A 216 cables synchronization trigger for linear transformer driver

As the peak power of linear transformer driver increases, the number of gas switches in the driver increases rapidly, and thus multi-output synchronization trigger becomes one of the key technical obstacles. The paper conceptually depicts a synchronization trigger, which consists of 36 40nF 120kV high voltage capacitors, 36 low inductance high-pressure gas spark switches and 216 150kV 75Ω coaxial cables. The multiple switches are interconnected in series via a transmission line transformer (TLT), in such a way that the breakdown of all switches can be synchronized automatically by overcharged voltage, like in a Marx generator, and only one fifth or a quarter of all switches requires external synchronization trigger. To gain insight into the principles and characteristics of this technology, an equivalent Pspice circuit model was developed. The simulation shows that when capacitors are charged to 120kV the 75Ω matched load can get a overdamped sinusoidal pulse, with a peaking voltage as high as 110kV, a pulse width approximately 300ns, and a risetime no more than 30ns. It was found that the closing of the first switch will overcharge the other switch, which subsequently forces the following to close. During this process, the discharging of capacitors is prevented due to the high secondary mode impedance of the TLT. When the closing process is finished and all switches are closed, the capacitors discharge simultaneously into the load via the TLT. Now the TLT behaves as a current balance transformer. An interesting feature of this topology is that the risetime of the output pulse will be mostly determined by the switch arc filament inductance and capacitor stray inductance. And the other benefit is that the voltage on any spot of whole configuration will not exceed the capacitors discharged voltage, which is unlike in a Marx generator. To demonstrate this technology, a one ninth prototype system was developed. The prototype has four high-pressure gas spark switches, four 40nF 100kV polypropylene film pulse capacitors and 24 75Ω 100kV high voltage coaxial cables. Output of each cable is connected to a matched low inductance load. Several measures, which usually be used in Marx, were taken. All of four switches are placed together in a house to share the UV photon of the first closing gas gap, which can excite a lots of free electrons to seed avalanche. Two of four switches were triggered by external high voltage signal leading a high ratio overvoltage. Both methods can decrease the jitter of the machine erection time as much low as possible. Meanwhile, an ultra-compact structure is adopted to decrease the inductance of loop. The prototype was tested and the experiment showed an 60kV peak overdamped sinusoidal pulse voltage with 30ns rise time in load, which can be used to trigger a HCEI high-pressure gas spark LTD switch.