The confinement of energetic particles in nuclear fusion devices is studied in the presence of an oscillating radial electric field and an axisymmetric magnetic equilibrium. It is shown that, despite the poloidal and toroidal symmetries, initially integrable orbits turn into chaotic regions that can potentially intercept the wall of the tokamak, leading to particle losses. It is observed that the losses exhibit algebraic time decay different from the expected exponential decay characteristic of radial diffusive transport. A dynamical explanation of this behaviour is presented, within the continuous time random walk theory. The central point of the analysis is based on the fact that, contrary to the radial displacement, the poloidal angle is not bounded and a proper statistical analysis can therefore be made, showing for the first time that energetic particle transport can be super-diffusive in the poloidal direction and characterised by asymmetric poloidal displacement. The connection between poloidal and radial positions ensured by the conservation of the toroidal canonical momentum, implies that energetic particles spend statistically more time in the inner region of the tokamak than in the outer one, which explains the observed algebraic decay. This indicates that energetic particles might be efficiently slowed down by the thermal population before leaving the system. Also, the asymmetric transport reveals a new possible mechanism of self-generation of momentum.

中文翻译：

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聚变等离子体中存在振荡径向电场时高能粒子的异常损失

在存在振荡径向电场和轴对称磁平衡的情况下研究了核聚变装置中高能粒子的约束。结果表明，尽管极向和环形对称，但最初可积分的轨道会变成混沌区域，可能会拦截托卡马克壁，导致粒子损失。观察到损失表现出代数时间衰减，这与径向扩散传输的预期指数衰减特性不同。在连续时间随机游走理论中提出了这种行为的动态解释。分析的中心点是基于这样一个事实，即与径向位移相反，极向角是无界的，因此可以进行适当的统计分析，首次表明高能粒子传输可以在极向方向上具有超扩散性，并以不对称极向位移为特征。由环形正则动量守恒所保证的极向位置和径向位置之间的联系意味着高能粒子在托卡马克内部区域花费的时间比在外部区域要多，这解释了观察到的代数衰变。这表明高能粒子在离开系统之前可能会被热人口有效地减慢。此外，不对称输运揭示了一种新的自生动量机制。由环形正则动量守恒所保证的极向位置和径向位置之间的联系意味着高能粒子在托卡马克内部区域花费的时间比在外部区域要多，这解释了观察到的代数衰变。这表明高能粒子在离开系统之前可能会被热人口有效地减慢。此外，不对称输运揭示了一种新的自生动量机制。由环形正则动量守恒所保证的极向位置和径向位置之间的联系意味着高能粒子在托卡马克内部区域花费的时间比在外部区域要多，这解释了观察到的代数衰变。这表明高能粒子在离开系统之前可能会被热人口有效地减慢。此外，不对称输运揭示了一种新的自生动量机制。