/ NOAA Technical Report ERL 393-SEL 40 Q 1 C »^j * ^. 50 keV, E o > 30 keV D. J. Williams Abstract. The Energetic Particles Experiment (EPE) carried aboard the NASA IMP 7 and 8 satellites was one of the first low energy (tens of kilovolts) magnetic/solid state detector ion-electron separation and analysis systems flown in space. Although we are now constructing substantially more sophisticated systems for space flight, it remains of interest to describe this early instrument, its calibration, its in-flight operation, and its ground data handling and display system. Normal operation with no failures has gone on for a combined IMP 7 and 8 total of 8.5 years in orbit. 1. INTRODUCTION This paper describes an ion- electron solid state detector/magnet- ic deflection system flown aboard the NASA satellites IMP 7 (Explorer 47) and IMP 8 (Explorer 50). This in- strument represents our initial effort in a series of such instru- ments whose goal is to achieve clean ion-electron separation down to energies of a few tens of keV at low weight and relatively large geometric factors. This goal has been achieved, and follow-on instrumenta- tion has been flown on board the earth orbiting satellites Explorer 45 (Williams et al., 1969; Longanecker and Hoffman, 1973) and ATS-6 (Fritz and Cessna, 1975) and the solar orbiting satellites Helios 1 and 2 (Keppler et al., 1976). Significant- ly improved instrumentation has been fabricated for the ISEE A and B spacecraft and will be described in a future paper. The IMP 7 and 8 energetic par- ticle experiment (EPE) cleanly separ- ates ions and electrons in the energy range from 30 keV through several MeV. In addition to the magnetic deflection system, complementary particle observations are obtained from a low-noise detector (-18 keV discriminator level) and a thin (-5 p) detector. IMP 7 and 8 were launched on September 23, 1972, and October 28, 1973, respectively, into roughly circular orbits (in the solar eclip- tic plane) at a geocentric distance of -35 Earth radii (35 R £ 224,000 km). Both satellites were spin sta- bilized (IMP 7, 48 RPM; IMP 8, 24 RPM) with their spin axes oriented perpendicular to the ecliptic plane. IMP 8 was initially positioned -180° from IMP 7. Subsequent in-orbit drift decreased the satellite sep- aration distance until a minimum separation of -2.5 Rp was reached on February 2, 1976, after which the separation distance once again slowly increased. These orbits have allowed a variety of solar-terres- trial studies using simultaneous observations from nearly identical instruments over a wide range of spatial separations in the Earth's magnetotail and magnetosheath, and in near-Earth interplanetary space. The EPE's on both IMP 7 and 8 have functioned normally up to the present with no malfunctions or failures. The following sections describe the instrument, its in- flight operation, and samples of ground data displays. VIqujul 7. A66mblnd EVE package.. 2. ENERGETIC PARTICLES EXPERIMENT (EPE) The EPE instrument is shown in Figure 1 in a standard IMP package configuration. Package depth and height are 25.4 cm and 12.7 cm, respectively, and requires watts. Power and calibrate The EPE weighs 3.18 kg a normal power of 2.6 levels during command sequences are 2.8 and 3.1 watts, respectively. One full 15° viewing cone perpendicular to the spin axis and two full 13° viewing cones 45° to the spin axis are used for the EPE particle observations. Angular distributions are measured by obtaining 8 or 16 samples (depending on particle type and energy) per satellite spin period. The effective bit rate of the EPE is -18.8 bits per second and a complete distribution sample is 20.4 seconds. energy-angular obtained every Comprehensive analog and digital housekeeping systems are used to keep track of experiment status and opera- tional condition. For example, rou- tine measurements are made of all detector-preamplifier RMS noise levels for comparison with prelaunch values. An extensive command system is used to control power supplies, discriminator levels, and logic selections. An electronic in-flight calibrator (Peletier, 1970) provides a thorough check of experiment elec- tronics from the preamplifiers through the output logic and permits routine calculations of discriminator level settings for comparison with prelaunch calibrations. These in-flight tests have shown the IMP 7 and 8 EPE's to have operated in a completely normal fashion to the present time, a total of ~8.5 years of in-flight operation. 