Saturated magnetic fields of Weibel instabilities in ultraintense laser-plasma interactions

Recent advancements in ultraintense, short pulse lasers have allowed for the exploration of many novel regimes in the field of laser-plasma interactions.Energetic charged particles generated by laser-plasma interactions can be used in many applications including the initiation of tabletop particle accelerators as well as fusion by fast ignition. The generation of energetic particles by the interaction of an ultraintense laser pulse with a plasma has been demonstrated in theoretical and experimental studies. A fast ignitor concept was proposed as the approach to efficiently ignite the high density fusion fuel plasmas with an ultraintense short pulse laser. In the fast ignitor scheme, the intense laser pulse propagates through a colonal plasma up to several times the critical density and delivers energy to high energy electrons. These highly energetic particles then transport the energy through the overdense plasma to the center of the compressed core and ignite the fuel there. It is known that interactions of ultraintense laser pulses with overdense plasmas lead to the generation of a magnetic field (the so called Weibel instability). The Weibel instability breaks up the high energy electron current into filaments. It is known that the self-generated magnetic fields play a crucial role in this energytransport. The self-generated magnetic fields are a serious obstacle to the realization of the fast ignitor scheme. There have been a number of many reports on the Weibel instability of self-generated magnetic fields. It is very important to determine the saturated magnetic fields. The interaction of ultraintense laser pulses with overdense plasmas is studied by theory as well as three-dimensional particle-in-cell simulations. Self-generated magnetic fields are observed in the plasma target owing to the Weibel instability. The growth rates of the self-generated magnetic fields and the saturated magnetic fields in our theory are in good agreement with the results of our simulations. It is found that the saturated magnetic fields of Weibel instabilities are determined by the laser intensity and the plasma density. (orig.)