Considerations for generating up to 10 Mbar magnetic drive pressures with the refurbished Z-machine (ZR)

The intense magnetic field generated in the 20 MA Z-machine is used to accelerate flyer plates to high velocity for EOS experiments. A peak magnetic drive pressure on the order of 2 Mbar can be generated, which accelerates an approximately 0.2 g aluminum (Al) disc to 21 km/s. In a planned refurbishment of Z, called ZR, it is expected that up to 26 MA will be delivered to certain loads (e.g., dynamic hohlraums). We have used magneto-hydrodynamic (MHD) simulations to predict the peak magnetic drive pressure (and flyer velocity) that can be generated in a shock physics load on ZR. MHD simulations show that motion of the electrodes during the rise to peak current significantly increases the load inductance, which limits the peak current to values less than the expected maximum. This reduces the peak drive pressure to a value below what would be estimated using the expected peak current in a static geometry. However, MHD simulations also show that starting with a load geometry that maximizes magnetic flux on one wall of the anode, it is possible to reduce dynamic geometry effects by tapering the rise of the voltage pulse in combination with using a stiff material for the cathode. Simulations predict that peak magnetic pressures of 6 Mbar in Al, and 10 Mbar in tungsten are possible on ZR. In addition, it is predicted that flyer velocities of 40 km/s and larger can be achieved.