The experiment is designed to measure the heavy ion environment at low altitude (HIEN-LO) in the energy range 0.3 to 100 MeV/nucleon. In order to cover this wide energy range a complement of three sensors is used. A large area ion drift chamber and a time-of-flight telescope are used to determine the mass and energy of the incoming cosmic rays. A third omnidirectional counter serves as a proton monitor. The analysis of mass, energy and incoming direction in combination with the directional geomagnetic cut-off allows the determination of the ionic charge of the cosmic rays. The ionic charge in this energy range is of particular interest because it provides clues to the origin of these particles and to the plasma conditions at the acceleration site. The experiment is expected to be flown in 1988/1989

Blake, J. B.

Hovestadt, D.

Klecker, B.

Mason, G. M.

Nicholas, J.

English

NASA Technical Reports Server

N89-10908
HIEN-LO - AN EXPERIMENT FOR CHARGE DETERMINATION OF
COSMIC RAYS OF INTERPLANETARY AND SOLAR ORIGIN
B. Klecker, D. Hovestadt
Max-Planck Institute fur Extraterrestrische Physik, 8046 Garching, FRG
G. M. Mason
Dept. of Physics and Astronomy, University of Maryland
College Park, MD 20742, USA
J. B. Blake
The Aerospace Corporation, Redondo Beach, CA, USA
J, Nicholas
Air Force Technical Applications Center, Patrick Air Force Base, FL, USA
Abstract
The experiment is designed to measure the Heavy lon Environment at _L°w
Altitude (HIEN-LO) in the energy range 0.3 - lOOMeV/n-ucle-on. In order to cover
This wide energy range a complement of 3 sensors is used. A large area ion drift
chamber (Sensor 1) and a time-of-flight telescope (Sensor 2) are used to determine
the mass and energy of the incoming cosmic rays (CR). A third omnidirectional
counter (Sensor 3) serves as a proton monitor. The analysis of mass, energy, and
incoming direction in combination with the directional geomagnetic cut-off allows
the determination of the ionic charge of the CR. The ionic charge in this energy
range is of particular interest because it provides clues to the origin of these
particles and to the plasma conditions at the acceleration site. The experiment
is expected to be flown in 1988/1989.
1. Introduction
In 1972 a new component of cosmic rays has been detected /1/, /2/ with a
composition very different from solar or galactic cosmic rays. Because of the
peculiar elemental abundances (predominantly helium, oxygen, and neon, no carbon)
this component has been called "anomalous cosmic rays" (ACR). A current hypo-
thesis associates the origin of ACR with the interstellar neutral wind. It is
assumed that the neutral wind is ionized by solar I/V radiation and charge exchange
with protons from the solar wind. After being picked up, by _he _olar_wind and the
interplanetary magnetic field the ions (predominantly He', N', 0", Ne') are swept
to the outer heliosphere. There the ions (still being singly ionized) are assumed
to be accelerated to energies high enough to re-enter into the inner solar system
against the effect of solar modulation /3/. The first step of this process has,
in fact, been observed recently for He with novel instrumentation onboard the
AMPTE/IRM spacecraft /4/. Model calculations, including transport and acceleration
are pretty successful in reproducing the observed spectra and abundances of ACR
/5/, /6/. However, the determination of the ionic charge would give direct
evidence for this hypothesis, lonic charge measurements of solar cosmic rays
carry important information on the plasma conditions (temperature, density) at
the acceleration site on the sun.
41
https://ntrs.nasa.gov/search.jsp?R=19890001537 2020-03-20T06:04:42+00:00Z
In order to cover a large range in massand energy the experiment consists of a
combination of 3 sensors. A large area ion drift chamber(Sensor i) and time-of-
flight telescope (Sensor 2) are used to determine mass, energy, and direction of
the incoming cosmic rays (CR). The energy and massranges of sensor 1 and 2 are
listed in Table i. Sensor I is optimized for the massand energy range of the
ACRcomponent. Sensor 2 covers the full massrange between helium and iron at low
energies. The omnidirectional Sensor 3 serves as a monitor to the proton radia-tion environment.
2. lonic Charge Determination
The ionic charge, Q, of an incoming particle can be determined by simul-
taneously observing the magnetic rigidity R = 43.3*(A/Q)*(E/A)O.5 and the energy
per nucleon, E/A, where A is the atomic massnumber. The instruments are designed
to measurethe energy, E, of each incoming ion. The mass (or nuclear charge) is
determined by the well-known dE/dX versus E method (sensor I) or by the time-of-
flight versus E method (sensor 2). The magnetic field of the earth serves as a
rigidity filter which gives access only to particles with rigidities exceeding the
local directional geomagnetic cut-off rigidity. This is shownschematically in
Figure 1. Only particles with R Rcutoff have access to the experiment. With
E, A, and Rcutoff anupper limit for the ionic charge Q can readily be computed.
3. Payload Description
The main systems of the experiment are shownschematically in Figure 2.
The experiment consists of 3 sensors, the sensor electronics, the central data
system (DPU), a tape recorder for data storage and a battery package. The GAS
payload will have a motorized door (MDA). Once in space the experiment is acti-
vated from the astronaut. This commandenables MDAopening and turns on power
to the DPU. The DPUthen controls all 3 sensors and the data transfer to the tape
recorder. At the end of the mission, the payload is returned to its quiescent
condition ready for landing by another commandof the astronaut. Figure 3 shows
