Conceptual designs of two petawatt-class pulsed-power accelerators for high-energy-density-physics experiments

We have developed conceptual designs of two petawatt-class pulsed-power accelerators: Z 300 and Z 800. The designs are based on an accelerator architecture that is founded on two concepts: single-stage electrical-pulse compression and impedance matching [Phys. Rev. ST Accel. Beams 10, 030401 (2007)]. The prime power source of each machine consists of 90 linear-transformer-driver (LTD) modules. Each module comprises LTD cavities connected electrically in series, each of which is powered by 5-GW LTD bricks connected electrically in parallel. (A brick comprises a single switch and two capacitors in series.) Six water-insulated radial-transmission-line impedance transformers transport the power generated by the modules to a six-level vacuum-insulator stack. The stack serves as the accelerator’s water-vacuum interface. The stack is connected to six conical outer magnetically insulated vacuum transmission lines (MITLs), which are joined in parallel at a 10-cm radius by a triple-post-hole vacuum convolute. The convolute sums the electrical currents at the outputs of the six outer MITLs, and delivers the combined current to a single short inner MITL. The inner MITL transmits the combined current to the accelerator’s physics-package load. Z 300 is 35 m in diameter and stores 48 MJ of electrical energy in its LTD capacitors. The accelerator generates 320 TW of electrical power at the output of the LTD system, and delivers 48 MA in 154 ns to a magnetized-liner inertial-fusion (MagLIF) target [Phys. Plasmas 17, 056303 (2010)]. The peak electrical power at the MagLIF target is 870 TW, which is the highest power throughout the accelerator. Power amplification is accomplished by the centrally located vacuum section, which serves as an intermediate inductive-energy-storage device. The principal goal of Z 300 is to achieve thermonuclear ignition; i.e., a fusion yield that exceeds the energy transmitted by the accelerator to the liner. 2D magnetohydrodynamic (MHD) simulations suggest Z 300 will deliver 4.3 MJ to the liner, and achieve a yield on the order of 18 MJ. Z 800 is 52 m in diameter and stores 130 MJ. This accelerator generates 890 TW at the output of its LTD system, and delivers 65 MA in 113 ns to a MagLIF target. The peak electrical power at the MagLIF liner is 2500 TW. The principal goal of Z 800 is to achieve high-yield thermonuclear fusion; i.e., a yield that exceeds the energy initially stored by the accelerator’s capacitors. 2D MHD simulations suggest Z 800 will deliver 8.0 MJ to the liner, and achieve a yield on the order of 440 MJ. Z 300 and Z 800, or variations of these accelerators, will allow the international high-energy-density-physics community to conduct advanced inertial-confinement-fusion, radiation-physics, material-physics, and laboratory-astrophysics experiments over heretofore-inaccessible parameter regimes.

Figure 1

Cross-sectional view of a three-dimensional model of the Z-300 accelerator. The model includes a person standing on the uppermost water-section electrode, near the centrally located vacuum section. The outer diameter of Z 300 is 35 m.

Figure 2

Cross-sectional view of a three-dimensional model of a ten-cavity 2-m-diameter LTD module. The anode and cathode are the electrodes of the module’s internal water-insulated coaxial transmission line. Each Z-300 module includes 33 such cavities.

Figure 3

Cross-sectional view of a single 2-m-diameter Z-300 LTD cavity. The upper terminal of one of the two capacitors is charged to $+100\mathrm{kV}$; the upper terminal of the other is charged to $-100\mathrm{kV}$. The lower terminal of each capacitor is initially at ground potential. When the capacitors are fully charged, the potential difference across the switch is 200 kV. After the switch closes, the peak voltage across the cavity’s output gap reaches $\sim 100\mathrm{kV}$. The ferromagnetic cores prevent most of the LTD’s current from flowing along the inner walls of the cavity, which allows most of the current to be delivered to the output gap.

Figure 4

Cross-sectional view of the centrally located vacuum section of Z 300. The section includes six water flares, six vacuum insulator stacks, six vacuum flares, and six conical outer MITLs. The six levels of this system are electrically in parallel. The outer radius of the stack is 2.39 m.

