Ulysses Data System Kiel Electron Telescope Description Institut für Experimentelle und Angewandte Physik der Christian-Albrechts-Universität zu Kiel Horst Kunow, mailto:hkunow@kernphysik.uni-kiel.de Bernd Heber, mailto:bheber@kernphysik.uni-kiel.de Reinhold Müller-Mellin, mailto:mueller-mellin@kernphysik.uni-kiel.de Kiel, March 10, 1998 ----------------------------------------------------------------------------- The Kiel Electron Telescope Sensor System Figure 1 (IMG1.GIF) displays in front the flight spare model sensor unit of the Ulysses Kiel Electron Telescope (KET) and in the back the electronics box. For comparison a five German mark coin is shown to demonstrate the size of the instrument. The KET is part of the Ulysses cosmic ray and solar particle investigation (COSPIN) experiment, which has been described in detail by Simpson et al. [4]. Figure 2 (IMG2.GIF) shows the COSPIN sensor units as they are mounted on the spacecraft. The KET (3) is mounted below the Low Energy Telescope (LET), the Anisotropy Telescope (AT), the High Energy Telescope (HET) and the High Flux Telescope (HFT). Figure 3 (IMG3.GIF) shows a schematic sketch of the KET sensor system. D1 and D2 are 0.5 mm thick semiconductor detectors, C1 is an aerogel Cerenkov- detector and A a plastic anticoincidence scintillator. C2 is a lead fluoride Cerenkov-detector and S2 a plastic scintillator. PM1 through PM4 are photomultipliers. Functionally, the detector system consists of two parts: an entrance telescope and a calorimeter, surrounded by a guard counter A. The entrance telescope is composed of a silica-aerogel Cerenkov detector C1 inserted between semi-conductor detectors, D1 and D2. Together with the guard counter A, this combination defines the geometry, selects particles with velocity beta>0.938 and determines the particle charge. The calorimeter consists of a 2.5 radiation length lead-fluoride (PbF2) crystal used as Cerenkov detector (C2) and a scintillator S2. In C2 an electromagnetic shower can develop. The number of electrons leaving the PbF2-crystal are counted in S2. The KET is designed to measure electron, proton and alpha particle fluxes in several energy windows ranging from a few MeV/n up to and above a few GeV/n. The values listed in the following table are based on mean energy losses and geometry of the instrument. Figure 4 (IMG4.GIF) summarizes the KET coincidence channels. The coincidence name and trigger condition are displayed in the first two columns. The particles and their corresponding energy range are listed in columns three and four. The geometrical factor and sectorization information of the coincidence channels are in columns five and six. ----------------------------------------------------------------------------- Monte-Carlo-Simulation of the KET A treatment of the response functions of particle telescopes, and a number of exact formulae for multi-element telescopes have been given by Sullivan, [5]. However, the determination of the response function of rather complex telescopes like the KET instrument, makes a Monte Carlo simulation mandatory. We assume that the differential coincidence counting rate of a particle telescope can be expressed as: dCi,k = dE Rik(E) Jk(E) (counts/s) where dCi,k is the differential coincidence counting rate in channel i, Jk(E) the flux of particle species k with kinetic energy E, and Rik(E) the response function for particle species k in channel i, to be determined by the simulation. To get the counting rate Ci for the channel i we have to integrate over E and sum up for all particle species. In general, the response function may depend on many variables like the angular distribution of the incident particle flux, the location where a particle penetrates a detector etc. Here we assume that R(E) is a function only of kinetic energy, valid for particle fluxes which are almost isotropic over the effective opening angle, and that the simulation properly averages over all other dependencies. The Monte Carlo simulation was performed with the CERN Library Program GEANT 3 (BRUN et al., [1]). Particles were followed down to a low energy cutoff (electrons