58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016;
San Jose, California
Session GI2: MFE: Pedestal & Impurities
9:30 AM–12:30 PM,
Tuesday, November 1, 2016
Room: 210 CDGH
Chair: Howard Wilson, University of York
Abstract ID: BAPS.2016.DPP.GI2.2
Abstract: GI2.00002 : Observation and Calculation of the ECRH Effect on the Tracer Impurity Accumulation in LHD*
10:00 AM–10:30 AM
Preview Abstract
Abstract
Author:
Naoki Tamura
(National Institute for Fusion Science, National Institutes of Natural Sciences)
In a magnetic confinement fusion reactor various Z impurities will exist
inside the plasma. When the amount of the impurities exceeds the acceptable
level by an accumulation, this will lead to impermissible plasma performance
degradation due to the radiation losses and plasma dilution. Therefore, it
is crucially important to develop effective schemes for controlling the
impurities in the core plasma and to understand the underlying physical
mechanisms of such schemes. Recent LHD experiments show the ability of ECRH
to control the impurity accumulation. Experiments on the LHD have used a
tracer-encapsulated solid pellet (TESPEL), which is embedded with vanadium,
to introduce the extrinsic and non-recycling impurity directly inside the
last-closed flux surface (LCFS) region. Therefore, the confinement time of
the vanadium impurity can be directly evaluated from the time history of
highly ionized vanadium ion. In cases where the collisionality between the
impurity ions and the bulk ion is in the Banana-Plateau regime (but close to
the collisional Pfirsch-Schl\"{u}ter (PS) regime), the impurities in the LHD
plasma are strongly accumulated into the core plasma. When the 1.5 MW 154
GHz ECRH is applied for such plasma just after the TESPEL injection, the
accumulation of the vanadium ions was almost completely suppressed. This
result indicates that applying ECRH changes the direction of the radial
vanadium particle flux from the inward to the outward. Although the
neoclassical ambipolar radial electric field in stellarators has a stronger
impact on the transport, particularly on the impurity transport, than in
tokamaks, there is no conclusive data regarding a radial electric field
measured with a charge exchange spectroscopy diagnostic to support the view
that the change in the radial electric field would be attributed to the
outward flow of the vanadium ions in the LHD plasma. In this contribution,
the results of ongoing evaluations of the neoclassical (e.g., PENTA/DKES
that includes the momentum conservation) and turbulent (e.g., GKV-X)
transport will be presented to elucidate their respective roles in 3D
toroidal plasmas.
*This work is mainly supported by a Grant-in-Aid for Scientific Research (B) (No.15H04234) from JSPS Japan and a budgetary Grant-in-Aid No. ULHH012 from NIFS.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2016.DPP.GI2.2