COSPIN LET User Notes - Ulysses
COSPIN / LET - User Notes
COSPIN/LET Contact:
Dr. R.G. Marsden
Research and Scientific Support Department of ESA, ESTEC
Postbus 299
2200 AG Noordwijk
The Netherlands
Phone: (31) 71 565 3583
Telefax: (31) 71 565 4697
E-mail: richard.marsden@esa.int
The COSPIN Low Energy Telescope (LET) measures the flux, energy spectra and elemental
composition of solar and heliospheric energetic particles and low energy cosmic ray nuclei
from hydrogen up to iron, covering an energy range from ~1 to ~75 MeV/n. Isotope separation
for light nuclei such as He is also achieved. The LET sensor consists of four solid-state
detectors in a telescope configuration that are surrounded by a plastic scintillator
anti-coincidence shield, together with associated analogue and digital electronics.
Detectors D1 (30 micron nominal thickness) and D2 (100 micron) are surface-barrier devices
with equal active area (6.0 cm2), while D3 and D4 are 2 mm-thick lithium-drifted devices of
10.0 and 12.5 cm2 active area, respectively. The LET utilises the standard dE/dX vs. E technique
in order to identify the nuclear charge, and in some cases the mass, of the incident particles.
For particles stopping in the detector stack, the energy lost in one or both of the thin detectors
D1 and D2, together with the residual energy deposited in the remaining detector(s), is measured.
Comprehensive on-board particle identifier electronics and an event priority system enable rare
nuclei to be analyzed in preference to the more common species. The telescope aperture is covered
by two thin foils, an inner Ti foil (~2 micron, 0.9 mg/cm2) for electrical shielding, and an outer
aluminised Kapton foil (~8 micron, 1.0 mg/cm2) for thermal protection.
Two main categories of scientific data are obtained from the LET system. Firstly, counting rates
for 22 different particle species/energy-range combinations, 2 of which are further sub-divided
into 8 angular viewing sectors in the spacecraft spin plane. At the highest available spacecraft
bit-rate (1024 bps real-time telemetry), counts are accumulated over 32- or 128-sec intervals
(telemetry-format synchronised) for the non-sectored channels, and over an integral number of spins
for the 16 spin-synchronised, sectored channels. The second type of data obtained consists of the
event-by-event pulse-height values from detectors D1, D2 and D3. Owing to telemetry limitations,
a maximum of one PHA event per second can be transmitted, the selected event being chosen by a priority scheme.
In addition to scientific data, the LET system also provides instrument housekeeping
data, such as detector currents, voltage monitors and thermistor temperature measurements.
COSPIN/LET RATE DATA
RECORD FORMAT:
IMPLICIT REAL(L)
DIMENSION L4_11(8),L13_20(8),L34_38(5)
C FREE FORMAT
READ(1,*)IYEAR,IDOY,IHOUR,IMIN,ISEC,
. L1,L2,L3,L4_11,L12,L13_20,L21,
. L22,L23,L24,L25,
. L26,L27,L28,L29,L30,L31,L32,L33,L34_38
C FIXED FORMAT
READ(1,100)IYEAR,IDOY,IHOUR,IMIN,ISEC,
. L1,L2,L3,L4_11,L12,L13_20,L21,
. L22,L23,L24,L25,
. L26,L27,L28,L29,L30,L31,L32,L33,L34_38
100 FORMAT(I5,X,I3,3(X,I2),38(X,G9.3))
PARAMETER LIST:
IYEAR: year
IDOY: day of year
IHOUR: hour
IMIN: minute
ISEC: second
L1: protons (0.9-1.2 MeV)
L2: " (1.2-3.0 MeV)
L3: " (1.8-3.8 MeV)
L4_11: " " sectors 1 to 8
L12: " (3.8-8.0 MeV)
L13_20: " " sectors 1 to 8
L21: " (8.0-19.0 MeV)
L22: alphas (1.0-5.0 MeV/n)
L23: " (1.9-3.7 MeV/n)
L24: " (3.7-8.4 MeV/n)
L25: " (8.4-19.0 MeV/n)
L26 Li,Be,B (1.9-4.9 MeV/n)
L27 " (4.9-26 MeV/n)
L28 C,N,O (2.6-7.1 MeV/n)
L29 " (7.1-39.0 MeV/n)
L30 Z>=10 (3.0-9.0 MeV/n)
L31 10<=Z<=20 (9.0-50 MeV/n)
L32 Z>=20 (12.0-75.0 MeV/n)
L33 electrons (0.3-1.0 MeV)
L34_38 single detector counting rates
FLUX UNITS: (/cm2/s/sr/MeV/nucleon)
TIME RESOLUTION: full resolution (ucosletf*****.dat)
10 minutes (ucosletr*****.dat)
(date/time given at start of averaging period)
NOTES:
1. Rate channel L1 (which nominally responds to protons in the energy range
0.9-1.2 MeV) is derived from a single-detector measurement, and as such is
sensitive to penetrating particles which lose part of their energy in the
detector. The background contribution depends on the energy spectrum of the
incident particle population, being negligible for (differential) energy
spectral slopes of -3.5 or steeper, increasing to 80% of the total counts
for a slope of -1.0 or harder.
