Closed jonmaddock closed 1 week ago
In GitLab by @mkovari on May 6, 2022, 16:23
A quick reading of this paper seems to show that it is thoroughly dishonest. Although they say their proposed formula applies to H-mode and L-mode, this isn't true. Their actual definition of the density limit of discharges with an H-mode phase is as follows.
the plasma undergoes first an L-H transition, then as the density is increased, plasma confinement degrades until an H-L transition occurs and, once in L-mode, a density limit is attained.
In other words, this is actually an L-mode density limit!
@stuartmuldrew @ajpearcey
In GitLab by @mkovari on May 17, 2022, 10:40
In principle, their formula could be used for L-mode reactors, and it would allow higher densities for suitable values of the parameters. However, the issue of confinement degradation with increasing edge density remains.
Comment from Francis Casson:
The Greenwald limit is now understood to be a L-mode or separatrix density limit:
Most present machines limited by fuelling from SOL
Reactor devices require core fuelling (pellets)
H-mode operation above Greenwald limit has been demonstrated in devices including DIIID and AUG
Exact nature of the limit in pellet fuelled reactor plasmas not well understood
Given there is no well understood alternative, and the Greenwald fraction is still used as the main density reference, I propose we just close this issue with no change. It can be moved to a discussion if needed.
In GitLab by @mkovari on Dec 4, 2019, 10:20
Origin of Tokamak Density Limit Scalings
D. A. Gates and L. Delgado-Aparicio, Phys. Rev. Lett. 108, 165004 – April 2012
They argue that the density limit is due to radiative effects.
This suggests to me that we should be using a physics-based density limit, rather than the empirical Greenwald limit.
Any thoughts - @rkemp @msiccini @skahn ?
PS Michael Fitzgerald's comment - "If someone had figured out the physical origin of the density limit we would have heard about it."