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CINEMA Science

CINEMA Science. Outline. Science Overview The ring current Electron Microbursts 1) Energetic Neutral Atom (ENA) Imaging of the ring current Requirements 2) Electron Microburst Spectrum Requirements 3) Mag Observations 4) Auroral Particle Observations. A quick tour: The Magnetosphere.

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CINEMA Science

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  1. CINEMA Science file:CINEMA PDR- SCI

  2. Outline • Science Overview • The ring current • Electron Microbursts • 1) Energetic Neutral Atom (ENA) Imaging of the ring current • Requirements • 2) Electron Microburst Spectrum • Requirements • 3) Mag Observations • 4) Auroral Particle Observations

  3. A quick tour: The Magnetosphere

  4. Magnetic Storms • Magnetic storms occur ~monthly • >10x enhancement of Ring current • Changes the magnetic field at earth’s surface: captured by Dst Index

  5. Ring current • The ring current is not always a ring, local time variations are important • IMAGE captured ENA images of the ring current from high above the magnetic poles

  6. Ring Current Loss Processes Energetic Ring Current Belt (1-300 keV) Density Isocontours Neutral Plasmapause Precipitation Dawn Ion Cyclotron Charge Waves Exchange Coulomb Collisions Between Ring Currents ( L~4) and Dusk Thermals (Shaded Area) ( L~8 ) ( L~6 ) Wave Scattering of Ring Current Ions [Kozyra & Nagy, 1991] Tutorial, GEM Workshop, 6/27/03 7

  7. Electron Microbursts • Microbursts are bursts (<0.25s) of electrons thought to be the result of a resonant wave particle interaction. • They occur from midnight to ~9am local time and are very intense • Extend from L=4-8

  8. uBursts Cont’d • Energy range extends to greater than 1MeV • Thought to be a significant loss process for the radiation belts at these high energies • Root waves may also be a significant source process • Observations suggest microbursts do not precip- itate electrons below ~20keV

  9. Science Objective 1 • Understand the detailed spectral, temporal, and local time evolution of the Earth’s Ring Current from 4-20KeV • Science Requirements: • make equatorial viewing energy resolved ENA scans of the ring current with local time resolution • Make LT resolved scans at a cadence >> magnetic storm onset time (~1hr) • Make energy resolved ENA scans of ring current precipitation, to evaluate precipitation as a loss process for ring current recovery

  10. Ring Current ENA requirements • make accurate (~1kev) spectral measurements of ring current ENAs from 4-20keV with the ability to unambiguously identify neutrals • Measure ENAs from 20keV-100keV with the ability to separate neutral anf charged particles based on extra information such as periodicity relative to the local field • for accurate local time imaging, the longitudinal field of view of the detector must be ~20 degrees FWHM. • Corresponds to ~1.5 hrs local time FWHM • Images of >8 hours of local time should be available at a cadence of several minutes • Requires spin axis perpendicular to local time plane • Requires Spin rate comparable to or greater than 1rpm • In order to make observations of ENA’s at high latitude we need a low earth orbit of inclination greater than 65 degrees.

  11. Ring Current ENA requirements 2 • The detector’s absolute orientation (ground reconstruction adequate) must be on the order of 10deg. • Expected count rates in the equatorial region of ~300cts/s • CINEMA must record and telemeter adequate spectral information and time resolution sufficient for ground-based energy-resolved image reconstruction. • 16bits per event implies average rate of this data source is 5kbps at >80%duty cycle • Expected counting rates at high latitude zone 3000 cts/s for 50kbps at ~10% duty cycle • Ability to recover from sunlight in detector within ~40 degrees

  12. Electron Microburst Spectrum • Understand variations in the low energy spectrum of electron microbursts • Science Requirements: • Make high resolution energy spectra of individual electron microbursts from 2keV to 100keV. • Measure microbursts across a range of local times, activity levels, and magnetic latitudes