2. Rate channel L2 is derived from a single detector measurement, and the nominal
energy response to protons (1.2-3.0 MeV) is approximate.
3. Please note that a software error in the LET data reduction algorithm
provided incorrect LET sector channels (L4-L11 and L13-L20) for all COSPIN/LET
rates data files submitted to the ESA and NASA archive prior to August 2012.
Full resolution and 10 minute averaged rates data files issued since September 2012
have corrected proton fluxes for the sector channels.
4. Rate channel L21 (which nominally responds to protons in the energy
range 9-19 MeV) is also sensitive to higher-energy particles which lose
part of their energy in the telescope structure. As in the case of L1, the
background contribution depends on the energy spectrum of the incident
particle population, being negligible for (differential) energy spectral
slopes of -2.0 or steeper, increasing to 80% of the total counts for a
slope of +0.75 or harder.
5. Rate channel L22 is derived from a single detector measurement, and the nominal
energy response to alpha particles (1.0-5.0 MeV/n) is approximate.
6. Rate channel L25 (which nominally responds to alpha particles in the energy range
8.4-19.0 MeV/n) is also sensitive to higher energy particles that lose part of their
energy in the telescope structure. As in the case of L21, the background contribution
depends on the energy spectrum of the incident particle population (negligible for
differential energy spectral slopes of -2.0 or steeper).
7. Rate channel L26 suffers from background due to pulse pile-up for proton fluxes in L2
greater than 10 protons/cm^2/s/sr/MeV.
8. Rate channel L27 suffers from background due to pulse pile-up for proton fluxes in L2
greater than 30 protons/cm^2/s/sr/MeV.
9. The energy for rate channel L28 is approximate (species dependent).
10. The energy for rate channel L29 is approximate (species dependent).
11. The energy for rate channel L30 is approximate (species dependent).
12. The energy for rate channel L31 is approximate (species dependent).
13. The energy for rate channel L32 is approximate (species dependent).
14. The energy range for rate channel L33 is approximate. L33 suffers from background
from the RTG and GCR.
15. Rate channel L34 includes all particles depositing energy greater than the
minimum discriminator level (D1).
16. Rate channel L35 includes all particles depositing energy greater than the
minimum discriminator level (D2).
17. Rate channel L36 includes all particles depositing energy greater than the
minimum discriminator level (D3).
18. Rate channel L37 includes all particles depositing energy greater than the
minimum discriminator level (D4).
19. Rate channel L38 includes all particles depositing energy greater than the
minimum discriminator level (D5).
(For further information, contact Dr. R.G. Marsden,
richard.marsden@esa.int)
COSPIN/LET PHA DATA
PHA Event Data
IYEAR: year
IDOY: day of year
ISEC: second of day (at start of 32 second accumulation period)
IGAIN1: gain setting (0 or 1) for detector 1 (D1)
ICHAN1: channel number (of 1024) in gain range for D1
EN1: energy (MeV) deposited in D1
IGAIN2: gain setting for D2
ICHAN2: channel number for D2
EN2: energy (MeV) deposited in D2
IGAIN3: gain setting for D3
ICHAN3: channel number for D3
EN3: energy (MeV) deposited in D3
IEV: event code (refer to table 4 of COSPIN instrument paper in A&A special issue (Vol. 92/2 January 1992)
or to Table 1.2 on page 27 of the LET Handbook)
INUC: number of nucleons
EN: total energy deposited in detectors (EN1+EN2+EN3)
EINC: particle incident energy (MeV/n) - energy in 3 detectors plus energy lost in foils
Z12: effective particle charge from D1:D2 measurement
Z23: effective particle charge from D2:D3 measurement
TIME RESOLUTION: one PHA event per second with a maximum of 32 events in a 32 second time period
NOTES:
1. Note that the instrument operates a priority system described below in the section
for PHA yearly plots.
