0RSTED satellite:

(1)

j

PRODEX-ESA-SSTC Contract No. 170724

The Charged Particle Detector (CPD)

on the 0RSTED satellite:

description and evaluation

Technical Report A

(version 1.0)

M. Cyamukungu (UCL-FYNU) Gh. Gregoire (UCL-FYNU) J. Lemaire (UCL-ASTR/BISA) P. Stauning (DMI)

Louvain-Ia-Neuve, September 1997

(2)

I \

I

[

(

Preface

It was in May 1993, at the NATO Advanced research Workshop in Norway, that the official announcement of the future 0RSTED mission was made to the space physics community.

It is there also that Peter Stauning (Danish Meteorological Institute, Copenhagen), pro- posed to J. Lemaire (BISA, Brussels), to become Co-Ion the Charged Particle Detector (CPD) which was planned to be part of the payload 0RSTED satellite.

The cooperation agreement between the Danish Meteorological Institute (DMI) and the Institute for Space Aeronomy (BISA) was formalized during a couple of visits and meetings in Brussels and Copenhagen.

The main scientific objective of the 0RSTED mission is to survey the geomagnetic field distribution with unprecedented accuracy. An additional objective of this mission is to use this low altitude platform to study the flux of energetic magnetospheric particles precipitated in the atmosphere at auroral latitudes as well as in the region of the South Atlantic Anomaly where the mirror points of trapped radiation belt particles have their minimum minimorum altitudes. It is the observations in this region of the South Atlantic Anomaly that BISA is mostly interested in. Comparison will be undertaken between the 0RSTED observations, the results predicted from existing empirical models for the radiation belt environment and observations from other spacecraft like SAMPEX, U ARS and the MIR station.

The CPD has been calibrated at GSFC (Greenbelt, Ma), in electron and proton beams of different energies. The results of this calibration were made available to BISA and to the Institute for Nuclear Physics (FYNU) of the Universite Catholique de Louvain (UCL) where software calibrations have been performed using the GEANT / Monte-Carlo simulation program to cross check the hardware calibration.

The response of the detector in the radiation belt environment has also been evaluated at UCL/FYNU using GEANT and energy spectra obtained from existing environment models available at BISA.

The present Technical Note contains the description of the CPD and of its installation on the 0RSTED satellite. The results of the hardware calibration are summarized and compared to those of Monte Carlo simulations.

This preliminary study constitute a part of the CPD User Manual, it will be useful for the analysis and interpretation of the CPD data when they will become available.

iv

(6)

i

(

Useful addresses

Belgian Institute for Space Aeronomy 3 avenue Circulaire, B-1180 Brussels, Belgium FAX: 32 2 3748423 TEL: 32 2 374 8121 Danish Meteorological Institute Solar-Terrestrial Physics Division Lyngbyvej 100,

DK-2100 Copenhagen, Denmark

FAX: 45 39 27 10 80 TEL: 45 39 15 75 00 ESA/ESTEC - PRODEX

P.O. Box 299

Keplerlaan 1, 2200 AG Noordwijk, The Netherlands FAX: 31 71 565 4693 TEL: 31 71 565 4350

Institut de Physique Nucleaire Universite Catholique de Louvain 2, chemin du Cyclotron,

B-1348 Louvain-La-Neuve, Belgium FAX: 32 10 45 2183 TEL: 32 2 47 3273 SSTC

Rue de la Science, 8 1000 Brussels, Belgium

FAX: 32 2 230 59 12 TEL: 32 2 238 34 11

v

(7)

Useful e-mail adresses and phone numbers

Eigil Friis-Christensen Torsten Neubert Peter Stauning

Mathias Cyamukungu Ghislain Gregoire Joseph Lemaire Daniel Heynderickx Michel Kruglanski Carlos Lippens Viviane Pierrard H. Olthof (PRODEX) J. Wautrequin (SSTC) J.W. Bernard (SSTC) M.C. Limbourg (SSTC)

