TENACIOUS IEPS functional block diagram. 

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... each sensor head, there is an independent detector board mount containing coupling capacitors and detector-biasing networks (typically 20V bias). Included also is circuitry for in-flight calibration with a charge pulser for each pixel and a field-effect transistor (FET) for each pixel. The outputs of this front-end analog signal are routed by mini-cables to the analog signal conditioning circuits via a pigtail. Each FET is coupled to standard charge sensitive preamplifiers that feed two stages of amplification, shaping, and baseline restoration. The shaping time is approximately 2.5 msec. The shaped signals are pulse-height analyzed on the digital preprocessor boards in a custom gate-array chip (KM-5) developed jointly with KMOS, Inc. for the POLAR mission. A stack of discriminators is built into the chip, allowing for up to 16 adjacent energy bins. The energy threshold and range of the analyzer can be adjusted by sending digital commands to digital-to-analog converters (DACs) internal to the chip. The chip can be run in one of two energy modes by selection of two independent resistor-divider chains in the chip: linear () E constant) or logarithmic () E/E = constant) bin spacing. The low-and high-energy reference voltage of each DAC can be controlled independently providing for a possible energy range of 0 to 1500 keV. Output logic pulses from individual bins are accumulated at high rate and then, for IEPS, are reduced in energy resolution to eight of the 16 possible bins. The data are accumulated in 24-bit scalers and read into memory at regular intervals, nominally 32 times per three-second spin. An in-flight calibration circuit is driven also from the digital board. It consists of two fixed precision amplitude pulses at 90 and 240 keV that drive the front-end electronics. A variable amplitude pulse generator, controlled via an 8 bit DAC, also provides calibration signals on command. A functional block diagram of the ion, neutral and electron sensors, and their analog and digital electronics is shown in Figure 6. Since we are sometimes in a charged particle foreground, it is important for us to know not only the ion pop- ulation but also the electron population at similar energies. The IEPS includes also a single electron head, using the same effective design as the ion/neutral head. The electron detector is thicker and has a thick front contact that stops the incident ions and neutrals from detection, thus providing a clean electron measurement. The electron sensor will, like the ions/neutrals, have a commandable energy range but spanning now from 15 to ¦ 500 keV. Compared to the POLAR instrument there is one principal difference in instrument design we propose and this will greatly enhance our ENA imaging. It is a value-added feature and if not fully implemented, will not in any manner compromise mission success. The extended design revolves around an inherent feature of the CEPPAD instrument. The POLAR/CEPPAD/IPS does not differentiate between ions and neutrals so it can only unambiguously identify the lower intensity neutrals when there is a negligible local energetic ion population (for example when it is near apogee, as in Figure ...