PHOTOCONDUCTIVE SWITCH FOR PULSED POWER HIGH FIELD GRADIENT LINAC'S

ULTRAFAST SOLID STATE PHOTOCONDUCTIVE SWITCHES MAY NOW MAKE POSSIBLE PULSED ELECTRIC FIELDS ON THE ORDER OF 1GV/M ON TIME SCALES OF 1-100 PICOSECONDS. VOLTAGE GRADIENTS OF THISMAGNITUDE ARE BECOMING POSSIBLE THROUGH ADVANCES IN TRANSMISSION LINE DESIGN AND ULTRAFAST PHOTOCONDUCTIVE POWERSWITCHING TECHNOLOGY AND WILL PERMIT SIGNIFICANT ADVANCES INPRODUCING HIGHER ENERGY, COMPACT LINEAR ACCELERATORS FOR SCIENTIFIC AND INDUSTRIAL APPLICATIONS. THE MAJOR OBSTACLESTO SUCCESSFUL APPLICATION OF PRESENT ULTRAFAST PHOTOCONDUCTIVE SEMICONDUCTORS TO PULSED POWER APPLICATIONS ARE LOW BREAKDOWN VOLTAGE, HIGH DARK CURRENT AND CONCURRENT THERMAL RUNAWAY EFFECTS AT HIGH PULSE REPETITION RATES. IN ORDER TO OVERCOME THESE PROBLEMS, IT IS NECESSARY TO CONSIDER VERY WIDE BANDGAP, LARGE DIELECTRIC STRENGTH SEMICONDUCTING MATERIALS SUCH AS DIAMOND. DIAMOND EXHIBITS ULTRAFAST PHOTOCONDUCTIVITY, HAS DARK RESISTIVITIES IN EXCESS OF 10(13) MICRON-CM, EXTREMELY HIGH THERMAL CONDUCTIVITY, AND SIGNIFICANTLY LARGER DIELECTRIC BREAKDOWN STRENGTH THAN EITHER SI, GAAS OR INP. THE PURPOSE OF THE PHASE I PROGRAM IS TO INVESTIGATE THE PHOTOCONDUCTIVE RESPONSE OF DIAMOND FILMS GROWN BY PLASMA ASSISTED CHEMICAL VAPOR DEPOSITION AND TO ASSESS THEIR POTENTIAL FOR HIGH VOLTAGE/HIGH POWER SWITCHING APPLICATIONS FOR HIGH GRADIENT LINEAR ACCELERATORS. PHASE II WILL EXTEND THE PHASE I PROGRAM TO INCLUDE FABRICATION, PACKAGING AND TESTING OF SEVERAL PROTOTYPE DEVICES.