Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: MMS direct observations of kinetic-scale shock self-reformation   Studies of shocks have long suggested that a shock can undergo cyclically
self-reformation in a time scale of ion cyclotron period. This process has been
proposed as a primary mechanism for energy dissipation and energetic particle
acceleration at shocks. Unambiguous observational evidence, however, has
remained elusive. Here, we report direct observations for the self-reformation
process of a collisionless, high Mach number, quasi-perpendicular shock using
MMS measurements. We find that reflected ions by the old shock ramp form a
clear phase-space vortex, which gives rise to a new ramp. The new ramp observed
by MMS2 has not yet developed to a mature stage during the self-reformation,
and is not strong enough to reflect incident ions. Consequently, these ions are
only slightly slowed down and show a flat velocity profile from the new ramp
all the way to the old one. The present results provide direct evidence for
shock self-reformation, and also shed light on energy dissipation and energetic
particle acceleration at collisionless shocks throughout the universe.

33
The categories of this paper are: plasm-ph
19
The categories of this paper are: eess
24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
11
The categories of this paper are: hep-lat
31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
16
The categories of this paper are: stat