1. RBSP Radiation Belt Storm Probes RBSP Radiation Belt Storm Probes RBSP/EFW I-PER 21 January 2011 21 EFW Science Overview Professor John R. Wygant, PI University of Minnesota

2. RBSP/EFW I-PER 21 January 2011Wygant 22 Instrumentation Four spin plane booms (2 x 40m and 2 x 50m) Two spin axis stacer booms (2 x 7m) Spherical sensors and preamplifiers near outboard tip of boom (400kHz response) Flexible boom cable to power sensor electronics & return signals back to SC Sensors are actively current biased by instrument command to be within ~ 1 volt of ambient plasma potential. 22  IDPU (main electronics box) Sensor bias control Filtering Analog to Digital Conversion Burst memory Commands and Telemetry EFW Science quantities include: E-fields:(V1-V2, V3-V4, V5-V6) Interferometric timing: SC-sensor potential (V1s, V2s, V3s, V4s, V5s, V6s) SC Potential: (V1+V2)/2, (V3+V4)/2 Survey (<15 Hz) and Burst Data (<200 Hz) Interfaces to/from EMFISIS Electric field signals to EMFISIS DC Magnetic field signals from EMFISIS AC Magnetic field signals from EMFISIS +Z 4 3 5 6 2 1 Not to Scale

3. RBSP/EFW I-PER 21 January 2011Wygant 23 Science Objective: Measure electric fields associated with a variety of mechanisms “causing particle energization and scattering” in the inner magnetosphere These mechanisms include: – Energization by the large-scale “steady state and storm time convection E-field” – Energization by substorm “transient fronts”propagating in from the tail – “Radial diffusion of energetic particles” mediated by “ULF waves” – Transport and energization by interplanetary “shock generated transient fronts” – Adiabatic and non-adiabatic energization by “electromagnetic and electrostatic” waves and (“random”) structures Level-1 Science and Measurement Objectives

4. RBSP/EFW I-PER 21 January 2011Wygant 24 Energetic Particle Acceleration/Transport 24 Mauk/APL

5. RBSP/EFW I-PER 21 January 2011Wygant 25 Level-1 Science Objectives for EFW Measurements The RBSP mission will determine local steady and impulsive electric and magnetic fields …These products will enable the the scientific goals of determining convective and impulsive flows, determining properties of shock generated shock fronts… The RBSP mission will derive and determine spatial and temporal variations of electrostatic and electromagnetic field amplitudes, frequency, intensity, propagation direction, spatial distribution and temporal evolution with sufficient fidelity to calculate wave energy, polarization, saturation levels, coherence, wave normal angle, phase velocity, and wave number for a) VLF and ELF waves, and b) random, ULF, and quasi- periodic electromagnetic fluctuations. These products will enable the scientific goals of determining the types and characteristics of plasma waves causing particle energization and loss including wave growth rates; quantifying adiabatic and non-adiabatic mechanisms of energization and loss........; determining conditions that control the production and propagation of waves High time resolution burst electric and magnetic fild measurements will provide understanding of the role in the prompt acceleration and loss of energetic particles of non-linear interactions with discrete large amplitude wave structures.

6. RBSP/EFW I-PER 21 January 2011Wygant 26 Electric Fields in the Active Radiation Belt 26 The shock induced magnetosonic wave created a 5 order of magnitude increase in 13MeV electron fluxes in <100 seconds resulting in a new radiation belt that lasted two years The large scale electric field produced a ~70 kV potential drop between L=2 & L-4 and injected ring current plasma. dDst/dt= - 40 nT/hr MHD waves: an important mechanism for radially diffusing and energizing particles. CRRES measurements of the E-field during a pass through the inner magnetosphere: interplanetary shock induced electric field, large scale MHD waves, and enhancement in convection electric field.

7. RBSP/EFW I-PER 21 January 2011Wygant 27 Primary Measurement Requirements Flow to EFW Instrument

8. RBSP/EFW I-PER 21 January 2011Wygant 28 EFW Burst Modes 1 and 2 In order to obtain high time resolution measurements of small scale waves and structures and not exceed its TM allocation the EFW instrument has two Bursts Modes with different memories and different means of selecting and playing back data: 1)Burst 1: Nominal sampling 512 samples/s of 3D E-field and 3D Search Coil (from EMFISIS), Spacecraft Potential Density (Thermal Plasma Fluctuations). 32 Gigabytes of Memory. Filled in ~40 days. During TM contacts low rate survey data is sent to ground. Then over several days survey data is evaluated by EFW scientist for time intervals of substorm injections, shocks, and other structures driving waves. Desired burst times and priority are up-linked and the instrument forms a queue and sends data down. Autonomous modes and commanded time tagged triggers available. (7.5% duty cycle) 2)Burst 2: Interferometric Timing Measurements from Single ended measurements. (6.5 kHz time resolution). Autonomously triggered off large amplitude excursions using on board signals from DCB (~200 Mbytes). Bursts placed in queue on basis of “best trigger quality” and best played first. No human intervention (0.1% duty cycle) 3)Diagnostic context for burst data over orbital scales is provided by spectra and cross spectra of E and B, broad band filters/peak detectors, and solitary wave counters. 4)Information on burst status is provided to other instruments via burst status word via Spacecraft

