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The CPD Experiment
 

The Charged Particle Detector (CPD) dedicated to measure the flux of charged particles along the satellite orbit was designed and calibrated by Dr. P. Stauning at the Danish Meteorological Institute (DMI). The instrument comprises an array of 6 solid-state silicon detector assemblies. The detectors are mounted in a box which also holds all electronic circuits involved in the experiment, that is, high-voltage supply for the detectors, charge- sensitive preamplifiers, pulse amplifiers, discriminators, counte circuits, and a computer system based on the intel 80186 processor circuits. The detector designations and locations are shown in Figure 1.

Figure 1: The CPD box and detector location. It is accomodated on the ORSTED satellite such that the Z1 axis looks in the direction of the satellite magnetometer boom.

Figure 2: Simplified electrical block diagram of the CPD particle experiment.


Figure 2 presents a simplified block diagram of the electronic system. Each detector has its own charge-sensitive pre-amplifier (CSA), pulse amplifier, 4- or 8-level pulse-height analyser (PHA) and buffer counter circuit. The individual pulses, when shaped by the CSA stage, have a width of 0.8 sec. The counters are sampled by a microprocessor system, which also samples housekeeping voltage and temperature data. The microprocessor controls the operation of the instrument; it receives mode shift commands from, and it communicates data and status to the satellite main central data handling (CDH) computer. A calibration circuit also controlled by the microprocessor may inject calibration pulses at the front end of the CSA stage. The experiment has been electrically tested and calibrated in the laboratory at DMI and calibrated in proton and electron beams at the High-Energy Radiation Facility at NASA Goddard Space Flight Center.
A first numerical calibration of the instrument was performed at the University of Louvain by Dr. M. Cyamukungu and Pr. Gh. Grégoire [2]. Following a change of the shielding thickness in September 1998, it was necessary to perform a second numerical calibration from which the characteristics summarized in Table 1 resulted.

Table 1: Properties of the CPD array. A - type detector: TU-011-050-300; B - type detector: TU-016-050-1000
Property DETECTOR
  P1 and P2 P3 P4 E1 and E2
Sight angle (degree) 90 0 90 90 90 0
F.O.V half angle (degree) 20.5 33.5 33.5 20.5
Aperture () 0.196 0.283 0.283 0.196
Geometric factor () 0.053 0.25 0.25 0.053
Entrance window ( ) 1.25/Ni 1000/Al 1000/Cu 1.25/Ni
Detector type A A A B
THRESHOLD ENERGIES (MeV)        
: .51 51.9 89.9 .51
  .53 52.0 90.1 .53
  .71 52.5 90.7 .71
         
: .23 12.9 22.3 .23
  .24 13.0 22.5 .24
  .29 13.2 22.8 .29
         
: .02 .68 1.75 .02
  .02 .78 2.2 .02
  .07 2.33 >6. .067
PEAK (PENETRATION) ENERGY:        
$\alpha $ 24. 59. 95. 48.
$p$ 6. 15. 24. 12.
$e^{-}$ .37 1.00 2.1 .88
MEAN ENERGY LOST IN Si at        
PEAK (PENETRATION) ENERGY:        
$\alpha $ 22.8 22.8 22.8 48.
$p$ 5.6 5.6 5.6 12.
$e^{-}$ .3 .3 .3 .8
ENERGY BIN LIMITS (keV):        
1 423 417 209 212 47
2 639 629 741 752 72
3 989 974 2183 2146 111
4 1500 1478 7742 7611 168
5 2146 2146     237
6 3241 3241     358
7 5015 5015     553
8 7611 7611     840

Also, new efficiency values had to be calculated. They are presented in Chapter 2 and serve as the basis for electron and proton spectra extraction. This spectrum extraction method is is described in Chapter 3 and applied in Chapter 4. The first chapter of this report is devoted to a survey of the ØRSTED/CPD raw data.

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