Zonal Flows in Helical Systems H. Sugama

1
Zonal Flows in Helical SystemsH. Sugama

• Examined the damping of zonal flows due to
  helically trapped particles
• Eulerian (Vlasov) simulation using a flux tube
  simulation
• Correction to the 1/(1q2/e) factor of Hinton
  Rosenbluth
• Conclusions
• Zonal flow potential becomes smaller in the
  long-time limit due to the helical-ripple-trapped
  particles
• Transition time, tc, however, becomes longer

2
Experimental Studies of MHD Instabilities in LHD
- S. Sakakibara

• Beta dependence of MHD activity
• Core MHD activity suppressed with b
• Edge MHD activity increased with b
• Optimization of Rax Rax gt 3.5 is better
• High A reduces Shafranov shift, can produce
  plasma with bdia 4
• Why are the MHD modes stabilized?
• (a) Profile flattening caused by MHD mode?
• (b) Stopping of mode rotation? (but frequency
  unchanged)
• (c) Variation of magnetic surface due to b?

3
Influences of Plasma Boundary on MHD
Instabilities in Heliotrons - N. Nakajima

• Discrepancy on MHD equilibria stability
• Experiment ltbgt gt 3 plasmas
• Theory Strong MHD instabilities for fixed
  boundary plasmas
• Finite pressure gradient beyond a clear vacuum
  LCFS
• Assume average flux surfaces in stochastic region
• Inward shifted configurations have narrowest
  stochastic layer
• For ltbgt 3, unstable for fixed boundary but
  marginally stable for free boundary
• Growth rates go down with ltbgt due to boundary
  modification