Study of Implosion Physics of High-Energy z-Pinches

High current z-pinches are an excellent way to produce high-energy plasmas as radiation sources for Inertial Confinement Fusion (ICF) and x-ray radiation effect studies. High current pulsed power z-pinch machines for these applications have a challenge that limits their ultimate capability, namely the high voltage on the insulator stack due to the large dI/dt. To reduce the high voltage, one of the methods is to decrease the dI/dt by using a longer rise-time driver. For example, a & gt;250-ns, 65-MA ICF driver might be built based on ZR (100-ns, 27-MA) technology, which will reduce the development cost and complexity of the driver compared to a 100-ns, 65- MA driver. In longer time implosions, larger initial diameter loads are necessary than for shorter implosion times to achieve the required ion kinetic energy while matching the mass of the load to the current. The key problem with a large initial radius is that the longer acceleration path can lead to increased RayleighTaylor (RT) instability growth, reducing the x-ray or neutron yield. For mitigating the RT instability, triple gas puffs to tailor the plasma density profiles and/or an external applied magnetic field, Bz, to suppress the hard implosion have been suggested. For studying the instabilities and understanding the implosion dynamics, energy coupling and stagnation physics of high-energy z-pinches, it is necessary to measure the density, temperature and current profiles with high spatial and temporal resolution. Teaming with Lab. of Plasma Studies (LPS) at Cornell University, JSI (JANX Service) proposes this SBIR to investigate gas puff z-pinch hydrodynamics and to develop a set of optical diagnostic instruments for time resolved plasma density, temperature, and implosion current profile. Success of the project will help develop i) advanced longer implosion z-pinch loads for ICF and efficient warm x-ray sources; and ii) user-friendly diagnostic instruments for the high- energy-density plasma communities. In Phase I, we will conduct initial z-pinch experiments on the ~200-ns, 1.1-MA COBRA at Cornell. Implosion of tailored gas puff loads with/without Bz field will be studied. Using a two-frame Laser-Wavefront Analyzer, the time resolved implosion plasma density and/or current profile will be measured, from which the implosion velocity, current sheath structure, and initial estimates of the RT instability wavelength and growth rate can be made. We will also develop a Faraday Rotation Sensor or laser polarimeter that can be used to study the Bz field compression and implosion stabilization. The goals are to mitigate RT instabilities either through tailoring the initial gas density profile or by the external applied Bz field. Compression of the applied Bz field will also be determined. In Phase II, we will continue the z-pinch hydrodynamics research and develop a complete set of instruments that measure the density, temperature, and current profiles from the initial gas phase through the implosion phase to the final pinch phase. These will enable a better understanding of the z-pinch physics and enhancement of the x-ray or neutron production. The data will be extremely valuable for validating MHD computer simulations. The goals of Phase II are to greatly improve our understanding of the R-T instability, to learn how to mitigate it, and to fully develop the suite of instruments to be used by z-pinch and/or other ICF communities for temperature, density and current profile measurements. Commercial Applications and Other Benefits: This SBIR will develop and validate advanced long implosion time z-pinch loads for Inertial Fusion Energy (IFE) and soft/warm x-ray source applications, where they could constitute the break-through needed in designing practical pulsed power drivers for IFE and for nuclear weapons effects testing. These are the most important benefits to DOE, the ICF community, the weapon effects testing community, and the American taxpayer. Also, a set of state-of-the-art high-energy-density plasma diagnostic instruments will be developed, which could have many commercial applications wherever precision optical measurements are required.