The development of hydrothermal energy for direct heat applications is being accelerated by twenty-two demonstration projects that are funded on a cost-sharing basis by the US Department of Energy, Division of Geothermal Energy. These projects are designed to demonstrate the technical and economic feasibility of the direct use of hydrothermal resources in the United States. Engineering and economic data for the projects are summarized. The data and experience being generated by these projects will serve as an important basis for future direct heat development.

Effort was directed toward the fabrication of a micron-spaced thermionic converter diode. This technique demonstrated that interelectrode spacings down to 1.5 ..mu..m could be obtained. Several methods of duplicating the emitter and collector surfaces were also investigated. Two new techniques are proposed; both stem from an earlier idea of using evaporation, photolithography, and etching techniques. These two fabrication methods yielded a one-piece diode structure with a thick-film copper collector, eliminating the need to physically duplicate the electrode surfaces and realign the electrodes. Effort has also been directed toward a more detailed theoretical analysis of micron-spaced thermionic converter performance. Taking into account heat losses through the interelectrode support structure, it is likely that the maximum energy conversion efficiency may be greatest at a spacing somewhat larger than 1 micron (..mu..m), but less than 10 ..mu..m.

The Advanced Test Accelerator (ATA) is a pulsed linear induction accelerator with the following design parameters: 50 MeV, 10 kA, 70 ns, and 1 kHz in a ten-pulse burst. Acceleration is accomplished by means of 190 ferrite-loaded cells, each capable of maintaining a 250 kV voltage pulse for 70 ns across a 1-inch gap. The unique characteristic of this machine is its 1 kHz burst mode capability at very high currents. This paper dscribes the pulse power development program which used the Experimental Test Accelerator (ETA) technology as a starting base. Considerable changes have been made both electrically and mechanically in the pulse power components with special consideration being given to the design to achieve higher reliability. A prototype module which incorporates all the pulse power components has been built and tested for millions of shots. Prototype components and test results are described.