Figure 5

Cross-sectional view of the water flare, insulator stack, and vacuum flare of the uppermost level of the six-level Z-300 insulator stack. The uppermost stack includes seven 5.72-cm-thick Rexolite-insulator rings and six 0.95-cm-thick anodized-aluminum grading rings.

Figure 6

Idealized representation of the inner MITL coupled to a MagLIF load.

Figure 7

Circuit model of the Z-300 and Z-800 accelerators. The quantities $L_s$, $C_s$, and $R_s$ are the series inductance, capacitance, and resistance, respectively, of the system of 90 parallel LTD modules; $R_{\text{shunt}}$ is the shunt resistance of the LTD system; $Z_{\mathrm{in}}$ and $Z_{\mathrm{out}}$ are the input and output impedances, respectively, of the system of six parallel transmission-line impedance transformers; $L_{\text{stack}}$ is the total inductance of the water flares, insulator stacks, and vacuum flares; $L_{\mathrm{MITLs}}$ is the inductance of the six parallel MITLs; $L_{\mathrm{con}}$ is the inductance of the triple-post-hole vacuum convolute; $L_{\text{inner}}$ is the inner-MITL inductance; $L_{\mathrm{load}}$ is the load inductance; and $R_{\text{inner}}$ is a resistive circuit element that models energy loss to the inner-MITL electrodes. We define the quantity $L_{\mathrm{load}}$ so that $L_{\mathrm{load}}(t=0)=0$. The $Z_{\mathrm{flow}}$ circuit element is used to model MITL-electron-flow current that is launched in the outer MITLs and lost to the anode surfaces of the convolute and inner MITL.

Figure 8

Idealized representation of an imploding liner. The quantity $a$ is the liner radius at time $t$, and $\ell$ is the length of the liner. For the MagLIF loads assumed in this article $a_i=0.5\mathrm{cm}$ and $\ell =1.0\mathrm{cm}$ [69].

Figure 9

Simulated electrical-power time histories at the output of the LTD system, the input to the insulator stack, and the liner for (a) a Z-300 shot conducted with a MagLIF load; (b) a Z-300 shot conducted with a dynamic hohlraum; (c) a Z-800 shot conducted with a MagLIF load; and (d) a Z-800 shot conducted with a dynamic hohlraum.

Figure 10

Simulated time histories of the voltage on the vacuum side of the insulator stack, current at the stack, and load current for (a) a Z-300 shot conducted with a MagLIF load; (b) a Z-300 shot conducted with a dynamic hohlraum; (c) a Z-800 shot conducted with a MagLIF load; and (d) a Z-800 shot conducted with a dynamic hohlraum.

Figure 11

Cross-sectional view of a three-dimensional model of the Z-800 accelerator. The model includes a person standing on the uppermost water-section electrode, near the centrally located vacuum section. The outer diameter of Z 800 is 52 m.

Figure 12

Cross-sectional view of the centrally located vacuum section of Z 800. This section includes six water flares, six vacuum insulator stacks, six vacuum flares, and six conical MITLs. The six levels of the system are electrically in parallel. The outer radius of the stack is 2.65 m.

Figure 13

(a) Measured insulator-stack and inner-MITL currents for Z-shot 1548 [37]. The load on this shot was a dynamic hohlraum. The inner-MITL current was measured 6 cm from the symmetry axis of the load. (b) Measured insulator-stack and inner-MITL currents for ZR-shot 2759, which also drove a dynamic hohlraum. The inner-MITL current was measured at the same distance from the symmetry axis.

Figure 14

Idealized circuit model of a coupled MITL-convolute-load system. This model is consistent with that given by Fig. 7, except here we represent the outer-MITL system as a transmission line instead of a lumped inductor.

Figure 15

Idealized version of the accelerator-circuit model illustrated by Fig. 7.

Figure 16

Time history of the electrical power delivered to the inductance $L_{\text{center}}$ of the idealized accelerator-circuit model illustrated by Fig. 15, assuming Eqs. (c7) and (c12).

Figure 17

Time history of the current delivered to the inductance $L_{\text{center}}$ of the idealized accelerator-circuit model illustrated by Fig. 15, assuming Eqs. (c7) and (c12).