Riemann's Contribution to Flight and Laser Fusion

started to fly again, there was a new center in Braunschweig.There I built my own wind tunnels. I came to ) von Braun. We Germans talked to each other so that wetunnels, but rocketry, too. It was then that I got to knowBraunschweig in 1936. Then I had a really different, transsonickind of a tunnel, with a very large diameter, and a ment. When they had experience, they told me about it,didn't spend a million reichsmarks on the same experi-supersonic tunnel with a small cross section. And I also ) and when we wanted a new experiment, we told eachhad a rocket test facility in the country. It was in the ! other. Of course, it is sometimes very good for twocountry, because a lot of people who invented rockets 5 different people to test the same thing. But we were notdied from the explosions; therefore, we couldn't build in i supposed to do that.the neighborhood of the town. But I had to go there a Icouple of times every month to see what they were doing. Question: What was the motivation for the research youTherefore, my problem was at that time not only wind i did on self-similar solutions in spherical geometry?Busemann's design of a conical focus for shock waveswas published in 1942 in Luftfarhrtforschung (vol. 79, p.737), the same journal that published K. Guderley'sfamous paper on self-similar solutions to the focusingof shock waves in a spherical geometry. Two of theview-graphs used in Busemann's secret 1940 talk onshaped charges are reproduced in a and b. Busemannreports that the initial motivation for these focusingFigure 2CONICAL FOCUSING OF SHOCK WAVESideas came from the conception of a dimensionalconstraint on the propagation of shock waves. Thus, ahighly symmetrical geometry is chosen, such as asphere, cylinder, or cone. The cone and sphere sharethe property of having a zero-dimensional focus (apoint), as opposed to the cylinder with a line focus.The result in practical terms is a technique for thegeneration of almost unlimited pressures at the focus.Some of the geometrical considerations in the reflection,interference, and concentration of shock wavesare shown in a and b. These flows are all steady, but itis possible to generalize these techniques if the numberof space dimensions is reduced by one, and then totreat nonsteady flows. Busemann notes that his firstnonsteady solutions, which are important in aerodynamics,were just adaptations of the conical supersonicsolutions.Laser fusion research today uses this idea to generatethe pressures and temperatures necessary for ignitionin a spherical target. The figure on page 29 shows aspherical compression scheme used at Lawrence LivermoreNational Laboratory for laser-compressed fusionfuel, using the geometry of Guderley.The conical geometry proposed by Busemann hasbeen extensively investigated in the Soviet Union, andhas resulted in the first fusion reactions produced byan electron beam (by Leonid Rudakov in 1976) and bychemical explosives (by a Polish group under the directionof General Kaliski). The theoretical work on theSoviet conical pellet design appeared in a paper by V.A. Belokogne in 1965 (see c). The Polish configurationis shown in d.38 FUSION October-November 1981