Architecture of petawatt-classz-pinch accelerators

Abstract

We have developed an accelerator architecture that can serve as the basis of the design of petawatt-class $z$-pinch drivers. The architecture has been applied to the design of two $z$-pinch accelerators, each of which can be contained within a 104-m-diameter cylindrical tank. One accelerator is driven by slow ($\ensuremath{\sim}1\text{ }\ensuremath{\mu}\mathrm{s}$) Marx generators, which are a mature technology but which necessitate significant pulse compression to achieve the short pulses ($\ensuremath{\ll}1\text{ }\ensuremath{\mu}\mathrm{s}$) required to drive $z$ pinches. The other is powered by linear transformer drivers (LTDs), which are less mature but produce much shorter pulses than conventional Marxes. Consequently, an LTD-driven accelerator promises to be (at a given pinch current and implosion time) more efficient and reliable. The Marx-driven accelerator produces a peak electrical power of 500 TW and includes the following components: (i) 300 Marx generators that comprise a total of $1.8\ifmmode\times\else\texttimes\fi{}{10}^{4}$ capacitors, store 98 MJ, and erect to 5 MV; (ii) 600 water-dielectric triplate intermediate-store transmission lines, which also serve as pulse-forming lines; (iii) 600 5-MV laser-triggered gas switches; (iv) three monolithic radial-transmission-line impedance transformers, with triplate geometries and exponential impedance profiles; (v) a 6-level 5.5-m-diameter 15-MV vacuum insulator stack; (vi) six magnetically insulated vacuum transmission lines (MITLs); and (vii) a triple-post-hole vacuum convolute that adds the output currents of the six MITLs, and delivers the combined current to a $z$-pinch load. The accelerator delivers an effective peak current of 52 MA to a 10-mm-length $z$ pinch that implodes in 95 ns, and 57 MA to a pinch that implodes in 120 ns. The LTD-driven accelerator includes monolithic radial transformers and a MITL system similar to those described above, but does not include intermediate-store transmission lines, multimegavolt gas switches, or a laser trigger system. Instead, this accelerator is driven by 210 LTD modules that include a total of $1\ifmmode\times\else\texttimes\fi{}{10}^{6}$ capacitors and $5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ 200-kV electrically triggered gas switches. The LTD accelerator stores 182 MJ and produces a peak electrical power of 1000 TW. The accelerator delivers an effective peak current of 68 MA to a pinch that implodes in 95 ns, and 75 MA to a pinch that implodes in 120 ns. Conceptually straightforward upgrades to these designs would deliver even higher pinch currents and faster implosions.