Studies On Hot Electron Transportation And Its Correlative Phenomenons

Since the concept was first suggested by M. Tabak in 1993, fast ignition is now an increasing research field for its merits that traditional inertial confine fusion (ICF) did not possess. But for its short time research, there are lot of physics need to be studied, among which, the transport of relativistic electrons in dense plasmas is an interesting and important subject.First of all, the basic contents of this thesis were outlined and recent researches on these topics were reviewed. Then the laser system and target chambers developed for experiments were introduced. In this part, the diagnostic equipments, such as CCD pinhole camera, electron spectrometer, ion spectrometer et al. were descriped in detail, including principles, characteristics and methods.Angular distributions and spectrums of hot electrons produced by femtosecond intense laser interaction with solid targets were measured in different laser polarizing manners. For P-polarizing laser, two emission peaks of hot electrons in front side of target were found, one is on the specular reflection direction of laser and another is on the direction of 60 with an angle of 15 to the normal of target (laser axis is 0), respectively. For the SP-polarizing laser, three emission peaks were found. Similar to P-polarizing laser situation, the peak on the direction of laser specular reflection still exists. Two other peaks are on the normal way of target and back reflection direction of incident laser, respectively. As a large prepulse was introduced before main pulse, only one wide emission peak emerged on the normal way of target. The electronemission peak near the normal of target is produced by resonance absorption, in the situation of P-polarizing, this emission peak will deflect a small angle from the normal of target due to the momentum component parallel to target surface. The emission peaks along the specular reflection and back reflection of laser is produced by breaking of plasma waves excited by stimulated forward and back Raman scattering. S-polarizing component will enhance the back reflecting laser through density modulation on critical surface of plasma.The temperature and yields of hot electrons emitting from the normal of metallic target with different Z number were compared. No obvious differences for middle-Z and lower-Z elements, but for high-Z elements, distinguishable increase in temperature and yields was observed.Collimated proton emitting from the backside of metallic film targets irradiated by fs and ps laser pulse were observed. In both situations, protons always emit from the normal way of back target surface, not varied with laser incidence angle. This was explained using so called "separated electrostatic field" set up by hot electrons transported from front surface. Picosecond laser is more effective on proton acceleration for its longer spatial length of pulse comparing to target thickness, which will result in electron recirculating in the target and increasing hot electron number.Hollow and filament proton patterns were observed. A new model different from others was used to explain these interesting patterns. We think the hollow and filament structure of protons is produced by the hot electron current with a same transverse distribution, which is connected with the instability of hot electrons transportation in solid target. At the beginning of transport, a large number of hot electrons were produced at the front surface by laser interaction with target during laser pulse duration. The current connected with these hot electrons is so large (farlarger than Alfven current limitation) that it cannot transport before the return current being recalled to cancel it. These hot electrons piled up at the front surface and built up a potential, which had a steepest gradient along the intercept to the rear surface. As a result, hot electrons will prompt to transport along this way after the return currents being invoked. But the conductivity will decrease fastly along this axis due to Ohm heating, the current will choose a an...