Positron Injection into a Magnetic Dipole Field for the Study of an Electron-Positron Plasma

在这个项目中，我们计划产生一个低能量，高亮度的正电子束，并将其用于第一次创建电子-正电子等离子体。与常规等离子体相比，预期该等离子体具有独特的性质，例如基本上无毒性。与电子-离子等离子体相比，这种独特性源于精确的质量对称性。一种新的磁场配置将被用来限制等离子体，即磁偶极子陷阱。粒子湮灭损失预计是足够低，允许长的约束时间，仍然足够高的湮灭可以用作等离子体诊断。然而，到目前为止，地球上还没有产生这样的等离子体。我们将利用两种最先进的技术来克服受控对等离子体研究中的两个主要瓶颈：正电子数量不足和约束不足。第一申请人在加尔兴FRM II研究反应堆上开发的NEPOMUC束线是一个独特的装置，用于利用核俘获反应产生高强度正电子束。NEPOMUC是目前世界上最强的慢正电子源。近年来，第二个申请人已经证明了悬浮超导电流回路的场对中性和非中性等离子体的良好限制。在本项目中，我们计划采取产生成对等离子体的道路上的最后一步，即将正电子束注入限制区域，并计划对成功注入后形成的等离子体进行首次研究。作为一个先决条件，我们将开发提取的正电子从NEPOMUC源在低直流偏置，以产生一个低能量的正电子束适合注入。对于注入，使用偏转板在闭合轨道上诱导ExB漂移的策略将与“旋转墙”状AC场相结合，以稳定随后的正电子轨道。另一种用于正电子注入的方法将通过在ExB过滤器之后立即使用钨单晶进行正电子再慢化来进行。这种方法将使我们能够很容易地将初级正电子束和亮度增强的再减速正电子束分离，以探索更有效地注入偶极场的潜力。

Within this project we plan to produce a low-energy, high-brightness positron beam and to use it for the first creation of an electron-positron plasma. This plasma is expected to have unique properties compared to conventional plasmas, for example to be essentially turbulence-free. The uniqueness stems from the exact mass symmetry, in contrast to electron-ion plasmas. A novel magnetic field configuration will be used to confine the plasma, namely a magnetic dipole trap. Particle losses by annihilation are predicted to be sufficiently low to allow long confinement times, and still high enough that the annihilations can be used as a plasma diagnostic. Yet, up to now, no such plasma has been produced on Earth. We will exploit two state-of-the-art technologies to overcome the two main bottlenecks in the study of controlled pair plasmas: Insufficient number of positrons, and insufficient confinement. The NEPOMUC beamline at the FRM II research reactor in Garching, developed by the first applicant, is a unique device for the production of high-intensity positron beams using a nuclear capture reaction. NEPOMUC is currently the most intense source of slow positrons in the world. Excellent confinement of both neutral and non-neutral plasmas by the field of a levitated, superconducting current loop has in recent years been demonstrated by the second applicant.In this project, we plan to take the last missing step on the path to production of a pair plasma, namely the injection of the positron beam into the confinement region, and plan to carry out first studies of a plasma formed after successful injection. As a prerequisite, we will develop the extraction of positrons from the NEPOMUC source at a low DC bias in order to generate a low-energy positron beam suitable for injection. For injection, a strategy using deflection plates to induce ExB drifts on closed orbits will be combined with a 'rotating wall'-like AC field to stabilize the ensuing positron orbits. An alternative approach for positron injection will be carried out by using a tungsten single crystal for positron re-moderation immediately after the ExB filter. This method would allow us to easily separate the primary positron beam and the brightness enhanced remoderated positron beam in order to explore the potential for more efficient injection into the dipole field.