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Stability of the trapped electron mode in steep density and temperature gradients

机译:在陡峭的密度和温度梯度下,俘获电子模式的稳定性

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The stability of the trapped electron mode is studied in conditions characteristic of internal transport barriers, namely steep density and temperature gradients. An analytic model allows a unified treatment of all collisionality regimes, from the dissipative limit to the weakly collisional regime ( when the velocity space boundary layer between passing and trapped populations of electrons plays a role). Furthermore, it reveals the key parametric dependences on wavelength, collisionality and eta(e) = d(ln T-e)/d(ln n(e)). The roles of shear damping and Landau-drift resonance are also discussed. The main outcome is that below a critical collisionality, defined by the parameter (nu) over cap = nu L-the(n)/upsilon(thi) (where the is the thermal electron collision frequency, L-n the density scale length and upsilon(thi) the ion thermal speed), there is strong stabilization of long wavelength modes, so the unstable spectrum may be restricted to shorter wavelengths as the collisionality falls and the density profile steepens. The predicted critical value of (nu) over cap is experimentally relevant and this theory suggests a mechanism for barrier formation.
机译:在内部传输势垒的特征条件下,即陡峭的密度和温度梯度,研究了俘获电子模式的稳定性。一个解析模型可以统一处理从耗散极限到弱碰撞状态(当在通过和被捕获的电子之间的速度空间边界层起作用时)的所有碰撞状态。此外,它揭示了关键参数对波长,碰撞性和eta(e)= d(ln T-e)/ d(ln n(e))的依赖性。还讨论了剪切阻尼和Landau漂移共振的作用。主要结果是,在临界碰撞能力以下,由cap上的参数(nu)定义为nu L-the(n)/ upsilon(thi)(其中,为热电子碰撞频率,Ln为密度标度长度和upsilon(离子热速度),长波长模式具有很强的稳定性,因此当碰撞性降低且密度分布变陡时,不稳定的光谱可能会限制在较短的波长上。 (nu)上限的预测临界值与实验相关,并且该理论提出了形成壁垒的机制。

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