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The plasma flow generated by turbulent nonlinear interaction can improve plasma confinement by suppressing turbulence and its driven transport. Turbulence can be driven by local gradients and propagate radially from far beyond its relevant length. Effects of electron cyclotron resonance heating (ECRH) modulation on edge turbulence driving and spreading are observed for the first time in the edge plasma of the HL-2A tokamak. These experiments are performed by a fast reciprocating Langmuir probe array. When ECRH modulation is applied, both the edge temperature and the edge plasma density are higher, and the radial electric field is stronger. The edge radial electric field, turbulence, and Reynolds stresses are all enhanced when the ECRH is applied, while the ion-ion collision rate is reduced. Figures (a)－(g) show the conditional averages of the ECRH power, turbulence intensity, turbulent Reynolds stress gradient, $ {\boldsymbol{E}}_{r}\times \boldsymbol{B} $ poloidal velocity, density gradient, turbulence drive rate and turbulence spreading rate, respectively. With ECRH applied, both the turbulence intensity and the Reynolds stress gradients increase. The maximum turbulence intensity appears at the beginning of the ECRH switch-off while the maximum stress gradient occurs at the end of the ECRH. The evolution of the $ {\boldsymbol{E}}_{r}\times \boldsymbol{B} $ poloidal velocity is very similar to that of the Reynolds stress gradient. This observation suggests that the poloidal flow is the result of the combined effect of turbulence nonlinear driving and damping. The enhancement of Reynolds stress during ECRH modulation mainly depends on the increase of the turbulence intensity, with the increase in radial velocity fluctuation intensity being more significant. The turbulence drive and spreading rates also increase with ECRH. The maximum drive rate appears at the beginning of the ECRH switch-off, while the maximum spreading rate occurs at the end of the ECRH. This analysis indicates that turbulence driving and spreading are enhanced, with the former being dominant. This result suggests that the enhancements of turbulence driving and spreading lead the turbulence and Reynolds stress to increase, and thus producing the stronger edge flows.
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Keywords:
- tokamak /
- electron cyclotron resonance heating modulation /
- edge flow and turbulence /
- Langmuir probes
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图 1 双台阶静电探针结构图
Figure 1. Structure of two-step electrostatic probe array.
图 2 等离子体参数的时间演化 (a) ECRH功率; (b)环向磁场强度$ {B}_{{\mathrm{t}}}; $ (c)等离子体电流$ {I}_{{\mathrm{p}}}; $ (d)线平均电子密度$ \left\langle{{N}_{{\mathrm{e}}}}\right\rangle; $ (e)探针位移
Figure 2. Time evolutions of plasma parameters: (a) ECRH power, (b) toroidal magnetic field $ {B}_{{\mathrm{t}}} $, (c) plasma current $ {I}_{{\mathrm{p}}} $, (d) line-averaged electronic density $ \left\langle{{N}_{{\mathrm{e}}}}\right\rangle $; (e) probe displacement.
图 3 边缘等离子体参数的时间演化 (a) ECRH功率; (b)温度; (c)密度; (d)悬浮电位; (e)离子饱和电流
Figure 3. Time evolutions of edge plasma parameters: (a) ECRH power; (b) temperature; (c) density; (d) floating potential; (e) ion saturation current.
图 4 有无ECRH调制的(a)温度, (b)密度和(c)径向电场的径向分布
Figure 4. The radial profiles of (a) temperature, (b) density, and (c) radial electric field with and without ECRH modulation.
图 5 (a) ECRH功率, (b)压强梯度$ {\nabla P}_{{\mathrm{e}}}/{en}_{{\mathrm{e}}}{Z}_{{\mathrm{i}}} $和(c)极向流$ -{v}_{{\mathrm{\theta }}}{B}_{{\mathrm{t}}} $贡献的径向电场, (d)径向电场$ {E}_{{\mathrm{r}}} $, (e)悬浮电位涨落(虚线)以及其时频图和(f)离子-离子碰撞率的时间演化
Figure 5. Time evolutions of (a) ECRH power, contributions of (b) pressure gradient $ {\nabla P}_{{\mathrm{e}}}/({en}_{{\mathrm{e}}}{Z}_{{\mathrm{i}}}) $ and (c) poloidal flows ($ -{v}_{{\mathrm{\theta }}}{B}_{{\mathrm{t}}} $) to the radial electric field, (d) radial electric field, (e) floating potential fluctuation (dash line) and its spectrogram and (e) ion-ion collision rate.
图 6 (a) ECRH功率, (b)湍流雷诺协强及其(c)梯度和(d) $ {\boldsymbol{E}}_{r}\times \boldsymbol{B} $极向速度的变化的条件平均
Figure 6. Conditional averages of (a) ECRH power, (b) Reynolds stress and (c) its gradient, and (d) $ {\boldsymbol{E}}_{r}\times \boldsymbol{B} $ poloidal velocity.
图 7 (a) ECRH功率, (b)雷诺协强(Rs), (c)极向速度涨落, (d)径向速度涨落, 径向和极向速度涨落的(e)相位差, 及其(f)相关系数的条件平均
Figure 7. Conditional averages of (a) ECRH power, (b) Reynolds stress (Rs) , (c) poloidal velocity fluctuation, (d) radial velocity fluctuation, (e) the phase difference between the radial and poloidal velocity fluctuations, and (f) their coherencies.
图 8 (a) ECRH功率, (b)密度的梯度, (c)湍流驱动的通量, (d)湍流驱动率($ {\omega }_{{\mathrm{D}}} $), (e)湍流传播率($ {\omega }_{{\mathrm{s}}} $), (f)湍流传播的通量和(g)密度涨落的平方的变化的条件平均
Figure 8. Conditional averages of (a) ECRH power, (b) density gradient, (c) turbulent driven flux, (d) turbulence drive $ {\mathrm{r}}{\mathrm{a}}{\mathrm{t}}{\mathrm{e}}\left({\omega }_{{\mathrm{D}}}\right) $, (e) turbulence spreading $ {\mathrm{r}}{\mathrm{a}}{\mathrm{t}}{\mathrm{e}}\left({\omega }_{{\mathrm{s}}}\right) $, (f) turbulent spreading flux, and (g) square of fluctuation intensity.
图 9 (a) ECRH功率, (b)粒子输运速度和(c)湍流传播平均射流度的变化的条件平均
Figure 9. Conditional averages of (a) ECRH power, (b) particle transport velocity, (c) and mean jet velocity of turbulence spreading.
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