TEL: 45 39 15 75 00 TEL: 45 39 15 75 00 TEL: 45 39 15 74 73 TEL: 32 10 47 3213 TEL: 32 10 47 3216 TEL: 32 2 373 0407 TEL: 32 2 373 0417 TEL: 32 2 373 0417 TEL: 32 2 373 0383 TEL: 32 2 373 0416 TEL: 31 71 565 46 93 TEL: 32 2 238 34 11 TEL: 32 2 238 35 83 TEL: 32 2 238 34 11

vi

Eigil. Friis@dmi.dk neubert@dmi.min.dk pst@dmi.dk

cyam@fynu.ucl.ac.be gregoire@fynu.ucl.ac.be

joseph.lemaire@bira-iasb.oma.be daniel.heynderickx@bira-iasb.oma.be- michel.kruglanski@bira-iasb.oma.be carlos.lippens@bira-iasb.oma.be vi viane. pierrard@bira-iasb.oma. be

(8)

Acknow ledgments

The authors of this Technical Report wish to thank Dr. P. Stauning and the OERSTED project manager, Dr. E. Friis-Christiansen for their offer to share the data of the Charged Particle Detector.

They would like to thank the Service des Affaires Scientifiques Techniques et Culturelles, for the financial support and the delegates of PRODEX for their cooperation and support with respect to administrative matters related to this project.

The authors are particularly grateful to Dr. D. Heynderickx, Dr. M. Kruglanski, Dr. C.

Lippens and Dr. V. Pierrard (BISA, Brussels) for their advise and collaboration during the preparation of this document. All the BISA team is acknowledged for the fruitful access to the UNIRAD Library developed at BISA and the Space Environment Information System (SPENVIS). The useful discussions the authors had with P. Davidsen (CRI, Copenhagen) were much appreciated.

Dr. D.S. Evans (NOAA, Boulder) has sent to us plots of auroral electron spectra and contributed fruitful comments, which spurred us on to search for suitable solutions to the pulse pile-up problem.

va

(9)

Introduction

Detector arrays are used in space applications to measure energy spectra of different kinds of particles. The SSJ* /4 dosimeter on the DMSP [1], the SFD on EQUATOR-S [2], the REM detector on STRV-1B and MIR [3] are examples of very light weight detector arrays which flew or are planned to fly on satellites to detect the particle fluxes in the space environment.

The ideal detector would have a specific and dedicated channel for each kind of particle within a well defined energy range. During the Data Analysis phase, the informations contained in all the channels would be combined and lead to particle spectra, assuming that the detector characteristics (a.o the response to particle spectra) are precisely known.

A real detector however has to cope with many constraints giving rise to situations where much more delicate analysis is compulsory in order to extract the true spectra.

The Charged Particle Detector (CPD) instrument was designed by P. Stauning at the Danish Meteorological Institute. It will be used to measure the high energy particle (electrons, protons and a-particles) fluxes on 0RSTED satellite orbit. This document contains a detailed simulation of its functions, as well as the methods to extract spectra from its raw data.

In Chapter 1, the CPD is decribed with reference, when needed, to the more detailed document in Appendix. The accomodation of the instrument on the 0RSTED satellite is shown, along with the simulation model of the whole setup.

The CPD characteristics and the numerical calibration are presented in Chapter 2. The detection efficiency for each channel and particle are shown; finally the response of the detector to space environment radiation is presented.

In Chapter 3, the Data Analysis protocol is described and illustrated by several examples as close as possible to conditions likely to be encountered on 0RSTED orbit.

A final chapter summarizes the main results of this study and outlines the tasks to be undertaken after a successful launch of the 0RSTED satellite.

1

(10)

1

I

Chapter 1 The 0RSTED /CPD Instrument

The Charged Particle Detector (CPD) is aimed to detect electrons, protons and a-particles within an energy range which depends on the Signal to Noise ratio on 0RSTED orbit. A complete description of the CPD experiment can be found in Appendix A, along with its scientific background. vVe, herewith quote from Appendix A, the main purposes of the CPD experiment, since they will be the leading criteria all along the CPD performance study. The CPD was designed to:

• Provide measurements of the energetic particle radiation in the upper polar atmosphere to be combined with absorption data from imaging riometer (relative ionospheric opacity - meter) installations on the ground in order to detect the dy- namical features of polar and auroral particle precipitation events.

