Solar Probe Plus Witness Plate Update David Malaspina Bob Ergun Zoltan Sternovsky Keith Drake

1. Solar Probe Plus Witness Plate Update David Malaspina Bob Ergun ZoltanSternovsky Keith Drake University of Colorado Laboratory for Atmospheric and Space Physics SPP AGU meeting 2012-12-01

2. Expected hits / day on SPP Based on Gruen 1985 collisional balance model ~100’s to 1000’s of hits / day / m^2 of micron or larger dust near close approach Multiply by ram cross-sectional area of SPP in m^2 and that can be a large number of dust spikes in the waveform data At ~1/min, these spikes unlikely to appear in survey spectra, may be averaged out in filterbank peak data But, may dominate burst waveform captures (!) Nano-dust flux much higher, if seen by SPP

3. This will require some dust filter for • the waveform captures • But, wave-form based spike filtering • Algorithms likely to toss out real signals: • Phase space holes • Double layers • Strongly localized wave packets • Non-linear ion-acoustic waves • One solution: a witness plate provides: • - dust flux survey data • - coincident observations of • plate and antenna waveforms • (understand what a dust hit looks • like in various plasma conditions) • Less precise option: Use antenna heat • shields as witness plates

4. Hypervelocity impact charge release calibration for Niobium and Tantalum/Tungsten Antennas measure: Vspike ~= Qrel / Cs/c Approximate power law: Qrel ~= αmβvγ But! α and γ different for each target material Used U. Colorado dust accelerator to performed calibrations for Niobium and Tantalum Results in a more accurate estimate of true Qrelfor antenna dust strikes Combined with model-based estimates of impact velocity, can ~recover particle mass But, Q, C fluctuate with plasma conditions (!) γ = 3.12 α =1.02 γ = 3.04 α =1.26

5. Witness Plate Prototype To ensure Qrel measured consistently, use a witness plate Constructed a prototype Testing carried out in the 3 MeV CU dust accelerator

6. Witness Plate Prototype Test results: (iron dust, gold target) Measureable signals from 1x10-14 C to 1x10-10 C Measured charge close to expected for 10V, 20V, 50V bias

7. Witness Plate Prototype Test results: (iron dust, gold target) Measureable signals from 1x10-14 C to 1x10-10 C Measured charge close to expected for 10V, 20V, 50V bias

8. Notional Witness Plate Mass: 97g (includes 45 g for amplifier, amp radiation shield, connector) Power: ~60 mW (4x OP262, half a dozen R’s and C’s )

9. Notional Witness Plate (exploded)

10. Notional Witness Plate Huge dynamic range to cover (160 dB) Use a divided target μ-plate (larger area for lower flux large dust) n-plate (smaller area for higher flux small dust) n-plate Qrel range already verified by prototype test

11. SPP Dust Measurement and Witness Plate Update Summary • Calibrations performed for charge release from SPP antenna materials • - Niobium • - Tantalum-Tungsten • Witness plate prototype successfully developed and tested w/ hypervelocity impacts • and charge release of 10-14 C • Notional witness plate model developed (97 gw/ shielded amp, ~60 mW) • NASA Heliophysics proposal recently funded: • "Laboratory investigation of dust impacts on antennas in space” • - will explore the detailed physics of antenna / dust coupling by • controlling each variable (s/c potential, dust properties, impact angle, plasma conditions) • in laboratory conditions

12. Reminder: STEREO / WAVES Dust workshop April 8 – 10, 2013 Meudon Observatory Contact: Chris St. Cyr Nicole Meyer-Vernet David Malaspina