KEYWORDS: Field effect transistors, National Ignition Facility, Streak cameras, Electrodes, Electronics, Logic, Capacitance, Imaging systems, Control systems, Data acquisition
The optical streak cameras currently used at the National Ignition Facility (NIF) implement the P510 electron tube from Photonis1. The existing high voltage electronics provide DC bias voltages to the cathode, slot, and focusing electrodes. The sweep deflection plates are driven by a ramp voltage. This configuration has been very successful for the majority of measurements required at NIF. New experiments require that the photocathode be gated or blanked to reduce the effects of undesirable scattered light competing with low light level experimental data. The required ~2500V gate voltage is applied between the photocathode and the slot electrode in response to an external trigger to allow the electrons to flow. Otherwise the slot electrode is held approximately 100 Volts more negative than the potential of the photocathode, preventing electron flow. This article reviews the implementation and performance of the gating circuit that applies an electronic gate to the photocathode with a nominal 50ns rise and fall time, and a pulse width between 50ns and 2000ns.
The National Ignition Facility requires a radiation-hardened, megapixel CMOS imaging sensor-based camera to be a
direct physical and operational replacement for the CCD cameras currently used in x-ray streak cameras and gated
imaging detectors. Camera electronics were selected to operate up to 10 krad(Si). The camera incorporates a fast dump
of the sensor followed by exposure and image readout. This allows the dumping of charge due to the prompt radiation
background and then readout of the longer persistence phosphor image from the x-ray diagnostics. Internal timing delays
and optical performance were measured for a radiation-tolerant camera, based on the 2k by 2k CMV4000 sensor from
CMOSIS Inc.
The ICF program at Livermore has a large inventory of optical streak cameras that were built in the 1970s and 1980s. The cameras include microchannel plate image-intensifier tubes (IIT) that provide signal amplification and early lenscoupled CCD readouts. Today, these cameras are still very functional, but some replacement parts such as the original streak tube, CCD, and IIT are scarce and obsolete. This article describes recent efforts to improve the performance of these cameras using today’s advanced CCD readout technologies. Very sensitive, large-format CCD arrays with efficient fiber-optic input faceplates are now available for direct coupling with the streak tube. Measurements of camera performance characteristics including linearity, spatial and temporal resolution, line-spread function, contrast transfer ratio (CTR), and dynamic range have been made for several different camera configurations: CCD coupled directly to the streak tube, CCD directly coupled to the IIT, and the original configuration with a smaller CCD lens coupled to the IIT output. Spatial resolution (limiting visual) with and without the IIT is 8 and 20 lp/mm, respectively, for photocathode current density up to 25% of the Child-Langmuir (C-L) space-charge limit. Temporal resolution (fwhm) deteriorates by about 20% when the cathode current density reaches 10% of the C-L space charge limit. Streak tube operation with large average tube current was observed by lluminating the entire slit region through a Ronchi ruling and measuring the CTR. Sensitivity (CCD electrons per streak tube photoelectron) for the various configurations ranged from 7.5 to 2,700 with read noise of 7.5 to 10.5 electrons. Optimum spatial resolution is achieved when the IIT is removed. Maximum dynamic range requires a configuration where a single photoelectron from the photocathode produces a signal that is 3 to 5 times the read noise.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.