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User guide for analysis of FAST mass spectrometer (TEAMS) data
Author: E. J.
Lund, UNH
Last revision: 09 March 2001
Contents of This Document
General Description
TEAMS (Time-of-flight Energy Angle Mass Spectrograph) consists of an electrostatic
analyzer to select E/q, a post-acceleration (PAC) voltage, and a time-of flight (TOF)
section. The TOF section measures the delay between the arrival of electrons knocked
off a carbon foil and the ion itself, yielding a measurement of m/q. TEAMS has 16
anodes with an instantaneous field of view of 360 * 8 degrees. The instantaneous look
plane is parallel to the spin axis, so within half a spin the full 4 * pi steradians
of the sky are covered. The nominal energy range is 1 to 12000 eV in logarithmically
spaced steps.
For further information, see E. Möbius et
al., The 3-D plasma distribution function analyzers with time-of-flight mass
discrimination for Cluster, FAST, and Equator-S, in "Measurement Techniques in Space
Plasmas: Particles" (Geophysical Monograph 102), edited by R. F. Pfaff et al., AGU,
Washington, 1998.
Back to the beginning
Content and Intended Use of TEAMS APID's
FAST data are sorted by type into various files. Each data type is assigned a
number called an APID (application identifier), starting from 1024.
TEAMS Survey Data (APID 1027)
3-D data, 48 energies * 64 solid angle bins * 4 mass bins. Maximum time resolution
2.5 s (0.5 spin) for H+/O+, 5 s (1 spin) for
He+/He++. H+/O+ always have twice the
time resolution of He. General purpose science data. Departures from gyrotropy should
be disregarded.
Angle bins are numbered according to the following map, which is in a
spacecraft-based coordinate system:
where theta is the look direction measured from the spin plane away from the spin
axis and phi is measured from the look direction of anodes 0-7 at the time of the
spacecraft sun pulse. Thus for 1/16 of a spin after the sun pulse anode 3 is looking
in angle bin 0 and anode 12 is looking in angle bin 16; half a spin later anode 3 is
looking at angle bin 16 and anode 12 is looking at angle bin 0. Note that the
definition of theta for TEAMS differs from the theta defined for the ESA's.
TEAMS HiMass Data (APID 1028)
3-D data, 16 energies * 16 solid angle bins * 64 mass bins. Maximum time
resolution 10 s. General purpose science data. Each energy step covers three energy
steps from the survey data. In practice, the primary use of this APID is to check for
H+ leakage into He++ channel or to detect minor ion species
(particularly O++). No definitive detection of molecular ions by TEAMS has
been reported.
Angle bins are numbered according to the following map, which is in a
spacecraft-based coordinate system:
where theta and phi have the same meaning as above.
TEAMS Pole Data (APID 1029)
32 energies * 2 angles * 4 mass bins. Looks along and opposite to the spacecraft
spin axis. Covers only the upper 32 energy steps of the survey data. Maximum time
resolution one sweep (either 78 ms or 156 ms depending on instrument mode). Intended
for high-resolution studies of transverse ion acceleration. Note, however, that
maximum time resolution approximately equals oxygen gyroperiod at apogee.
TEAMS Monitor Rates Data (APID 1030)
Intended for monitoring in-flight calibration. Not for scientific use.
TEAMS PHA Data (APID 1031)
PHA stands for Pulse Height Analysis. Gives pixel and time of flight for all
events (up to a certain maximum per spin) at an energy step which is incremented once
per spin. Consult with a TEAMS experimenter before using.
TEAMS Burst Data (APID 1047)
2-D data, 48 energies * 16 angles * 4 mass bins. Time resolution is one sweep
(either 78 ms or 156 ms depending on instrument mode). Coverage of off-perpendicular
pitch angles is spin phase dependent. Intended for high-resolution studies of
transverse ion acceleration. Limited to burst intervals.
TEAMS Housekeeping Data (APID 1059)
Intended for monitoring TEAMS instrument status. Not for scientific use.
Housekeeping Analog Control (APID 1080)
Requested by SDT when loading TEAMS data with Data Manager.
Back to the beginning
TEAMS IDL Science Routines
TEAMS IDL routines fall into five general categories: get routines, routines for
plotting data, moments routines, low-level calibration routines, and summary plot
routines.
TEAMS get routines
The keywords for these routines are similar to the keywords for the ESA get routines.
