Pulsed power accelerator for material physics experiments

Abstract

We have developed the design of Thor: a pulsed power accelerator that delivers a precisely shaped current pulse with a peak value as high as 7 MA to a strip-line load. The peak magnetic pressure achieved within a 1-cm-wide load is as high as 100 GPa. Thor is powered by as many as 288 decoupled and transittime isolated bricks. Each brick consists of a single switch and two capacitors connected electrically in series. The bricks can be individually triggered to achieve a high degree of current pulse tailoring. Because the accelerator is impedance matched throughout, capacitor energy is delivered to the strip-line load with an efficiency as high as 50%. We used an iterative finite element method (FEM), circuit, and magnetohydrodynamic simulations to develop an optimized accelerator design. When powered by 96 bricks, Thor delivers as much as 4.1 MA to a load, and achieves peak magnetic pressures as high as 65 GPa. When powered by 288 bricks, Thor delivers as much as 6.9 MA to a load, and achieves magnetic pressures as high as 170 GPa. We have developed an algebraic calculational procedure that uses the single brick basis function to determine the brick-triggering sequence necessary to generate a highly tailored current pulse time history for shockless loading of samples. Thor will drive a wide variety of magnetically driven shockless ramp compression, shockless flyer plate, shock-ramp, equation of state, material strength, phase transition, and other advanced material physics experiments.

Impedance-matched Marx generators

“…Such IMGs have already been developed, and serve as the prime-power source of the new Thor accelerator [18,20,[22][23][24][25]27]. Presently, each Thor brick drives four polyethyleneinsulated 11-Ω coaxial transmission lines connected electrically in parallel.…”

“…The impedance of the set of four parallel lines is approximately matched to that of a single brick. Sandia National Laboratories is presently building a prototype Thor machine that could eventually be driven by as many as 288 bricks [18,20,[22][23][24][25]27].…”

“…VIII, the simplest form of an IMG is a single brick that drives an impedance-matched load. Such IMGs have already been developed and serve as the prime-power source of the new Thor accelerator [18,20,[22][23][24][25]27]. (The first Thor machine has been designed and is being assembled at Sandia.)…”

“…Motivated by these observations, we have conceived a new class of prime-power sources that do not use ferromagnetic cores: impedance-matched Marx generators (IMGs) [18,20,[22][23][24][25][26][27]. An IMG comprises a single stage or several stages distributed axially and connected electrically in series.…”

A Primer on Pulsed Power and Linear Transformer Drivers for High Energy Density Physics Applications

“…By connecting several of these brick-driven cable lines together in parallel at the load, precise control over pulse shaping can be achieved. These machines are typically referred to as cable pulsers [105]. Bricks are also now being used to drive X-pinches for portable and efficient radiography sources [106], [107].…”