and gamma-rays 50 keV, protons 300 keV), once reaching this cutoff the particles were considered to be stopped and to have deposited all of their kinetic energy in the traversed material. The geometry of the detectors, mountings, foils, and the relevant structure material as well as the energy resolution of the readout electronics were accounted for in the simulation. KET geometry is shown in figure 5 (IMG5.GIF). This figure is a model of the KET sensor unit in the simulation. Shown are three possible tracks of 120 MeV protons. Two of these tracks are triggering the channel P32 and on of them is counted in P116. Energy loss distribution: In addition to the count rates in all coincidence channels, the energy losses in D1, D2 and number of photons in C1, C2 and S2 are transmitted. Particle instruments are calibrated by using a particle beam provided by an accelerator (see SIERKS, [3]). In space, particles of different species, incident directions and energies are observed nearly simultanously. Such an environment cannot be simulated at an accelerator but can be simulated using an appropriate computer model. As an example figure 6 (IMG6.GIF) shows the simulated energy distribution of isotropic protons and alpha-particles in the semiconductor detectors D1 and D2 triggering the P32 and A32 coincidence channels. Calculated D1-D2 PHA-distribution (energy loss), using a proton and alpha distribution which is a function of energy and isotropic in direction. The solid lines show the mean energy losses. Marked on these lines are the expected energy losses for 35, 40, 50, 70 and 120 MeV/n. The dotted lines display the electronics thresholds. In comparison figure 7 (IMG7.GIF) shows a PHA distribution measured in space. Measured P32-protons and A32-alpha-particle D1-D2 matrix in January 1991. The entries below the dotted line could be identified as background random coincidences (HEBER, [2]). As is discussed in detail in HEBER, [2], the proton and alpha-tracks in that matrix are well described by the Monte-Carlo simulation. One important result of the analysis are the determination of the geometrical factors as a function of energy: (IMG8.GIF) Response functions RSimi(E) for isotropic protons and alpha-particles. The rectangular boxes indicate the response functions expected by using the Sullivan [5] theory. For the low energy channels this theory is a good approximation. G/(cm2 sr MeV/n) E /(MeV)/n Sigma;E/(MeV)/n --------------------------------------------------------------- protons K3 --------------------------------------------------------------- S | 57.8 | 81.0 | 26.1 --------------------------------------------------------------- alpha-particles K33 --------------------------------------------------------------- S | 52.7 | 78.2 | 24.0 --------------------------------------------------------------- protons K34 --------------------------------------------------------------- S | 83.3 | 190 | 42 --------------------------------------------------------------- alpha-particles K29 --------------------------------------------------------------- S | 23.4 | 164 | 25 --------------------------------------------------------------- protons K12 --------------------------------------------------------------- 1 | 230 | 315 | 160 2 | 500 | 700 | 390 3 | 1370 | 1250 | 420 4 | 1500 | 950 | 490 --------------------------------------------------------------- alpha-particles K31 --------------------------------------------------------------- A | 220 | 315 | 150 B | 480 | 700 | 390 C | 1320 | 1250 | 420 D | 1500 | 950 | 490 ----------------------------------------------------------------------------- KIEL ELECTRON TELESCOPE readme This readme was last modified March 10, 1998 and shall explain the file structure of the KET files provided for the Ulysses Data System (UDS). The previous sections "The Kiel Electron Telescope Sensor System" and Monte-Carlo-Simulation of the KET" explain the instrument. Only count rates are provided for the UDS, because the geometrical factors may change in future. The geometrical factors provided in the previous section should be checked against the values on our homepage: