Dynamics of charge-displacement channeling in intense laser-plasma interactions

The dynamics of transient electric fields generated by the interaction of high intensity laser pulses with underdense plasmas has been studied experimentally with the proton projection imaging technique. The formation of a charged channel, the propagation of its front edge and the late electric field evolution have been characterized with high temporal and spatial resolution. Particle-in-cell simulations and an electrostatic, ponderomotive model reproduce the experimental features and trace them back to the ponderomotive expulsion of electrons and the subsequent ion acceleration.

Weibel-induced filamentation during an ultrafast, laser-driven plasma expansion

The development of current instabilities behind the front of a cylindrically expanding plasma has been investigated experimentally via proton probing techniques. A multitude of tubelike filamentary structures is observed to form behind the front of a plasma created by irradiating solid-density wire targets with a high-intensity (I~1019??W/cm2), picosecond-duration laser pulse. These filaments exhibit a remarkable degree of stability, persisting for several tens of picoseconds, and appear to be magnetized over a filament length corresponding to several filament radii. Particle-in-cell simulations indicate that their formation can be attributed to a Weibel instability driven by a thermal anisotropy of the electron population. We suggest that these results may have implications in astrophysical scenarios, particularly concerning the problem of the generation of strong, spatially extended and sustained magnetic fields in astrophysical jets.

Large quasistatic magnetic fields generated by a relativistically intense laser pulse propagating in a preionized plasma

Two spatially separated toroidal magnetic fields in the megagauss range have been detected with Faraday rotation during and after propagation of a relativistically intense laser pulse through preionized plasmas. Besides a field in the outer region of the plasma oriented as a conventional thermoelectric field, a field with the opposite orientation closely surrounding the propagation axis is observed, in conditions under which relativistic channeling occurs. A 3D particle-in-cell code was used to simulate the interaction under the conditions of the experiment.

Megagauss magnetic field generation and plasma jet formation on solid targets irradiated by an ultraintense picosecond laser pulse

The spatial and temporal evolution of spontaneous megagauss magnetic fields, generated during the interaction of a picosecond pulse with solid targets at irradiances above 5 x 10(18) W/cm(2) have been measured using Faraday rotation with picosecond resolution. A high density plasma jet has been observed simultaneously with the magnetic fields by interferometry and optical emission. Two-dimensional magnetohydrodynamic simulations reproduced the main features of the experiment and showed that the jet formation is due to pinching by the magnetic fields.

Plasma parameter characterization of a reflex plasma source operating in oxygen

A reflex discharge plasma, obtained as a hybrid between a Penning discharge plasma (PDP) and a hollow-cathode discharge (HCD) plasma, is analysed as a possible direction-current, high-density plasma source. The experiment is run in oxygen at pressures of 10 mTorr and 1 mTorr, and for discharge currents of 100 to 200 mA. Although the gas pressure is considerably lower than those used in HCDs, the hollow-cathode effect (HCE) occurs for current levels higher than 100 mA and leads to plasma densities comparable with those obtained using inductive plasma sources. The presence of a constant magnetic field leads to the enhancement of electron emission from cathodes under ion bombardment, and to the decreasing of the ion loss by diffusion to the wall.

Role of low-energy electrons in Ar emission from low-pressure radio frequency discharge plasma

Optical emission spectra from a low-pressure Ar plasma were studied with high spatial resolution. It has been shown that the intensity ratios of Ar lines excited through metastable levels to those excited directly from the ground state are sensitive to the shape of electron energy distribution function. From these measurements, important information on the spatial variation of plasma parameters can be obtained. (C) 1999 American Institute of Physics. [S0003-6951(99)01629-0].

Sheath dynamics observed in a 13.56 MHz-driven plasma

We have established, through time correlated plasma emission and electrode and plasma potential measurements, that the near electrode emission observed in asymmetric capacitively coupled 13.56 MHz-driven hydrogen plasmas is caused by field reversal that leads to sheath collapse. Near-electrode emission has now been observed in Ar and He. The field reversal appears to be due to collision-induced electron drag. (C) 1997 American Institute of Physics.

Langmuir probe measurements of plasma parameters in the late stages of a laser ablated plume

A simple Langmuir probe technique has been used to measure the electron density, electron temperature, and plasma potential in the late stages (>5 mu s) of a laser ablated plasma plume. In the plasma, formed following 248 nm laser irradiation of a copper target, in vacuum at a laser fluence of 2.5 J cm(-2), electron densities of similar to 10(18) m(-3) and temperatures of similar to 0.5 eV were measured. These values are comparable with those reported previously using Faraday cup detectors and optical emission spectroscopy, respectively. (C) 1997 American Institute of Physics.

OPTICAL-ABSORPTION SPECTROSCOPY STUDY OF THE ROLE OF PLASMA CHEMISTRY IN YBA2CU3O7 PULSED LASER DEPOSITION

Time-resolved optical absorption spectroscopy techniques were used to study Ba, metastable Ba+, and YO absorptions in the laser-produced plasma plume from a YBa2Cu3O7 target. Results obtained indicate an initial explosive removal of material from the target sur-face followed by a subsequent evaporation process. Some YO is ejected from the target in molecular form, particularly at laser fluence