• Conduct monitoring of the level of solar-geophysical activity during events, like major solar flares and geomagnetic storms, where intense and variable high-energy particle radiation may occur.

• Monitor the long-term high-energy particle radiation dose at the satellite for inves- tigations of possible radiation damages on other on-board experiments and systems.

Section 1.1 contains a summary of the CPD mechanical assembly. In Section 1. 2, the 0RSTED mission and orbit analysis are presented. The CPD experiment is described within the general frame of 0RSTED mission [4]. The accomodation of the CPD on the satellite and the 0RSTED GEANT model are presented in Section 1.3 and Section 1.4, respectively.

1.1 Mechanical details

The CPD mechanical assembly is made of six 3.5 cm diameter and 4.7 cm height detector units similar to the one shown in Figure 1.1. These units are accomodated in a 260 x 175 x 55 mm³aluminum box shown in Figure 1.2 (see also Figure 6 in Appendix A). The

2

(11)

I {

l

J

dimensions of all detector subunits are given in Appendix A. The specific features of these subunits may be better grasped from the description summarized in Table 2.1.

Solar panel structure

(0.2 g/cm 2 solarcell + 0.3 g/cm 2 AI)

Collimator (Brass)

Detector House (Delrin) Top cover (1 mm AI) Collimator (Brass) Collimator C 3 (Brass) . Shielding foil (Nickel)

Solid state silicon detector Locking end piece (Delrin) Top of detector box (2 mm ^AI)

Figure 1.1: General layout of the Charged Particle Detectors.

PI

"",

".., E2

." ^..

Pz

Figure 1.2: The CPD box and detector location.

3

(12)

I 1 I

1.2 Mission and orbit analysis

See Appendix B and Reference [4].

1.3 Accomodation of the CPD detector on the satellite

The 0RSTED satellite is well described in Appendix C. A picture of the satellite, showing the CPD accomodation is given in Figure 1.3.

The interior of the 0RSTED satellite is partly shown in Figure 1.4. As will be seen in Chapter 2, the radiation background level in the CPD will be determined by the filling factor of the satellite box. Figure 1.4 suggests that background radiation coming from the bottom is not likely to reach the CPD sensitive elements.

GPS receiver

Solar panels

GPS

sensor

particle detectors Figure 1.3: Accomodation of the CPD detector on the satellite.

4

(13)

Figure 1.4: Satellite main body and CPD surrounding elements.

1.4 The GEANT model of the Charged Particle De- tector

The 0RSTED satellite model is shown in Figure 1.5 to 1.8. The CPD components were modelized following a detailed plan of the whole detector. The CPD box is accomodated inside the satellite body (of outer dimensions 72 x 45 x 34 cm³⁾made of 0.376 mm thick GaAs solar cells on a 1 mm thick aluminum plate backing. No other information than Figure 1.3 and 1.4 was available about the components inside 0RSTED, thus we consider that the CPD accomodation to the satellite modelized herein could still be refined. As part of the needed refinements, the characterization of the shielding efficiency of the CPD surrounding elements is of paramount importance. Indeed, as stated above, these elements could contribute to reduce the radiation background level.

5

(14)

Figure 1.5: The 0RSTED model used in numerical simulation with GEANT 3.21.

Figure 1.6: 0RSTED model: projected view along the boom axis.

J

⁶

(15)

I ~ lee)

Figure 1. 7: 0RSTED model: projected view along the horizontal detector symmetry axis.

P1B I

Figure 1.8: 0RSTED model: projected view along the perpendicular to the detector symmetry axes.

7

(16)

Chapter 2 The simulation of the CPD

The CPD properties were determined using the mechanical model decribed in Chapter 1.

Some of these properties (described in Section 2.1) are not ajustable anymore once the CPD hardware is definitely frozen.

The others will be tuned at calibration time to match the experimenter's requirements.

