Initial Results from the Radiation Belt Storm Probes
EMFISIS/Waves InstrumentW. S. Kurth (1), G. B. Hospodarsky (1), O.
Santolik (2,3), C. A. Kletzing (1), S. R. Bounds (1), J. R. Wygant
(4), J.W. Bonnell (5), M. W. Chutter (6)
(1) U. of Iowa, Iowa City, Iowa, USA, (2,3) Inst. of Atmospheric
Physics, Prague, Czech Republic, (3) Charles University, Prague,
Czech Republic, (4) U. of Minnesota, Minneapolis, MN, USA, (5) U.
of California, Berkeley, CA USA, (6) U. New Hampshire, Durham, NH,
USA
Abstract
The twin Van Allen Probes were launched on or after August 30,
2012. The Electric and Magnetic Field Instrument Suite and
Integrated Science (EMFISIS) investigation in-cludes a plasma wave
instrument (Waves) designed to measure three orthogonal com-ponents
of the wave magnetic field from ~10 Hz to 12 kHz and, with the
support of the Electric Fields and Waves (EFW) instrument sensors,
three components of the wave electric field from ~10 Hz to 12 kHz
and a single electric component up to 500 kHz. For the wave
magnetic fields, Waves uses a set of orthogonal triaxial search
coils. EFW uti-lizes two spin-plane booms with tip-to-tip lengths
of 100 m and a spin axis boom with a nominal tip-to-tip length of
~13 m to be determined on orbit. Commissioning of the spacecraft
and their instruments was completed within about two months of
launch, at the end of October. In this paper we plan to provide
initial observations from Waves in-cluding an assessment of
in-flight performance and early observations of plasma waves
thought to play significant roles in the acceleration and loss of
radiation belt. The vari-ous classes of waves we anticipate
studying include whistler-mode chorus, plasma-spheric hiss, and
magnetosonic equatorial noise. EMFISIS/Waves may, at times, be able
to measure the upper frequency extent of electromagnetic
ion-cyclotron waves. At the other end of the spectrum, the Waves
instrument will also detect electron cyclotron harmonic emissions
and the band at the upper hybrid resonance frequency. The latter
band will be used to determine the local electron density as an
important parameter of the plasma required for various modeling and
simulation studies.
EMFISIS/Waves has a number of operating modes, but they can be
considered a basic survey mode plus various burst modes which
provide additional temporal and/or spec-tral resolution over the
survey mode:
• The survey mode provides spectral matrices for the 10 Hz - 12
kHz frequency range based on 468 ms waveforms from all 6 sensors
plus an HFR spectrum.
• Burst modes, including:• Continuous waveforms -- nearly 6
seconds of waveforms from all 6 sensors• 30 msec mode -- spectral
matrices every 30 milliseconds• Fast survey -- survey spectral
matrices every second• Onboard WNA -- wave propagation parameters
as fast as every 30msec
The two triaxial search coil assem-blies for Van Allen Probes A
and B are shown on pre-launch test fix-tures. The search coils
consist of 40-cm mu-metal rods and 10,000 turns of fine wire.
Radiation tol-erant preamps are housed in the cylindrical fixture
which doubles as the structure holding the search coils at the end
of one of the sensor booms. Performance of this system is
excellent, given the superb dy-namic range afforded by the 16-b A/D
converters used in the 6-chan-nel Wavefrom Receiver
The EMFISIS/Waves instrument on the twin Van Allen Probes
utilize a complete array of plasma wave sensors. Three orthogonal
components of the wave magnetic field are obtained from a triaxial
search coil magne-tometer on a 3-m boom. Three orthogonal electric
field components are obtained from the EFW (Electric Fields and
Waves) sen-sors including 2 spin plane booms 100 m tip-to-tip and
an axial boom approximately 13.4 m, tip-to-tip.
The Waves instrument comprises a 6-chan-nel waveform receiver
for frequencies be-tween 10 Hz and 12 kHz and a high frequen-cy
receiver (HFR) covering frequencies up to 500 kHz. A set of four
FFT engines are floating point accelerators optimized for Fast
Fourier Transforms. In addition, they compute spectral matrices
required for car-rying out wave-normal analyses (WNA). The FFT
engines are controlled by the CDPU which also includes the
capability to complete WNAs and determine various propagation
characteristics of waves on-board.
A basic capability of the Waves multi-component waveform
measurements is the determination of wave propagation
characteristics such as wave-normal angle, Poynting flux,
polarization, etc. These parameters -- magnetic and electric
spectral density, polar angle of the Poynting flux, wave-normal
angles, ellipticity, and polarization were all computed on-board at
30 msec intervals. As is now expected, the chorus near 2 kHz
propagates away from the equator.
