ABSTRACT
The fusion diagnostic community, including the National Ignition Facility, the Laboratory for Laser Energetics, Megajoule in France, and others require optical recording instruments with precise time resolution covering a dynamic range of many orders of magnitude. In 2012, LLE, Photek, and Sydor Instruments embarked on the re-design of an improved streak tube for fusion diagnostics. As a baseline we started with the Photek ST-Y streak tube which is a member of the RCA design dating back to 1957, because the tube body can accommodate a 35 mm long photocathode, and consequently more fibre coupled diagnostic channels than smaller designs. Electron optical modelling was carried out by both Paul Jaanimagi in the US and by Photek with different software packages in a parallel exercise. Our goal was to address some of the short-comings of this tube, the initial approach being to increase the field between the photocathode and extractor electrode from 700 to 1300 V/mm to reduce space charge effects and to improve time resolution. Many changes and modifications were made: the time resolution was improved to 5 ps, the usable cathode length was increased from 20 mm to 32 mm under high extraction field operation, and the off-axis spatial resolution was substantially improved compared to other tubes of this format. Several tubes have been built and tested in Sydor ROSS-5800 streak cameras.
ABSTRACT
Fusion diagnostics that utilise high speed scintillators often need to capture a large area of light with a high degree of time accuracy. Microchannel plate (MCP) photomultiplier tubes (PMTs) are recognised as the leading device for capturing fast optical signals. However, when manufactured in their traditional proximity focused construction, the time response performance is reduced as the active area increases. This is due to two main factors: the capacitance of a large anode and the difficulty of obtaining small pore MCPs with a large area. Collaboration between Photek and AWE has produced prototype devices that combine the excellent time response of small area MCP-PMTs with a large active area by replacing the traditional proximity-gap front section with an electro-optically focused photocathode to MCP. We present results from both single and double MCP devices with a 40 mm diameter active area and show simulations for the 100 mm device being built this year.
ABSTRACT
We describe the evaluation of a microchannel plate (MCP) photomultiplier tube (PMT), incorporating a 3 µm pore MCP and constant voltage anode and cathode gaps. The use of the small pore size results in PMTs with response functions of the order of 85 ps full-width-half-maximum, while the constant electric field across the anode and cathode gaps produces a uniform response function over the entire operating range of the device. The PMT was characterized on a number of facilities and employed on gas Cherenkov detectors fielded on various deuterium tritium fuel (DT) implosions on the Omega Laser Facility at the University of Rochester. The Cherenkov detectors are part of diagnostic development to measure Gamma ray reaction history for DT implosions on the National Ignition Facility.
ABSTRACT
Depression and ataxia was seen in 24-day-old chicks accidentally fed excess zoalene from 14 days of age. The presence of a small amount of furazolidone in the ration probably exacerbated the effect. There were no deaths. No other causes could be found for the condition and replacing the rations with food containing less than the recommended level of zoalene and no furazolidone resulted in recovery within 4 to 5 days. In an experimental study the syndrome was reproduced in baby chicks with as little as 2(1/2) times the recommended level of zoalene in the food. Increasing the amount of zoalene hastened the onset and increased the severity of symptoms and markedly depressed weight gains; the addition of a small amount of furazolidone had a synergistic effect. Inappetance may be largely responsible for the depression in weight gain, and damage to Purkinje cells seems to account for the ataxia and nervous signs. In laying birds 10 times the recommended level of zoalene in the food over 30 days caused inappetance, cessation of egg production, and progressive weakness, but no nervous signs.
