Title: Prediction of divertor heat flux width for ITER pre-fusion power operation using BOUT++ transport code

Abstract

Prediction of divertor heat flux width is performed for the first and the second pre-fusion power operation (PFPO) phases specified in the new ITER research plan using BOUT++ transport code (Li et al 2018 Comput. Phys. Commun.228 69–82). Here the initial plasma profiles inside the separatrix are taken from CORSICA scenario studies. Transport coefficients in transport code are calculated by inverting the plasma profiles inside the separatrix and are assumed to be constants in the scrape-off-layer. An anomalous thermal diffusivity scan is performed with E × B and magnetic drifts. The results in two scenarios identifying two distinct regimes: a drift-dominant regime when diffusivity is smaller than the respective critical thermal diffusivity χ_c and a turbulence-dominant regime when diffusivity is larger than it. The Goldston heuristic drift model and the ITPA multi-machine experimental scaling yield a lower limit of the width λ_q. From transport simulations, we obtain the critical thermal diffusivity χ_c = 0.5 m² s^–1 for the PFPO-1 scenario with toroidal magnetic field B = 1.77 T and plasma current I_p = 5 MA, and χ_c = 0.3 m² s^–1 for the PFPO-2 scenario with toroidal magnetic field B = 2.65 T and plasma current I_p = 7.5 MA. Separatrix temperature and collisionality also have a significant impact on the heat flux width in the drift-dominant regime. The investigation clearly yields a scaling for critical thermal diffusivity $${\chi }_{\text{c}}\propto {A}^{1/2}/(Z{\left(1+Z\right)}^{\frac{1}{2}}{B}_{\text{p}}^{2})$$ using ITER scenarios with fixed safety factor q₉₅, major radius R, aspect ratio R/a, and the separatrix temperature T_sep, and establishes the connection with CFETR and C-Mod discharges. This scaling implies that for a given tokamak device with q₉₅, R, R/a, and T_sep fixed, a reduction of poloidal magnetic field by a factor of 3 leads to a 9 times higher critical value of thermal diffusivity χ_c, possibly yielding a transition from turbulence- to drift-dominant regime.

Authors:

He, Xiaoxue X.  ^[1];

• Search DOE PAGES for author "He, Xiaoxue X."
• Search DOE PAGES for ORCID "0000-0001-8192-718X"

Xu, Xueqiao Q.  ^[2];

• Search DOE PAGES for author "Xu, Xueqiao Q."
• Search DOE PAGES for ORCID "0000-0003-1838-9790"

Li, Zeyu Y.  ^[3];

• Search DOE PAGES for author "Li, Zeyu Y."
• Search DOE PAGES for ORCID "0000-0003-3932-9244"

Zhu, Ben  ^[2];

• Search DOE PAGES for author "Zhu, Ben"
• Search DOE PAGES for ORCID "0000-0003-2225-045X"

Liu, Y. ^[4]

---

+ Show Author Affiliations

1. Dalian Univ. of Technology (China); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
3. Oak Ridge Associated Univ., Oak Ridge, TN (United States)
4. Dalian Univ. of Technology (China)

Publication Date:

Wed Mar 16 00:00:00 EDT 2022

Research Org.:

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA); Chinese Scholarship Council; National Key Research and Development Program of China

OSTI Identifier:

1872278

Report Number(s):

LLNL-JRNL-815224
Journal ID: ISSN 0029-5515; 1024415; TRN: US2306856

Grant/Contract Number:  

AC52-07NA27344; 201906060127; 2018YFE0303102

Resource Type:

Accepted Manuscript

Journal Name:

Nuclear Fusion

Additional Journal Information:

Journal Volume: 62; Journal Issue: 5; Journal ID: ISSN 0029-5515

Publisher:

IOP Science

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ITER; heat flux width; transport; drift