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arXiv 2106.02790astro-ph.HEphysics.plasm-ph
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中等磁化天体物理对等离子体三维电流片演化中的重联和粒子加速

Reconnection and particle acceleration in 3D current sheet evolution in moderately-magnetized astrophysical pair plasma

Gregory R. Werner, Dmitri A. Uzdensky

摘要:

磁重联是一种将磁能转化为粒子动能的等离子体过程,常被用来解释脉冲星风星云和黑洞喷流等天体物理源中高能耀斑的磁能释放。重联通常被视为撕裂不稳定性破坏薄电流片的非线性演化(基本上是二维的)。为了测试这个过程在3D中是如何运作的,我们进行了一个全面的粒子模拟研究,比较了中等磁化、无碰撞、相对论热的电子-正电子等离子体中长而薄的电流片的2D和3D演化,并发现了巨大的差异。我们首先系统地描述了这个过程中的二维,经典的,分层的等离子体团链重连决定能量释放,并探讨了广泛的初始配置,引导磁场强度,和系统的大小。然后,我们表明,类似的配置的三维模拟表现出多样性的行为,包括一些能量释放是由非线性相对论漂移扭结不稳定性。因此,3D电流片的演变并不总是从根本上经典的重新连接与扰动的3D效果,而是一个复杂的相互作用的多个线性和非线性不稳定性,其相对重要性敏感地依赖于周围的等离子体,未成年人的配置细节,甚至随机事件。它通常产生比2D更慢但更持久的最终更大的磁能释放。有趣的是,非热粒子加速非常稳健,这取决于上游磁化和引导场,但在2D和3D中产生类似的粒子能量谱。虽然潜在的电流片行为的多样性是有趣的,但整体能量释放和粒子谱的相似性可能更显着。

英文摘要:

Magnetic reconnection, a plasma process converting magnetic energy to particle kinetic energy, is often invoked to explain magnetic energy releases powering high-energy flares in astrophysical sources including pulsar wind nebulae and black hole jets. Reconnection is usually seen as the (essentially 2D) nonlinear evolution of the tearing instability disrupting a thin current sheet. To test how this process operates in 3D, we conduct a comprehensive particle-in-cell simulation study comparing 2D and 3D evolution of long, thin current sheets in moderately-magnetized, collisionless, relativistically-hot electron-positron plasma, and find dramatic differences. We first systematically characterize this process in 2D, where classic, hierarchical plasmoid-chain reconnection determines energy release, and explore a wide range of initial configurations, guide magnetic field strengths, and system sizes. We then show that 3D simulations of similar configurations exhibit a diversity of behaviours, including some where energy release is determined by the nonlinear relativistic drift-kink instability. Thus, 3D current-sheet evolution is not always fundamentally classical reconnection with perturbing 3D effects, but, rather, a complex interplay of multiple linear and nonlinear instabilities whose relative importance depends sensitively on the ambient plasma, minor configuration details, and even stochastic events. It often yields slower but longer-lasting and ultimately greater magnetic energy release than in 2D. Intriguingly, nonthermal particle acceleration is astonishingly robust, depending on the upstream magnetization and guide field, but otherwise yielding similar particle energy spectra in 2D and 3D. Though the variety of underlying current-sheet behaviours is interesting, the similarities in overall energy release and particle spectra may be more remarkable.

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