ABSTRACT
The Sun is a particle accelerator par excellence. Not only does it generate the solar wind which is the driving force for particle acceleration in and around the Earth’s and other planetary magnetospheres, but it produces in the explosive events known as solar flares [224, 225] copious numbers of electrons, protons and heavier particles up to the ultra-relativistic energies which classify the Sun as a cosmic-ray source, albeit a relatively minor one. There are seemingly insuperable difficulties, though, in trying to investigate its workings. Due to the hostile environment of the Sun’s outer atmosphere, or corona, where much of the acceleration is thought to take place, there are, as yet, no direct measurements of either sources or immediate products. Neither are there measurements of the electric and magnetic fields which create one from the other. Enough is known, though, from indirect measurements made from the Earth’s environment and from deep-space probes to make a tantalising and intriguing puzzle.