part of the experiment package in flight configuration: Sensor I (on top), the
analog electronics (middle), and the battery box (bottom).
4. Sensor Description
A schematic diagram of Sensor 1 is shown in Figure 4. It consists of a
three element ion drift chamber(ICI, IC2, IC3) with a thin entrance window
(40_AI) followed by an array of 16 solid state detectors (SSD) and a Csl scintil-
lation counter which is viewed by 4 light sensitive diodes. The first and the
third elements of the drift chamberare sensed by two position sensitive propor-
tional counters (PCl, PC2) with back-gammonshapedcathodes. In the first element
also the drift time (TOD) of electrons generated along the track of the incoming
particle is determined. The drift time is the time elapsed between the response of
the SSDsand the anode of PCI. Drift time and position response of PCI provide
two coordinates for the incoming ion at the top of the sensor. At the bottom the
position response of PC2and the information on the detector row triggered by the
incoming ion provide another two coordinates. From these 4 coordinates, then,
the incident direction of the incoming ions can be derived. Theionization chamber
operates with isobutane at a pressure of 75 torr (at 20 C). The density of the
isobutane is actively controlled by a gas regulation system providing a continuous
flow-through of isobutane. The gas supply consists of 180 g of liquid isobutane
42
stored in a T1 tank. The geometrical factor of the sensor is 35 cm2sr.
Figure 5 shows results from a calibration measurementat the HahnMeitner
Institue in Berlin. For this measurementa 800 MeVbeamof S32 has been scattered
on a thick target and the reaction products have been measuredwith the experiment.
The figure showsa matrix of the ionization chamberversus energy signal and
demonstrates the high mass resolution and low background of the system. In orbit
the multi dE/dX - E measurement (PCI, IC2, PC2, SSD and/or Csl) will provide even
better mass resolution and background rejection.
Sensor 2 (LAT) serves to identify and analyze the particles below 6 MeV/
nucleon from H to Fe. The particles are identified by measuring the time, TOF,
required to travel between a thin aperture foil and an array of solid state
detectors. The timing signals are obtained from secondary electrons emitted when
the particles penetrate the foil and the front surface of the solid state detec-
tors: these electrons are accelerated and deflected onto microchannel plates
which produce fast pulses suitable for START and STOP signals for a timing measure-
ment. The solid state detector measures the kinetic energy E = 1/2 mv2 after
taking account of the energy loss in the entrance foil and in the detector by
nuclear defect. Since the flight path length between the foils and the detectors,
_, is known, the TOF and E measurements may be combined to yield the particle mass
via A = 2*E*(TOF/_) 2, In the configuration shown in Figure 6 the time-of-flight
sensor has a flight path length, _, of 50 cm, and a geometrical factor of i cmZsr.
For a threshold of 0.3 MeV/nucleon for heavy ions, such a geometrical factor is
large enough to analyze contributions from solar flare particles to the fluxes
observed by sensor i above 6 MeV/nucleon. If a solar energetic particle event
occurs during the mission, it would be possible to resolve isotopes of all ele-
ments from Helium through Silicon (and would resolve elements and some isotopes
beyond Silicon). Figure 7 shows the He4 track in a TOF E matrix obtained from
the prototype Sensor 2. The particles are from an alpha source. The alpha par-
ticles in the test pass through a variety of foil thickness to yield a range of
incident energies centered around 0.6 MeV/nucleon. Notice the excellent mass
resolution (a m = 0.06 amu) and low background in the matrix.
5. Acknowledgement
We acknowledge the effort of many individuals at the Aerospace Corporation,
the Air Force Technical Applications Center, the University of Maryland, and the
Max-Planck Institue fur Extraterrestrische Physik who contributed to the design,
manufacturing, and testing of the instrumentation.
References
1. M. Garcia-Munoz, G.M. Mason, J.A. Simpson, 1973, Ap. J. (Lett.) 182, L81.
2. D. Hovestadt, O. Vollmer, G. Gloeckler, and C.Y. Fan, 1973, Phys. Rev. 31,
650.
3. L.A. Fisk, B. Kozlowsky, and R. Ramaty, 1974, Ap. J. (Lett) 190, L35.
4. E. Mobius, D. Hovestadt, B. Klecker, M. Scholer, G. Gloeckler, and F.M.
Ipavich, 1985, Nature 318, 426.
5. B. Kecker, 1977, J. Geophys. Res. 82, 5287.
6. J.R. Jokipii, 1986, J. Geophys. Res. 91, 2929.
43
Table I: Om<0.6 AMU
(ADJACENT ELEMENTS RESOLVED)
Species
Energy Range (MeV/nucleon)
Sensor I Sensor II
4He
12c
160
2ONe
24Mg
28Si
32s
56Fe
3.5 - 95 0.30 - 6.1
6.0 - 150 0.36 - 8.9
6.8 - 120 0.40 6.6
7 - I00 0.41 5.6
7 I00" 0.58 - 4.5
* 0.43 - 3.85
* 0.46 - 3.10
* 0.56 - 1.26
*Separation possible only for every other element
I
J
I0-20%
TRANSHISSION
nHnH
RCUTO_:F R_IOITY
"CUT-OFF" TRAJECTORY
/
!
/
/
Fig. 1: Schematic picture of cosmic ray trajectories
impinging from different directions with respect to
the experiment axis.
44
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SOLID STATE DETECTOR ENERGY
255
Fig. 5: Ionization chamber versus energy left in the solid state
detector. Data are obtained with the flight unit at the HMI
cyclotron in Berlin.
47
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Fig. 7: Time-of-flight versus energy left
in the SSD. Data are obtained with the
prototype instrument using an alpha source.


HIEN-LO: An experiment for charge determination of cosmic rays of interplanetary and solar origin

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