A multi-frame, megahertz CCD imager
June 1, 2009
The Los Alamos National Laboratory's Dual Axis Radiographic Hydrodynamic Test Facility (DARHT) generates flash radiographs of explosive experiments using two linear induction electron accelerators situated at right angles. The DARHT second axis accelerator generates an 18-MeV, 2 kA, 2 sec electron beam which is converted or "chopped" into four individual pulses ranging from 20 to 100 nsec in length at 2 MHz frequency. The individual electron beam pulses are down-converted by a segmented lutetium oxyorthosilicate scintillator, creating four visible light flashes, to image explosively driven events. To record these events, a high efficiency, high speed, imager has been fabricated which is capable of framing rates of 2 MHz. This device utilizes a 512 512 pixel charge coupled device (CCD) with a 25 cm2 active area, and incorporates an electronic shutter technology designed for back-illuminated CCD's, making this the largest and fastest back-illuminated CCD in the world. Characterizing an imager capable of this frame rate presents unique challenges. High speed LED drivers and intense radioactive sources are needed to perform basic measurements.We investigate properties normally associated with single-frame CCDs such as read noise, gain, full-well capacity, detective quantum efficiency (DQE), sensitivity, and linearity. In addition, we investigate several properties associated with the imager's multi-frame operation such as transient frame response and frame-to-frame isolation while contrasting our measurement techniques and results with more conventional devices.