They are summarized in Section 2.2. In particular, the detection efficiency, which is the basis of all count rate predictions is given in Subsection 2.2.2. Table 2.1 summarizes a large number of both fixed and ajustable CPD characteristics. The Section 2.4 reports the counting rate based on the detection efficiency and the space radiation characteristics.

2.1 The CPD fixed characteristics

2.1.1 View direction

As stated in Chapter 1, the six detectors which compose the CPD are oriented either towards the up direction (90°, i.e. looking" along" the boom direction) or horizontally oriented (0°, i.e. perpendicular to the boom direction).

The field of view (F.O.V.) half angle are 20.5° for detector units PI, P2, E1 and E2 and 33.5° for detectors P3 and P4. These F.O.V. are determined taking into account the fact that the collimators are not deep enough to shield the outer rims of the sensitive detector surfaces.

The aperture values given in Table 2.1 refer to the aperture of the last collimator set before the detector sensitive element, whereas the actual aperture involves the whole sensitive surface of the detectors.

8

(17)

2.1.2 The Geometrical Factor (GF)

The geometrical factor values in Table 2.1 are valid for particles of energy above the thresholds and below the energies at which the collimators are no longer efficient. This point is illustrated in Figure 2.1, where the count rates per unit flux (Le. the GF) are plotted as a function of particle energy. One can see that the GF is a well defined constant for electrons penetrating in PI and El with an energy between 0.3 MeV and 1.5 MeV, whereas the GF is still increasing at electron energy equal to 5 MeV. It never reaches a constant value for detector P3 and P4 due to straggling of electrons crossing the 1 mm thick aluminum and copper entrance windows.

The geometrical factor of protons (see Figure 2.2) is constant up to 10 MeV in PI and El. At this energy, a significant number of protons begin reaching the sensitive element through the collimator C3. This number increases with the proton energy, up to 41 MeV, - the proton energy value at which they completely traverse the 3 mm thick brass plate -, making it totally inefficient. At this energy, the GF value equals the one obtained when no collimator is installed between the detector entrance and the detector sensitive element. The protons thresholds for P3 and P4 are ^rv50 MeV and ^rv90 MeV, respectively, well above the value ( 41 MeV) for which the proton flux may be considered as collimated. This fact is reflected in the GF of P3 and P4 for protons: the value (0.25 cm²sr) is exactly the same as the one obtained for a no collimated proton beam in P3 and P4.

The general characteristics of the GF of PI, P3, P4 and El for a-particles (see Figure 2.3) are very similar to the protons one. The Figures 2.4, 2.5 and 2.6 show the asymptotic variation of the GF for detectors PI and El and for the electrons, protons and a-particles, respectively.

The difference between the GF mean values given herewith and the values in Appendix A are due to the differences in aperture used: in Appendix A, the aperture value of 0.20 cm² (corresponding to the collimator aperture) was used, whereas 0.50 cm²corresponding to the whole sensitive area is used herein.

2.1.3 Detector type

The detector type referred to as A and Bare ORTEC manufactured U-Oll-050-300-T and B-016-050-1000-T respectively. A-type detector are 300j.Lm thick silicon and B-type are 1000j.Lm thick silicon, both with sensitive area equal to 50 mm².

2.1.4 Entrance windows and threshold energies

The entrance windows are made of a 0.75j.Lm thick nickel foil for PI, P2, El and E2 and establish threshold energies for those detectors. The 1 mm thick aluminum window and 1 mm thick copper window determine the threshold energy for detectors P3 and P4

9

(18)

J

---... ^0.1 ---... ^0.1

C/l P1 detector ^C/l E1 detector

NE ^0.09 NE ^0.09 ^!:::-

MEAN G,= 0.053 em' sr MEAN G,= 0.054 em' sr

~ 0.08 ~ 0.08 ~

... '-

0.07

0 0 0.07 !:::-

u U

2 ⁰^.06 ~~~~ .. ~ .. L\ .. 4"4" 2 ^0.06 ^::... 4 4 4 4

0 0.05 ⁰ 0.05 =- t.44Mil..A.liA6A~li4 ... 4

u u

.c: .c: 4t..

V ^0.04 # ^V ^0.04 ^=-t..

