Power Flow in a Recyclable Transmission Line of a Z-Pinch Driven Inertial Confinement Fusion Energy System

Abstract

Summary form only given. The recyclable transmission line (RTL) is a conical magnetically insulated transmission line that connects the pulsed power generator to the Z-pinch load driving an inertial confinement fusion target. The electric field stresses on the cathode of the RTL exceed the turn-on threshold and cause electron emission; however, electrons are magnetically insulated from the anode by the high currents. Because of the distributed current of the electron flow, the effective impedance of the RTL is reduced from the vacuum impedance Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> to the flow impedance Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> . Before power reaches the load, the RTL runs at Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SL</sup> , the self-limited impedance. Once current flows in the initially low impedance Z-pinch load, a re-trapping wave propagates back up the RTL, reducing the voltage, returning some of the electron flow to the cathode, tightly insulating the remaining electron flow, and increasing Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> to a value close to Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . When the pinch begins to implode strongly, the rapidly changing load inductance drives the voltage up and the flow impedance again decreases toward Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SL</sup> . As long as the anode does not emit ions, the RTL can be confidently designed to efficiently deliver power to the load. However, high current density can resistively heat the anode to a sufficient temperature to desorb gas, which can ionize to form anode plasma. Near the load, the heating can be so severe that surface melting can occur. In this work, the effects on power flow of ion emission from anode plasmas are considered. Ion emission over a significant length of the RTL could result in large current losses. On the other hand, ion current losses could be mitigated by magnetic insulation of the ions. Analytic theory is being developed and PIC simulations are being carried out to evaluate the power flow efficiency in this environment. Available results will be discussed, and other issues, such as electrode plasma expansion, will be identified