56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014;
New Orleans, Louisiana
Session GI1: Runaways, Divertors, and Edge Physics
9:30 AM–12:30 PM,
Tuesday, October 28, 2014
Room: Acadia
Chair: Glen Wurden, Los Alamos National Laboratory
Abstract ID: BAPS.2014.DPP.GI1.4
Abstract: GI1.00004 : A convective divertor utilizing a 2nd-order magnetic field null*
11:00 AM–11:30 AM
Preview Abstract
Abstract
Author:
Thomas Rognlien
(LLNL)
New results motivate a detailed study of a magnetic divertor concept
characterized by strong plasma convection near a poloidal magnetic field
(B$_{\mathrm{p}}$) null region. The configuration is
that of a near-2nd-order B$_{\mathrm{p}}$ null (B$_{\mathrm{p}}\propto
\Delta $r$^{\mathrm{2}})$, as in a snowflake divertor [1,2]. The concept
has 2 key features: (A) Convection spreads the heat flux between multiple
divertor legs and further broadens the heat-flux profile within each leg,
thereby greatly reducing target-plate heat loads [2]. (B) The heat flux is
further reduced by line radiation in each leg in detachment-like ionization
zones. Theory indicates that convective turbulence arises when the poloidal
plasma beta, $\beta_{\mathrm{p}}=$2$\mu
_{\mathrm{0}}$nT/B$_{\mathrm{p}}^{2}$ \textgreater \textgreater
1. Measurements in TCV [4] now more fully quantify earlier NSTX and TCV
observations of plasma mixing [5.6], and related modeling of TCV indicates
that strongly enhanced null-region transport is present [7]. Convective
mixing provides a stabilizing mechanism to prevent the ionization fronts
(hydrogenic and impurity) from collapsing to a highly radiating core MARFE.
Also, the radiating zone maps to a very small region at the midplane owing
to the very weak B$_{\mathrm{p}}$ in the convective region, thus minimizing
its impact on the core plasma. Detailed calculations are reported that
combine features A and B noted above. The plasma mixing mechanisms are
described together with the corresponding transport model implemented in the
2D UEDGE edge transport code [2]. UEDGE calculations are presented that
quantify the roles of mixing, impurity radiation, and detachment stability
for a realistic snowflake configuration. Work in collaboration with D.D.
Ryutov, S.I. Krasheninnikov, and M.V. Umansky.\\[4pt]
[1] D.D. Ryutov et al., PPCF \textbf{54} (2012) 124050.\\[0pt]
[2] T.D. Rognlien et al., J. Nucl. Mat. \textbf{438} (2013) S418.\\[0pt]
[3] D.D. Ryutov et al., accepted, Physica Scripta (2014).\\[0pt][4] W. Vijvers et al., Nucl. Fusion \textbf{54} (2014) 023009.\\[0pt]
[5] V.A. Soukhanovskii et al., Nucl. Fusion \textbf{51} (2011) 012001 and Phys. Plasmas \textbf{19} (2012) 082504.\\[0pt]
[6] H. Reimerdes et al., PPCF \textbf{55} (2013) 124027.\\[0pt]
[7] T. Lunt et al., PPCF \textbf{56} (2014) 035009.
*Performed for the U.S. DoE by LLNS, LLC, LLNL, under Contract DE-AC52-07NA27344.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.DPP.GI1.4