Unveiling the Physics of High-Density Relativistic Pair Plasma Jets in the Laboratory

伽马射线暴（GRBs）是宇宙中能量最高的事件之一。它们发生在宇宙距离上，是大质量恒星坍缩或中子星合并的结果，伴随着电子-正电子对的相对论“火球”的发射。从天体物理观测中，我们已经收集到大量关于导致如此强烈辐射的机制的信息，领先的模型预测，这是由于光束在穿过周围等离子体时爆炸造成的。这会产生激波和流体磁乱流，产生同步加速器发射，潜在地加速到超高能量的质子，在地球上观测到的是宇宙射线。然而，没有直接证据表明伽马射线暴会产生磁场或宇宙射线。估计通常基于粗略的能量均分论证或理想化的数值模拟，难以捕捉到极端的等离子体条件。我们建议通过在CERN进行实验室实验来模拟射流通过其周围等离子体的传播来解决这一空白。这样的实验将使等离子体特性的原位测量成为可能，其精确的细节是其他地方无法实现的。这些实验还补充了数值模拟，提供了很长的测量时间，延伸到非线性区域，而目前数值模拟是不可能的。提出的实验将研究grb的基本物理过程，揭示grb的微观物理，并解决以下尚未回答的关键问题：1)什么机制驱动高能光束不稳定及其长期演化？2)在粒子加速到最高能量的过程中，湍流的作用是什么？3)磁场与粒子之间的相互作用是什么？这对观测到的电磁发射有何影响？我们将利用新颖的地球实验室实验为高能天体物理学提供一个新的窗口。

Gamma-ray bursts (GRBs) are among the most energetic events in the Universe. They occur at cosmological distances and are the result of the collapse of massive stars or neutron stars mergers, with emission of relativistic 'fireballs' of electron-positron pairs. From astrophysical observations, a wealth of information has been gleaned about the mechanism that leads to such strong emission of radiation, with leading models predicting that this is due to the disruption of the beam as it blasts through the surrounding plasma. This produces shocks and hydromagnetic turbulence that generate synchrotron emission, potentially accelerating to ultra-high energies the protons which are observedon Earth as cosmic rays. However, there is no direct evidence of the generation of either magnetic fields or cosmic rays by GRBs. Estimates are often based on crude energy equipartition arguments or idealized numerical simulations that struggle to capture the extreme plasma conditions. We propose to address this lacuna by conducting laboratory experiments at CERN to mimic the jet propagation through its surrounding plasma. Such experiments will enable in situ measurement of the plasma properties, with exquisite details that cannot be achieved elsewhere. The experiments also complement numerical simulations by providing long measurement times extending into the non-linear regime where numerical simulations are not possible today. The proposed experiments will study fundamental physics processes, unveil the microphysics of GRBs, and address the following, yet answered, key questions:1) What mechanisms drive the energetic beams unstable and their long-term evolution?2) What is the role of turbulence in the acceleration of particles to the highest energies?3) What is the interplay between magnetic fields and particles and how does this affect the observedelectromagnetic emission?We will provide a new window in high energy astrophysics using novel Earth-based laboratory experiments.