We report the first experimental observation of zonal flow (ZF) formation through phase patterning. Here the ‘phase’ refers to the eikonal phase carried by streamer-like mode. It is observed that the phase-gradient profile tends to form ‘shock’ layer structures in regions where there are strong streamer-ZF interactions. The emergence of phase-gradient shock layers invalidate the constant-phase-gradient hypothesis, which is frequently employed in the modulational instability models of ZF generation, and is consistent with a recent theoretical work (Guo et al 2016 Phys. Rev. Lett. 117 125002), which predicts that the phase-curvature (gradient of the phase-gradient) can produce a new Reynolds force and accelerate the ZF. By decomposing the Reynolds’ force of the tilted streamers into a phase curvature driven piece and an amplitude inhomogeneity driven one, it is found that inside the shock layers the phase curvature plays a prominent role in accelerating the ZF. We also explore the formation mechanism of the phase pattern and its consistent dynamics with phase-curvature-driven ZF. These findings potentially open a new way to understand the various elusive self-organization phenomena in plasma turbulence.

The helicon wave plasma (HWP) sources have well-known advantages of high efficiency and high plasma density, with broad applications in many areas. The crucial mechanism lies on mode transitions, which has been an outstanding issue for years. We have built a fluid simulation model and further developed the Peking University Helicon Discharge (PHD) code. The mode transitions also known as density jumps of a single-loop antenna discharge are reproduced in simulations for the first time. It is found that large-amplitude SHWs are responsible for the mode transitions, similar to those of a resonant cavity for laser generation. This paper intends to give a complete and quantitative standing helicon wave (SHW) resonance theory to explain the relationship of the mode transitions and the SHWs. The SHW resonance theory reasonably explains several key questions in helicon plasmas, such as mode transition and efficient power absorption, and helps to improve future plasma generation methods.

A Multi-Color (MC) gas puff imaging diagnostic has been developed on HL-2A tokamak. This diagnostic can simultaneously measure two-dimensional (2D, radial, and poloidal) electron density and temperature distributions with a good spatial resolution of 2.5 × 2.5 mm2 and a temporal resolution of about 100 µs at best in edge plasmas. The 2D electron density and temperature distributions are inferred from the ratios of intensities of three different neutral helium emission lines; therefore, it is also referred to as helium beam probe or beam emission spectroscopy on thermal helium. A compact light splitter is used to split the inlet visible emission beam into four channels, and the specific neutral helium lines of the wavelengths λ1 = 587.6 nm, λ2 = 667.8 nm, λ3 = 706.5 nm, and λ4 = 728.1 nm are measured, respectively. This MC diagnostic has been experimentally tested and calibrated on a linear magnetic confinement device Peking University Plasma Test device, and the measured 2D electron density and temperature distributions are compared with the Langmuir probe measurements.

The field-reversed configuration (FRC) is a promising magnetic confinement fusion concept [M. Tuszewski, Nucl. Fusion 28, 2033 (1988)] and is often chosen as the target plasma for magneto inertial fusion [S. A. Slutz and M. R. Gomez, Phys. Plasmas 28, 042707 (2021)]. In FRCs, the toroidal magnetic field is essentially zero, and the poloidal magnetic field ([Formula: see text]) pressure is comparable with the plasma pressure. Applying the traditional [Formula: see text] diagnostics to FRCs is a major challenge because [Formula: see text] is small, and reversal occurs across the core region of FRCs. The laser-driven ion-beam trace probe (LITP) is a newly developing diagnostic method to measure [Formula: see text] and the radial electric field ([Formula: see text]) in tokamak. Here, the principles of using LITP to diagnose [Formula: see text] in FRCs are proposed, verified, and numerically implemented using an iterative method to reconstruct the [Formula: see text] profile. Least square tomography employing a dissipative term is used to solve the nonlinear tomography problem, which arises when applying LITP to the unique FRC magnetic topology. Numerical modeling results show that the relative errors of the reconstruction are mostly below 10%, verifying the feasibility of LITP diagnostics for FRC internal magnetic field measurements. Ion beam orbits and detector arrangements are optimized to meet the experimental requirements of FRCs. LITP can still be applied to diagnose [Formula: see text] in FRCs when there is 5% measurement errors.

The waves in a magnetic null could play important roles during 3D magnetic reconnection. Some preliminary clues in this paper show that the ion Bernstein wave (IBW) may be closely related to transport process in magnetic null region. The magnetic null configuration experiment reported here is set up in a linear helicon plasma device, Peking University plasma test device (PPT). The wave modes with frequencies between the first and third harmonics of local ion cyclotron frequency ( ω ci ) are observed in the separatrix of magnetic null, which are identified as the IBW based on the dispersion relation. Further analysis shows that IBW could drive substantial particle flux across the magnetic separatrix. The theoretical radial particle flux driven by IBW and the measured parallel flow in PPT device are almost on the same order, which shows that IBW may play an important role during 3D reconnection process.