3. SENSOR HEADS AND ELECTRONICS The EPE particle detector assem- bly consists of a main magnet-detec- tor assembly and two auxiliary detec- tor heads. All detectors are fully depleted, surface barrier, solid state detectors, and are operated with bias voltages 1.25-1.5 times the values required for full depletion. To minimize radiation damage effects, all detectors directly exposed to ion fluxes are mounted with the aluminum contact exposed to the incoming beam. In this way catastrophic detector failure due to radiation damage is extended to the 10 16 -10 18 protons/cm 2 range (Coleman et al., 1968 a,b). On the basis of observed fluxes, radia- tion damage is not yet a problem for the EPE. The main magnet-detector assem- bly is shown schematically and in various stages of completeness in Figure 2. It consists of a three- element telescope (detectors A, B, C), a sweeping magnet that keeps low energy electrons (E e <200-300 keV) away from the telescope, and two detectors (D and E) to detect the swept electrons. The telescope cov- ers the proton energy range 50 keV 6embted magnetic con^igaAaUon A/iowuig 6lucld< n and col- Lunaton. Look-angle i* onte.nted 90° to lateZJUte ^i>\ avti The housing for the auxiliary detectors (F and G) is shown schemat- ically in Figure 3. Detector F is a selected low-noise device employing a single discriminator in the 15-20 keV region to measure low energy protons and electrons. Detector G is a very thin (~5 u) device employing discrim- inator levels to measure alpha par- ticle and Z >3 particle intensities. The characteristics of the IMP 7 and 8 EPE detectors G have been described in detail by Wilken and Fritz (1974, 1976; their detectors D8 and D5). The detector ABC telescope has the following geometric factors: detector A, 1. ll(10)- 2 cm 2 ster; detec- tor AB, 1.07(10)- 2 cm 2 ster; detectors ABC, 0.97(10)- 2 cm 2 ster. The electron detectors, D and E, have a maximum calculated geometric factor of 0. 97(10 ) _2 cm 2 ster. Accounting for measured energy and angle-dependent efficiencies, approximate detector D and E geometric factors are 1.5(10) -3 cm 2 ster and 0.9(10)~ 3 cm 2 ster. Detec- tor characteristics, discriminator levels, and logic outputs are given in Tables 1 and 2. A simplified block diagram is shown in Figure 4. TABLE 1. EPE DETECTOR CHARACTERISTICS 13° LOOK ANGLE COLLIMATOR, HOUSING AND STRUCTURE INSULATOR AND CUP ASSEMBLY WIRE WASHER 'FUZZ" BUTTONS EXPERIMENT PACKAGE | ] OUTER WALL Vigu/ic 3. Schematic Ahouxing housing {on. detectons V and G. Look angle. oriented 45° to satclUXe spin. Bias Detector Area* Thickness Voltage Current (mm 2 ) Cm) (uA) Satellite 7 A 25 54.2 30 .25 B 50 514 150 .55 C 50 501 150 .66 D 18 300 150 .27 E 18 300 150 .32 F 25 100 30 .08 G 10 6.0 2.5 .007 Satellite 8 A 25 54.7 30 .23 B 50 491 150 .27 C 50 508 150 .52 D 18 300 150 .54 E 18 300 150 .30 F 25 100 30 .09 G 10 5.87 are 6mm x 1.6 3mm rectan .03 *Detectors D and E gular units. All others are circul ar. a CD B C3- c an » 0- D— ["J-IaEEJ 1-2 — MULTI- PLEXER OUTPUT- BUFFER 1 F- Si — L 3 . — MULTI- PLEXER OUTPUT- BUFFER 2 L 7 . — >-» — L 5 — L 6 — MULTI- PLEXER OUTPUT- BUFFER 3 G 2 ~- Ls— MULTI- PLEXER OUTPUT- BUFFER 4 Lii" — Gj — 16 SAMPLES ' PER SPIN PA = PREAMP-AMP ViauJin 4. Simplified block dia- gram o{ EVE electn.onici> . Cali- bhjatlon, housekeeping, command, and timing function* an.e not shown. In case o{ logic {all- u/ie, dLschJjminaton. level output can be routed by command to the multiplexer . TABLE 2. EPE NORMAL DISCRIMINATOR LEVELS AND OUTPUT LOGIC Nuclear Di scriminator* Output Desig- Charge Samples Detector Le vel s Logic Channels nation Range per spin (MeV) (MeV) A Al 0.03 A^gBj 0.05 - 0.22 Li Z > 1 16 A2 0.20 A 2 A 4 §i 0.22 - 0.80 1-2 Z > 1 16 A3 0.50 A 3 A 4 B 2 B 3 C 4.5 - 8.5 Ls Z = 1 8 A4 0.80 A 4 A 5 B, 0.80 - 2.1 L 3 Z > 1 16 A5 2.5 A 4 A 5 BiB 2 C 2.1 - 4.5 1-4 Z = 1 16 A6 3.5 A 6 B,C 8.4 -16.0 Ln Z = 2 8 A 2 BiC background L 9 8 B Bl 0.10 A 5 B, 2.2 - 8.4 Lio Z > 2 8 B2 3.6 A 5 A 6 B 2 C 16.0 -35.0 Liz Z = 2 8 B3 9.0 C C 0. 