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PRODID:-//Memento EPFL//
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SUMMARY:Recent Progress in Quiescent H-mode (QH-mode) Research on DIII-D T
 okamak
DTSTART:20160909T103000
DTEND:20160909T113000
DTSTAMP:20261005T052822Z
UID:3975e2ec9397832b2133e2c13c2716b73ce2b3f560ef5a579e5c3539
CATEGORIES:Conferences - Seminars
DESCRIPTION:Xi Chen\, General Atomics\, San Diego\, CA\, USA\nIn a recent 
 discovery\, the Quiescent H-mode (QH-mode) regime in DIII-D has been found
  to bifurcate into a new state at low torque in double-null shaped plasmas
 \, characterized by increased pedestal height\, width and thermal energy c
 onfinement. This regime has been sustained at net-zero NBI torque for 12 t
 au_E with excellent confinement (H98y2 ~ 1.46\,  beta_N~ 2). This provide
 s an alternate path for achieving high performance ELM-stable operation at
  low torque\, in addition to the low-torque QH-mode sustained with applied
  3D fields. Measurements and simulation indicate that in the “wide-pedes
 tal” state\, the decreased edge (rho>0.9) ExB shear destabilizes broadba
 nd turbulence\, which relaxes edge pressure gradients\, improves peeling-b
 allooning stability and enables a wider and thus higher pedestal\; in addi
 tion\, increased outer-core (0.7<rho<0.9) ExB shear improves transport in 
 that region and synergistically enhances the global energy confinement. In
  parallel\, new experimental study and modeling of low\, experimentally-re
 levant toroidal mode number (n≤5) Edge Harmonic Oscillation (EHO)\, whic
 h regulates the conventional QH edge\, validate the proposed hypothesis of
  edge rotational shear in exciting the EHO. The observed minimum edge ExB 
 shear required for EHO decreases linearly with pedestal electron collision
 ality\, which is favorable for operating QH-mode in low collisionality and
  low rotation machines such as ITER. The ability to accurately simulate th
 e EHO and maintain high performance QH-mode at low torque is an essential 
 requirement for projecting QH-mode operation to ITER and future machines.
LOCATION:PPB 019
STATUS:CONFIRMED
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