E E

0 0.0.3 ₀ 0.0.3 :0...

Q) Q)

c.? 0.02 ^l:) 0.02 -

0.01 0.01 ::-

0 0 I I

0 _~5 1 ~5 0 0.5 1 ~5

Energy of incident e- (MeV Energy of incident e- (MeV

---^Co.C/l ^0.2 ^---^Co.C/l ^0.1

NE ^0.1⁸ NE ⁰^.09

~ 0.16 P3 detector _~_0.08 P4 detector

... ^I.-

.3 ^0.14 ^t..4t.. .3 ^0.07

u t.t.t. ^u

2 ⁰^.12 ^4t. .E ^0.06

-0 _0.1 ^t.t.. -0 _0.05 _t.

u t..t. u

·c _t..4 ·c _~t.

V ⁰^.08 _t.t.. V ^0.04

"""

E E

0 0.06 0 0.0.3

Q) Q)

c.? 0.04- ^l:) 0.02

0.02 0.01

0 0

0 ' 1 2 .3 4 5 2 .3 4 5

Energy of incident e- (MeV) Energy of incident e- (MeV)

Figure 2.1: Geometrical Factor for electrons as a function of energy. The name of the detector is indicated in the insert, along with the mean value of the GF in the plateau regIOn.

respectively. The three threshold energies given for each particle are to be interpreted as maximum energy values (at the given precision) at which 1/1000, 1/100 and 50/100 of the particles penetrating the detector perpendicularly to the windows planes hit the sensitive element.

2.1.5 The peak (penetration) energy

The peak (penetration) energy is mainly determined by the entrance window and the sensitive element thicknesses. The values given in Table 2.1 are defined as incident energy for which the average energy lost (over 10⁵particles) in the sensitive element is maximum.

In this case too the particles are impacting perpendicularly the detector.

10

(19)

Property _DETECTOR

PI 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 (cm²⁾ 0.20 0.28 0.28 0.20

Geometric factor (cm²sr) 0.053 0.25 0.25 0.053

Entrance window (J.lm/ compound) 0.75/Ni 1000/ Al 1000/Cu 0.75/Ni

Detector type A A A B

THRESHOLD ENERGIES (MeV)

a: .243 51.92 89.88 .243

.243 52.07 90.11 .243

.291 52.54 90.73 .291

p: .174 12.89 22.36 .174

.179 12.96 22.48 .179

.206 13.19 22.83 .206

e-: _.018 _.682 _1.67 _.018

.018 .738 1.97 .018

.032 1.228 3.71 .032

PEAK (PENETRATION) ENERGY:

a 24. _~ _~ 48.

P 6. 15. 24. 12.

e - _.37 _1.00 _2.10 _.88

MEAN ENERGY LOST IN Si at PEAK (PENETRATION) ENERGY:

a 22.8 22.8 22.8 48.

P 5.6 5.6 5.6 12.

e - _.3 _.3 _.3 _.8

ENERGY BINS:

1 [0.00-0.33[ [0.00-0.33[ [0.00-0.33[ [0.00-0.03[

2 [0.33-0.54[ [0.33-1.43[ [0.33-1.43[ [0.03-0.053[

3 [0.54-0.88[ [1.43-6.20[ [1.43-6.20[ [0.053-0.093[

4 [0.88-1.43[ [6.20-23.4[ [6.20-23.4[ [0.093-1.16[

5 [1.43-2.33[ [0.16-0.29[

6 [2.33-3.80[ [0.29-0.51[

7 [3.80-6.20[ [0.51-0.90[

8 [6.20-23.40[ [0.90-23.4[

Table 2.1: Properties of the CPD array. A - type detector: TU-011-050-300 (see Appendix A for details). B - type detector: TU-016-050-1000

11

(20)

J

~ ... _V"l O. i

NE ^0.09

~ 0.08

... 0 0.07

2 U ^0.06

0 0.05

·c u

V ^0.04 E _0.03

(l) 0 Cl 0.02

0.01

a

~ ... _V"l 0.4

NE ^0.35

u

~

... 0.3

U o

~ 0.25

S ⁰^.2

'c ~ ^0.15

o

(l) 0.1 Cl

0.05

o

P 1 detector

MEAN GF= 0.052 em' sr

I!. I!.

