Overview of recent results from the triggered plasma opening switch experiment

Summary form only given. The Triggered Plasma Opening Switch (TPOS) at Sandia National Laboratories is a unique device that exploits the high conductance and zero tensile strength of plasma. The purpose of the TPOS is to take the initial /spl sim/.8 MA (/spl sim/250 ns rise time) storage inductor current and deliver /spl sim/.5 MA, with a rise time of approximately 10 ns, to a load of about 5-10 /spl Omega/. Advantages of this configuration include low current jitter, power gain, low resistive voltage drop, and minimization of trigger input power as the result of using stages. First, plasma is introduced into the TPOS´s A-K gap from plasma flash board sources. Current then flows through the plasma effectively shorting the A-K gap. Next, the switch is triggered when a pulse (50-150 ns rise time) is sent through a magnetic field coil. The energized coil gives rise to an axial magnetic field that pushes the plasma away from the cathode via the j/spl times/B force. (Clearly, this assumes that the magnetic field does not substantially penetrate the plasma, and that the plasma is azimuthally uniform.) Finally, the device triggers another similar stage in series with the first thus creating power amplification. The two stage design is novel, and this experiment is the first to implement magnetically triggered stages. In order for the switch to open correctly the plasma must travel sufficiently far away from the cathode. The plasma travels at the Alfven speed which is proportional to the magnetic field strength and inversely proportional to the density and mass of the plasma. Small percentages of water and oxygen exist, but the plasma is assumed to be dominantly composed of carbon. Therefore, since the mass and magnetic field are known, it is possible to infer the density by observing the opening speed. This is accomplished by measuring the plasmas location combined with the knowledge of the time dependent inductance and electron current. Specifically, if one assumes an a- ial field of /spl sim/1T, and an Alfven speed of approximately 1/spl times/10/sup 5/ to 1/spl times/10/sup 6/ m/s, this equates to a density of roughly 4/spl times/10/sup 21/ to 4/spl times/10/sup 19/ m/sup -3/. If the density is much higher, the switch may not open properly since the plasma´s velocity is not sufficient to traverse the gap in the allotted time. Careful study of these characteristics is being carried out via side apparatus and magnetic field calculations. Hopefully, analysis leads to an ample characterization of the switch and ultimately a better understanding of the manner in which the two stages function.