10 AaBjC 8.5 -25.0 U Z = 1 8 D Dl D2 0.030 0.100 Ma 0.03 - 0. 10 L7 electrons 16 E El E2 0.100 0.200 E,E 2 0.10 - 0.20 L 8 electrons 16 F Fl 0.015 Fi >0.015 F electrons and ions 16 G Gl 0.60 G, >0.6 G, Z > 2 16 G2 1.0 G 2 >1.0 G 2 Z > 2 8 G3 2.0 G 3 >2.0 G 3 Z > 3 8 * Levels A, and D, are commandable to 50 keV. Level Fj is commandable to 30 keV. **Low energy proton response is 50 keV due to aluminum dead layer. For the same reason, detector F low energy proton response is 0.024 MeV and 0.038 MeV on IMP 7 and 8 respectively. As a safeguard against possible failure in the logic circuitry, a commandable mode was incorporated into the EPE whereby all discrimina- tor levels could be routed to the multiplexers, thereby giving discrim- inator output counts only. Further safeguards include commandable low- level discriminators on detectors A, D, and F to protect against possible detector noise increases, and bias voltages commandable in four steps from normal operating bias to one- half that value to guard against excessive detector bias current. None of these safeguard modes has been required to date. For refer- ence, routinely monitored EPE status and housekeeping functions are listed in Tables 3 and 4. TABLE 3. EPE STATUS MONITORS TABLE 4. EPE HOUSEKEEPING MEASUREMENTS EPE Status Indicator Function 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Calibrator ON/OFF A, Level 30/50 Dj Level 30/50 F Level 15/30 Spare 30 V Supply. Level 30, 27, 24, or 15 set V at Detector C Coincidence ON/OFF 150 V Supply. Level set at 150,135, 120, or 75 V Command System GO/NO GO Calibrator Power ON/OFF Timing Information Test Connector Activated/ Not Activated Spare Logic or Discriminator Output EPE Analog Measurement Function 1 Temperature 2 150 V Bias Line 3 Variable L50 V Line 4 Variable . 30 V Line 5 20 V Buss 6 Reference Ground 7 5 V Reference 8 6 V Buss 9 -6 V Buss 10 A Channel Noise 11 B Channel Noise 12 C Channel Noise 13 D Channel Noise 14 E Channel Noise 15 F Channel Noise 16 G Channel Noise to obtain high The use of the interconnection NPN almost dou- of the circuit. Each EPE preamplifier (Gary, 1970; Hogrefe, 1970) is a common source FET stage driving a PNP common base with an NPN emitter follower. A preamplifier circuit is shown in Figure 5 for the low energy A, D, and F detectors. The emitter follower base resistor and the stray capaci- tances from the base interconnection are "boot-strapped" gain and bandwidth, guard ring around the between the PNP and bles the band width All EPE preamplifiers have a test input accessible externally for last- minute calibration checks in the spacecraft. As the EPE uses no foils in front of the detectors, the preampli- fier design had to accommodate the existence of a sun pulse on detector A once each spin (e.g., a 78-millisec sun pulse illuminates the aluminum contact of detector A during each spin of IMP 7). Several months of prelaunch laboratory tests showed that such solar stimulations do no apparent harm to the detector. How- ever, to insure rapid preamplifier recovery and to avoid breakdown of the FET gate-to-source junction in reverse bias, a 0.001 uF input coup- ling capacitor, 10 MQ bias and feed- back resistors (R. and R fb )> and protective diodes were employed. Tests showed the 2N2369 to be suit- able for use in the low-noise chan- nels and the 1N3064 to be suitable in the less stringent noise channels. The resulting preamplifier noise TZqujih 5. Schematic, ol doXicXoK A curve is shown in Figure 6. No del- eterious effects have been observed in detector A in-orbit operation. Because of the relatively thick (0.054 and 0.060 mg/cm 2 ) aluminum layer, detector A shows no response to the sun stimulus. However, detector D sees light reflected from detector A, and data loss occurs for the solar oriented sector and four succeeding sectors. 