J.M. Kindel

Theoretical derivation of laser induced plasma profiles

The hydrodynamic modification of an expanding plasma by coherent radiation for polarization out of the plane of incidence is investigated theoretically in the absence of parametric and modulational instabilities. The pondermotive force of the incident wave modifies the plasma flow from that of a rarefaction wave into a subsonic flow in the overdense region with a transition to supersonic flow at less than critical density. A constraint imposed at the sonic transition point allows a complete determination of the equilibrium as observed in simulations. The theory predicts that the average flow in the subcritical density region scales as the square root of the incident power.

Collapse of very large amplitude ion waves

Recently extremely large supersonic amplitude ion waves have been observed in simulations of backscatter instabilities, electron beam interactions, and large amplitude Langmuir waves, which break in an unconventional symmetrical x‐type manner. The conditions necessary for this type of breaking and simulations to support this theory are presented.

Vacuum insulation as a way to stop hot electrons

In laser fusion plasmas, most of the absorbed laser energy can go into the generation of suprathermal electrons, which potentially can preheat the pusher and/or fuel. An approach of using a vacuum to shield the pusher or fuel against these energetic electrons is discussed in some detail. Both qualitative and quantitative kinetic calculations governing vacuum insulation in plane and spherical geometry are developed. The principal effect of vacuum insulation is to convert an electron time scale to an ion time scale.

Studies of the Plasma Droplet Accelerator Scheme

In the plasma droplet accelerator scheme, proposed by R. Palmer, a sequence of liquid micro-spheres generated by a jet printer are ionized by an incoming intense laser. The hope is that the micro-spheres now acting as conducting balls will allow efficient coupling of the incoming laser radiation into an accelerating mode. Motivated by this we have carried out 2D, particle simulations in order to answer some of the plasma physics questions hitherto unaddressed. In particular we find that at least for laser intensities exceeding vo/c=0.03 (~1013w/cm2 for a CO2 laser), the incident laser light is rather efficiently absorbed in a hot electron distribution. Up to 70% of the incident energy can be absorbed by these electrons which rapidly expand and fill the vacuum space between the microspheres with a low density plasma. These results indicate that it is advisable to stay clear of plasma formation and thus put on an upper limit on the maximum surface fields that can be tolerated in the droplet-accelerator scheme.

Two Dimensional Simulations of Intense Laser Irradiation of Underdense Plasmas

The interaction between an intense laser and an underdense plasma results in many different phenomena. In particular, the interaction may result in collective processes called parametric instabilities, some of which produce plasma waves1,2,3. The plasma waves can eventually produce energetic electrons as they damp away their energy. The generation of energetic electrons is detrimental for laser fusion4, essential for plasma particle accelerators5 and essential in current drive in tokamaks6, to name a few subject areas.