https://phys.org/news/2018-11-magnetic-fields-deep-space-wiggle.html

Past research has focused on dynamos as they might occur in so-called collisional plasmas, in which particles collectively behave as a fluid. But intergalactic plasmas are collisionless, so past experiments are not necessarily relevant. This new research is meant to address that gap. "We wanted to see how the dynamo would behave in the collisionless regime," said Denis St-Onge, graduate student in the Princeton Program in Plasma Physics at PPPL and lead author of the paper.

St-Onge and Kunz focused on the ways in which the velocities and magnetic fields of individual particles within collisionless plasma are directly linked. This linkage—if one quantity increases or decreases, the other must, too—would seem to rule out the existence of a dynamo. "If this were the whole story, it would be disastrous for the dynamo," said St-Onge. "To match what we observe in space, the dynamo would have to increase the strength of the seed magnetic field by at least a factor of one trillion, but the energy of the particles would also have to increase, and there's just not enough available energy in the dynamo for that to happen."