration characteristics of supersonic molecular beam injection (SMBI) are described.