Eu
Ev
Bu
Bv
Bw
Eu, Ev or Ew
10 - 500 kHz High Frequency Receiver
10 Hz - 12 kHz
10 Hz - 12 kHz
10 Hz - 12 kHz
10 Hz - 12 kHz
10 Hz - 12 kHz
To Spacecraft
6-Channel Waveform Receiver
10 Hz - 12 kHz
Ew
FFTEngines
CDPU
+
-
+
-
+
-
Eu
Ev
Ew
Bu
Bv
Bw
EMFISIS/Waves Block DiagramEFW
Van Allen Probes
Van Allen Probe A Integrated Magnetic Field Spectral Density
Inte
grat
ed M
agne
tic F
ield
0.1
to 0
.5 fc
e, n
T2
Van Allen Probe A Lower Band Chorus Occurrence
nT2
Van Allen Probe A Orbit 169, November 1, Day 306, 2012
Freq
uenc
y (k
Hz)
Rel
ativ
e P
ower
R = 5.8 Re; MLAT = 1.7 Deg. MLT = 6.2 Hr
fce/2
Van Allen Probe A, Orbit 130, October 17, Day 291, 2012
Freq
uenc
y (H
z)
Van Allen Probe AElectron Density vs R
Radial Distance (Re)
1 2 3 4 5 6
Ne (
cm -3
)
1
10
100
1000
10000
Orbit 130October 17, Day 291, 201216:09 - 24:00 UT
0123
012
012
012
012
012
012
Freq
uenc
y (k
Hz)
E S
DB
SD
P
oyn
W
NA
SV
DW
NA
SV
DE
llipt
icity
Pol
ariz
atio
n
10:32:00 10:32:30 10:33:00 10:34:0010:33:30
Van Allen Probe B, Orbit 123, 30 msec mode WNA, October 15, Day
289, 2012
R = 5.7 Re; MLAT = 4.2 Deg.; MLT = 6.4 Hr; L = 5.8
EFW Spin PlaneWire Boom
EFW Spin PlaneWire BoomEFW Spin Plane
Wire Boom
EFW Spin PlaneWire Boom
EFW AxialBoom
EFW AxialBoom
EMFISIS SearchCoil Magnetometer
EMFISIS Flux GateMagnetometer
Sensors Used by EMFISIS/Waves
Van Allen Probe B Orbit 168, November 1, Day 306, 2012
EuEu
Sum of BuBu, BvBv, BwBw
Freq
uenc
y (H
z)Fr
eque
ncy
(Hz)
Freq
uenc
y (H
z)
fce/2
fce/2
The major premise of the Van Allen Probes mission is that having
two spacecraft traversing the radiation belts with an evolving
orbital phase be-tween them provides an array of multipoint
measurements of a highly dy-namic system. In this comparison of
data from the two probes, spacecraft B is trailing A in orbit by
about an hour. While the basic wave spectra are very similar
between the two positions, they are not identical. Such comparisons
will enable the determination of the temporal and/or spatial
evolution of the radiation belts. These spectrograms represent the
HFR data in the upper panels, and the electric and magnetic field
spectra in the middle and bottom panels, respectively. The duration
of each plot is about 9 hours, or one orbit from periapsis to
periapsis. A gray line at fce/2 is in-cluded in the bottom panels
to highlight the boundary between upper- and lower-band chorus.
Narrowband electron cyclotron harmonic emissions are seen at higher
frequencies and plasmaspheric hiss and equatorial mag-netosonic
waves at lower frequencies.
An obvious capability of the Van Allen Probes plasma wave
measurements is to enable synoptic studies of the occurrence of
plasma wave phenomena such as whis-tler-mode chorus which is known
to be an effective accelerator of electrons as well as a loss
mechanism through pitch-angle scattering. The upper panel shows
data from probe A early in the mission repre-senting the intensity
of lower band cho-rus (0.1 to 0.5 fce) as a function of MLT and
radial distance. Clearly, there are in-tensifications in the chorus
during times of enhanced activity as shown in the time history of
the intensity of the lower-band chorus shown in the lower
panel.
The frequency of the up-per hybrid band as seen in the HFR
provides direct information on the elec-tron density Ne which is a
fundamental plasma pa-rameter required for nu-merous magnetospheric
models.
The basic data collected by Waves are waveforms. This is an
ex-ample of the continuous waveform burst capability, acquired in
two 6-second intervals. While all 6 components are captured, this
panel only shows the spectrum for the Bu component. An onboard
algo-rithm selects such captures based on the amplitudes in the
chorus bands above and below fce. The EM-quiet spacecraft and 16-b
dy-namic range make for an excellent data set.
Van Allen Probe B, Orbit 129, October 17, Day 291, 2012The basic
survey output of the EMFI-SIS/Waves instrument is a set of spectral
matrices covering the frequency range of 10 Hz to 12 kHz utilizing
six chan-nels (3 E and 3 B) and a single-channel spectrum for the
HFR frequency range of 10 kHz to 500 kHz. While this spec-trogram
shows little in the way of am-plitude differences between the
chan-nels, the spectral matrices capture phase differences between
the various wave components and allow later determina-tion of wave
propagation parameters.
Van Allen Probe A Orbit 169 November 1, Day 306, 2012
EuEu
Sum of BuBu, BvBv, BwBw
fce/2
fce/2
