The unique design features of an ICF power system relate to the reaction chamber and ancillary components. Underlying these features-with critical consequences on design criteria-are the nuclear-atomic energetics processes leading to fusion with the evident requirement of economic and self-sustaining performance of the system.

Fuel pellet manufacture involves spherical coating technology at the micro­scale of composition and geometry. Entry of the pellets into the bum chamber will occur by gravity combined with pneumatic injection demanding, however, extreme trajectory precision. Then, an inordinate quantity of energy has to be deposited into this small pellet by laser or ion beam impingement within the short time of about 10’9 s. The expected multiplied quantity of energy over the bum time Хь = 10’8 s, now residing in the high kinetic energy of the fusion reaction products as well as in various electromagnetic flows and an assortment of debris, will spread out striking a liquid or metallic first wall surface. Both surface and internal radiation damage will occur as well as energy deposition-which needs to be recovered at the average rate that it is deposited. Simultaneously, tritium breeding by neutron capture will occur providing thereby eventual replacement of the scarce tritium fuel. Further aspects of the processes and reaction involved in the blanket surrounding the fusion chamber are addressed in Ch. 13.

Following each pulse, rapid purging of the reaction chamber needs to be undertaken in preparation for the next pulse. This operational cycling is expected to be at a frequency of about 1 Hz or greater, the associated fuel injection rate correspondingly being F+i* as previously introduced.

Extremes of power transport, energy conversion, material flow, radiation damage, and highly co-ordinated electro-mechanical functions will evidently characterize the eventual operation of an ICF power system. Considerable research, design, and testing will still need to be undertaken to arrive at the continuingly elusive goal of such a working power station.

Problems

11.1 Evaluate Ть, Eq.( 11.10) as a function of fb for kT = 20 keV; take рь = 500 Pt-

11.2 Discuss the averaging process for < OV >dt and explain the approximation for it made to evaluate Eq.(l 1.15).

11.3 Derive a relation between pR and the compression ratio, pb < pt, of a simple spherical target. Is a spherical target (e. g. microballoon) target advantageous compared to a disk or planar target?

11.4 Calculate the laser energy required to heat a spherical 50:50% D-T pellet, which attains pbRb = 3 g em’2, to an average kinetic temperature of kT = 20 keV as a function of the pellet density p assuming that only 5% of the laser light is absorbed in the pellet fusion plasma. Evaluate this expression for the cases of

(a) solid density (frozen state) ps = 0.22 g em’3

(b) pb=104ps

and ascertain the corresponding pellet radius in each case as well as the respective confinement times, XjC, the laser power requirements and the fusion energy release for a 10% bumup fraction.

11.5 Formulate the exact calculation of Efu* in Eq.(11.33). Can the suggested

Inertial Confinement Fusion proportionality be validated?

11.6 Undertake an analysis of the difference between the physical processes involved in energy deposition by laser beams and ion beams.