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We investigate the competition of magnetic reconnections in self-generated and external magnetic fields in laser-produced plasmas. The temporal evolution of plasma structures measured with self-emission imaging shows the vertical expansions and horizontal separation of plasma, which can be signatures of reconnection outflows in self-generated and external magnetic fields, respectively. Because the outflows in self-generated magnetic fields are not clear in the presence of the external magnetic field, the external magnetic field can suppress the magnetic reconnection in self-generated magnetic fields. [ABSTRACT FROM AUTHOR]

Collective Thomson scattering (CTS) has been applied to laser-produced plasmas with Gekko XII HIPER laser facility. A scheme of stimulated Brillouin scattering (SBS) has been used in CTS measurements for the first time. Utilizing SBS shortens the probe pulse, which increases the scattered power, and thus collected scattered signal of CTS. Therefore, a lower energy probe laser can be used for given background emission levels to avoid probe heating, which is crucial for plasmas with low electron temperature. Both electron and ion features of CTS have been successfully detected by using the SBS technique. The spatial profile of electron density, temperature, and drift velocity have been estimated in an ablation plasma. In addition to the local measurements with CTS, a global structure of plasmas has been obtained with optical imaging of the self-emission of plasmas and the interferometry. In the aspects of drift velocity and plasma density, the local and global information are in good agreement. [ABSTRACT FROM AUTHOR]

Magnetic reconnection is experimentally investigated in laser produced plasmas. By irradiating a solid target with a high-power laser beam, a magnetic bubble is generated due to the Biermann effect. When two laser beams with finite focal spot displacements are utilized, two magnetic bubbles are generated, and the magnetic reconnection can take place. We measure the spatial and temporal plasma evolutions with optical diagnostics using framing camera. We observed the plasma jets, which are considered to be reconnection out flows. Spatial and temporal scales of the plasma jets are much larger than those of laser. The magnetic reconnection time has been estimated from the expansion velocity, which is consistent with the Sweet-Parker model. [ABSTRACT FROM AUTHOR]

We have implemented laser Thomson scattering for local plasma measurement of electron and ion temperatures, electron density, flow velocity, and charge state. The electron density increases by two times in the interaction of two plasma flows, indicating collisionless interaction. The density and velocity show fluctuations only at t = 40 ns, and the density suddenly decreases, indicating the plasma ejection from the interaction region, which can be explained by a magnetic reconnection. The electron temperature in the double-flow is larger than that in the single flow. This may be explained by the energy transfer from the plasma kinetic energy to thermal energy. The ion temperature is much larger than electron temperature in the double-flow, and this may be explained by collisional effects between two plasmas, and/or possibly interpreted as a thermalization due to magnetic reconnection. [ABSTRACT FROM AUTHOR]

We perform a one-dimensional full particle-in-cell (PIC) simulation of a quasi-parallel collisionless shock with the Alfvén Mach number 6.6 and a shock angle of 20 degrees between the upstream magnetic field and the shock normal direction. The backstreaming ions are self-consistently generated by reflections of the incoming ions at the shock. They generate the Alfvénic electromagnetic wave via the right-handed resonant ion-ion instability, as the ions travel toward the upstream region. The energy distribution of the backstreaming ions far upstream splits into two populations as it approaches the shock. The energy threshold of the populations is approximately the energy gained by a single specular reflection at the shock. The maximum energy of the backstreaming ions near the shock is about 10 times larger than the specularly reflected ion energy. Nonlinear phase bunches of the high-energy backstreaming ions and the background ions are found near the shock, due to the resonant and non-resonant trappings by the excited waves, respectively. [ABSTRACT FROM AUTHOR]