Prototyping the Giga-Range Imaging Detector (GRID), 15-R8111

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Principal Investigators
F. Allegrini
S. Livi
D. McComas
S. Weidner
M. Maple
J. Roberts
 

Inclusive Dates:  10/14/09 – 02/15/10

Background - A microchannel plate (MCP) detector, which is sensitive to particles and photons, consists of an array of pores that act as miniature electron multipliers. A single microchannel plate has a gain of ~103 to 104. When mounted in pairs, a gain of a few 107 electrons per incident particle (or photon) is achieved. MCPs are typically used in counting and/or imaging mode in space plasma spectrometers where a single instrument can simultaneously count particles within a large field-of-view (e.g., ~8 x 360 degrees with a top-hat energy analyzer) and still determine their incoming direction by imaging the impact location of the particles on the detector. Although a dynamic range of ~106 can be achieved, it can come short in some circumstances. To overcome this limitation, this project proposes a concept that extends by ~3 decades the dynamic range of an imaging detector.

Approach - SwRI researchers applied known techniques and combined them to form a new detector that is capable of much more than the sum of the two techniques taken separately. The design approach was to use a two-gain stage, where the two stages are mounted in series. The low-gain measurement is done with one MCP and a current measurement. The high-gain measurement is done with a pair of MCPs and an anode. Both stages have imaging capabilities with different resolutions (coarser with the low-gain, finer with the high-gain). This new detector, called the Giga-Range Imaging Detector (GRID), requires very little additional resources compared to a conventional MCP detector. The project was divided into three major tasks:

  • Design and build a prototype with at least two pixels for the low gain and for the high-gain stage.

  • Characterize the low-gain stage.

  • Cross calibrate the low- and high-gain stage in the overlapping region.

Accomplishments - The project team built and tested a prototype of the GRID for particles or photons. The low-gain stage was successfully tested on the bench. However, when connected to the GRID prototype, the noise induced by the surrounding equipment prevented the team from making a current measurement. The project team also characterized the effects the low-gain stage on the imaging resolution of the high-gain stage. A good understanding of the prototype was acquired during testing, but a lack time and availability prevented implementation of further changes to allow for better performances. Even though the detector did not fully meet the objectives, a series of improvements that should bring this concept to a working detector was identified. The project team strongly believes that the concept works and that it is a matter of time before GRID delivers outstanding results.

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