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Title: Increased heat dissipation with the X-divertor geometry facilitating detachment onset at lower density in DIII-D

Abstract

The X-Divertor geometry on DIII-D has demonstrated reduced particle and heat fluxes to the target, facilitating detachment onset at ~20% lower upstream density and higher H-mode pedestal pressure than a standard divertor. SOLPS modeling suggests that this effect cannot be explained by an increase in total connection length alone, but rather by the addition of connection length specifically in the power-dissipating volume near the target, via poloidal flux expansion and flaring. But, poloidal flaring must work synergistically with divertor closure to most effectively reduce the detachment density threshold. Furthermore, the model also points to carbon radiation as the primary driver of power dissipation in divertors on the DIII-D floor, which is consistent with experimental observations. Sustainable divertor detachment at lower density has beneficial consequences for energy confinement and current drive efficiency in the core for advanced tokamak (AT) operation, while simultaneously satisfying the exhaust requirements of the plasma-facing components.

Authors:
 [1];  [2];  [2];  [2];  [1];  [3];  [4];  [4];  [5]
  1. General Atomics, San Diego, CA (United States)
  2. Univ. of Texas, Austin, TX (United States)
  3. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  5. Chinese Academy of Sciences (CAS), Beijing (China). Inst. of Plasma Physics
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1390611
Grant/Contract Number:
FC02-04ER54698
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 8; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Covele, Brent, Kotschenreuther, M., Mahajan, S., Valanju, P., Leonard, Anthony W., Watkins, Jonathan G., Makowski, Michael A., Fenstermacher, Max E., and Si, H. Increased heat dissipation with the X-divertor geometry facilitating detachment onset at lower density in DIII-D. United States: N. p., 2017. Web. doi:10.1088/1741-4326/aa7644.
Covele, Brent, Kotschenreuther, M., Mahajan, S., Valanju, P., Leonard, Anthony W., Watkins, Jonathan G., Makowski, Michael A., Fenstermacher, Max E., & Si, H. Increased heat dissipation with the X-divertor geometry facilitating detachment onset at lower density in DIII-D. United States. doi:10.1088/1741-4326/aa7644.
Covele, Brent, Kotschenreuther, M., Mahajan, S., Valanju, P., Leonard, Anthony W., Watkins, Jonathan G., Makowski, Michael A., Fenstermacher, Max E., and Si, H. Fri . "Increased heat dissipation with the X-divertor geometry facilitating detachment onset at lower density in DIII-D". United States. doi:10.1088/1741-4326/aa7644.
@article{osti_1390611,
title = {Increased heat dissipation with the X-divertor geometry facilitating detachment onset at lower density in DIII-D},
author = {Covele, Brent and Kotschenreuther, M. and Mahajan, S. and Valanju, P. and Leonard, Anthony W. and Watkins, Jonathan G. and Makowski, Michael A. and Fenstermacher, Max E. and Si, H.},
abstractNote = {The X-Divertor geometry on DIII-D has demonstrated reduced particle and heat fluxes to the target, facilitating detachment onset at ~20% lower upstream density and higher H-mode pedestal pressure than a standard divertor. SOLPS modeling suggests that this effect cannot be explained by an increase in total connection length alone, but rather by the addition of connection length specifically in the power-dissipating volume near the target, via poloidal flux expansion and flaring. But, poloidal flaring must work synergistically with divertor closure to most effectively reduce the detachment density threshold. Furthermore, the model also points to carbon radiation as the primary driver of power dissipation in divertors on the DIII-D floor, which is consistent with experimental observations. Sustainable divertor detachment at lower density has beneficial consequences for energy confinement and current drive efficiency in the core for advanced tokamak (AT) operation, while simultaneously satisfying the exhaust requirements of the plasma-facing components.},
doi = {10.1088/1741-4326/aa7644},
journal = {Nuclear Fusion},
number = 8,
volume = 57,
place = {United States},
year = {Fri Jun 23 00:00:00 EDT 2017},
month = {Fri Jun 23 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on June 23, 2018
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Cited by: 3works
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  • SOLPS modeling has been carried out to assess the effect of tightly closing the lower divertor in DIII-D, which at present is almost fully open, on the achievement of cold dissipative/detached divertor conditions. To isolate the impact of other factors on the divertor plasma solution and to make direct comparisons, most of the parameters including the meshes were kept as similar as possible. Only the neutral baffling was modified to compare a fully open divertor with a tightly closed one. The modeling shows that the tightly closed divertor greatly improves trapping of recycling neutrals, thereby increasing radiative and charge exchangemore » losses in the divertor and reducing the electron temperature T et and deposited power density q dep at the target plate. Furthermore, the closed structure enables the divertor plasma to enter into highly dissipative and detached divertor conditions at a significantly lower upstream density. The effects of divertor closure on the neutral density and pressure, and their correlation with the divertor plasma conditions are also demonstrated. The effect of molecular D 2- ion D + elastic collisions and neutral-neutral collisions on the divertor plasma solution are assessed.« less
  • One of the major challenges facing the design and operation of next-step high-power steady-state fusion devices is to develop a divertor solution for handling power exhaust, while ensuring acceptable divertor target plate erosion, which necessitates access to divertor detachment at relative low main plasma densities compatible with current drive and high plasma confinement. Detailed modeling with SOLPS is carried out to examine the effect of divertor closure on detachment with the normal single null divertor (SD) configuration, as well as one of the advanced divertor configurations, such as x-divertor (XD) respectively. The SOLPS modeling for a high confinement plasma in DIII-D finds that increasing divertor closure with SD reduces the upstream separatrix density at the onset of detachment frommore » $$1.18\times {{10}^{19}}\,{{{\rm m}}^{-3}}$$ to $$0.88\times {{10}^{19}}\,{{{\rm m}}^{-3}}$$. Furthermore, coupling the divertor closure with XD further promotes the onset of divertor detachment at a still lower upstream separatrix density, down to the value of $$0.67\times {{10}^{19}}\,{{{\rm m}}^{-3}}$$, thus, showing that divertor closure and advanced magnetic configuration can work synergistically to facilitate divertor detachment.« less
  • This paper explores the physics of the recently installed Radiative Divertor Plasma divertor (RDP) in DIII-D through the use of UEDGE simulation with experimentally derived plasma parameters. The RDP is a nearly closed baffle and cryopumping system in the upper divertor of DIII-D. [l] One measure of the effectiveness of the RDP is the achievement of a detached plasma with a lower core density than in the open divertor (present in the lower divertor in DIII-D). Plasma detachment, observed on all diverted tokamaks, is a change in the plasma state which results in a decrease in both the ion currentmore » and heat load on the divertor plate. These reductions together with the related drop in electron temperature are important for divertor design in high power devices such as ITER, in which detached operation is assumed [2]. Both UEDGE modeling and DIII-D experiments show a reduction of 25% to 50% in the core density necessary for plasma detachment in the RDP compared to the open divertor.« less