A HIGH ENERGY FAR-INFRARED SOURCE FOR COLLECTIVE THOMSON SCATTERING DIAGNOSTICS

A CRITICAL NEED EXISTS FOR A DIAGNOSTIC INSTRUMENT TO MEASURE THE ENERGY DISTRIBUTIONS AND DENSITIES OF CONFINED ENERGETIC ION COMPONENTS IN DEUTERIUM-TRITUIM (D-T) BURNING FUSION TOKAMAKS (E.G., CONFINED ALPHA-PARTICLES WITH 3.5 MEV BIRTH ENERGY). COLLECTIVE THOMSON SCATTERING (CTS) IS RECOGNIZED AS THE MOST ATTRACTIVE APPROACH FOR OBTAINING THIS INFORMATION. A CO2 LASER-PUMPED FAR-INFRARED (FIR) LASER, OPERATING AT A WAVELENGTH OF 100 MUM, APPEARS TO OFFER THE OPTIMUM SOURCE FOR THIS CTS APPLICATION. THIS LASER SOURCE COULD BE OPERATED IN A SINGLE LONG-PULSE ( 10 MUS), HIGH ENERGY ( 10 J/PULSE) MODE, OR IN A REPETITIVELY PULSED MODE ( 30 HZ) WITH MODERATE PULSE LENGTH ( 1 US) AND ENERGY ( 1 J/PULSE). THE FIRST MODE WOULD PROVIDE HIGH TEMPORAL RESOLUTION. THE LATTER MODE, WHICH WOULD REQUIRE INTEGRATING OVER 10 PULSES, COULD BE ACHIEVED WITH A COMPACT, LOW COST SYSTEM IN PHASE II. THE ADVANTAGES OF THE FIR SOURCE ARE (1) AVOIDANCE OF DENSITY LIMITS AND OF CONSTRAINTS IMPOSED BY PLASMA REFRACTION/EMISSION, AND LOWER COST RELATIVE TO GYROTRONS; (2) MUCH LOWER COST, SIZE, AND COMPLEXITY RELATIVE TO FREE-ELECTRON LASERS; AND (3) LARGER SCATTERING ANGLE AND A LOWER COST RECEIVER SYSTEM RELATIVE TO A CO2 LASER SOURCE. PHASE I FOCUSES ON DESIGN STUDIES FOR A LABORATORY PROTOTYPE FIR LASER SYSTEM. DEVELOPMENT AND DEMONSTRATION IS PLANNED FOR PHASE II.