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Recent works have shown that strongly magnetized plasmas characterized by having a gyrofrequency greater than the plasma frequency exhibit novel transport properties. One example is that the friction force on a test charge shifts, obtaining components perpendicular to its velocity in addition to the typical stopping power component antiparallel to its velocity. Here, we apply a recent generalization of the Boltzmann equation for strongly magnetized plasmas to calculate the ion–electron temperature relaxation rate. Strong magnetization is generally found to increase the temperature relaxation rate perpendicular to the magnetic field and to cause the temperatures parallel and perpendicular to the magnetic field to not relax at equal rates. This, in turn, causes a temperature anisotropy to develop during the equilibration. Strong magnetization also breaks the symmetry of independence of the sign of the charges of the interacting particles on the collision rate, commonly known as the “Barkas effect.” It is found that the combination of oppositely charged interaction and strong magnetization causes the ion–electron parallel temperature relaxation rate to be significantly suppressed, scaling inversely proportional to the magnetic field strength.
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Model for temperature anisotropy relaxation in non-neutral plasmas
Non-neutral plasma experiments are excellent benchmarks for validating transport models, including in strongly coupled conditions. Experiments with Penning–Malmberg traps operate under the Brillouin limit, which means that the plasma is also strongly magnetized in the sense that the gyrofrequency exceeds the plasma frequency. This is an unusual regime that is not described by traditional plasma kinetic theory, particularly when strong coupling and strong magnetization are both present. Here, we apply a recently developed generalized Boltzmann kinetic theory to compute the temperature anisotropy relaxation rate in this regime. Strong magnetization is found to severely suppress energy exchange during collisions, leading to a drastically reduced anisotropy relaxation rate. The results exhibit good agreement with previous work by Glinsky et al. when the plasma is weakly coupled and extend the calculation to the strongly coupled regime as well. Results are compared with published experimental measurements, demonstrating good agreement. Furthermore, the model is tested using molecular dynamics simulations over a broader range of parameters than the experiments reached. These simulations utilize a new Green–Kubo relation, enabling an equilibrium simulation method that is more accurate than previous non-equilibrium methods that have been applied to this problem. Finally, a discussion of detailed balance in strongly magnetized plasmas is provided. Specifically, it is shown that despite the absence of time-reversal symmetry, which is usually used to mathematically prove detailed balance, the results satisfy detailed balance to a high degree of numerical precision.
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- Award ID(s):
- 2205506
- PAR ID:
- 10613456
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- Physics of Plasmas
- Volume:
- 32
- Issue:
- 7
- ISSN:
- 1070-664X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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