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 Wind @ 1 AU (Collier et al. 1996)

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

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)

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…

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).

Radio sounding