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In weakly collisional astrophysical plasmas, such as the intracluster mediumof galaxy clusters, the amplification of cosmic magnetic fields by chaoticfluid motions is hampered by the adiabatic production of magnetic-field-alignedpressure anisotropy. This anisotropy drives a viscous stress parallel to thefield that inhibits the plasma's ability to stretch magnetic-field lines. Idemonstrate through the use of kinetic simulations that in high-$\beta$plasmas, kinetic ion-Larmor scale instabilities sever the adiabatic linkbetween the thermal and magnetic pressures, reducing this viscous stress andthereby allowing the dynamo to operate. Two distinct regimes of the fluctuationdynamo in a magnetized plasma are identified: one in which these instabilitiesefficiently regulate the pressure anisotropy and one in which this regulationis imperfect. I elucidate the role of these kinetic instabilities on the plasmaviscosity and determine how the fields and flows self-organize to allow thedynamo to operate in the face of parallel viscous stresses. In the case ofefficient pressure-anisotropy regulation, the plasma dynamo closely resemblesits more traditional Pm ~ 1 MHD counterpart. When the regulation is imperfect,the dynamo exhibits characteristics remarkably similar to those found in thesaturated state of the MHD dynamo. A novel set of microphysical closures forfluid simulations that bridges these two regimes are constructed, exhibitingexplosive magnetic-field growth caused by a field-strength-dependent viscosity.The dynamos in both collisionless and weakly collisional plasmas are thenclosely compared to each other, revealing substantial differences in howsub-parallel viscous motions behave. The former (collisionless) scenarioexperiences a cascade of stretching motions to sub-Larmor scales that lead toincreasingly fast dynamo as the magnetic Reynolds number is increased.

Fluctuation Dynamo in Collisionless and Weakly Collisional Magnetized Plasmas