Difference between alfven waves and magnetic fluctuations in solar corona I have read in this paper https://arxiv.org/abs/1911.07973 about particles being accelerated in the solar corona either by Alfven waves (to my understanding when the turbulence is weak) or by magnetic fluctuations (strong turbulence). Could someone explain the difference, please?
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...particles being accelerated in the solar corona either by Alfven waves (to my understanding when the turbulence is weak) or by magnetic fluctuations (strong turbulence)...

I do not think you realize just how complicated this question is, but it is extremely complicated (not a criticism, just a clarification).  The simplest explanation is that the wave has a well defined relationship between the frequency and wave number, called a dispersion relation, while the generic idea of turbulence does not.  Note this is not correct either because nuances cause overlap between both ideas (i.e., there is something called Alfvenic turbulence [will discuss below] in plasmas).  Typically, waves are radiated by instabilities while turbulence is driven by a cascade of energy from large-to-small scales.  Again, this is a gross over simplification but it's about all one can say without being too misleading or overly verbose.

Could someone explain the difference, please?

Not without belaboring several detailed points, but here's a superficial explanation.  There can be what is called Alfvenic turbulence (i.e., specific type of MHD turbulence) and there are also Alfven waves.  The former is generically driven by large-scale motions of the plasma that cascade to smaller scales through various processes eventually dissipating at small enough scales to directly couple to the plasma (called kinetic scales or the dissipation range).  The latter is driven by some sort of kinetic instability due to a free energy source (e.g., an ion/ion two-stream instability).  The waves and turbulence can be similar and share properties but the fundamental difference is their source.  Further, the turbulence version tends to be characterized by a broad spectrum in wave number whereas the wave form tends to be focused in wave number and frequency (again, gross over simplification).
