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Fusion Science and Technology
Latest News
Commercial nuclear innovation "new space" age
In early 2006, a start-up company launched a small rocket from a tiny island in the Pacific. It exploded, showering the island with debris. A year later, a second launch attempt sent a rocket to space but failed to make orbit, burning up in the atmosphere. Another year brought a third attempt—and a third failure. The following month, in September 2008, the company used the last of its funds to launch a fourth rocket. It reached orbit, making history as the first privately funded liquid-fueled rocket to do so.
S. Krupakar Murali, J. F. Santarius, G. L. Kulcinski
Fusion Science and Technology | Volume 57 | Number 3 | April 2010 | Pages 281-291
Technical Paper | doi.org/10.13182/FST10-A9471
Articles are hosted by Taylor and Francis Online.
Inertial electrostatic confinement devices can generate secondary, thermionic, photo, and field emission electrons from the cathode grid, which is a drain on the system. Of the various electron emission contributions, methods to study and minimize the thermionic emission current are explored in this paper using a new diagnostic called "chordwire" - wire placed in the form of a chord of a circle inside the cathode that intercepts particles. This chordwire intercepts particles and gets heated; the rise in temperature can be monitored externally using a pyrometer. Local power balance on the chordwires can then be used to infer the particle flux reaching the chordwires. This diagnostic helps show that to accurately estimate the ion current reaching the central grid, the thermionic electron emission has to be taken into account. The thermionic emission could become significant even for low power operation (<10 kW) in the presence of asymmetric grid heating. The asymmetric grid heating can be mitigated by homogenizing the ionization source around the chamber. The ion-recirculation current equation has been updated to accommodate the thermionic emission current. This ion-recirculation current equation shows that while the electron current increases nonlinearly with the power-supply current (when the grid is thermionically active for input power that is >10 kW), the ion current increases only in a less-than-linear fashion. Hence, the scaling of the fusion productivity with the power-supply current appears to be less than linear. Material selection and device operation should be aimed at reducing this electron energy drain for optimum performance. The overall thermionic emission from the cathode could be reduced through the selection of appropriate grid material with high work function (e.g., Re and W-25%Re). Moreover, this material also has lower sputter yield relative to Type 304 stainless steel, thus helping in high-voltage operation of the device.