Dr Ruth Bamford, RAL
K. J. Gibson2, A. J. Thornton2, J. Bradford1,
R. Bingham1,6, L. Gargate1,3, L.O. Silva3, R.A. Fonseca3,
M. Hapgood1, C. Norberg4, T. Todd5, R. Stamper1
1 Space Plasmas, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, UK
2 Department of Physics, University of York, Heslington, York,YO10 5DD, UK
3 Centro de Física dos Plasmas, Inst Superior Técnico, 1049-001 Lisboa, PORTUGAL
4 Umea University, Box 812, 981 28 Kiruna, SWEDEN.
5 UKAEA, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK
6 Physics Department, University of Strathclyde, Glasgow G4 0NG, UK
The physics behind the mini-magnetosphere spacecraft shield
Energetic ions in the solar wind plasma are a known hazard to both spacecraft electronics and to astronauts’ health. Of primary concern is the exposure to keV--MeV protons on manned space flights to the Moon and Mars that extend over long periods of time. Along with other approaches to protect spacecraft, like material barriers and biological inhibiters, there is the more exotic approach of considering some sort of “active shield” technology. Long thought of as impractical due the dimension involved (magnetic bubbles of > ion Larmor orbit or ~10 - 100km across) this has recently been determined to be a not be the case.
Here we describe an experiment to test the shielding concept of a dipole-like magnetic field and plasma, surrounding the spacecraft forming a “mini magnetosphere”. Initial laboratory experiments have been conducted to determine the effectiveness of a magnetized plasma barrier to be able to expel an impacting, low beta, supersonic flowing energetic plasma representing the Solar Wind. The laboratory device used was a co-axially, magnetically confined, linear plasma device whose primary purpose was as a tokamak divertor simulator.
Optical and Langmuir probe data of the plasma density, the plasma flow velocity, and the intensity of the dipole field clearly show the creation of a narrow transport barrier region and diamagnetic cavity virtually devoid of energetic plasma particles. This demonstrates the potential viability of being able to create a small “hole” in a Solar Wind plasma, of the order of the ion Larmor orbit width, in which an inhabited spacecraft could reside in relative safety. The experimental results have been quantitatively compared to a 3D particle-in-cell ‘hybrid’ code simulation that uses kinetic ions and fluid electrons, showing good qualitative agreement and excellent quantitative agreement. Together the results demonstrate the pivotal role of particle kinetics in determining generic plasma transport barriers. 
 R Bamford et al., “The interaction of a flowing plasma with a dipole magnetic field: measurements and modelling of a diamagnetic cavity relevant to spacecraft protection.” 2008 Plasma Phys. Control. Fusion 50 124025 (11pp) doi: 10.1088/0741-3335/50/12/124025