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VAN ALLEN PROBES A AND B FORMERLY RBSP-A AND RBSP-B

VAN ALLEN PROBES A AND B FORMERLY RBSP-A AND RBSP-B. Launched September, 2012 into equatorial orbits with apogee ~5 RE, low perigees Their purpose is to understand the rapid acceleration of electrons to relativistic energies in the inner Van Allen belts

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VAN ALLEN PROBES A AND B FORMERLY RBSP-A AND RBSP-B

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  1. VAN ALLEN PROBES A AND B FORMERLY RBSP-A AND RBSP-B Launched September, 2012 into equatorial orbits with apogee ~5 RE, low perigees Their purpose is to understand the rapid acceleration of electrons to relativistic energies in the inner Van Allen belts Electric field experiment designed and built at Berkeley, Minnesota, Colorado, with John Wygant as P.I. OUTLINE OF TALK • Gee-whiz plots of data • Science relevant to SPP • Instrument operation relevant to SPP

  2. GEE-WHIZ-1 • Amplitude scale is 0.5 mV/m. There has never been electric field data plotted on this scale. • Top two plots are raw electric field data that have sine waves due to rotation of sensors in the quasi-static field. • Fine steps in raw data are one bit steps of 16 bit A-D converter. From smoothness of the steps, there is no noise at this level. • Bottom two plots are despun data. They show quasi-static fields and waves with amplitudes of ~0.1 mV/m.

  3. GEE WHIZ-2 • The plasmapause has been thought to be an electrostatic barrier with corotational plasma flow inside and magnetospheric convection outside. • The electric fields that produce this flow have never been well-measured • Top panel is spacecraft potential which shows that plasma density decreased by about two orders-of-magnitude at the plasmapause. • Bottom three panels give components of the electric field that show the plasmapause IS an electrostatic barrier with a field ~1 mV/m outside it and with low frequency waves.

  4. RELATIVISTIC ELECTRON ACCELERATION IN THE VAN ALLEN RADIATION BELTS Early theories involved slow acceleration by quasi-linear diffusion due to whistler waves having amplitudes less than 1 mV/m CRRES observed relativistic electron acceleration on very short time scales ~100 mV/m whistler waves observed by Wind in the magnetosphere These led to the currently popular theory of fast acceleration in large amplitude whistler mode waves. RBSP sees such waves more frequently than had been expected. Several (September 19, October 1, October 13) medium DST ~ -100 injection events in 3 months have been associated with large amplitude whistlers, relativistic electrons, and formation of a new radiation belt.

  5. SEPTEMBER 19, 2012 00:00-24:00 RBSPB MULTIPLE INJECTION EVENT Electron data from MagEIS_low Vertical scale is 36 -200 keV. Several (3-4) rapidinjections starting at ~ 19 UT. - SC potential. SC charged to -40 volts during the injection events Electric field, .001-.1 mV/m/sqrt(Hz) Amplitudes ≤ 100 mV/m Frequency, 2-10,000 Hz. Magnetic field in nT/sqrt(Hz). Amplitude range of 0.01-0.0001. E/B ratio Color coded scale ranges from 1000 km/s (black) to 100,000 km/s (red)

  6. INSTRUMENT OPERATION RELEVANT TO SPP • Ground command, allows control of 3 parameters: • Bias current to probes to put them near plasma potential. • Voltages on two surfaces called Guard and Usher. • During slow sweeps, these three parameters are varied to optimize the operation (panels 4, 5, and 6) • The spacecraft potential (top panel) is strongly dependent on the bias current. • Such a dependence was not seen on ISEE, Polar, FAST, Cluster or THEMIS. • It must be because the area of the spacecraft ground surface is inadequate. • THIS IS A VIOLATION OF THE ELECTROSTATIC CLEANLINESS SPECIFICATION

  7. OVERVIEW OF A VAN ALLEN SATELLITE The on-axis booms are similar to those on SPP The spin axis is approximately sun pointing, but the sphere on the anti-sunward side is always in sunlight. Part of the aft boom in shadow all the time. This geometry is a little like that on SPP whose forward booms may be partially in the wake.

  8. EFFECT OF ADJUSTING PARAMETERS ON THE ON-AXIS MEASUREMENT 12 hours of data giving the three components of the de-spun electric field. Perigee, with its big vxB electric field is near the middle of the time interval. The on-axis boom signal is in the bottom panel. Before the parameter changes at the vertical line, the spurious on-axis signal was about 30mV/m. After the parameter change, it was ~5 mV/m. The required parameter values were not anticipated before the flight. The ability to adjust these parameters saves the 3-component measurement.

  9. LESSONS LEARNED RELATIVE TO SPP • SPP will see very large amplitude waves and low frequency signals. • More attention to electrostatic cleanliness MUST be paid. • Good to have knobs to turn. • One such knob is a mechanism to move all four booms forward from the plane perpendicular to the spin axis

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