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 < ω < ωTAE, and these modes are highly localized near qmin, i.e. r/a ∼ 0.25. A group of modes characterized by down-sweeping frequency with qmin decrease due to qmin > 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 Alfvén eigenmode code analysis supports that the down-sweeping modes are kinetic reverse shear Alfvén 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.

The three-dimensional characteristics of the geodesic acoustic mode zonal flows (GAMZFs) and the ambient turbulence (AT) at the edge of the HuanLiuqi-2A tokamak [Y. Liu et al., Nucl. Fusion 45, S203 (2005)] are investigated with Langmuir probe arrays and the results are presented in detail. The toroidal and poloidal symmetries, and the radial scale of the GAMZFs are simultaneously identified. The envelopes of the high frequency components of the AT in the presence of the GAMZFs are analyzed. The GAM frequency components (GAMFCs) of the coherent envelopes are also shown to have poloidal and toroidal symmetries, and similar radial scales as the GAMZF does. The correlation between the GAMFCs of the envelopes and the GAMs is high, with phase shifts between π/2 to π, indicating that the GAMZFs may regulate the AT and the regulation is embodied in the envelopes. Three-wave coupling between GAM and AT is found to be a plausible formation mechanism for the former, which acts on the whole spectra of the latter within its scale length. The temporal evolutions of the total fluctuation power, the GAM and the AT powers show that the AT power decreases when GAM power increases and vice versa, indicating possible regulating effects of the latter on the former.

HL-2M is a new medium-sized tokamak under construction at the Southwestern Institute of Physics, dedicated to supporting the critical physics and engineering issues of ITER and CFETR. Analyzing integrated plasma scenarios is essential for assessing performance metrics and foreseeing physics as well as the envisaged experiments of HL-2M. This paper comprehensively presents the kind of expected discharge regimes (conventional inductive (baseline), hybrid and steady-state) of HL-2M based on the integrated suite of codes METIS. The simulation results show that the central electron temperature of the baseline regime can achieve more than 10 keV by injecting 27 MW of heating power with a plasma current of I p  =  3 MA and Greenwald fraction f  G  =  0.65, with the thermal energy and β N reaching 5 MJ and 2.5, respectively. The hybrid regime with f  ni  =  80%–90% can be realized at I p  =  1–1.4 MA with f  G around 0.5, where β N is 2.3–2.5 with H 98(y ,2)  =  1.1. Because of the effect of the on-axis NBCD, the hybrid steady state, at I p  =  1.0 and 1.2, can be achieved more easily than the steady state regimes with reversed shear, corresponding to β N  =  2.6 and 3.4. Such studies show that HL-2M is a flexible tokamak with a significant capacity for generating a broad variety of plasmas as a consequence of the different heating and current drive systems installed.

Recent experimental results that are associated with the core-localized (i.e. normalized radius

Two distinct regimes of turbulence are identified with Langmuir probe arrays in the edge plasmas of the HuanLiuqi (HL)-2A tokamak for the first time. The spatial and temporal coherent characteristics of the low frequency fluctuations (LFFs) of 20-100 kHz are found in significant contrast to the high frequency ambient turbulence (HFAT) of 100 kHz or higher. In the LFF regime, the deviations from the regular linear dispersion relations of the HFAT are observed. The poloidal and toroidal correlation lengths of the former are measured one order of magnitude longer than that of the latter. The ratio of the temporal scales of the fluctuations in the LFF and HFAT regimes is estimated to be of the same order as that for the spatial scales. The LFF may coexist with and differentiate from the geodesic acoustic modes. The bispectrum analysis of the data indicates that nonlinear three wave coupling between the LFF and HFAT is a possible creation mechanism for the former. The possible correlation of the results with the theory and simulation predictions on quasimodes is discussed.