4. CALIBRATIONS Calibrations of the EPE were performed at the Goddard Space Flight Center and Naval Research Laboratory accelerator facilities. An example of the high energy calibrations (E p <1 MeV) performed at the Naval Re- search Laboratory is given in Figure 7, where we show absolute efficien- cies for the L3 and Lll levels in the IMP 7 EPE. These results agree well with the normal passband values given in Table 2. Since protons and electrons in the low tens of keV range were being separated and measured for the first time in interplanetary space by using surface barrier solid state detec- tors, considerable attention was given to the low energy calibrations, all performed at Goddard Space Flight Center. Figure 8 shows the absolute detection efficiency for the lowest level of EPE detector A. Both IMP 7 and 8 results are shown for an A x discriminator level of 30 keV. The resulting 50% efficiency points of 50 keV and 52 keV for IMP 7 and 8 give respective aluminum layers of 54 pg/cm 2 and 60 pg/cm 2 . These are to be considered effective aluminum layers as they include the effects of any silicon dead layer and pulse height defects. Although we were unable to obtain thinner aluminum layers for the IMP 7 and 8 EPE units, we have since purchased and flown a number of detectors with significant- ly thinner (-20-40 pg/cm 2 ) aluminum layers. In addition, P-type surface barrier detectors have been produced having thin (-10 pg/cm 2 palladium windows (Elad et al . , 1973; Inskeep et al. , 1974). 50 40 2 30 X UJ 20 in O z LOW NOISE PREAMP l -10MA C lt ,=lpf. R FB = 10M R Blis =10M 2N3227 PROTECT DIODE 10 50 100 TOTAL INPUT CAPACITANCE pf 500 1.2 I.C o z y 6 y 5 Ll L ) a )*-.B,BjC •f\ .2-? I iJH- normal E p (MeV) L„ A,B,C NORMA! _i_i_ 10 E a (Mev) 22 ElguAc 6. UoAjiZ vcaaua Input capacitance ^oa. doXcctoK A pfizampti^loA uuXh pno tcctlon diode and 10 Mfi Redback and blaA tizA-LbtoKA . Flgntc 7. Absolute, c^lclcncn o& EPE L 3 and L n logic IcvcU' obtained fasiom acczJLcAatoi cat blatlon. UoAmal bandwidth ffl Tabic 1 bhom foh comparison. The IMP-8 EPE AE versus E curves for the ABC telescope are shown in Figure 9. The ideal detector A curve is shown as a dashed line and the actual curve, including the 60 pg/cm 2 aluminum layer, is shown as the solid 1 ine. A calibration run was performed to measure the effectiveness of the sweeping magnet to keep low energy electrons from detector A. In addi- tion, runs were performed at higher energies to measure the effectiveness of the coincidence circuitry and to measure effects of large-angle elec- tron scattering in detector A. These results are shown in Figure 10 where the absolute electron detection efficiency in detector A is plotted against electron energy. It can be seen that electron- ion separation is very clean over our energy range. Note that while a few electron ener- gies in the 130 keV range attain a 3- 4(10)~ 3 probability of reaching de- tector A, this probability is gen- erally <10 -3 and is <10 -4 for E <50 keV. e Detector F proton and electron efficiencies are shown in Figure 11. Comparing the F discriminator level setting with the proton 50% effi- ciency point gives effective detector F aluminum layers of 31 ug/cm 2 and 49 ug/cm 2 for IMP 7 tively. The quieter thinner aluminum layer a 50% 24 keV. and 8 respec- detector and on IMP 7 gives proton detection threshold of Detector G efficiencies and proton pile-up curves are shown in Figures 12 and 13. 1.0 0.8 >~ 0.6 0A 0.2 0.0 1 1 1 1 1 r -> 1 1 1 — i 1 1 r DETECTOR A PROTON EFFICIENCY LEVEL A, = 30keV 20 40 60 80 100 120 140 160 Ep(keV) FlguAc 8. EPE low o{ ±10% a/12. estimated ^oh. tko, abholutd c^icizncy nonmatlza- tionb. NORMAL DETECTOR THICKNESS A = 54.7(i B=491|j C = 508n A / >v- ; B s. / C N. < // N. // N. _ // / / - / / . / / / / ■j / / / . / , . . 