SILICON JUNCTION DIODE ABSOLUTE RADIOMETERS FOR PLASMA DIAGNOSTICS IN THE SOFT X-RAY AND VACUUM ULTRAVIOLET SPECTRAL REGION

SILICON P-N JUNCTION PHOTODIODES HAVE RECENTLY BEEN DEVELOPED WITH STABLE, THEORETICALLY PREDICTABLE QUANTUM EFFICIENCIES IN THE VACUUM ULTRAVIOLET AND SOFT X-RAY (XUV) SPECTRAL REGION. SCIENTISTS IN GERMANY HAVE INDEPENDENTLY CONFIRMED THAT THE CALCULATED QUANTUM EFFICIENCY OF THESE XUV SILICON DIODES CAN BE USED TO ESTABLISH AN INDEPENDENT RESPONSIVITY SCALE IN THE XUV SPECTRAL REGION. A TYPICAL PRESENT PLASMA DIAGNOSTIC SYSTEM IN THE XUV REGION IS BASED ON THE EXTERNAL PHOTOELECTRIC DETECTORS, I.E., ON VACUUM PHOTODIODES AND MICROCHANNEL PLATES. QUANTUM EFFICIENCIES OF THESE ELECTRON TUBE TYPE OF DETECTORS ARE SUSCEPTIBLE TO MINUTE SURFACE CONTAMINANTS, NECESSITATING THEIR ROUTINE CALIBRATION. ADDITIONAL DISADVANTAGES OF THESE DEVICES ARE THEIR HIGH VOLTAGE REQUIREMENTS FOR THE OPERATION, THEIR LIMITED DYNAMIC RANGE, AND SENSITIVITY TO MAGNETIC FIELDS. IN PHASE I, SINGLE-ELEMENT, HIGH BANDWIDTH (>1 GHZ) AND EIGHT-ELEMENT XUV PHOTODIODES WITH STABLE, KNOWN QUANTUM EFFICIENCIES FOR PLASMA DIAGNOSTICS ARE BEING FABRICATED. DURING PHASE II, FABRICATION OF 1,024-ELEMENT LINEAR ARRAYS AND TWO-DIMENSIONAL XUV DIODE ARRAYS FOR SPECTROSCOPY, IMAGING, AND POSITION SENSING IN THE XUV SPECTRAL REGION ARE TO BE INVESTIGATED. THE ADVANTAGES OF XUV PHOTODIODES INCLUDE LARGE DYNAMIC RANGE (>8 DECADES), EASE IN EXPERIMENTAL IMPLEMENTATION, ABILITY TO OPERATE IN PRESENCE OF GASES, INSENSITIVITY TO MAGNETIC FIELDS, AND LOW COST.