To use AMTS integrator in OPAL-T, add the attribute-value pair TIMEINTEGRATOR="AMTS" to the
TRACK element. Another attribute DTSCINIT on the same element controls the initial time step (in
seconds) used for space charge. The multiple time stepping scheme uses an outer time step for space
charge integration, and inner time steps for basic integration. The inner steps are roughly constant
and equal to the value specified with the DT attribute. The outer step can change freely if space
charge forces change their magnitude. Example of a TRACK command where a reduced space charge solve
frequency is used:

    track,line=IW2Line, beam=beam1, MAXSTEPS=56000, DTSCINIT=5.0e-10, DT=1.0e-11, ZSTOP=100.0, TIMEINTEGRATOR="AMTS";

AMTS does not (and will probably never) support emission simulation. In such a case, use a short
track with the default integrator (MAXSTEPS set such that emission is just finished) and use AMTS in
the follow-up track.

AMTS does not yet support boundary geometry, wake fields, surface physics. This should be possible
to add without problems, and the only reason it is not supported yet is that it made the initial
implementation shorter.

As the (outer) time step size is no more constant, some question arises how this is handled. AMTS
makes a statistics (.stat) and phase space (.h5) dump at the same times when the default integrator
would have done it. Therefore, AMTS dumps at multiple of times DT * STATDUMPFREQ and DT * PSDUMPFREQ.
To reach these times exactly, the variable step size is shortened if necessary. Be careful to not
set the *DUMPFREQ-numbers too low, as this limits the freedom of AMTS' step size choice. AMTS stops
exactly at time DT * MAXSTEPS, or after ZSTOP has been crossed. Repartitioning happens if the last
repartitioning is at least DT * REPARTFREQ in the past (here no extra stop is made to
reach the old repartitioning times exactly).

As said earlier, AMTS can save time in many simulations where a reduced space charge solve frequency
is still enough precise. For gun simulations, an initial high space charge solve frequency can be
used, as it is lowered automatically when space charge forces decrease in magnitude.

Later, we can put AMTS into user guide.