DIP C 7.2 Investigation of plasma under pulsed energy deposition

Prof. Yitzhak Maron, The Weizmann Institute of Science, Rehovot

Prof. Dieter H.H. Hoffmann, Technische Universität Darmstadt

http://www.weizmann.ac.il/acadsec/Scientific_Activities/current/Particle_Physics.html

Executive summary:

Of particular note is the participants' decision to pursue the challenging measurement of the magnetic field in dense laser-produced plasmas. Such ultra-high magnetic fields could be generated in the plasmas produced by the powerful lasers in Jena and GSI. A possible mechanism for the generation of the magnetic filed is depicted in Figure 1. In the course of the project we have developed and implemented a number of innovative spectroscopic approaches, supported by extensive theoretical programs. A novel application of laser-spectroscopy for the investigation of electric and magnetic fields, yielding simultaneous high temporal and 3D spatial resolutions, was developed and demonstrated in WIS. The scheme for investigating the electric fields using Li I lines is demonstrated in Figure 2.

We obtained time-dependent radial distribution of the electron temperature in a cylindrical imploding plasma, which allowed for studying the history of the magnetic field energy coupling to the plasma. The program of ultra-high magnetic field measurements was further advanced by developing high-resolution X-ray spectroscopy (see Figure 3) and the planning of new target design. The structure of the Neon Lyá satellites obtained with a resolving power of 6700, from which the conversion of the ion kinetic energy into the radiation is obtained (see Figure 4). The crystals used for the X-ray measurements are designed and produced in Jena, and the development of the spectroscopic methods is performed in WIS.

These methods will be implemented in the laser-produced plasma and ion beam experiments in GSI. Advances were achieved in investigating fast-varying electric fields produced in a metal near a focal spot of a short-pulse laser. A new phenomenon of simultaneous fast magnetic field penetration into the heavy component of the plasma and reflection of light ions was revealed in current-carrying plasmas. This unpredicted phenomenon suggests an important role for the plasma composition. We also showed that the plasma behind the propagating magnetic field significantly deviates from Maxwellian distribution. The newly developed methods and scientific results are presented in more than a dozen publications.

 
Figure 1. A suggested mechanism of the magnetic field development in plasmas produced by powerful lasers.

 
Figure 2. Laser spectroscopy for electric field measurements. Left panel: 4l levels of Li I are populated using a laser radiation. The intensity ratio of the allowed 2p-4d to the forbidden 2p-4f transition is sensitive to electric fields. Right panel: Temporally resolved electric fields (crosses) and current (solid line) measured in a current carrying plasma. The spatial resolution of the measured electric field is determined by the cross section of the pumping laser beam.

 
Figure 3. A doubly-curved crystal system coupled to a time resolved detector is used to obtain high- spectral, temporal, and spatial resolution X-ray spectra.

 
Figure 4.