# Design of a Compact 1-MV-Class Radial Closing Switch for Tesla Type Generator
## 1 Introduction  
The closing switch is an essential component for most pulsed power systems, since it is not only related to the performance of the system but also relevant to its overall weight and size [1; 2; 3; 4; 5; 6]. Due to its importance, a great effort has been undertaken to improve the main characteristics of the closing switch such as jitter, lifetime, operating voltage, and weight. Different types of switches have been developed, such as the single gas-gap switch [7; 8], the trigatron switch [9; 10; 11], the V/N switch (voltage-division number) [12; 13; 14], the corona-triggered switch [15; 16; 17], and the radial switch [18; 19].  
Each kind of closing switch has its own advantages and disadvantages. For example, the single gas-gap switch can conduct a high current up to hundreds of kilo amperes (kA), but the repetition rate is limited and the jitter can be relatively large [7; 8]. The trigatron switch, designed with a needle-like electrode placed in the center of the low-voltage (LV) electrode of the gas gap to initiate the breakdown, can partially solve the problem of jitter [9; 10; 11]. In order to increase the repetition rate and further lower the jitter of the single gas-gap switch, the V/N switch and the corona switch were developed, the former using the technology of the LC circuit (inductance and capacitor) to revert the voltage to realize trigger [12; 13; 14] and the latter using the technology of corona discharge to initiate and stabilize the discharge [15; 16; 17]. Both switches, working in a SF\({}_{6}\) atmosphere, can reduce the jitter within a range of 5% [12; 16] and can work at a voltage level of 1 MV.  
Aside from these switches, some other types of switches which can operate at a voltage higher than 1 MV were also reported, such as the 2-MV self-triggered switch [20], the 2.4-MV annulus flat water switch [21], the 3-MV UV illumination switch [22], and the 3-MV multi-channel multi-stage reduced-model switch [23]. All these types of switcheswere designed with the discharge channel in the axial direction, which is also the direction of the energy transmission.  
Switches with radial discharging channels are needed in some specific occasions. In ref. [18], the design criteria for such a switch was reported and a wide-band switch was designed and tested. The switch in ref. [18] was used in satellite communication mobile terminals, rather than in the pulsed power domain. Later, a higher power (10 kV, 40 kA) radial switch was reported in ref. [19], working with 24-atm H\({}_{2}\) gas as the insulation media.  
Even there are two types of radial switches reported, they just operate in a relatively low voltage level. There is no radial switch which operates at a voltage either in the hundred-kilo-volts class or in the MV class reported.  
In this paper, a MV-class radial switch was designed for a Tesla-type pulsed power generator. Main features of the switch are as follows: (1) Having MV-class and radial working mode; (2) using only SF\({}_{6}\) as the insulating gas (1 atm \(\approx 10^{5}\) Pa = 1 bar); (3) having a gas chamber as small as 3.2 L in volume; (4) enclosing the electrodes with reliably-insulated supporting insulators. Section 2 is devoted to the general considerations for the design of such a switch. Section 3 is devoted to calculating the operating parameters of the switch. Section 4 deals with numerical simulation of the electrical characteristics and further optimization. Section 5 presents the preliminary testing of this switch. The paper ends presenting a few conclusions.