clusters/halo: Rewrite turbulence acceleration & diffusion coefficient!

The previous calculation of the turbulence acceleration efficiency has
significant problems, which is too low, i.e., the acceleration timescale is
too large (~10 Gyr).  However, it is reported that turbulent acceleration has
a timescale ~100 Myr (0.1 Gyr).  I believe this problem is due to the
over-simplification to the formula proposed by [cassano2005].

Rewrite the turbulence acceleration and diffusion coefficient calculations,
adopting the method proposed by [brunetti2016].  To this end, two new options
"f_lturb" and "f_acc" are introduced to tune the results.

1 files changed, 12 insertions, 2 deletions

diff --git a/fg21sim/configs/20-extragalactic.conf.spec b/fg21sim/configs/20-extragalactic.conf.spec
index 75ea0ec..32311a0 100644
--- a/fg21sim/configs/20-extragalactic.conf.spec
+++ b/fg21sim/configs/20-extragalactic.conf.spec
@@ -132,8 +132,18 @@
 
   # Giant radio halos for clusters with recent major mergers
   [[halos]]
-  # Roughly the fraction of turbulence energy transformed to accelerate
-  # the electrons, describing the efficiency of turbulence acceleration.
+  # The turbulence is generally injected at the cluster center during
+  # a merger.  This option parameterize the turbulence injection scale
+  # to be a fraction of the virial radius of the (main) cluster.
+  f_lturb = float(default=0.5, min=0.1, max=1.0)
+
+  # The custom option to tune the turbulent acceleration timescale, which
+  # controls the relativistic particle acceleration efficiencies.
+  f_acc = float(default=1.5, min=0.1, max=10)
+
+  # The fraction of cluster thermal energy originating from turbulent
+  # dissipation, which describes the turbulence intensity in the ICM,
+  # and determines its Mach number.
   eta_turb = float(default=0.2, min=0.1, max=1.0)
 
   # Ratio of the total energy injected into cosmic-ray electrons during