COSPIN/KET homepage: http://www.ifctr.mi.cnr.it/Ulysses/ All Ulysses data system files (UDS files) have the name UCOSKETAYYDOY.DAT Herein YY is the year (eg. 90) and DOY the day of the year (eg. 365 of year 90 is 31.12.90). ----------------------------------------------------------------------------- RECORD FORMAT for the KET The KET files are written on a VMS machine using Fortran 77 Routines. The format used is: IMPLICIT REAL(K) WRITE(40,'(6I5)') IYEAR,IDOY,IHOUR,IMIN,ISEC,ICOV WRITE(40,'(10G11.3)') 1 K1,K21,K22,K23,K24,K25,K26,K27,K28,P4 WRITE(40,'(10G11.3)') 1 K3,K34,K12,K10,K2,K33,K29,K31,K30,K13 WRITE(40,'(10G11.3)') 1 K14,K15,K16,K17,K18,K19,K20,E4,K11,K32 WRITE(40,'(6G11.3)') 1 D10,D20,C10,C20,A01 Parameters are: IYEAR: year IDOY: day of year IHOUR: hour IMIN: minute ISEC: second ICOV coverage in percent KET channel energy range A&A energy range Monte-Carlo simulation K1: protons (2.7-5.4 MeV) K21-K28: " (5.4-23.1 MeV) sectors 1 through 8 P4: " (5.4-23.1 MeV) omnidirectional K3: " (34.1-125.0 MeV) K34: " (125.0-320.0 MeV) (125.0-250.0 MeV) backward penetrating particles (160.0-260.0 MeV) K12: " (320.0-2100.0 MeV (250.0-2200.0 MeV) backward penetrating particles (260.0-2200.0 MeV) K10: " (>2100.0 MeV) (>2200.0 MeV) backward penetrating particles (>2200.0 MEV) K2: helium (6.0-20.4 MeV) K33: " (34.2-125.0 MeV) K29: " (125.0-320.0 MeV) (125.0-155.0 MeV) backward penetrating particles (155.0-225.0 MeV) K31: " (320.0-2100.0 MeV) (250.0-2100.0 MeV) backward penetrating particles (250.0-2100.0 MeV) K30: " (>2100.0 MeV) K13-K20: electrons (2.5-7.0 MeV) sectors 1 through 8 E4: " (2.5-7.0 MeV) omnidirectional K11: " (7.0-170.0 MeV) K32: " (>170.0 MeV) D10 - A01: single detector count rates Note: Data are Rates not Intensities and given in (/s). Accumulation time is 10 minutes. RTG corrections not included. Flag -707: data gap ----------------------------------------------------------------------------- Caveats: 1. Only rates C are given, since no simple estimate of the intensities can be done. Intensities (I) must be derived by dividing through the integral geometric factor Gi, and by correcting through Pulse Height Analysis. I = C / Gi Values of geometrical Factor Gi = (counting rate)/(Intensity): KET channel Gi K1 18 K21 - K28 120 P4 120 K3 70.0 K34 152.0 K12 3300.0 K10 na K2 120 K33 70.0 K29 88.0 K31 3200.0 K13-K20 na E4 na K11 na K32 na Check against our COSPIN/KET homepage: http://www.ifctr.mi.cnr.it/Ulysses/ 2. Background fluxes of K1 are a combination of components, including a high RTG background rate. This channel should be used only during event times. 3. On 10 min averages some of the channels have limitations because of RTG background. Very slow increases are a sign that background levels are reached (a few percent per year). =============================================================== GET LOW FLUX VALUES FROM THE PI ON LONGER ACCUMULATION PERIODS =============================================================== send request to KET PI: e-mail: hkunow@kernphysik.uni-kiel.de The daily averaged and 27 day averaged data are also provided. See readme.daily 3.3 and readme.27days 3.4. 4. Fluxes of K11, K13-K20 and E4 below 2.0e-4, 2.5e-3 are a combination of different components including RTG background. The exact amount of background relative to real electrons are unknown. =============================================================== Levels below 3.0e-3, 2.5e-3 should not be considered. =============================================================== 5. Fluxes of K32 are contaminated by high energy protons. Reliable fluxes needs an PHA correction on longer accumulation periods. 6. Determination of the intensities of K29 needs a PHA correction on longer accumulation periods (several hours). 7. Time periods when KET is saturated or is working in a "calibration mode" have been omitted: eg. March event 1991 peak fluxes in the June to August period 1991 Jovian encounter. 