Andreas J. Kemp

Ignition conditions for magnetized target fusion in cylindrical geometry

Ignition conditions in axially magnetized cylindrical targets are investigated by examining the thermal balance of assembled DT fuel configurations at stagnation. Special care is taken to adequately evaluate the energy fraction of 3.5 MeV alpha particles deposited in magnetized DT cylinders. A detailed analysis of the ignition boundaries in the ρR,T parametric plane is presented. It is shown that the fuel magnetization allows a significant reduction of the ρR ignition threshold only when the condition BR 6 × 105G cm is fulfilled (B is the magnetic field strength and R is the fuel radius).

Modeling ultrafast laser-driven ionization dynamics with Monte Carlo collisional particle-in-cell simulations

Ionization dynamics of cold dense matter induced by ultrashort (<100 fs) laser pulses is studied for intensities at the onset of the relativistic regime by one-dimensional kinetic simulations. As a model we use a particle-in-cell code that includes field and electron collisional ionization, as well as elastic binary Coulomb collisions. As examples for the different ionization mechanisms, we give the spatial and temporal evolution of laser-induced ionization dynamics in helium gas and solid boron targets. Special attention is paid to the quasi-static electric fields at the rear surface of laser-irradiated targets that are important for laser-ion acceleration.

Implosion and ignition of magnetized cylindrical targets driven by heavy-ion beams

Implosions of cylindrical targets, directly driven by heavy-ion beams irradiated along the cylinder axis, are investigated by one-dimensional magneto-hydrodynamic simulations. In order to reduce heat losses from the hot fuel, which is enclosed by a metallic tamper, an axial magnetic field is introduced in the targets prior to implosions. We find that diffusive loss of magnetic flux out of the fuel leads to an accumulation of fuel material next to the cold pusher, causing a major problem for the efficiency of magnetized implosions. Magnetized target fusion (MTF) is an important application of magnetized cylindrical implosions. Looking for an optimum reference configuration for MTF with heavy-ion beams, we find the ignition threshold of magnetized cylindrical fusion targets to be at a driver pulse energy of about 10 MJ per centimetre target length; this value is nearly independent of target size and driver power, while the fuel temperature is required to be larger than 50 eV prior to implosions. Finally, we compare our reference case of an igniting MTF target to a standard indirect-drive heavy-ion fusion target.

Ignition conditions for magnetically insulated tamped ICF targets in cylindrical geometry

The ignition conditions of cylindrical ICF targets, magnetically insulated and inertially confined by a tamper, are investigated by means of one dimensional hydrodynamic simulations. The central point of interest is the effect of the tamper on the minimum fuel ?R value required for igniting pre-assembled fuel configurations. These configurations are studied for complete suppression of heat conduction losses and full re-deposition of alpha particles in the fuel due to the magnetic field. It is found that the value of ?R required for ignition depends significantly on the tamper volume and the tamper entropy at stagnation, and that it scales with the fuel mass m per unit length as (?R)ign m-?, where 0.65 ? ? ? 1.0.

Magnetized cylindrical targets for heavy ion fusion

Ignition conditions for magnetized cylindrical fusion targets are investigated by means of one-dimensional hydrodynamic calculations. Of particular interest is the effect of a tamper surroundingthe fuel at the time of stagnation. The key assumption in this paper is that the targets are magnetically insulated, i.e. electronic and ionic heat conduction as well as the diffusion of 3.5 MeV alpha particles are suppressed. It is found that magnetically insulated targets can be ignited at significantly reduced values of the fuel rR, but, in contrast to conventional fusion targets, the value of the fuel rR at ignition depends on the fuel mass as well as on the tamper entropy. # 2001 Elsevier Science B.V. All rights reserved.

Kinetic theory of alpha particles production in a dense and strongly magnetized plasma

In connection with fundamental issues relevant to magnetized target fusion, the distribution function of thermonuclear alpha particles produced in situ in a dense, hot, and strongly magnetized hydrogenic plasma considered fully ionized in a cylindrical geometry is investigated. The latter is assumed in local thermodynamic equilibrium with Maxwellian charged particles. The approach is based on the Fokker–Planck equation with isotropic source S and loss s terms, which may be taken arbitrarily under the proviso that they remain compatible with a steady state. A novel and general expression is then proposed for the isotropic and stationary distribution f(v). Its time-dependent extension is worked out numerically. The solutions are valid for any particle velocity v and plasma temperature T. Higher order magnetic and collisional corrections are also obtained for electron gyroradius larger than Debye length. f(v) moments provide particle diffusion coefficient and heat thermal conductivity. Their scaling on colli...

Magnetized target fusion in cylindrical geometry

Abstract General ignition conditions for magnetized target fusion (MTF) in cylindrical geometry are formulated. To attain an MTF ignition state, the deuterium–tritium fuel must be compressed in the regime of self-sustained magnetized implosion (SSMI). We analyze the general conditions and optimal parameter values required for initiating such a regime, and demonstrate that the SSMI regime can already be realized in cylindrical implosions driven by ∼100 kJ beams of fast ions.