The harsh radiation environment of Lawrence Livermore’s National Ignition Facility (NIF) requires radiation tolerant scientific cameras for our wide array of diagnostics. Our current scientific cameras, SI-1000 CCD cameras developed by Spectral Instruments, have a multitude of problems on high neutron yield NIF experiments including upsets that cause complete loss of experimental data as well as significant damage to the sensors. Our goal was to develop a CMOS-based scientific camera platform that would be significantly more radiation tolerant than the current suite of CCD cameras used in NIF diagnostics. That is, the camera electronics would operate through high neutron yield experiments and that the sensors would sustain far less damage thus increasing their life expectancy. That camera platform, the 1600S CMOS cameras, developed by Spectral Instruments (SI) was designed to accept a variety of different sensors up to 60 mm x 60 mm depending on the specific application. In this paper we will discuss the development, general performance, and radiation performance of the CIS-54, a dump and read 1600S CMOS camera with a Stanford Research Institute (SRI) developed 4k x 4k sensor.
Lawrence Livermore’s National Ignition Facility (NIF) requires a radiation tolerant video camera to remotely monitor varied activities in and around the NIF target chamber. Our present suite of monitor cameras must be either, removed during high yield shots, requiring substantial resources or left in place which greatly reduces their life expectancy. Our goal was to develop a relatively inexpensive, radiation tolerant monitor camera which could be left in place during high yield laser experiments yet continue to give quality data for up to (5) years of operation or about 250 high yield shots. The camera was built around the CMOSIS CMV 2000 / 4000 sensor. Camera components were chosen based on their radiation tolerant performance at the Cobham radiation test facility in CO Springs. The prototype camera was tested both at Cobham and on the NIF during high yield shots. We will present test results as well as predictions for camera life expectancy.
The National Ignition Facility’s (NIF) harsh radiation environment can cause electronics to malfunction during high-yield DT shots. Until now there has been little experience fielding electronic-based cameras in the target chamber under these conditions; hence, the performance of electronic components in NIF’s radiation environment was unknown. It is possible to purchase radiation tolerant devices, however, they are usually qualified for radiation environments different to NIF, such as space flight or nuclear reactors. This paper presents the results from a series of online experiments that used two different prototype camera systems built from non-radiation hardened components and one commercially available camera that permanently failed at relatively low total integrated dose. The custom design built in Livermore endured a 5 × 1015 neutron shot without upset, while the other custom design upset at 2 × 1014 neutrons. These results agreed with offline testing done with a flash x-ray source and a 14 MeV neutron source, which suggested a methodology for developing and qualifying electronic systems for NIF. Further work will likely lead to the use of embedded electronic systems in the target chamber during high-yield shots.
We present new designs for the launch and receiver boards used in a high speed x-ray framing camera at the National Ignition Facility. The new launch board uses a Klopfenstein taper to match the 50 ohm input impedance to the ~10 ohm microchannel plate. The new receiver board incorporates design changes resulting in an output monitor pulse shape that more accurately represents the pulse shape at the input and across the microchannel plate; this is valuable for assessing and monitoring the electrical performance of the assembled framing camera head. The launch and receiver boards maximize power coupling to the microchannel plate, minimize cross talk between channels, and minimize reflections. We discuss some of the design tradeoffs we explored, and present modeling results and measured performance. We also present our methods for dealing with the non-ideal behavior of coupling capacitors and terminating resistors. We compare the performance of these new designs to that of some earlier designs.
X-ray framing cameras based on proximity-focused micro-channel plates (MCP) have been playing an important role as diagnostics of inertial confinement fusion experiments [1]. Most of the current x-ray framing cameras consist of a single MCP, a phosphor, and a recording device (e.g. CCD or photographic films). This configuration is successful for imaging x-rays with energies below 20 keV, but detective quantum efficiency (DQE) above 20 keV is severely reduced due to the large gain differential between the top and the bottom of the plate for these volumetrically absorbed photons [2]. Recently developed diagnostic techniques at LLNL require recording backlit images of extremely dense imploded plasmas using hard x-rays, and demand the detector to be sensitive to photons with energies higher than 40 keV [3]. To increase the sensitivity in the high-energy region, we propose to use a combination of two MCPs. The first MCP is operated in low gain and works as a thick photocathode, and the second MCP works as a high gain electron multiplier [4,5]. We assembled a proof-of-principle test module by using this dual MCP configuration and demonstrated 4.5% DQE at 60 keV x-rays.
As neutron yields increase at the National Ignition Facility (NIF) the need for neutron ‘hardened’ diagnostics has also
increased. Gated Imagers located within the target chamber are exposed to neutrons which degrade image quality and
damage electronics. In an effort to maintain the signal to noise ratio (S/N) on our images and mitigate neutron induced
damage, we have implemented numerous upgrades to our X-ray framing cameras. The NIF Gated X-ray Detector
(GXD), design has evolved into the Hardened Gated X-ray Detector, HGXD. These improvements are presented with
image data taken on high yield NIF shots showing enhanced image quality. Additional upgrades were added to remotely
locate sensitive electronics and ease operational use.
We present evidence of an artifact in gated x-ray framing cameras that can severely impact image quality. This artifact
presents as a spatially-varying, high-intensity background and is correlated with experiments that produce a high flux of
x-rays during the time before the framing camera is triggered. Dedicated experiments using a short pulse UV laser that
arrives before, during, and after the triggering of the framing camera confirm that these artifacts can be produced by light
that arrives in advance of the voltage pulse that triggers the camera. This is consistent with these artifacts being the
result of photoelectrons produced uniformly at the active area of the camera by early incident light and then selectively
trapped by the electromagnetic (EM) fields of the camera. Simulations confirm that the EM field above the active
surface can act to confine electrons produced before the camera is triggered. We further present a method to suppress
these artifacts by installing a conducting electrode in front of the active area of the framing camera. This device
suppresses artifacts by attracting any electrons liberated by x-rays that arrive before the camera is triggered.
We have performed pulsed neutron and pulsed laser tests of a CVD diamond detector manufactured from DIAFILM, a commercial grade of CVD diamond. The laser tests were performed at the short pulse UV laser at Bechtel Nevada in Livermore, CA. The pulsed neutrons were provided by DT capsule implosions at the OMEGA laser fusion facility in Rochester, NY. From these tests, we have determined the impulse response to be 250 ps fwhm for an applied E-field of 500 V/mm. Additionally, we have determined the sensitivity to be 2.4 mA/W at 500 V/mm and 4.0 mA/W at 100 V/mm. These values are approximately 2 to 5x times higher than those reported for natural Type IIa diamond at similar E-field and thickness (1mm). These characteristics allow us to conceive of a neutron time-of-flight current mode spectrometer based on CVD diamond. Such an instrument would sit inside the laser fusion target chamber close to target chamber center (TCC), and would record neutron spectra fast enough such that backscattered neutrons and (gamma) rays from the target chamber wall would not be a concern. The acquired neutron spectra could then be used to extract DD fuel areal density from the downscattered secondary to secondary ratio.
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