Detector resistive anode encoder

Resistive Anode Encoder (RAE). This detector has the advantage that the single-ion events are detected digitally. It therefore it delivers quantitative results, irrespective of local differences in the amplification of the channel plate. One disadvantage is that the count rate is limited to 200000. 

For detection of secondary ions a laterally resolving detector is necessary. In the first step a channel plate for amplification is used secondary electrons from the output of this device are accelerated either to a fluorescent screen or to a resistive anode. If a fluorescent screen is used the image is picked up by a CCD camera and summed frame by frame by use of a computer. The principal advantage of this system is unlimited secondary ion intensities, but compared with the digital detection of the resistive anode encoder the lateral and intensity linearity is not as well-defined. 

The above discussion is presented merely to give an idea of the types of EUV detectors and their applications in use on present fusion plasma experiments. It is by no means an exhaustive list of possibilities. Indeed, several different detectors are in use or being planned in future experiments. Resistive anode encoders will probably see more use in fusion experiments as they become commercially available. However, the low count rates available ( 10 to 10 sec-1) will result in these detectors being used mostly for line profile studies (e.g., ion temperature measurements via Doppler broadening measurements). Intensified CCD arrays (back-illuminated or otherwise), vidicon or CID systems, lens-coupled intensifiers, and anode detectors have all seen some use on tokamak experiments or are planned for the near future, but have not been widely used as yet. However, in terms of availability, pixel format, dynamic range, insensitivity to magnetic fields, compact package, and moderate cost, the IPDA remains the most versatile multichannel EUV detector for plasma spectroscopy. 

FIGURE 5.2 A schematic of a SIMS device that includes two ion sources (Duoplasmatron and cesium), a sample chamber with a transfer rod, a magnetic sector mass spectrometer with a Faraday cup (FC), resistive anode encoder (RAF), and electron multiplier (EM) detectors. (From Betti, M., Int. J. Mass Spectrom., 242,169, 2005. With permission.)... 

Figure 10.48 shows the arrangement of the lenses, the detector and the chamber. The position sensitive resistive anode encoder provides the x- and y-coordinates of every incident photon. The photons are counted into the appropriate positions in the image memory and the image is accumulated over time to any required number of photons per pixel. Photon intensity at each image pixel is quantified with the same high sensitivity characteristics of other photon counting methods. The positional data and photon intensity are feed into a computer where the data are accumulated and processed. 

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