8. Data for the Jovian encounter are available on a 4 min bases. ================================================= Caution: Very high fluxes for KET !!!! ================================================= ----------------------------------------------------------------------------- Readme, KET90-96.DAILY The daily averaged file KET90-96.DAILY contains a subset of KET coincidence channels which can be corrected by using Pulse Height Analysis (see Heber [2]). As an example the masks choosen for K3 and K34 are shown in figure (IMG9.GIF). Definition of PHA masks in K3, K33 Matrix using the result of a GEANT simulation. figure 10 (IMG10.GIF) Definition of PHA masks in K34, K29 Matrix using the result of a GEANT simulation. In contrast to the upper panel inflight data are shown. Note that we used a for figure 10 a time period of 30 days. Because of the low PHA-statistics for K29 no daily averaged corrected rates are given on a one day basis. The KET file was written on a VMS machine using Fortran 77 Routines. The format used is: IMPLICIT REAL(K) WRITE(40,'(I2,1X,I3,1X,I3,1X,8G10.3/10X,6G10.3)') 1 IYEAR,IDOY,ICOV 1 K3,EK3,K34,EK34,K12,EK12,K10,EK10, 1 K33,EK33,K31,EK34,K30,EK30 Parameters are: IYEAR: year IDOY: day of year ICOV coverage in percent KET channel energy range A&A energy range Monte-Carlo simulation K3: protons (34.1-125.0 MeV) EK3: error of preceeding value K34: " (125.0-320.0 MeV) (125.0-250.0 MeV) backward penetrating particles (160.0-260.0 MeV) EK34: error of preceeding value K12: " (320.0-2100.0 MeV (250.0-2200.0 MeV) backward penetrating particles (260.0-2200.0 MeV) EK12: error of preceeding value K10: " (>2100.0 MeV) (>2200.0 MeV) backward penetrating particles (>2200.0 MEV) EK10: error of preceeding value K33: helium " (34.2-125.0 MeV) EK33: error of preceeding value K31: " (320.0-2100.0 MeV) (250.0-2100.0 MeV) backward penetrating particles (250.0-2100.0 MeV) EK31: error of preceeding value K30: " (>2100.0 MeV) EK30: error of preceeding value Note: Data are Rates not Intensities and given in (/s). Accumulation time is 1 day. Flag -707: data gap or less than 4 entries in PHA selection. ----------------------------------------------------------------------------- Readme, KET90-96.27DAYS The KET files are written on a VMS machine using Fortran 77 Routines. The format used is: IMPLICIT REAL(K) WRITE(40,'(4I3,2G13.4)') IYEAR,IDOY,IHOUR,IMIN,E4,EE4 Parameters are: IYEAR: year IDOY: day of year IHOUR: hour IMIN: minute KET channel energy range A&A energy range Monte-Carlo simulation E4: " (2.5-7.0 MeV) omnidirectional EE4: error of preceeding value Note: Data are Rates not Intensities and given in (/s). Accumulation time is 26 days. PHA corrections included. Flag -707: data gap ----------------------------------------------------------------------------- References 1 R. Brun, F. Bruyant, M. Maire, A. C. McPherson, and P. Zanarini. GEANT3. CERN DATA HANDLING DIVISON, 1987. (DD/EE/84-1). 2 B. Heber. Modulation galaktischer kosmischer Protonen und alpha-Teilchen in der inneren dreidimensionalen Heliosphäre: Messungen des Kiel Electron Telescopes an Bord der Raumsonde Ulysses. PhD thesis, Christian-Albrechts-Universität Kiel, 1997. 3 H. Sierks. Auswertungen der Eichmessungen des Kieler Elektronen-Teleskops zur Erstellung von Energiespektren an Bord der Raumsonde ULYSSES (International Solar Polar Mission). Master's thesis, Christian-Albrechts-Universität Kiel, 1988. 4 J.A. Simpson, J.D. Anglin, A. Barlogh, M. Bercovitch, J.M. Bouman, E.E. Budzinski, J.R. Burrows, R. Carvell, J.J. Connell, R. Ducros, P. Ferrando, J. Firth, M. Garcia-Munoz, J. Henrion, R.J. Hynds, B. Iwers, R.M. Jacquet, H. Kunow, G.A. Lentz, R.G. Marsden, R.B. McKibben, R. Müller-Mellin, D.E. Page, M.A. Perkins, A. Raviart, T.R. Sanderson, H. Sierks, L. Treguer, A.J. Tuzzolino, K.-P. Wenzel, and G. Wibberenz. The ULYSSES cosmic-ray and solar particle investigation. Astron. Astrophys. Suppl., 92(2):365-399, 1992. 5 J. D. Sullivan. Geometrical Factor and directional Response of single and multi-element Particle Telescopes. Nucl. Instr. and Meth., 95:5-11, 1971. About this document ... Ulysses Data System Kiel Electron Telescope Description Institut für Experimentelle und Angewandte Physik der Christian-Albrechts-Universität zu Kiel The translation was initiated by Bernd Heber on Tue Mar 10 17:17:11 MET 1998