A NOVEL OPTICAL CONCEPT FOR RAPID SCANNING TWO-DIMENSIONAL THOMSON SCATTERING

KNOWLEDGE OF THE ELECTRON TEMPERATURE AND DENSITY THROUGHOUT THE CROSS-SECTION OF A PLASMA FUSION DEVICE IS NEEDED FOR DETAILED UNDERSTANDING OF ITS PERFORMANCE. PRESENT THOMSON SCATTERING TECHNIQUES, WHICH EMPLOY A FIXED OPTICAL ARRANGEMENT, ARE CAPABLE OF PROVIDING SIMULTANEOUS MEASUREMENTS OF THE ELECTRON TEMPERATURE AND DENSITY AT MULTIPLE LOCATIONS ALONG A SINGLE PATH TRAVERSED BY A LASER BEAM THROUGH THE PLASMA. FUTURE NONCIRCULAR TOKAMAKS, SUCH AS ALCATOR C-MOD AND CTT (THE COMPACT IGNITION TOKAMAK), ARE EXPECTED TO HAVE ASYMMETRIC TEMPERATURE AND DENSITY PROFILES BUT TO BE OPERATED FOR LONG STEADY-STATE PERIODS. SWITCHING THE OPTICAL PATH TO BEFOLLOWED BY A 50-HZ ND:YAG LASER DURING THE 20-MSEC-PERIOD BETWEEN PULSES AND PROPERLY DESIGNING THE THOMSON SCATTERED LIGHT COLLECTION OPTICS WOULD ENABLE TWO-DIMENSIONAL ELECTRON TEMPERATURE AND DENSITY PROFILES TO BE DETERMINED WITHIN A SINGLE TOKAMAK DISCHARGE. A SYNCHRONOUSLY POSITIONED OPTICAL ELEMENT (E.G., A MIRROR) WOULD DIRECT THE BEAM ALONG SEPARATE, NEARLY VERTICAL CHORDS FOR SUCCESSIVE LASER PULSES. TECHNIQUES TO SIMULTANEOUSLY DIRECT THE LASER BEAM AND COLLECT THE SCATTERED LIGHT RELIABLY FROM A TWO-DIMENSIONAL ARRAY OF LOCATIONS USING A LIMITED NUMBER OF SPECTROMETERS WILL BE EVALUATED. IN ADDITION, IMPORTANT ISSUES THAT MUST BE CONSIDERED IN DESIGNING SPECTROMETERS FOR THE HIGH TEMPERATURES (5-10-KEV)EXPECTED IN NEXT-GENERATION TOKAMAKE WILL BE EVALUATED.