10" E n (MeV) VlguAn 9. AEp vzaaua Ep {on the. IMP ABC tetucopc. VcUihoi line, ion dctcctoJt A Akom Ideal cu/ivc (no abi>oKb) , and i>otid lino. i>hom actual ca6n Including the. mojo^vJind 60 \xg/cm 2 aluminum layoA. 8 10" cc o h- O LU t— LU O 5 10- >- CJ z LU CJ LU u LU t— LU Q Z o a: h- u LU _J LU 10 4 10 -5 T 1 1 1 I I I I I 1 1 1 1 I I I I v ? t'i _l I 1_ _1_|J I I I I I I ' i 10 100 E p (keV) 1000 FiguAn 10. hicuin magnut cu>6) (U a function o& dZucX/ion mangy. Detailed electron efficiency measurements were made for detectors D and E, both in a plane perpendicu- lar to the magnet pole faces and in a median plane between and parallel to the pole faces. From the magnet orientation in the satellite, these planes are labeled respectively the ecliptic plane and the plane perpen- dicular to the ecliptic plane. Absolute efficiency contours_ are shown in both planes for the DD 2 and EE 2 logic for IMP 8 in Figures 14 and 15. While the indicated efficiencies are reasonable for near-Earth elec- tron detection, it is obvious that the magnet was used mainly for sweep- ing rather for focusing, Our present units for the ISEE A and B satellites employ focusing techniques and have a greatly extended energy range. E,(keV) ViguA.2. 1 1 . Lou) zneAgy dutacZoK F abiolutu pioton and oXncXficn dutzction e^iclzncieA . F £eve£ = 16 feel/', IMP; 23 KeV, IMP %. E (He 3 ), Mev FiguAz 11. Absolute. doXacXion Gj and G 2 . Runi poA- ^oKmud \xiiXh He 3 beam. -o- IMP7 *+~ IMPS u ai i/i in s* - (- o a. a. > •i JC 8 ,„i -4 10' I0 : 10 10° G, counts/sec (»63tkeV) Figure 13. MeaAote oi dn proton contamination du pfioton pile -up electa. 320 > r 1/1 o o -z. < 320 < _l UJ X TO ECLIPTIC PLANE -i 1 1 1 1 1 I i I i I i l_ I 1 ' 1 1 1 r- 20 30 40 50 60 70 80 90 100 E e (keV) Eiguxe 14. Absolute electnon detection eHi.cienei.ei ion. the detecton V, ViV 2 output chaumeZ. ContouAA ofi constant absolute e^iciency one given in two angle- enengy pn.ojectA.om. Tke. ecliptic plane pn.oje.ctU.on aj> in a plane. peAp2.ndi.c.ulan to the. magnetic pole £ace6. The. pex- pe.ndic.ulan. to eclipttc plane. pn.oje.cXi.on ij> in a plane. cen- tered between and panjallel to the. pole. ^aceA. 320 310 UJ LU cr o LU Q O < LU > < _J UJ cr. 300 320 ECLIPTIC PLANE H T- 310 300 _L TO ECLIPTIC PLANE 100 200 300 iOO E p (keV) Vigu/ie. 7 5. Absolute. ele.cXn.on detection eHicienciei fan. the detection E, EiE 2 output. 5. IN-FLIGHT PERFORMANCE As stated earlier, both IMP 7 and 8 EPE's have operated as expected and without malfunction since launch. Figures 16 and 17 present EPE house- keeping and calibration data from selected channels of the IMP 7 and 8 instruments. All channels display the same type of normal behavior as shown in Figures 16 and 17. As described earlier, no prob- lems or data losses were observed in the low energy proton channels (de- tector A) due to the occurrence of a sun pulse once each spin. However, the low energy threshold (30 keV) and lack of a protective foil does make the LI channel (50-220 keV protons) sensitive to solar X-rays. This 10 30 29 2 28 £ 5.9 5.8 K i ' r Detector Bias i ■ 1 > 1 > r Logic Voltage 30 28 22 20 50 40 30 > 20 * 14 12 10 10 8 8 6 _ 4 O 20 a> 10 o a> Q. E Discriminator Level-Det.A Discriminator Level-Det.F' Noise -Det.G Noise -Det. C Noise - Det. A Noise -Det.F J i l i l i L Sep 23, 1972 200 400 600 800 1000 1200 1400 Days after launch, I MP 7 — I— — (— H- — (— -4- —I— H Janl, 73 Jul 1/73 Janl/74 Jull/74 Janl.75 Jul 1/75 Jan 1,76 Jul 1,76 VIqujih 16. StveAal-yeaA in- flight opeAcutional kutoiij o\ tha IMP 7 EPE. sensitivity has been measured in orbit using simultaneous data from IMP 7, IMP 8, and X-ray sensors on board the N0AA geostationary weather satellites, the SMS/GOES series (Unzicker and Donnelly, 1974; Grubb, 1975). A scatter plot of X-ray events observed by both SMS/GOES and the IMP 7 EPE is shown in Figure 18 (H. Sauer, personal communication) for both the soft (0.5-2 A) and hard (2-8 A) X-ray components. The higher sensitivity to the hard component is clear. The normal quiet time back- ground rate for channel LI is ~0.1- 0.2 counts per sector. IMP 8 data show nearly identical results. 