•.... !:.: ..•. I!. .... -6 .... ts. .... ..,. ... A ...... .

a ² ⁴ ⁶ ⁸ ¹⁰

Energy of incident p (MeV)

P3 detector

MEAN GF-0.26 em' sr

.. . I!.A ... A···u .... a .. ·A .. ·I!.· .. ·/S: .. ·/i. .. ·4,.···,A.· ..

100 150 200 250 ~oo

~ ... _V"l 0.1

NE ^0.09

~ 0.08

... ₀ _0.07

~ U ⁰^.06

0 0.05

·c u

V ^0.04 E _0.03

0 (l)

Cl 0.02 0.01

0

~ ... _V"l 0.4

NE ^0.35

v --:: 0.3

o

U 0.25

~

0 _0.2

'v c

V E ^0.¹⁵

0

(l) 0.1

Cl 0.05

a

E 1 detector

MEAN GF~ 0.053 em' sr

..... ··A ... ... I!. ... I!.. . ...... .. I!. .. .

0 2 4 6 8 10

P4 detector

MEAN GF~ 0.25 em' sr

./s../i. ... ts. ... A .. ·I!. .. ··A· .. I!.·· .. /s.· .. ,A .. ·,A. .. ·I!. .... ·

100 150 200 250 ~oo

Figure 2.2: Geometrical Factor for protons as a function of energy. The name of the detector is indicated in the insert, along with the mean value of the GF in the plateau region.

2.1.6 The response of the CPD detectors to monoenergetic par- ticles.

The response of detector E1 to an isotropic flux of monoenergetic particles was simulated for a sample of energies: 2 10⁵particles penetrating the detector at uniformly distributed positions within the 0.915 em radius and uniformly distributed in a 27r-solid angle were tracked through the detector. The energy loss in the sensitive element was recorded. The Figures 2.7 to 2.9 show the different spectra for electrons, protons and a, respectively at several energies.

Some general conclusions may be drawn from these output spectra:

• The detected particles may be classified into four categories: (i) those which cross the inner edge (0. to 3 mm thickness) of the last collimator (C3), and lose the remaining energy in the sensor, (ii) those which lose a fraction of their energy in

12

(21)

~ 0.1 ~ 0.1

' - ' -

(f)

NE ^0.09 P1 detector ^(f)

E ^0.09 ^{E 1 detec}^t^or

~ 0.08 MEAN GF= 0.053 em' sr

~ 0.08 MEAN GF= 0.05.3 em' 9r

.8 '-_u ^0.07

.2 ^0.06

0 0.05 u

.A. _··_A·

·C

V ^0.04-

E _0.03

0

Q.)

G 0.02 0.01 0

0 10 20 .30 40 ?o

Energy of incident 0: (MeV)

~ 0.4-

'-(f) P3 detector

NE ^0.35 _{MEAN GF=}_0.₂₅_{em' 9r}

~ _'- 0.3

B u 0.25

..2

-0 _0.2

u

..... ~-A&A.AA./.~~~,..,....~

~

·c V 0.15

E 0

Q.) 0.1

G 0.05

0

200 400 600 &00

B '-_u ⁰^.07

.2 ⁰^.06

0 0.05

·c u

V ⁰^.04- E ₀_.03

0

Q.)

G _0.02 0.01 0

~ 0.4- '-(f)

0

NE 0.35 - u --:: 0 . .3 -

o

U 0.25 _

.2

S ^0.2 ^- S 0.15 f- AA

A

Q.)

E o

Q.) 0.1 f0-

G

0.05 f- o

···.·A ..... .

10 20 .30 40 ?O

A A

I

P4 detector

MEAN GF= 0.25 em' 9r

.. . .4t:.A"'A4AAAA A J¥t.I:>:AA~Al!.