2. For a three parameter event (ie. with non zero values for EN1, EN2 and EN3), the effective
charge (Z12) derived from the D1:D2 measurement is given as zero.
3. A D1:D2 event (Z23 equal to zero) may have a value of 0.1437 MeV for EN3. This value
for EN3 may be considered as resulting from an instrumental background effect.
PHA Derived H and He Fluxes
IYEAR: year
IDOY: day of year
IHOUR: hour of day
E1: 2-4 MeV Protons (/cm2/s/sr/MeV)
EE1: Error in E1
E2: 4-6 MeV Protons (/cm2/s/sr/MeV)
EE2: Error in E2
E3: 6-8 MeV Protons (/cm2/s/sr/MeV)
EE3: Error in E3
E4: 8-16 MeV Protons (/cm2/s/sr/MeV)
EE4: Error in E4
E5: 16-20 MeV Protons (/cm2/s/sr/MeV)
EE5: Error in E5
H1: 4-6 MeV/n Helium (/cm2/s/sr/MeV/n)
EH1: Error in H1
H2: 6-9 MeV/n Helium (/cm2/s/sr/MeV/n)
EH2: Error in H2
H3: 11-20 Mev/n Helium (/cm2/s/sr/MeV/n)
EH3: Error in H3
TIME RESOLUTION: daily (date/time given at mid-point of averaging period)
PHA Derived O, N and Ne Fluxes
IYEAR: year
IDOY: day of year
IHOUR: hour of day
O1: 4-8 MeV/n Oxygen (/cm2/s/sr/MeV/n)
EO1: Error in O1 "
O2: 8-12 MeV/n Oxygen (/cm2/s/sr/MeV/n)
EO2: Error in O2 "
O3: 12-16 MeV/n Oxygen (/cm2/s/sr/MeV/n)
EO3: Error in O3 "
O4: 16-20 MeV/n Oxygen (/cm2/s/sr/MeV/n)
EO4: Error in O4 "
N1: 4-7 MeV/n Nitrogen (/cm2/s/sr/MeV/n)
EN1: Error in N1 "
N2: 8-20 MeV/n Nitrogen (/cm2/s/sr/MeV/n)
EN2: Error in N2 "
Ne1: 4-8 MeV/n Neon (/cm2/s/sr/MeV/n)
ENe1: Error in Ne1 "
Ne2: 9-30 MeV/n Neon (/cm2/s/sr/MeV/n)
ENe2: Error in Ne2 "
TIME RESOLUTION: 20 days (date/time given at mid-point of averaging period)
Yearly PHA Plots
Each plot provides a qualitative representation of pulse height measurements made by the
COSPIN/LET instrument over a complete year, indicating periods of significant heavy ion
fluxes. The plots are constructed using the charge histograms derived from the PHA
analysis of the D1 and D2 detectors of the LET instrument. The number of PHA events in a
charge bin (having a width of 0.01 of a unit of atomic number) is accumulated over a period
of a day, colour coded and plotted as a filled box.
During periods of enhanced particle fluxes, well defined peaks can be seen for typical solar
energetic nuclei. Persistent horizontal banding for certain ions (for example O, N and Ne)
indicates the presence of anomalous cosmic ray (ACR) populations.
Note that the number of PHA events for a given species shown in the plot does not necessarily
reflect its true abundance. This is due to the priority system used by the instrument that
maximizes the collecting efficiency of rarer ions. Further normalization is required to produce
accurate composition ratios (for example, p/He and He/O). Note also that the majority of events
that appear in the region between He and C (i.e., Li, Be, B) are due to background effects in the
instrument.
COSPIN/LET HOUSEKEEPING DATA
PARAMETER LIST:
IYEAR: year
IDOY: day of year
ISEC: second of day
ID1: D1 detector current (micro Amps)
ID2: D2 detector current (micro Amps)
ID3: D3 detector current (micro Amps)
ID4: D4 detector current (micro Amps)
T: LET thermistor temperature (C)
EPS1: Experiment power supply 1 temperature (C)
EPS2: Experiment power supply 2 temperature (C)
HV: High voltage monitor (V)
VP15: +15V voltage monitor (V)
VP85: +8.5V voltage monitor (V)
VM6: -6V voltage monitor (V)
VM15: -15V voltage monitor (V)
VP75: +7.5V voltage monitor (V)