1. Modern observation and simulation of the physics of kinetic cascade leading to production of internal energy
Organizers: William H Matthaeus, Tulasi N Parashar & Michael A Shay
Scene Setters: Paul Cassak & Alessandro Retino

2. Questions At a theoretical level:
What quantities do we need to accurately measure (or simulate) to fully understand cascade and dissipation in weakly collisional plasmas?
What are the roles of specific interactions such as J.E, wave-particle correlations, cyclotron resonance, Landau damping, pressure-stress, and collisions?
What is the relationship of these to wave modes and instabilities?
At an empirical level:
What have observations shown so far about these quantities in the most accessible turbulent space plasmas – the magnetosheath and the solar wind?

3. Major points of discussion
How to really define dissipation?
Loss of fluctuation energy?
Increase in internal energy?
“Irreversible” increase in internal energy?
Which definition of entropy is relevant?
What kind of theoretical and experimental diagnostics would help us move forward?

4. Dissipation
Multiple measures available: Zenitani, non-gyrotropy (Scudder & Daughton; Aunai; and Swisdak), pressure-stress, and field particle correlations (Klein & Howes)
Some based on fluid moments, some require studying detailed features of distribution function
It is possible to construct model situations (e.g., interpenetrating beams that “trick” some of these measures
Some measures are subject to big fluctuations
Measures of non-Maxwellianity can be useful in extracting some interesting information

5. Comparison of “Dissipation” Measures
Each of the measures does a reasonable job of identifying features of the diffusion region
Note, non-Maxwellianity is even bigger in exhausts than diffusion region (see Drake et al., 2006; Greco et al., 2012, Loureiro et al., 2013)
Observations are being used to compare these different measures.

6. Observations of Dissipation Measures

7. Need more accurate and high time cadence measurements of VDFs!!!
Good idea to compute some of the popular measures (De, J.E, non- Maxwellianity, Pi-D etc.) on-board
Problems with processing data on-board
Can we be sure we have the right information?
High time cadence is important to distinguish b/w perpendicular temperature and “sloshing” of VDFs

8. Summary and Prospects
Need to be careful with our definitions of entropy, heating etc.
Consider focusing on energy transfer/conversion/exchange using various measures instead of obsessing about issues of (ir)reversibility.
Wave-like vs. coherent structures? Discussion continues.
Need even higher cadence measurements of VDFs compared to MMS.
Always need to be aware of instrumental limitations (space, time, velocity space resolution, noise levels, etc)
Work to do: new indicators/measures of dissipation (e.e., Pi-D, particle-field correlator, V-space cascade…) need to be studied and better understood, including their relationships with one another.