11 1 — ; 1 1 1 1— Discriminator Level-Det.A 38 36 ^ 34 > 19 ir 17 - 15 30 20 ai 10 * lOh Discriminator Level- Det.F Noise - Det. G Noise- Det. C 8 6 4 8 6 _ 4 <-> 20 o 23 keV, E p >34 keV and Gl(E a >634 keV). The last column, labeled G, contains 10 times the proton spectral index y obtained from LI and L2, assuming a spectral form E~ Y . Figure 20 clearly shows proton bursts observed outside the dusk magnetosphere. However, such low energy proton angular and energy distributions are significantly dis- torted by solar wind convection effects (50 keV protons have a veloc- ity <7 times the solar wind velocity) and by the interplanetary _motional electric field, E = - 1/c V sw x B. Consequently, in order to interpret low energy proton observations such as those shown in Figure 20, trans- forms into various physically mean- ingful coordinate frames have to be performed (Gold et al., 1975). These programs require solar wind velocity and/or interplanetary magnetic field data. A sample of the output of such transformation programs is given in Figure 21. Polar plots of the 50-220 keV proton intensities observed by the IMP H EPE on October 31, 1972, are shown in various coordinate frames. Important directions and principal axes are. shown at the top of the figure; V sw = solar wind velocity vector, B = A interplanetary magnetic field, _and B = unit vector in direction of B. Panel (a) of Figure 21 shows a 6-minute intensity average centered at 2034:15 hours and obtained during an intense burst of particles stream- ing from the magnetosphere. Solar and dotted lines give respectively the intensities observed in the satellite frame of reference and those transformed into the solar wind frame using the measured solar wind velocity of 728 km/sec (Gold et al., 1975). Panel (b) shows a high time resolution snapshot of 20.4 seconds at 2033.34 hours and within the panel (a) '6-minute average. The solid line shows the distribution observed in the satellite frame of reference. 14 1/14/75 (014) H0UR=15 IHPJ XSE« .3 VSE- 32.7 ZSE» -10.6 XSPK3 VSH- 33.6 ZSM- -7.3 ■- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 IS 16 Ll L7 1 2 3 4 5 6 7 B :/:«/l » u agbt*!! !*••• m* . 1. 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IK 12 37 59 • 4 * : s : 5 4|( 17 4 5 3 2 II l( 3 42 5135 ( 9 14 2: 3( II 117 III 122 33 12 5 1 * ( s 55( 14 5 3 :33 : 42 39 .3 :: ■ « ■■1 21 4: 92 227 .22 121 25 4 ; 2 ( 9 9 45: 3( 2 3 * ( 2 4 1: 3 4* :» 54 3 1 12 22 45 112 111 !SS III 14 37 3: 24 :: :2 ( 5C 11 : 2: ! * 3 3 3 "9 93 3 44 39 IS l 22 23 *2 ::: ::( .(' ill i( II :5 " * 25 J 5 33( *( • 23 : TiguKd 20. Po or- man' 4 plot*. Highest timz resolution print-out lor all 6zztor6 oft Ll and Ll . Timz run* vzrticallij doionaxird, and 6cc- tou [anglz in the. actlptlc planz) nun ^nom le.&£ to fUghJt. Tlvti faonm ofa pAA.nt-out Xjk> an ■inzxpdn&ivo. approximation o& gtay code. Proton buAAtA and thiblz in thz display. Ml Ll and Ll data oaz avaitablz in tkli> format. 15 However, in panel (b) the dotted line shows the distribution transformed according to the electric field drift velocity V c = V__ . - §§-V. sw sw Finally panel (c) shows the particles' pitch angle distribution. Note that panel (c) shows large intensities of ~50 keV protons fill- ing the hemisphere along the field line viewing the magnetosphere. Also note that strong azimuthal pitch angle gradients are observed, imply- ing the presence of strong spatial gradients having scale lengths of a 50 keV proton gyroradius (=2.50 (10) 3 km). SUN_ EARTH V E =V SW -BB.V SW 2500cts/sector 1 -PITCH ANGLES NOT SAMPLED a VlguJie 21. Polax plot* o£ 50-220 feel/ pnoton Intensities In hevehal {names o{ n.e{eAence. \J anions directions o{ Interest