9. RBSP/EFW I-PER 21 January 2011Wygant 29 EFW Driving Requirements Spin plane component of E-field at DC-15 Hz (>0.3 mV/m or 10% sensitivity) over a range from 0 to 500 mV/m at R>3.5 Re …(IPLD 38) Spin axis component of E at DC-15 Hz (>4 mV/m or 20% sensitivity) over a range from 2-500 mV/m at R>3.5Re (IPLD 44) Spacecraft potential measurements providing estimates of cold plasma densities of 0.1 to ~50 cm-3 at 1-s cadence (dn/n<50%) (IPLD 55) Programmable high time resolutions burst recordings of large amplitude (Req.: 0.4 -500 mV/m capability: 0- 4V/m) E-fields ; B-fields and cold electron density variations 0.1-50 cm-3 with sensitivity of 10% (derived from SC potential) over frequency range from dc to 250 Hz (IPLD 42,47,71, 59) Burst Interferometric timing of intense (0.1-300mV/m) small scale electric field structures and non-linear waves: timing accuracy of.06 ms for velocities of structures over 0-500 km/s (IPLD 61) Broad Band Filters (8 freq bins-peak or average) power in wave electric field at 8 samples/s. Burst Triggers/Selection Diagnostic; Solitary Wave Counter: Burst Diagnostic (IPLD 42,47,71,59,61) Spectra & Cross Spectra of average/peak electric and magnetic fluctuations from 1 Hz to 300 Hz with a cadence of 1/8 seconds over a range 80 dB as a diagnostic of large amplitude wave properties over orbital scales. (IPLD 66,68). Low noise 3-D E-field waveforms to EMFISIS: 10 Hz to 400 kHz; maximum signal 30 mV/m. For spin plane sensors: range of 100 dB & sensitivities of 3 x 10-14 V2/m2Hz at 1 kHz and 3 x 10-17 V2/m2Hz at 100 kHz. For spin axis sensor pairs: range x 10 less & sensitivity x 100 less (IPLD 245, 246) 29

10. RBSP/EFW I-PER 21 January 2011Wygant 30 EFW STATUS Two flight units consisting of IDPU box and four spin plane and two spin axis boom deployment units and sensor systems have been fabricated and undergone system wide “end to end” testing at SSL The EFW team has preformed CPT, Software, and Science Calibration Tests on FM1 and FM2 that demonstrate: the E-field sensors can be voltage and current biased allowing measurements of electric fields over the range of plasma sheath impedances of the RBSP orbit the instrument has the correct dynamic range, frequency response, and sensitivity for dc and ac measurements noise levels are with-in requirements and are low enough to allow detection of threshold signals recording of burst data and playback through telemetry spin plane and spin axis booms can be deployed with correct rates/lengths with appropriate diagnostic information flight software is functional including:instrument mode control, burst operations, TM formatting, boom deployment, and Space Weather products Calibrations to be discussed in detail later

11. RBSP/EFW I-PER 21 January 2011Wygant 31 EFW-EMFISIS Interface Testing Level 1 Requirements Document: The RBSP mission will “derive and determine spatial and temporal variations of electrostatic and electromagnetic field amplitudes, frequency, intensity, propagation direction, spatial distribution and temporal evolution with sufficient fidelity to calculate wave energy, polarization, saturation levels, coherence, wave normal angle, phase velocity, and wave number for a) VLF and ELF waves, and b) random, ULF, and quasi-periodic electromagnetic fluctuations.” At instrument level there are requirements for the transfer of E and B signals between EMFISIS and EFW: IPLD 245; 246; 244; 243, and 585 In order to fulfill the Level 1 requirements, it is necessary to determine: –1) phase and gain of signals as a function of frequency –2) polarity of signal –3) response to impulses –4) dynamic range for signals transferred between the two instruments Requires “sensor to telemetry” EMFISIS-EFW calibrations of E and B signals A preliminary EFW-EMFISIS interface check-out was carried out using ETU units prior to CDR Both EFW and EMFISIS have exchanged test procedures and there has been joint planning with APL for such a test after arrival of instruments to APL EFW is happy with these arrangements with APL and EMFISIS and their level of maturity and believes this test is crucial to achieving RBSP science and measurement goals.

12. RBSP/EFW I-PER 21 January 2011Wygant 32 Phases Example of high frequency whistler waveforms from a UMN sounding rocket for which end-to-end E-field and search coil gain and phase information is available This allows the reconstruction of the original wave fields, the polarization, and determination of the direction and velocity of propagation as shown in the next slide.

