AUTHOR=Allanson Oliver , Ma Donglai , Osmane Adnane , Albert Jay M. , Bortnik Jacob , Watt Clare E. J. , Chapman Sandra C. , Spencer Joseph , Ratliff Daniel J. , Meredith Nigel P. , Elsden Thomas , Neukirch Thomas , Hartley David P. , Black Rachel , Watkins Nicholas W. , Elvidge Sean 

TITLE=The challenge to understand the zoo of particle transport regimes during resonant wave-particle interactions for given survey-mode wave spectra

JOURNAL=Frontiers in Astronomy and Space Sciences

VOLUME=Volume 11 - 2024

YEAR=2024

URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2024.1332931

DOI=10.3389/fspas.2024.1332931

ISSN=2296-987X

ABSTRACT=Quasilinear theories have been shown to well describe a range of transport phenomena in magnetospheric, space, astrophysical and laboratory plasma `weak turbulence' scenarios. It is well known that the resonant diffusion quasilinear theory for the case of a uniform background field may formally describe particle dynamics when the electromagnetic wave amplitude and growth rates are sufficiently `small', and the bandwidth is sufficiently `large'. However, it is important to note that for a given wave spectrum that would be expected to give rise to quasilinear transport, the quasilinear theory may indeed apply for given range of resonant pitch-angles and energies, but may not apply for some smaller, or larger, values of resonant pitch-angle and energy. That is to say that the applicability of the quasilinear theory can be pitch-angle dependent, even in the case of a uniform background magnetic field. If indeed the quasilinear theory does apply, the motion of particles with different pitch-angles are still characterised by different timescales. Using a high-performance test-particle code, we present a detailed analysis of the applicability of quasilinear theory to a range of different wave spectra that would otherwise `appear quasilinear' if presented by e.g. satellite survey-mode data. We present these analyses as a function of wave amplitude, wave coherence and resonant particle velocities (energies and pitch-angles), and contextualise the results using theory of resonant overlap and small amplitude criteria. In doing so, we identify and classify 5 different transport regimes that are a function of particle pitch-angle. The results in our paper demonstrate that there can be a significant variety of particle responses (as a function of pitch-angle) for very similar looking survey-mode electromagnetic wave products, even if they appear to satisfy all appropriate quasilinear criteria. In recent years there have been a sequence of very interesting and important results in this domain, and we argue in favour of continuing efforts on: (i) the development of new transport theories to understand the importance of these, and other, diverse electron responses; (ii) which are informed by statistical analyses of the relationship between burst- and survey-mode spacecraft data.