axe. shown at the top o& the. {IguJie. Panel [a): 6-mln averages obtained at 2034:15 houAS, 31 October 1976. The 6otid line shows the. obser- vations In the. IMP 7 {name o{ reference. The dotted tine thorn the transformed distribution -In the bolar wind {name o{ refer- ence using the simultaneously measured solar wind velocity oft 12% km/sec. Panel (fa): A 20-sec snapshot within the panel- (a) 6-mln average at 2033:34 hours. The solid Line again lb In the satellite {rame. The dotted tine 16 In the moving {rame defined by the Interplanetary motional electric fiield dnl{t velocity vector Vp'Vaw-BB'Vaw. Panel (c) : Pitch angle distribution o{ panel- (fa) observations. 16 Figure 21 clearly shows the inherent difficulty of interpreting low energy (tens to hundreds of keV) ion fluxes observed in interplanetary space in a satellite frame of refer- ence. Data reduction must include appropriate transformations to coor- dinate systems of physical interest. The low ion energies (50 keV protons) and relatively large geo- metric factor (~10~ 2 cm 2 ster) attained by the EPE have made it possible to estimate thermal plasma flow veloci- ties and temperatures. Assuming a flowing Maxwellian plasma, EPE absolute proton fluxes and angular distributions have been used to obtain plasma flow velocities and temperatures in the geomagnetic tail with a sensitivity down to ~50 km/sec and -1 keV for densities >10 -1 cm -3 (Roelof et al., 1976; KeatrT et al., 1976). Additional reduction, analysis, and display programs exist to allow easy access to and handling of the EPE data. A detailed description of them is not appropriate here. How- ever, they consist primarily of averaging programs, gray and color code programs, and display programs. Such a heavy investment in data handling is mandatory since the productivity of large experimental data sets is proportional to their accessibil ity. EPE successfully through several difficult situations. The following individuals provided invaluable and major contributions in the areas indicated; C. 0. Bostrom, Co-investi- gator, all phases of the experiment; J. R. Cessna and T. A. Fritz, detec- tors, detector head assembly and calibration; A. F. Hogrefe, R. Cash- ion, S. A. Gary, and D. P. Peletier, electronics, EPE assembly and test, spacecraft integration; G. Glaeser, mechanical design; J. Crawford, detector qualification; R. Thomson, fabrication; J. W. Kohl, calibration; S. Brown and The Goddard Space Flight Center calibration facility; the Naval Research Laboratory accelerator staff; M. Gallucci, data reduction and display system; W. Burkey, data and housekeeping logs. Finally I wish to acknowledge the efforts of the Goddard Space Flight Center IMP project office in making the IMP 7 and 8 programs so successful. Their mixture of professionalism, pragma- tism, and wit made this not only a successful mission but also an en- joyable one. I wish to acknowledge and thank A. Lazarus and R. Lepping for making readily available the solar wind velocity and magnetic field data that are required for the transforms shown in Figure 21. ACKNOWLEDGMENTS REFERENCES The EPE project was a collabora- tive effort between the National Oceanic and Atmospheric Administra- tion Space Environment Laboratory and the Johns Hopkins University Applied Physics Laboratory, and it is not possible to acknowledge all the people who contributed to its suc- cess. However, I do wish to acknowl- edge those who had major responsibil- ities and those whose efforts got the Coleman, J. P. , D. P. Love, J. H. Trainor, and D. J. Williams (1968a): Low energy proton damage effects in silicon surface barrier detectors. IEEE Trans . Nucl . Sc i . , NS-15(1), 482. Coleman, J. P. , D. P. Love, J. H. Trainor, and D. J. Williams (1968b): Effects of damage by 0.8 MeV-5.0 MeV protons in silicon surface barrier detectors. IEEE Trans . Nucl . Sci. , NS-15(3), 363. 