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

在这个项目中，我们计划生产一种低能量、高亮度的正电子束，并将其用于第一次创造电子-正电子等离子体。与传统的等离子体相比，这种等离子体有望具有独特的性质，例如基本上是无湍流的。这种独特性源于与电子-离子等离子体不同的精确的质量对称性。一种新的磁场结构将被用来限制等离子体，即磁偶极子陷阱。据预测，粒子湮灭造成的损失将足够低，以允许长时间的限制时间，并且仍然足够高，可以用来作为等离子体诊断。然而，到目前为止，地球上还没有产生过这样的等离子体。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：正电子数量不足和限制不足。Garching FRM II研究反应堆的NEPOMUC光束线由第一个申请者开发，是利用核俘获反应生产高强度正电子束的独特装置。NEPOMUC是目前世界上最强烈的慢正电子源。近些年来，第二个应用证明了悬浮的超导电流环场对中性和非中性等离子体的良好限制。在这个项目中，我们计划在产生一对等离子体的道路上采取最后一个缺失的步骤，即将正电子束注入到限制区域，并计划对成功注入后形成的等离子体进行第一次研究。作为先决条件，我们将发展在低直流偏压下从NEPOMUC源中提取正电子，以便产生适合注入的低能正电子束。对于注入，一种使用偏转板在封闭轨道上诱导ExB漂移的策略将与类似旋转墙的交流磁场相结合，以稳定随后的正电子轨道。正电子注入的另一种方法是在ExB滤光片之后立即使用钨单晶进行正电子再慢化。这种方法将使我们能够很容易地分离初级正电子束和亮度增强的再增强正电子束，以便探索更有效地注入偶极场的可能性。

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.