Extension of HPM Pulse Duration by Cesium Iodide Cathodes in Crossed-field Devices

Much pulse shortening in HPM devices arises from motion of plasma. A major development is the introduction of cathodes made from Cesium Iodide-coated carbon fiber, which has plasma velocity reduced by factors of a few from uncoated carbon fiber. Reduced CsI velocity has been demonstrated for macroscopic electric fields of 10's of kV/cm. However, many HPM sources, such as the crossed-field devices the MILO and the Relativistic Magnetron, work at higher E-fields. For them 300 kV/cm is required for GW power.For the heavy ions from CsI to dominate the plasma, lighter elements, particularly Hydrogen, must be eliminated from diode surfaces. Techniques for this are known and must be introduced into HPM to achieve the full benefit of the CsI cathode.We will demonstrate that diode plasmas can be controlled by the use of CsI cathodes and hard tube techniques. Specific tasks: 1) Measure CsI diode closure velocity in the electric field regime 100 kV/cm < E < 500 kV/cm. 2) Design methods of introducting hard tube techniques rigorously into HPM crossed-field sources. These constitute Phase I; building a CsI cathodecrossed-field HPM source will be Phase II.