7th Asia-Pacific Conference on Plasma Physics, 12-17,11.2023, Nagoya, JapanLong Time-scale dynamics of E×B staircase in flux-driven gyro-kinetic
simulations under various heating conditions
Wei Wang1, Yasuaki Kishimoto2, Kenji Imadera2, Jiquan Li1, and Masatoshi Yagi3
Southwestern Institute of Physics, Chengdu 610041, China
Graduate School of Energy Science, Kyoto University, Uji, Kyoto 611-0011, Japan
3
National Institutes for Quantum Science and Technology, Aomori 039-3212, Japane-mail (speaker): wangwei@swip.ac.cn
1
2

In the L-mode plasmas of Tokamak devices, aquasi-regular and quasi-stationary shear flow
pattern, known as the “E×B staircase”, is observedin several recent experiments [1] and global gyrokinetic simulations [2]. This quasi-regular shear
flow structure is accompanied by isomorphic
temperature gradient corrugations, showing aquasi-stationary existence and is prominent when
the turbulence is near critical. Mechanisms for theformation and sustainment of E×B staircase arediscussed theoretically [3] and numerically [2].
However, characteristics and dynamics of E×Bstaircase in the confinement time scale 𝜏! , andthe dependence with different input powers arestill not fully understood. In this work, a set offlux-driven gyro-kinetic simulations with different
input powers are performed using GKNET code
under adiabatic electron approximation, theimpact of E×B staircase on turbulent transport,
and the long-time scale evolution of E×B staircase
coupled with local/global avalanches are discussed.

Staircase long time-scale dynamics withdifferent heat input configurations: In figure 1(a),radial profiles of E×B staircase with 4MW and16MW input power are shown. The spacing
between staircase shear layers is about 15~20𝜌" ,and almost constant under different input power.
Through the profile of temperature reversed scale
length (red lines), we also observed anincreasement of the mean gradient in the E×Bstaircase region (75𝜌" < 𝑟 < 150𝜌" ), while keeping
a similar level in the inner part ( 𝑟 < 75𝜌" ),indicates a stiffness phenomenon in the power
scan. A radially propagating type E×B staircase
structure is observed, for which the speed varies
depends on the input power. In the 4MW case,showing a quasi-stationary existence, i.e., a nearzero propagation velocity 𝑣#$% as seen in figure1(b-1). As input power increases to 16MW, thequasi-stationary staircase shows a radialpropagation, coupled with a slow time scale weakavalanches as seen in figure 1(b-2). The
propagation velocity can be estimated as𝑣&'$% ~0.25(𝜌" ⁄𝑅)𝑐( . This propagation is believed
to be caused by the background mean flow shear
which initialized from the radial force balance.
The higher input power will cause larger
temperature gradient and enhance the positive
shear in this region.

References:[1] Hornung G, et al., Nuclear Fusion 57 014006 (2017).
[2] Wang W, et al., Nuclear Fusion 58 056005 (2018).
[3] Yan Q, et al., Nuclear Fusion 62 126032 (2022)
Fig. 1. (a) Profiles of E×B staircase with 𝐸) field(blue lines) and reversed temperature scale length
𝑅/𝐿* (red lines), and time evolutions of (b) radial
electric field 𝐸) and (c) turbulent transport 𝑄+,)with 4MW input power (case 1) and 16MW input
power (case 2).