17 Elad, E. , C. M. Inskeep, R. A. Sareen, and P. Nestor (1973): Dead layers in charged particle detectors. IEEE Trans . Nucl . Sci. , NS-20(1), 534. Fairfield, D. H. (1971): Average and unusual locations of the earth's magnetopause and bow shock. J. Geophys . Res . , 76, 6800. Fritz, T. A., and J. R. Cessna (1975): ATS-6 NOAA low energy proton experi- ment. IEEE Trans , on Aerosp . and Electronics Systems , AES-11(6), 1145. Gary, S. A. (1970): EPE preamplifiers/ channels F and G. Applied Physics Laboratory Internal Report S1P-591- 70. Gold, R. E., C. 0. Bostrom, E. C. Roelof, and D. J. Williams (1975): Aniso- tropy of ~50 keV solar protons in the spacecraft and co-moving frames. Proc . Int . Conf . Cosmic Rays 14th, 5, 1801. Grubb, R. N. (1975): The SMS/GOES space environment monitor subsystem. NOAA Technical Memorandum ERL SEL-42. Hogrefe, A. F. (1970): Preamplifiers for the energetic particle experiment IMP H and J. Applied Physics Laboratory Internal Report S1P-615-70. Inskeep, C. , E. Elad, and R. A. Sareen (1974): Surface barrier structures with various metal electrodes. IEEE Trans . Nucl . Sci. , NS-21(1), 1. Keath, E. P., E. C. Roelof, C. 0. Bostrom, and D. J. Williams (1976): Fluxes of >50 keV protons and >30 keV electrons at 35 R -2 morphology and flow patterns in the magnetotail. J. Geophys . Res . , 81, 2315. Keppler, E. , B. Wilken, K. Richter, G. Umlauft, K. Fischer, and H. P. Win- terhoff (1976): Ein spektrometer fur geladene teilchen mittlerer energien-experiment E8, HELIOS. Bundesministerium fur Forschung und Technologie, Forschungs-bericht BMFT- FBW 76-14, Max-Planck-Institut fur Aeronomie. Longanecker, G. W. and R. A. Hoffman (1973): S 3 -A spacecraft and experi- ment description. J. Geophys . Res . , 78, 4711. Peletier, D. P. (1970): IMP H and J EPE in-flight calibrator. Applied Phys- ics Laboratory Internal Report S1P- 614-70. Roelof, E. C. , E. P. Keath, C. 0. Bostrom, and D. J. Williams (1976): Fluxes of >50 keV protons and >30 keV elec- trons at 35 R '1 velocity anisotropy and plasma flow in the magnetotail. J. Geophys . Res . , 81, 2304. Unzicker, A., and R. F. Donnelly (1974): Calibration of X-ray ion chambers for the space environment monitoring system. NOAA Technical Report ERL 310-SEL 31. Wilken, B. , and T. A. Fritz (1974): The response of very thin semiconductor detectors to heaving ions: I. Pro- tons and helium. Nucl . Inst , and Methods , 121 , 365. Wilken, B. , and T. A. Fritz (1976): Energy distribution functions of low energy ions in silicon absorbers measured for large relative energy losses. Nucl . Inst , and Methods , 138 , 331. Williams, D. J., R. A. Hoffman, and G. W. Longanecker (1969): The small scien- tific satellite (S 3 ) program and its first payload. IEEE Trans . Nucl . Sci, NS-16(1), 322. 18 then watersheds; forecasts lake ice conditions GFDL Geophysical l Studies the dynan systems (the atrr, and the cryosphe analysis and numerical simulation us ful. high-speed digital con : APCL Atmospheric Physics and Chemistry Labo tory. Studies cloud and precipit chemical and particulate comp atmosphere, atmosprv- and atmospheric heat tran developing methods of ben. ither modification NSSL National Severe Storms Labora' severe-storm circulation and dynarr develops techniques to detect and pf' tornadoes, thunderstorms, and squall lim WPL Wave Propagation Laboratoi propagation of sound waves and ele f magnetic waves at milhm^ optical frequencies to develop for remote measuring of the geophy. environment ARL Air Resources Laboratories. Studies diffusion, transport, and dissipation of atn phenc pollutants; develops methoc predicting and controlling atmr tion; monitors the glol to detect climatic chai AL Aeronomy Laboi and chemical pro ionosprv other pla SEL Space Environment Laboratory Studies solar-terrestrial physics (interplanetary, mag- netosphenc. and ionospheric), develops tech- niques for forecasting solar disturbances, provides real-time monitoring and forecasting of the space environment ^ U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration BOULDER, COLORADO 80302 PENN STATE UNIVERSITY LIBRARIES ADDDD7EDElflT7