The magnetic activity of the Sun directly impacts the Earth and human life. Likewise, other stars will have an impact on the habitability of planets orbiting these host stars. Although the magnetic field at the surface of the Sun is reasonably well characterised by observations, the information on the magnetic field in the higher atmospheric layers is mainly indirect. This lack of information hampers our progress in understanding solar magnetic activity. Overcoming this limitation would allow us to address four paramount long-standing questions: (1) How does the magnetic field couple the different layers of the atmosphere, and how does it transport energy? (2) How does the magnetic field structure, drive and interact with the plasma in the chromosphere and upper atmosphere? (3) How does the magnetic field destabilise the outer solar atmosphere and thus affect the interplanetary environment? (4) How do magnetic processes accelerate particles to high energies? New ground-breaking observations are needed to address these science questions. We suggest a suite of three instruments that far exceed current capabilities in terms of spatial resolution, light-gathering power, and polarimetric performance: (a) A large-aperture UV-to-IR telescope of the 1-3 m class aimed mainly to measure the magnetic field in the chromosphere by combining high spatial resolution and high sensitivity. (b) An extreme-UV-to-IR coronagraph that is designed to measure the large-scale magnetic field in the corona with an aperture of about 40 cm. (c) An extreme-UV imaging polarimeter based on a 30 cm telescope that combines high throughput in the extreme UV with polarimetry to connect the magnetic measurements of the other two instruments. Placed in a near-Earth orbit, the data downlink would be maximised, while a location at L4 or L5 would provide stereoscopic observations of the Sun in combination with Earth-based observatories. This mission to measure the magnetic field will finally unlock the driver of the dynamics in the outer solar atmosphere and thereby will greatly advance our understanding of the Sun and the heliosphere.

太阳的磁活动直接影响地球和人类生活。同样，其他恒星也会对围绕这些宿主恒星运行的行星的宜居性产生影响。虽然太阳表面的磁场可以通过观测得到合理的特征，但关于较高大气层磁场的信息主要是间接的。这种信息的缺乏阻碍了我们在了解太阳磁活动方面的进展。克服这一限制将使我们能够解决四个长期存在的重要问题：(1) 磁场如何耦合大气的不同层，以及它如何传输能量？(2) 磁场结构如何，驱动色球层和高层大气中的等离子体并与之相互作用？(3) 磁场如何破坏太阳外大气层的稳定，从而影响行星际环境？(4) 磁性过程如何将粒子加速到高能？需要新的突破性观察来解决这些科学问题。我们建议使用三种在空间分辨率、聚光能力和偏振性能方面远远超过当前能力的仪器：(a) 1-3 m 级大口径紫外到红外望远镜，主要旨在通过结合高空间分辨率和高灵敏度来测量色球中的磁场。(b) 一个极紫外到红外的日冕仪，旨在测量日冕中的大尺度磁场，孔径约为 40 厘米。(c) 基于 30 cm 望远镜的极紫外成像偏振计，它将极紫外的高通量与偏振测量相结合，以连接其他两个仪器的磁测量。放置在近地轨道上，数据下行链路将最大化，而位于 L4 或 L5 的位置将与地球观测站相结合，提供对太阳的立体观测。这项测量磁场的任务将最终解开太阳外大气层动力学的驱动力，从而极大地促进我们对太阳和日光层的理解。而位于 L4 或 L5 的位置将与地球观测站相结合，提供对太阳的立体观测。这项测量磁场的任务将最终解开太阳外大气层动力学的驱动力，从而极大地促进我们对太阳和日光层的理解。而位于 L4 或 L5 的位置将与地球观测站相结合，提供对太阳的立体观测。这项测量磁场的任务将最终解开太阳外大气层动力学的驱动力，从而极大地促进我们对太阳和日光层的理解。