WORKSHOP SUMMARY NOTES

Actions from the workshop (see below) are directly most immediately toward the SWT review of PSI operations that will take place at GSFC on Tues. 4 November, 1730 hrs, after the TIDE team meeting here on 3-4 Nov. and the initial day of the ISTP correlative science workshop that week. An agenda for the TIDE-PSI meeting will be sent in the near future. Contributions and suggestions are welcome.

We discussed the electrical configuration and operational characteristics of PSI, noting that it tends to regulate the s/c at an indicated potential of ~ +2 V relative to the plasma. The +/- 10 V bias supply allows the s/c to be swung from +5 V to near zero V, but there is a stong tendency to regulate near +2V.

There was a brief discussion [Mike Chandler] of the methods used to reflect the indicated s/c potential in the analysis of count rates to physical units of phase space density. This is either so well established or so mysterious that it came up for little questioning. Reference is made to Moore et al., Kinetic core plasma diagnostics  [AGU Monograph on Space Plasma Measurement Techniques, in press, 1997].

A summary of recent PSI operations experience [Paul Craven] pointed out the presence of a new noise that appears in the total ion data, and is evenly distributed throughout the energy range and spin range, with the exception of a "shadow" when TIDE looks opposite to the sunward direction. Chandler said this noise is present even when the TIDE mirrors are shut down, so it does not appear to be a real ion signature, but that makes the sun shadow more than mysterious.

The Hydra data set was described [Craig Pollock and Chris Olsen] and the concerns of Jack Scudder were discussed. Subtle anisotropies of the electrons, i.e. heat fluxes, are a core science interest of his; hence his concern with PSI sheath effects on his electrons. While photoelectrons are greatly subdued with PSI running, they are not completely suppressed below the low energy limit of ~ 10 eV.

The PWI data set from the axial boom directly in the PSI plume was described and discussed [Dennis Gallagher]. A few hours of study have not revealed any obvious way to infer characteristics of the PSI plasma from wave features. However, a great deal of structured emissions are seen, with frequency variations over timescales of an hour or more. These may be more diagnostic of the PSI internal plasma than its external domain.

The EFI data set obtained from the current mode operations on 14 May 97 were described and discussed [Thompson]. The spin modulations previously noted were shown to be well organized  by the local B, and perhaps by the sun as well. In particular, there was a clear spin modulation asymmetry about the magnetic field, with a distinct depression [enhancement] of the measured probe potential on one side of the spin, and an inverse enhancement [depression] of the probe current on the same side of the spin, with somewhat opposite behavior on the alternate side of the spin. This suggests that in fact there is an electric field directed across the magnetic field at the spacecraft, that is produced by PSI sheath space charges.

The sheath scenario was described and discussed [Hugh Comfort], and the new EFI results were thought reasonably consistent with the scenario described in Comfort et al. [AIAA manuscript, 1997].

A discussion of the conditions appropriate for modeling of the PSI sheath resulted in the following parameter definitions:
 

PSI PLASMA VELOCITY DISTRIBUTIONS

Photoelectrons:

PSI Electrons:

PSI Ions:

WORKSHOP ACTIONS:

* TBD if examples exist of useful observations.