13. RBSP/EFW I-PER 21 January 2011Wygant 33 Poynting flux Upper panel shows high frequency portion of “pulse” is composed of 3 pairs of dispersive pulses Lower panel - RHS - shows –the first wave in each pair is propagating upward (red) originating from the ground –the second wave in each pair is propagating downward (blue) from the spacecraft Lower panel - LHS - shows the systematic switch from left handed polarization to right handed polarization

14. RBSP/EFW I-PER 21 January 2011Wygant 34 Backup

15. RBSP/EFW I-PER 21 January 2011Wygant 35 Polar Observations of Intense Waves Motivating High Time Resolution Burst Measurements Observations of large amplitude turbulent electric fields  E~+/-500 mV/m Duration of spike 20-200 Hz Polarized perpendicular to B  B~0.5 nT (not shown) Hodograms for E and B Complicated quasi 3D structure full 3D and 3DB Waves electrostatic with phase fronts ~perp to B Large amplitude thermal plasma variations measured from SC potential variations:Result in order of magnitude changes in index of refraction wave time scales: trapping motivates SC potential measurements Position R=5.2, Mlat 25 deg, MLT=0.5 Observed during nearly conjugate ~400 keV electron microburst interval by low altitude SAMPEX High Time Resolution Bursts

16. RBSP/EFW I-PER 21 January 2011Wygant 36 Accuracy of vxB subtraction S ince the SC is moving relative to the Earth there is a motional electric field VxB (where V is the spacecraft velocity and B is the measured magnetic field of the Earth) which must be subtracted from the measured electric field in order to determine the electric field in the rest frame of the Earth Angular uncertainties in the attitude of the spacecraft or orientation of electric field or magnetic field or determination of spacecraft velocity measurements create errors in the electric field which must obey MRD/ELE 42 Plots of typical motional electric field and uncertainties in the measured electric field for 1 deg and 3 deg attitude errors as a function of radial distance for an ensemble of orbits is presented in the next slide Required limits on angular error are defined in the subsequent slide All errors are at the 3 sigma level Time independent errors can be reduced significantly (factor of 2-3) by on the ground cross calibration of the measured electric field and V x B for quiet time orbits as indicated by CRRES experience –Time independent errors are dominant contributions to the magnetometer boom angular uncertainties and electric field sensor alignment uncertainties CRRES was able to achieve an accuracy of ~ 0.1 mV/m after somewhat extensive ground calibration –This calibration is part of “scientific analysis” The present RBSP EFW requirement is 0.3 mV/m at a distance of 3.5 Re –CRRES pointing accuracies were less stringent than RBSP

17. RBSP/EFW I-PER 21 January 2011Wygant 37 Aspects of alignment calibration The magnetic field measurement compared to the magnetic field will provide a strong constraint on the alignment of the spacecraft within a rotation angle around the magnetic field This angle can be constrained by comparison of the measured E to VxB during geomagnetically quite times Kp<2. The orthogonality of the V12 and V34 boom pairs can be constrained by using time intervals when VxB has a significant component in the spin plane. The sine waves measured by the rotating orthogonal booms pairs should be 90 degrees out of phase. Comparison of amplitudes of the sine waves to projection of VxB into spin plane provides calibration of magnitude. We can also use the 40m and 50 m boom baseline difference to calibrate the electric field magnitude. Attitude manveuvers will take place event ~27 days. After the attitude maneuvers it is possible that the sun pulse will provide the most accuracy attitude measurement. Since the sun sensor is most accurate when the spin axis points away from the sun. Many calibrations of time independent boom alignment error quantities are best preformed at these times. An interesting question is how much attitude will from orbit to orbit once we have calibrated due to various torques

18. RBSP/EFW I-PER 21 January 2011Wygant 38 IPLD-71 Measure AC Magnetic Field (Burst) Each EFW instrument shall measure burst AC magnetic field, as follows: -- using EMFISIS magnetic search coil data; -- frequency range: 10 Hz-250 Hz (TBR); -- magnitude range: 90 dB (TBR); -- cadence: 512 samples/sec; -- sensitivity: 0.3 pT/Hz^1/2 @ 100 Hz (TBR). Rationale: -- [MIS-153] (2.1.2.0-3) 3-D AC Magnetic Field Waveform (Burst)

19. RBSP/EFW I-PER 21 January 2011Wygant 39 IPLD-42 Measure Spin Plane DC Electric Field (Burst) Each EFW instrument shall measure an electric field component perpendicular to the observatory spin axis (burst), as follows: -- frequency range: DC to 250 Hz; -- magnitude range: 0.3 - 500 mV/m; -- cadence: 512 samples per second; -- sensitivity: 1x10 -12 (V/m) 2 /Hz at 30 Hz, 1x10 -14 (V/m) 2 /Hz at 300 Hz. Rationale: -- [MIS-162] (2.1.2.0-5) Spin Plane DC Electric Field (Burst)

20. RBSP/EFW I-PER 21 January 2011Wygant 40 Contributions to E field accuracy of transformation from spacecraft frame to inertial GSE frame E= Em-VxB

21. RBSP/EFW I-PER 21 January 2011Wygant 41 Spin Plane Electric Field Measurement STARD Requirement at different altitudes including validity requirement

22. RBSP/EFW I-PER 21 January 2011Wygant 42 This page intentionally almost blank