Stability, or instability, is the central theme for plasma physics. In this talk, I will prove and demonstrate using examples from plasma physics the following facts.
1) The only route for a conservative system to become unstable is through the resonance between a positive-action mode and a negative-action mode.
It is not the “free energy” that drives the system unstable.
2) For most stable systems, stability is a consequence of being symplectic (or G-unitary for complex systems), instead of the existence of
dissipation or damping.
3) Dissipation can destabilize a system by breaking the symplectic (or G-unitary) condition.
4) By not preserving the symplecticity, numerical and analytical models for conservative systems diverge quickly from the true dynamics.
 R. Zhang, H. Qin et al., arxiv:1801.01676 (2018)
 R. Zhang, H. Qin et al., Phys. Plasmas 23, 072111 (2016)
 J. Xiao, H. Qin & J. Liu, Plasma Sci. Tech. 20, 110501 (2018)
*Things in this context include conservative systems, numerical and analytical models thereof.
The DOE workshop on “Integrated Simulations” has identified a number of critical aspects in the integration of physics modules in a whole device model for tokamak simulations. Challenge includes not only the need for physics description, but also a need for hardware infrastructure, software integration and difficulties in integrating multi-scale coupling.
This seminar summarizes the conclusions from the integrated simulations workshop on MHD stability and disruptions, boundary physics and core transport, as well as a need for research on innovative workflows that enable the integration.