Fast Ignition and Related Plasma Physics

Abstract

Fast ignition is a new ignition scheme which is expected to provide higher fusion gain than the conventional central hot spark ignition. The report starts with the comparison of gain curves for the fast ignition (which is called off-center ignition) and that for the central hot spark ignition. By the use of a two dimensional hydrodynamic code with alpha heating, the two ignition schemes are studied to find the ignition conditions. After the ignition, a nuclear burning wave is seen to propagate through the cold main fuel with a velocity of 2 3x10⁸cm/sec. The spark energy required for the off-center ignition is 2-3kJ and 10-15kJ for the core density of 400g/cm³ and 200g/cm³, respectively. It is demonstrated that a core gain higher than 2000 is possible for a core energy of 100kJ with a hot spark energy of 13kJ. The requirement for the heating time is discussed.

Reviewed also is the plasma physics research related to the fast ignition. In this concept, the laser channeling in the plasma corona surrounding dense fusion plasmas and energy deposition of a relativistically intense laser pulse are key issues. Recent experiments at ILE, Osaka University, indicate that the lOOpsec tightly focused laser pulse is self-focused and channeled deeply into the overdense plasmas.

The 100TW laser was also used to investigate generation mechanisms of multi-MeV electrons and ions which are expected to carry the energy into dense plasmas and to form the hot spark. The recent experiments show that intense MeV electron jets come out from the critical density region. It is also found that collimated MeV ion beams are also generated and penetrate into the overdense plasmas to produce non-thermal neutrons. These phenomena are widely investigated by ID and 2D particles in cell simulations. The channeling and MeV particle generations reasonably agree with the experimental results. Those experimental and theoretical results are applied to the target design of the fast ignition.