Experimental research of microsecond plasma interrupting switch (PCIS). Canal concept of PCIS operation

摘要

Main results on plasma current interrupting switch (PCIS) or plasma erosion opening switch research are reported. A canal concept allowing to compare microsecond and nanosecond generators with PCIS and a model of PCIS operation are proposed. Plasma opening switch research [1,2] show that they are prospective for microsecond inductive energy storage systems. The scheme of high power generators including PCIS is prospective for industrial applications. From the other hand physical processes taking place in the rear plasma (concentration of (1012–1014) cm−3) with high current (amplitude 100–1000 kA, current rising time (10–100) ns) are interesting for theoretical and experimental research. Further progress in experimental field is connected with both generalization and new results on detailed physical picture of PCIS operation appearance. With generalization of experimental results [3,4] it is worth to outline a certain concept of PCIS operation which proposes plasma volume division onto parallel operating canals (fig. l). They have certain values of impedance on stages of erosion and current interruption and these values are determined by concrete geometry and plasma concentration. Experiments used different variants of plasma guns displacement (at inner and/or outer electrode of PCIS going along a circle or along a cylindrical surface with the length exceeding electrode diameter). It was shown that charge density limit exists and charge goes through inner surface of PCIS outer electrode — qlim= (1–3) mKl/cm2. This value limits energy flow density through plasma volume. Attempting to exceed charge density limit with concentration growth makes interruption impossible. If not to take into account plasma gun construction it is possible to divide plasma volume on parallel canals with single square on outer electrode surface. To increase charge value going through PCIS or t- increase current drive amplitude or its rising time it is necessary to increase geometrical dimensions: diameter or length. In experiment with "wide" PCIS it was shown (fig.2) [4] that with current rising more and more PCIS area (and plasma canals) are captured by current. Both current and charging time growth requires more plasma canals that results in impedance decrease. If no more new canals could be created then interruption before drive current maximum occurs. The plasma canal which permits higher current increases its impedance earlier. That results in current redistribution and equalizes the interruption time from each canal.