- get_fa_t??.pro
- The first ? stands for data type: s for survey, b for burst, and p for pole. The
second ? stands for species: p for protons, a for alphas (He++), h for
He+, and o for oxygen. These are the general-purpose get routines. For
example, to get the first sample of burst oxygen data in SDT (time must be defined in
advance; it can be initialized to 0.D):
oburstsamp = get_fa_tbo(time, /start)
- get_fa_ts?_eq.pro
- The ? stands for species, as above. These routines process survey data from the
anodes nearest the spin plane into a 2-D format (48 energies * 16 angles) compatible
with the structures returned by the ESA IDL
routines. Use these routines if you want pitch angle or distribution function
plots. For example, the next sample of spin-plane survey He+ data is
obtained thus:
nexteqsamp = get_fa_tsh_eq(time, /advance)
- get_fa_ts?_sp.pro
- The ? stands for species, as above. These routines produce spin averaged data,
which differ from the generic data only for H+/O+ at maximum
resolution.
- get_fa_ts?_eq_sp.pro
- The ? stands for species, as above. These routines produce spin averaged data
from the anodes nearest the spin plane, as with the *_eq.pro routines. They are used
to produce the pitch angle panels in TEAMS summary plots and CDF's and are obsolete
for all other purposes.
- get_fa_th_3d.pro
- This is the get routine for the HiMass data product. Note that the structure has
additional components corresponding to the mass per charge. Unfortunately, the
possibility of selecting a particular mass range for energy or pitch angle
spectrograms or for moments was not forseen.
- get_fa_tb_hdr.pro, get_fa_th_hdr.pro, get_fa_tpah_hdr.pro, get_fa_tpop_hdr.pro,
get_fa_tsah_hdr.pro, get_fa_tsop_hdr.pro
- These routines extract header information from the following respective TEAMS
data packets: burst, HiMass, pole (He), pole (H+/O+), survey
(He), and survey (H+/O+).
Routines for plotting data
Note that because TEAMS survey and high mass resolution data are at much lower
time resolutions than ESA data, you should set the GAP_TIME keyword to ensure that
slow survey data are correctly plotted. Adequate values are 30 for
H+/O+ survey data, 60 for He survey data, and 120 for high mass
resolution data.
- get_en_spec.pro
- Plots an energy spectrogram. Can be called with any TEAMS get routine. See the ESA help page for more information. Remember to specify
four angles (theta min and max, phi min and max) if you set the ANGLE keyword when
calling with 3-D survey data. For example, to plot an energy spectrogram of alpha
pole data in differential energy flux units, type
get_en_spec, 'fa_tpa', units = 'eflux', gap_time = 60
- get_pa_spec.pro
- Plots a pitch angle spectrogram. Call only with the *_eq.pro get routines. See
the ESA help page for more information. For example,
to plot a pitch angle spectrogram of protons below 1 keV, type
get_pa_spec, 'fa_tsp_eq', energy = [1, 1000], gap_time = 30
- get_tms_hm_spec.pro
- Plots a mass spectrogram. Call only with get_fa_th_3d.pro. Keywords are the same
as for get_en_spec.pro and get_pa_spec.pro. The simplest calling sequence is
get_tms_hm_spec, 'fa_th_3d', gap_time = 120
- conv_units.pro
- Function to change the units of your data structure to something more convenient.
For example, if you want differential number flux, call
fluxdat = conv_units(dat, 'flux')
Moments routines
There are routines n_3d.pro, j_3d.pro, ... which are analogous to the 2-D moment
routines for ESA data. Call as in the following example:
get_2dt, 'n_3d', 'fa_tsp'
which gives the proton density. It is also possible, but not recommended for reasons
given in the Pitfalls and Limitations section, to call
get_2dt, 'n_2d', 'fa_tsp_eq'
Do not attempt to take 2-D moments of 3-D data, 3-D moments of 2-D data, or any
moments of pole or burst data--this puts garbage in and you will get garbage out.
Low-level calibration routines
Most users will not need to know anything about these routines other than to leave
them in the FAST IDL directory.
- convert_tms_units.pro, convert_tms_units2.pro
- One of these procedures is called when converting data between any two of counts,
'ncounts' (counts corrected for geometric factor), rate (counts per second), 'nrate'
(rate corrected for geometric factor), energy flux, number flux, or distribution
function. Usually called from conv_units.pro.
- fa_ts_eff.pro
- Function to calculate survey efficiencies. Calls FA_TTOF_CALIBRATION and takes
into account the fact that two different anodes contribute to each angle bin at
different times.