  13. uBurst Requirements • Requires an energy range from 2kev to 100kev • Energy resolution of ~2keV. • Time resolution of better than 0.1 seconds. • Ability to handle count rates of 5000 counts/second/pixel with <1keV energy resolution loss • Ability to attenuate electron fluxes by factor of 100 to observe large range in uBurst fluxes • Attenuator must be thick enough to stop <50keV electrons • Attenuator should have automated actuation based on commandable parameters such as count rate and geographic location. • The ability to choose modes in our voltage sweep: • Pegged high: Maximum reduction of low energy counts in central pixel • Pegged low: Counts in central detector assumed to be electrons based on context/time structure provides minimum distortion of energy spectrum • sweeping with a sweep rate comparable to the angular resolution (20deg.) divided by spin rate (~30deg./second)

  14. uBurst req’ts continued • Microburst science requires orbit requirements latitude > 65degrees • Field of view should be defined with angular aperture that minimizes scattering of electrons onto the detector • The detector field of view relative to the local magnetic field must be able to be reconstructed to 10deg at a time scale such that the angular resolution blur due to spin is small. Interpolation on 1s magnetometer data is adequate. • Accurately record event information at 5000 cts/s • Average data generation rate of 500cts/s at orbit duty cycle of 20% for an estimated orbit averaged data rate of 1.6kbps

  15. Magnetometer • Test predictions on the orientation and speed of ULF waves launched from the region around the Earth’s bowshock. • Background: Cluster allows tomographic reconstruction of shape and size of foreshock ULF waves, including flow-perpendicular scale • Archer et al., JGR, 2005

  16. Crossing the perpendicular scale Parallel scale crossing • Predict ~30s (steady, observed) Perpendicular scale crossing • Predict 2-5 minutes (variable) • Quasi-periodic enhancements of |B|, accompanied by whistlers • Look like SLAMS • Also, modulation of ULF wave amplitude

  17. FTE periodicities? • Hypothesis • ULF waves generate ~few minutes periodic forcing at magnetopause • Cause of ~few minutes occurrence rate of FTEs? • Test • Compare dayside ULF wave signatures and FTEs (CINEMA) with upstream and magnetopause data (THEMIS, Cluster) • Also use THEMIS ground-based magnetometer chain (+others?) • Compare: occurrence, wavelength, phase fronts, propagation direction of ULF wave signatures

  18. Magnetometer • Test predictions on the orientation and speed of ULF waves launched from the region around the Earth’s bowshock. • Magnetic field direction knowledge 1deg • Spin axis orientation knowledge <1 deg • Ability to pulse torque coils in order to determine absolute orientation of outboard magnetometer to 1deg about the stacer axis • Knowledge of the spin phase to ~10ms • Absolute field measurement to 500nT • Spin-variable magnetic interference at outboard sensor <500nT (ideally much less than this) • Gain knowledge (including temperature variations) to 0.5% • Knowledge of absolute position for comparison to magnetic field models in quiet times of 50km (complete guess – Horbury)

  19. Magnetometer cont’d • Measurement of physical field variations at better than 1s • Science mode cadence of 10 vector/s • Essential: resolution of phenomena at amplitudes of 100nT on timescales of few seconds • Instrument resolution of 50nT, noise below 50nT at 1Hz • Hence effective 11 bits • Desirable: resolution of phenomena at amplitudes of 1nT on timescales of few seconds • Instrument resolution of 0.5nT, noise below 1nT at 1Hz • Hence effective 19 bits • Expect 20 bits/axis, effective science data rate 640bits/s

  20. Auroral Particle Precipitation • Correlate in situ measurements of particle precipitation with ENA imaging of ring current populations. • Measure the spectrum, time evolution and location of precipitation at low earth orbit from 4keV to 100keV. • Separate ions and electrons up to 20keV

  21. Auroral particles • Electrostatic potential to separate ions and electrons • Sweeping of voltage for varying which low energies ion/electron pixels on time scales faster than auroral pulsations (10s of seconds) • Knowledge of detector FOV with respect to local magnetic field better than 10deg. • Attenuator action based on count rate should be autonomous, but with adjustable thresholds • Attenuator flux reduction of ~100x. • Adjustable attenuator stowage period • Commandable decimation scheme to handle large data rates, limit auroral science data rate to ~1kbps orbit averaged

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