Development of a Two Reference Beam Holographic Technique to Measure the Density Distribution in a Plasma Opening Switch

A GOOD MODEL FOR PREDICTING THE CONDUCTION AND OPENING CHARACTERISTICS OF PLASMA OPENING SWITCHES IS REQUIRED IF SWITCH- ES CURRENTLY IN USE ARE TO BE SCALED UP TO THE CURRENT AND VOLTAGE RATINGS REQUIRED BY THE FAMILY OF THREAT SIMULATOR. EMPIRICAL VERIFICATION OF THE NUMEROUS MODELS WHICH HAVE EVOLVED AROUND DIFFERENT CONDUCTION PROCESSES HAVE MET WITH LIMITED SUCCESS BECAUSE SWITCH CHARACTERISTICS DEPEND WEAKLY ON THE SWITCH PARAMETERS VARIED AND IT IS DIFFICULT TO VARY ONLY ONE SWITCH PARAMETER AT A TIME. MEASUREMENTS OF THE PLASMA DISTRIBUTION WITHIN THE SWITCH, WITH GOOD SPATIAL RESOLUTION, WOULD REVEAL HOW THE PLASMA RESPONDS TO THE SELF GENERATED FORCES IN THE SWITCH. DOMINANT PHYSICAL PROCESSES, INFERRED FROM THESE MEASUREMENTS, COULD THEN BE USED TO CONSTRUCT REALISTIC MODELS OF THE SWITCH. HY-TECH PROPOSES TO USE A TWO REFERENCE BEAM TECHNIQUE TO RECORD A DOUBLE PULSE HOLOGRAPHIC INTERFEROGRAM OF THE PLASMA CROSS-SECTION USING A SHORT PULSE LASER TO "FREEZE" THE PLASMA MOTION. THE PHASE OF THE RECONSTRUCTED INTERFEROGRAM WOULD BE ANALYZED USING PHASE SHIFTED INTERFEROMETRIC TECHNIQUES TO OBTAIN SPATIALLY RESOLVED MEASUREMENTS OF THE PLASMA DENSITY. A PHASE SHIFT RESOLUTION OF 1 X 10-4 FRINGES WITH A SPATIAL RESOLUTION OF O.OLCM IS ANTICIPATED. THESE DENSITY MEASUREMENTS SHOULD INDICATE WHETHER PLASMA ACRETION ASSOCIATED WITH AXIAL SNOW PLOW MOTION OCCURS, HOW MAGNETIC FORCES DISTORT THE PLASMA PROFILE, AND WHETHER EVIDENCE EXISTS FOR THE FORMATION OF A MAGNETICALLY INSULATED VACUUM GAP.