BEGIN:VCALENDAR
VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-3783
DTSTART:20151214T180000Z
DTEND:20151214T190000Z
DTSTAMP:20240329T154623Z
LAST-MODIFIED:20151203T161017Z
LOCATION:2241 Physics Bldg
SUMMARY:Plasma Microinstability Saturation in Toroidal Plasmas\, Plasm
a Physics (Physics/ECE/NE 922) Seminar\, Paul Terry\, UW Madison
DESCRIPTION:The question of how microinstabilities saturate in toroida
l plasmas is often overlooked or
\ngiven insufficient attention. T
his is particularly true in comprehensive numerical
\nsimulations\
, like gyrokinetics\, where beyond ascertaining that there is a physic
ally
\nmeaningful saturated state\, most of the analysis is best d
escribed as characterization of
\nfluctuations and the transport t
hey produce. As a result\, certain widely held ideas about
\nsatur
ation do not hold up under closer scrutiny. In this talk we examine ne
w
\ndevelopments in the understanding of how ion temperature gradi
ent (ITG) turbulence
\nsaturates. We present evidence from gyrokin
etic simulations that ITG turbulence
\nsaturates primarily by ener
gy transfer to damped modes within the wavenumber range of
\nthe i
nstability\, rather than by a cascade to small scale. Zonal flows cata
lyze this transfer\,
\nproviding an efficient energy transfer chan
nel while absorbing very little of the
\ntransferred energy. Zonal
flow shearing is not the primary saturation mechanism\, but is a
\nsecondary (weaker) effect at best. We also show that zonal-flow-cata
lyzed transfer
\nexcites stable modes with tearing parity. These g
ive rise to a stochastic magnetic field at
\nvery low beta values\
, and electron thermal transport. While small at low beta\, this flutt
erinduced
\ntransport becomes significant at beta approaching 1%.
Magnetic fluctuations
\ncreated by transfer to damped modes affect
zonal flows. Above a critical beta\, they
\ninduce irreversible c
harge loss from rational surfaces\, shorting out zonal flow potentials
\nand leading to a state of very high transport. This phenomenon\
, called the non zonal
\ntransition (NZT)\, has long been observed
in gyrokinetic simulations\, and in experiment
\ncould limit grad
ients in stiff discharges.
URL:https://www.physics.wisc.edu/events/?id=3783
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