High-Energy-Density Physics Studies With the Gas Puff Platform

In this seminar, I will discuss high-energy-density physics research at the COBRA (COrnell Beam Research Accelerator) pulsed power facility using the gas puff platform. The COBRA generator compresses ≈ 100 kJ into a 1 MA current pulse with a 100–220 ns rise time, utilizing state-of-the-art technology, notably the magnetically insulated transmission line. The triple-nozzle gas puff delivers a Mach-5 flow into the cathode-anode region, preionized before the main COBRA pulse forms a plasma column that pinches and stagnates on axis, creating a Z-pinch plasma.

Studies suggest the plasma column formed during implosion and stagnation is likely turbulent. X-ray spectroscopy revealed a discrepancy between total ion kinetic and ion thermal energies, while Thomson scattering required an additional Gaussian broadening term. This ambiguity, whether due to velocity gradients or turbulence, underscores the need to understand kinetic energy conversion into radiation, crucial for fusion applications.

In this talk, I will present the imaging refractometer diagnostic, which detects angular deflections of the laser beam caused by plasma density fluctuations. Results show that the Z-pinch plasma near stagnation randomizes the beam, generating speckles that indicate turbulence, supported by 3D Beam Propagation Method simulations. I will also discuss recent 3D XMHD PERSEUS runs, highlighting Z-pinch morphology and the role of the Hall term and anomalous resistivity. This research investigates the structure of the current-carrying plasma sheath and contributes to the general understanding of Z-pinches. Finally, I will introduce the exploding gas puff setup on COBRA, which produces high-Mach flows relevant to high-energy-density physics, astrophysics, and material science.