Astounding Science Fiction, February 1952 (British Edition) — page 50: what you’re looking at

Machine-transcribed from the original scan — historical spelling and the odd misread are preserved.

48 Brennan snorted. “Do you expect me to take this seriously? There isn’t a substance known that wouldn’t be a thin gas at that temperature!” | “Wait a minute; here’s the idea in a single dose: the reaction is designed to run in the center of an evacuated sphere. By the time the radiation reaches the walls of the sphere it will be distributed according to the in- verse cube law and the energy per unit area of shell surface will be something that can be handled. A circulating fluid in the shell, perhaps gaseous mercury or liquid silver, Will act as a coolant to keep the shell below its melting point and will serve also as a heat exchange agent coupled to an engine to per- form useful work. If mercury were used, some sort of turbine would be a convenient apparatus.” Brennan chewed on it a while and nodded. “Sorry if I snapped; I’m beginning to get the idea. All that’s necessary now is to get the deuterons packed in the center of the chamber, get them up to eight hundred thousand degrees, and keep ’em coming!” “T think it will be easier to explain if we consider the reaction in operation. The in- ternal shell wall will be at white heat, limited only by the melting point of the material, and in that condition it will both radiate and reflect back into the reactor an ’ appreciable part of the reaction energy. Since the shell is spherical, the focus of this radiation will be at the center. Now about those eight hundred degrees: a temperature ‘of this order is really meaningless, since the ordinary concept of temperature reduces to just a molecular jiggling. What is important is the energy flux per unit volume or the number of high energy photons passing through a given volume at a given time. if the focus is sharp enough, the energy fiux at the center of the reactor will be sufficient to initiate the required deuteron-deuteron collisions. “Now suppose that deuteron beams which have been highly accelerated are focused at the center of the sphere. Since they are of like positive charge they will repel each other and the result will be a momentarily compressed cloud of high deuteron concen- tration at the point of greatest energy flux, which is the condition for initiating reaction. The reaction will propagate and then damp out almost insfantly for two reasons: the first is that the region of high deuteron con- centration and therefore of high collision probability, is very small. The second reason concerns the immense radiation pressure ASTOUNDING SCIENCE FICTION generated by the chain reaction, which will disrupt the deuteron cloud and the i0n beams. After dampout and dissipation of the energy to the walis of the sphere, the ion beams realign and the process repeats. For additional control we could actually run the ion beams in timed pulses. Some of my col- leagues believe it is possible to use gaseous deuterium or even heavy-water vapor jets instead of the ion beams but the decrease in sharpness of focus would mean a larger sphere.” “This reaction of yours will be intermittent then. A sort of variable star.” “Fortunately, yes. No scheme would serve to handle the energy output of a continuous chain reaction.” “You've shown how ithe process would maintain itself, once started. How do you get the sphere up to temperature to begin with?” “That’s no problem; we could run the mercury coolant in reverse to heat the sphere from an external energy source, The thing will be insulated of course, probably buried underground for radiation protec- tion.” “And the deuterium? I understand that heavy hydrogen is an expensive item.” “It’s cheap enough for this use. Besides, we could easily breed deuterium by proton- proton collision if we diluted our deutertum with ordinary hydrogen. The reaction product would be collected on a negative erid and drawn off. Furthermore, there is another reaction using ordinary hydrogen that runs at a higher temperature and which can be substituted after the required energy flux is established. This process goes by successive collisions from hydrogen through deuterium and tritium to ordinary helium. The energy output is even greater than in the AHGT reaction but the higher tempera- ture requirement would mean a larger sphere.” “Could you give me some idea of the apparatus itself; the dimensions involved, materials of construction, and so on?” “T'll outline our present thinking. The ‘material for the inner lining of the sphere will be graphite brick. Carbon begins to sublime at thirty-five hundred degrees cen- tigrade, far above any known metal or alloy, and will permit us to keep the dimen- sions of the shell small. It is also a good heat conductor at high temperature, quite as good as steel. That will enable a high rate of-energy take-off by the coolant which will circulate through it. Carbon oO MIGIOO (S@) SHalG©