- fa_ttof_calibration.pro
- Function to apply the calibration to TEAMS data. Called from FA_TS_EFF for survey
data and directly from the get routines for burst, HiMass, and pole data.
Summary plot routines
The following routines deal with summary plots and CDF's: gen_fa_k0_tms_gifps.pro,
load_fa_k0_tms.pro, and plot_fa_k0_tms.pro.
Back to the beginning
Known Pitfalls and Limitations
These are the known ways, other than those listed above, in which naive use of
TEAMS data can get you into trouble. Workarounds are listed where known.
Mismatch between PAC voltage and lookup table
Cause: PAC discharge, change in nominal PAC voltage, or DPU
reset
APID's affected: All
Period affected: See the Lockheed
TEAMS site for a list of affected intervals
Comments: Do not use data from these periods
Self-stimulation
Cause: A test mode occasionally requested by the
experimenters
APID's affected: All
Comments:Creates an artificial signal at a commandable pixel and
time of flight. Should be obvious as the signal overwhelms any naturally occurring
signals. Do not use data from these periods
Changes in nominal MCP voltage
Cause: Request by experimenters
APID's affected: All TEAMS science data
Period affected: See the Lockheed
TEAMS site for a list of affected intervals
Comments: Do not compare data across an MCP voltage change. Do not
use data from 16-26 June 1998 (orbits 7188-7296), as the MCP voltage was changed
several times during this period in order to conduct an instrumental experiment.
H+ counts contaminate He++ channel
Cause: Inherent width of H+ TOF peak
APID's affected: 1027, 1029, 1047
Period affected: Entire mission
Comments: Use HiMass data to check degree of contamination; if no
separate He++ peak, do not use He++ data. A similar problem
affected He+ data from the Freja mass spectrometer
Elevated noise floor at all times of flight
Cause: Accidental coincidences at high counting rates
APID's affected: All
Period affected: Cusp and radiation belt crossings; periods affected
by ram or spacecraft charging
Workaround: Some routines allow background subtraction (check the
IDL documentation for details)
Counts displaced into wrong solid angle bin
Cause: Timing error in accumulator board logic
APID's affected: 1027
Period affected: Intermittently from spring 1997 onward
Workaround: A technique described in K. Seki et al., J. Geophys.
Res. 105, 15931, 2000, allows recovery of the initial distribution by assuming the
angular distribution is identical to that of the IESA
Peaks at 6 and 9 AMU/q ("C++" and "Be+")
Cause: Resonance frequencies in TEAMS electronics
APID's affected: 1028
Period affected: Intermittent periods during entire mission
Long TOF tail for O+
Cause: Energy loss when passing through carbon foil
APID's affected: 1028
Period affected: Entire mission
Comments: This limitation has prevented the detection of molecular
ions
Efficiency drifts
Cause: Aging of MCP's; for anodes nearest spin plane, ram
accelerated the aging process. Temperature variations also contribute
APID's affected: All TEAMS science data
Period affected: Starting winter 1997 and progressively
worsening
Comments: A fix is in progress and will be released as soon as we
have completed testing
Intermittent dropouts of high-energy counts
Cause: Not determined; believed to be timing error in DPU
logic
APID's affected: 1027
Period affected: Northern hemisphere passes from December 1996
onward
Comments: Believed to be interference from certain fields modes,
aggravated during contacts
Ram
Cause: Spacecraft velocity with respect to background plasma
APID's affected: 1027, 1028, 1030, 1031, 1047
Period affected: Traversals of any region with significant cold
(< 10 eV) O+
Comment: Primarily affects O+, since the kinetic energy
of O+ at 7 km/s (a typical spacecraft speed) is about 8 eV. Can skew
moments calculations since these codes assume that the spacecraft velocity is
negligible compared to particle velocities
Spacecraft charging
Cause: Photoelectron emission and/or problems with E-field sphere
bias
APID's affected: All
Period affected: Intermittently during fall 1996; all traversals of
density cavity when spacecraft is in darkness; all data from fall 2000 onward
Comments: Obvious in the low energy ion spectra. Current moment
calculations do not account for the spacecraft potential
Incorrect magnetic field phase in the header
Cause: Data collected while magnetometer is off
APID's affected: 1027, 1028
Period affected: Low-latitude (equatorward of 60 degrees invariant)
data from about June 2000 onward
Comments: Primarily affects calculations involving pitch angle.
Should be fixable in the same way as for the ESA data.
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