The evolutions of laser ablation plasma, expanding in strong (∼10 T) transverse external magnetic field, were investigated in experiments and simulations. The experimental results show that the magnetic field pressure causes the plasma decelerate and accumulate at the plasma-field interface, and then form a low-density plasma bubble. The saturation size of the plasma bubble has a scaling law on laser energy and magnetic field intensity. Magnetohydrodynamic simulation results support the observation and find that the scaling law ( V _max ∝ E _p / B ² , where V _max is the maximum volume of the plasma bubble, E _p is the absorbed laser energy, and B is the magnetic field intensity) is effective in a broad laser energy range from several joules to kilo-joules, since the plasma is always in the state of magnetic field frozen while expanding. About 15% absorbed laser energy converts into magnetic field energy stored in compressed and curved magnetic field lines. The duration that the plasma bubble comes to maximum size has another scaling law t _max ∝ E _p ^{1 / 2} / B ² . The plasma expanding dynamics in external magnetic field have a similar character with that in underdense gas, which indicates that the external magnetic field may be a feasible approach to replace the gas filled in hohlraum to suppress the wall plasma expansion and mitigate the stimulated scattering process in indirect drive ignition.

A pulsed intense magnetic field device was developed for the Shanghai Shenguang-II (SG-II) laser facility. The device using a double-turn coil with 12 mm diameter is capable of producing a peak current of 42 kA with 280 ns rising edge and 200 ns flat top width. A peak magnetic field of 8.8 T is achieved at the center of the coil. A two-section transmission line composed by a flexible section and a rigid section is designed to meet the target chamber environment of SG-II laser facility. The flexible section realizes the soft-connection between the capacitor bank and the target chamber, which facilitates the installation of the magnetic field device and the adjustment of the coil. The rigid section is as small as possible so that it can be inserted into the target chamber from any smallest flange, realizing elastic magnetic field configuration. The magnetic coil inside the chamber can be adjusted finely through a mechanical component on the rigid transmission line outside the target chamber. The adjustment range is up to 5 cm in both radial and axial directions with ∼50 µm precision. The device has been successfully operated on SG-II laser facility.

Flute instability produced by laser plasma expanding in a 10 T external magnetic field was studied in experiments. The plasma was generated by a 0.3 J ns laser ablating an aluminum target. The external magnetic field of approximately 10 T was provided by a pair of Helmholtz coils aligned parallel to the target surface. Initially, the plasma plume expands freely. The external magnetic field confines the plasma plume and, finally, forms a plasma cavity with a sharp plasma–field interface. Flute instability was observed at the plasma–field interface, which presents a salient kinetic feature rather than classical fluid instability. In the initial linear phase, the growth rate of the perturbation has good agreement with Large Larmor radius instability, which is larger than ion gyrofrequency. In the later nonlinear growth phase, the flute instability shows an obvious “fishbone” structure of kinetic instability, and the initial short wavelength perturbation shifts continually to longer wavelength mode and, finally, close to the density scale length. Our experiment reveals a new region of parameter space that reproduces the flute instability in the space experiments of an active magnetospheric particle tracer experiment and a combined release and radiation effects satellite.

Fermi acceleration is believed to be the primary mechanism to produce high-energy charged particles in the Universe, where charged particles gain energy successively from multiple reflections. Here, we present the direct laboratory experimental evidence of ion energization from single reflection off a supercritical collisionless shock, an essential component of Fermi acceleration, in a laser-produced magnetized plasma. A quasi-monoenergetic ion beam with two to four times the shock velocity was observed, which is consistent with the fast ion component observed in the Earth’s bow shock. Our simulations reproduced the energy gain and showed that ions were accelerated mainly by the motional electric field during reflection. The results identify shock drift acceleration as the dominant ion energization mechanism, which is consistent with satellite observation in the Earth’s bow shock. Our observations pave the way for laboratory investigations of the cosmic accelerators, also be beneficial to laser fusion and laser-driven ion accelerator.

Magnetic reconnection explosively converts magnetic energy into plasma heating and particle acceleration. At Earth's magnetopause, reconnection governs solar wind‐magnetosphere coupling and drives global convection. Understanding these processes requires resolving reconnection's spatiotemporal evolution, which is difficult for in situ observations but achievable in laboratory experiments. However, building a geometry like the real magnetopause in laboratory remains a key challenge. Here, we present the first laboratory experiment at the Space Plasma Environment Research Facility trying to replicates Earth's magnetopause configuration. Using a dipole magnet (mimicking magnetosphere) and coaxial flux cores (simulating solar wind), we establish a magnetopause‐like current sheet via dynamic plasma compression. Measured Hall magnetic fields confirm Hall reconnection, transitioning from an asymmetric multiple x ‐lines state to a symmetric single x ‐line state. This dynamic evolution will impact global energy conversion and transport at magnetopause.

We experimentally demonstrate a novel scheme for efficiently generating intense terahertz surface plasmon polaritons (SPPs) on a subwavelength-diameter meter-long metal wire. Driven by a subrelativistic femtosecond laser ( a 0 = 0.3 , 3 mJ) focused at the wire’s midpoint, single-cycle 10-MW terahertz SPPs are excited and propagate bidirectionally along it over 25 cm. The measured laser-to-SPPs energy conversion efficiency is reaching up to approximately 2.4%, which is the highest value at present. It is proved that the terahertz SPPs are excited by coherent transition radiation of the subrelativistic-laser-produced escaping electrons. Particle-in-cell together with CST simulations confirm the experimental observations. Our scheme of using readily available subrelativistic laser should thus be useful to applications requiring terawatt level single-cycle terahertz SPPs.