A4A

I I

200 400 600 ~oo

Figure 2.3: Geometrical Factor for alpha-particles as a function of energy. The name of the detector is indicated in the insert, along with the mean value of the GF in the plateau region.

the entrance window and cross the sensitive element depositing a fraction of their energy, (iii) particles which lose a fraction of their energy in the collimator and cross the sensitive element depositing a fraction of their energy. (iv) those which lose a fraction of their energy in the entrance window and deposit all the remaining energy in the sensitive element;

• All those particles contribute to differents bins (channels) of the detector, with a possible "peak generation" effect as shown in Figure 2.9: a 200 MeV flux of ^(¥- particles produces two main peaks in the detector. This case deserves a careful analysis, since such a behaviour spoils the detector energy resolution.

13

(22)

J

~ 0.1 '-C/)

.... E ^0.0⁹ ^{P 1}^detector

~ 0.08 '-0 0.07

~ ti ^0.06

0 0.05

·c u

V ^0.04- E _0.0.3

0

<l) (:) 0.02

0.01

0 o 2.5 .3 .3.5 4 4.5 5

Energy of incident e- (MeV)

~ 0.1

'- C/)

.... E ^0.09 E 1 detector

~ ^0.08

'-0 0.07

U ~ 0.06

0 _0.05

·c u

V ^0.^04- E _0.0.3

0 V (:) 0.02

0.01

a o 0.5 2 .3 .3.5 4 4.5 5

Energy of incident e- (MeV)

Figure 2.4: Asymptotic variation of the GF of PI and El as a function of electron incident energy.

Figure 2.10 illustrates the results of an analysis of the detector response split into its different contributions: the a-particles which follow the "normal" path deposit 9.5 MeV in the sensitive element. Their spectrum is shown in Figure 2.10 (up - right). This category constitutes more than 50% of all the detected particles. Figure 2.10 (down - left) shows the spectra of the particles which reach the sensitive element after losing less than 1 00 Me V in the collimator C3. This precisely means that those particles run across less than a 3 mm long path in the brass collimator. The energy deposit ranges from 9.5 to 18 MeV. Much of the contributors to the energy loss spectrum near the a MeV limit is due to partial energy loss in the sensor and partial energy loss in the other collimators. In Figure 2.10 (down - right) the spectrum of a-particles which cross the .3 mm thickness of collimator C3 loosing more than 100 MeV is shown. A peak appears at 18 ^j^'yfe V) simulating ^f'-I 18 MeV and ^f'-I93 LVI eVa-particles reaching the sensor through the" normal" path.

14

(23)

1

J

I

J

... 0.2

"-

en

"'E ^O.l^B

~ 0.16

"- 0 0.14

-2 U ^0.¹²

0 0.1

·c u Q) ^O.OB

E _0.06

0

<U 0 0.04

0.02 0

... 0.2

"-

en

"'E ^O.lB

u 0.16

~

"-

.3 ^0.14

u

-2 ^0.¹² '0 _0.₁

·C u Q) ^O.OB

E _0.06

0

<U

0 _0.04 0.02 0

r-

l-

f- I-

P 1 detector

MEAN GF ~ 0.1 em'sr

_ a/:"';:;.AaA .. l:i,.I:l. .. a ..... A ... A ... ~ .. ... 'b,." ... a " ... t;,; ... .. .I:l. . . ·A .. .. ·a .. · .. ,

-

I I I I I

0 50 100 150 200 250 ~oo

- E1 detector

- MEAN GF - 0.1 em' or

r- r- r-

. a

a .. ·"6. .. ·A .. -br ... ~ ... A ... a·· ...... "6.· .. ·· .. ··l:i, ... ··A·· .. ·· .. n: .. · .... ·l:i,· .. · .. ··a· ... ·A .... · .. ·_· ... ·

r- a

~

^{a a}

f-

J ^I ^I I

0 50 100 150 200 250 ~oo

Figure 2.5: Asymptotic variation of the GF of PI and El, as a function of proton incident energy.

The kind of analysis described above was also made for 50 Me V protons. The conclusion is that 50 Me V protons going across the" normal" path give a signal of Î"V2.4 Me V, whereas the 50 MeV protons crossing 3 mm through the C3 collimator deposit Î"V4.7 l'vl e V in the sensor, simulating both Î"V4.7 MeV and Î"V23 MeV protons.

