M.M. Basko

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).

An improved version of the view factor method for simulating inertial confinement fusion hohlraums

A modified version of the view factor equations is proposed which improves the accuracy of the description of temporal effects in energy redistribution by thermal radiation in cavities driven by power pulses typical for inertial confinement fusion (ICF). The method is applied to analyze the process of radiative symmetrization in the simplest type of closed cylindrical hohlraums heated by two x‐ray rings on the sidewall of the hohlraum case. Such hohlraums may be used in certain types of ICF targets driven by ion beams.

Hotraum target for heavy ion inertial fusion

A new version of indirect drive target is proposed for heavy ion inertial fusion (HIIF), in which the cavity for radiative symmetrization is filled with a low density low Z material and is called a hotraum. When heated to a temperature T ≥ 100 eV, the hotraum becomes transparent to thermal X-rays and ensures radiative smoothing of the energy flux which implodes the fuel capsule enclosed in the cavity. Ion beams are focused on the full target cross-section and deposit their energy in the high Z casing and in the outer region of the hotraum. The initial target configuration is spherical and requires no special orientation in the reactor chamber. Enhanced hydrodynamic efficiency of the capsule implosion, resulting from tamped ablation inside the hotraum, compensates for the high losses in the hotraum and leads to a beam-to-fuel energy coupling of about 5% and target gains in the range of 50-100. Hydrodynamic mapping of deposition nonuniformities onto the fusion capsule can be avoided by fast initial heating of the hotraum. A regime is found in which the ablating capsule insulates itself from hydrodynamic disturbances in the hotraum. The low density required for the hotraum fill allows stopping ranges of up to 100 mg/cm2, corresponding to 6 GeV 209Bi ions

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.

High gain DT targets for heavy ion beam fusion

In a parametric study of reactor size DT targets driven by beams of heavy ions it was found that spark ignition and high energy gains can be achieved in four-layer single-shell targets irradiated by a nonshaped box pulse of 10 GeV 209Bi ions. With an input energy of Ein ≈ 6 MJ delivered in tin ≤ 10 ns, one-dimensional energy gains of G 400 are possible in the optimum cases. It is shown that, to obtain spark ignition and high energy gain, two conditions must be necessarily met: (1) a high enough implosion velocity, U∞ 6.2 × 107 Ω-1/2 cm/s, must be reached, and (2) the fuel compression must be accomplished with a low enough pusher/fuel mass ratio, Mp/MDT 5-7 (Ω is a dimensionless parameter determined by the density distribution in the compressed target core). It was found also that when the ρΔr of the cold part of the compressed fuel is 2-5 g/cm2, the main portion of the fuel is ignited owing to the heating by 14 MeV neutrons emitted from the central hot region

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.

Symmetry of illumination and implosion of hotraum targets for heavy ion inertial fusion

The symmetry of implosion of the hotraum target that has been proposed by J. Meyer-ter-Vehn and the author is analysed in the case when the target is driven by a non-spherical ensemble of heavy ion beams. The ion beams, each with a final focus radius rbf L R (R is the target radius), are all assumed to irradiate the target at the same angle CY,, and symmetrically with respect to the equatorial plane. Separate one dimensional (1-D) simulations for the pole and equator target sectors indicate that the t = 2 mode in the asymmetry of fuel implosion vanishes for a,, = 36. The P = 4 mode can also be eliminated by adjusting the ion current profile across each beam. It is conjectured that the higher asymmetry modes with h E 6 will be smoothed out by radiative symmetrization to 5 1 %. A 1-D average (over the target latitude) energy gain of G = 57 is calculated.

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.

On target design for heavy-ion ICF and gain scaling

SummaryFirst, gain scaling for ignition experiments recently published by the Livermore group is interpreted within the isobaric gain model. Secondly, two options for indirect drive of fusion targets with heavy-ion beams are compared, one having localized converter elements and the other using low-Z foam in the hohlraum for conversion. In addition, the new code MULTI2D for two-dimensional radiation hydrodynamics simulation is briefly discussed, and also progress in high-Z opacity calculations; both topics are relevant for future target work.

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.