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Theoretical investigation of a photoconductively switched high-voltage spark gap
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10.1063/1.2204756
/content/aip/journal/jap/99/12/10.1063/1.2204756
http://aip.metastore.ingenta.com/content/aip/journal/jap/99/12/10.1063/1.2204756
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

(Color online) The fraction of the voltage that is switched by the spark gap as a function of the input voltage as presented in Ref. 5. For high voltages, almost all the voltage is switched, and only a small fraction of the voltage is lost across the spark gap. With decreasing voltage, an increasing fraction of the voltage is lost across the spark gap. The input voltage is limited to because of self break down.

Image of FIG. 2.
FIG. 2.

(Color online) A schematic drawing of the spark gap switch adapted from Refs. 4 and 5. The gap is an interruption in a coaxial transmission line structure and is filled with either nitrogen or air. By focusing a terawatt laser in a line focus in the spark gap, a laser-produced plasma bridges the gap between the electrodes, switching the voltage that is over the gap.

Image of FIG. 3.
FIG. 3.

(Color online) Schematic representation of model approximation of the laser-produced plasma. The plasma is assumed to be uniform in the and directions. In the cathode fall model of Sec. III, the plasma is also assumed to be uniform in the direction. In the arc model of Sec. IV, the plasma properties vary along ; the grid in which the numerical calculation of the plasma properties is performed is shown, superimposed on a cross section of the plasma. Symmetry is used, and only the top half of the plasma is simulated. On the top left, the coordinate system, as used throughout this work, is drawn. The size of the slab is based on measurements detailed in Ref. 5. The radius of curvature of the electrodes is , hence, they can be considered as planar on the length scale of the plasma.

Image of FIG. 4.
FIG. 4.

(Color online) A schematic explanation of the cathode fall formation. The cathode is at , and the anode is at . (a) The femtosecond laser pulse produces a plasma on a time scale that is essentially instantaneous for the plasma we are interested in. (b) The electrons move because of the applied electric field, creating a cathode fall in which the field is compressed. This field facilitates electron emission by the cathode. The heavier ions are essentially motionless on this time scale.

Image of FIG. 5.
FIG. 5.

(Color online) The field emission current as a function of the electric field at the cathode surface, for values of the work function corresponding to copper and tungsten cathode material. The field emission current of the actual cathode material lies between the two curves in this graph.

Image of FIG. 6.
FIG. 6.

(Color online) The electron density in the spark gap as a function of and , for .

Image of FIG. 7.
FIG. 7.

(Color online) The electron temperature in the spark gap as a function of and , for . The electron temperature is less relevant outside of the central ionized channel, because is very low there (cf. Fig. 6).

Image of FIG. 8.
FIG. 8.

(Color online) The heavy temperature in the spark gap as a function of and , for .

Image of FIG. 9.
FIG. 9.

(Color online) The electrical conductivity in the spark gap as a function of and , for .

Image of FIG. 10.
FIG. 10.

(Color online) The densities of various plasma constituents as a function of .

Image of FIG. 11.
FIG. 11.

(Color online) Left axis: the total resistance of the spark gap plasma at , as a function of . The resistance increases dramatically for decreasing currents. Right axis: the simulated and measured (cf. Ref. 5) percentages of the applied voltage that is switched by the spark gap. The match is good, in particular, for lower currents, although for higher currents, the simulated gap resistance is higher than the observed resistance.

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/content/aip/journal/jap/99/12/10.1063/1.2204756
2006-06-22
2014-04-20
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Theoretical investigation of a photoconductively switched high-voltage spark gap
http://aip.metastore.ingenta.com/content/aip/journal/jap/99/12/10.1063/1.2204756
10.1063/1.2204756
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