2.2 Numerical simulation of a calibration

2.2.1 The CPD channels

The energy lost by particles at peak (penetration) energies depends on the sensor thickness. It has been calculated for all the detectors and the mean values over Pl, ... P4 and

El, E2 respectively are tabulated. These mean values are used in the design of CPD bins

(channels), according to the method described in Appendix A.

15

(24)

..-.. ^0.2

' - (J1

NE ^0.1⁸

..::;.. 0.16

0 ^0.14 .2 U ^0.12

0 0.1

.g V ^0.08

E _0.06

0

<J.)

Cl 0.04 0.02 0

..-.. ^0.2

' - (J1

"'E ^0.18 ..::;.. ^0.1⁶

.3 _u ^0.14

-2 ^0.12

Ci u 0.1

·C

V ⁰^.08 E _0.06

0

<J.)

Cl 0.04 0.02 0

0

-

f- f-

o

100

I 100

P1 detector

MEAN GF ~ 0.1 em' or

200 JOO 400 500 600 700 ~oo

Energy of incident ex (MeV)

E 1 detector

MEAN GF - 0.1 em' sr

I I I I I I

200 300 400 500 600 700 ~OO

Energy of incident ex (MeV)

Figure 2.6: Asymptotic variation of the GF of PI and EI, as a function of a-particles incident energy.

In a first design attempt, the mean energy values were majorated by the calculated un- certainty for protons and a-particles, and by 10% for electrons, in order to avoid the best possible bin crosstalk.

The resulting energy bin limits are shown in Table 2.1 as values of the energy lost in detector sensors.

16

(25)

en E = 0.5 MeV ^~¹⁴⁰

C 1400 c- _C E = ^{1.5 MeV}

:::l :::l

0 0 120

U 1200 c-- ^U

100 1000 ^~

800 ^~ 80

600 ^~ 60

400 ^~ 40

200 ^~ 20

a Î Î Î 0

a ¹ ² ^J ⁴ ⁰ 1 2 J 4

Energy lost in the Si element (MeV) Energy lost in the Si element (MeV)

200 400

~ ~

c ₁₈₀ E = ^{2. MeV} ^c ^E= ^{5. MeV}

:::l :::l 350 i-

0 0

U 160 U

JOO ,....

140

120 250 f -

100 200 ^{f -}

80 150 ^~

60

100 -

40

20 50 -

a 0

...

^L ^I ^I

a ¹ ² J 4

Energy lost in the Si element (MeV) ⁰Energy lost in the Si element (MeV) ^{1 2 3} ⁴

Figure 2.7: Spectrum of the energy lost in the E1 sensor by monoenergetic electrons.

Simulations by GEANT [16J revealed that still many electrons were counted in Bin 2, for PI detector, due to energy straggling. The energy channels of Table 2.1 were recalculated by use of the maximum energy deposited by ^rv8 10⁶particles gathered from random positions and directions onto each up-looking detector. This number of particles is expected from a Is counting time in a flux of 10⁶particles/(s cm²sr). The energy bins obtained using this method are shown in Table 2.2. They will be used throughout the rest of this document. The main task of the CPD electronic unit is to record any detected particle in one of the 40 incrementable registers. The electronic unit does not perform particle discrimination, neither does it discriminate low energy particles stopped in the sensitive elements from high energy particles depositing the same amount of energy. The way the signal is handled from the sensor to the registers is shown schematically in Figure 4 in Appendix A.

17

0RSTED satellite:

The Charged Particle Detector (CPD)

on the 0RSTED satellite:

description and evaluation

Technical Report A

Contents

I \

[

(

Preface

i

Useful addresses

Useful e-mail adresses and phone numbers

Acknow ledgments

Introduction

I

Chapter 1

The 0RSTED /CPD Instrument

l

J

1.4 The GEANT model of the Charged Particle De- tector

J

Chapter 2

The simulation of the CPD

J

"""

J

J

1

I

~

...