Corona-stabilized gas spark gap switch for a double forming line with 300 kV working voltage

A high-current self-breakdown gas switch stabilized by corona preionization was developed for closing of 300 kV repetitively operated at 10 pps water insulated double-forming line ( Blumlein) of a nanosecond electron accelerator. The switch is installed at the end of the Blumlein and is used for closing of outer of two coaxial lines. High stability of the self-breakdown voltage (within +/- 1%) at fast charging of Blumlein (during approximate to 1.4 mu s) is achieved by gas preionization in the spark-gap by additional pulsed corona discharge. The spark-gap electrode system includes two main toroidal electrodes and an additional corona needle that is located in the cavity of one of them (negative during the operation). It combines two parallel gas discharge gaps - the main spark gap and an additional corona discharge gap. Separating the functions of the spark and corona gaps makes it possible to optimize the geometry of the electrodes of each gap and provide both the ability to switch high currents and high dynamic characteristics for a long operating time. Dried air is used as a working gas at pressure of 3-4 atm (abs.). Gas blowing system includes 4 gas inlets located at outer flange supporting the high voltage insulator (water-gas interface) and one outlet in the cavity of the grounded main electrode. This scheme of gas flow protects the insulator from deposition of electrode erosion products and minimizes gas flow (approximate to 20 l/min) for stable operation of the switch by removing of the hot gas throw the cavity of the grounded electrode.The design of the switch together with the main results of the working tests will be presented and discussed.