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In situ particle detection
Next time mass spectrometers Faraday cups electrostatic analyzers ... collect charged particles (from a given solid angle, in a certain kinetic energy range) & convert them to currents. If enough energies & angles collected, one gets the velocity distribution function. Collisionless space plasmas show departures from thermal Maxwellians... Helios @ 0.3–1 AU (Marsch 1991) B 1 AU (Collier et al. 1996)
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In situ particle detection
Next time mass spectrometers Faraday cups electrostatic analyzers ... collect charged particles (from a given solid angle, in a certain kinetic energy range) & convert them to currents. Challenge: how to disentangle spatial/time fluctuations in single-point data? Taylor’s hypothesis: “eddies” flow past spacecraft much more rapidly than they evolve (i.e., ~all variation is spatial) Solution: deploy > 1 spacecraft, with known separations. CLUSTER, MMS
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In situ electric & magnetic fields
Magnetometers: electromagnet on long boom. “Input” current is varied in time; “output” current is measured ... imbalance between input & output gives B. Langmuir probes: similar antenna concept (replace current with fixed potential drop) to measure the electric field. → Lots of possible sources of contamination! spacecraft electronics, solar photoelectric effect, etc. Fourier spectra of a long time series of B(t), E(t) data show power-law energy distributions, indicating turbulent cascade. Departures from classical fluid turbulence (Kolmogorov 1941) tell us even more about collisionless kinetic effects. (Sahraoui et al. 2009)
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Heating rates in the heliosphere
Internal energy conservation: if time-steady, it gives dT/dr for a specific heating rate Q. If Q = 0, we expect T ~ r–4/3. Observed T(r) is flatter, so Q > 0. If we know all other terms in conservation equations, we can solve for Qp ≠ Qe Cranmer et al. (2009) … but see also Vasquez, Stawarz,, Travnicek, etc. Overall magnitude of (Qp + Qe) is consistent with expectations from MHD turbulence models. In inner heliosphere, Qp/Qe ≈ 1 In outer heliosphere, Qp/Qe ≈ 4 You know what we’re waiting for…
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Radio sounding “When the target is not the target.” A known source’s radio signal is distorted by passing through plasma being probed. Refractive index depends on density (plasma freq.) & B-field (Faraday rotation) Fluctuations in Faraday rotation data probe “stirring scales” of solar wind turbulence (Hollweg et al. 2010).
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Radio sounding
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