Configuration

An ebtel++ run is configured by a single XML configuration file. The table below lists all of the input parameters needed for a run. An example configuration file is included in the GitHub repository. The configuration file can be written manually or configured via Python as is done in the included examples.

Parameter	Type	Description
total_time	float	duration of the simulation (in s)
tau	float	timestep (in s); if using adaptive solver, the initial timestep
tau_max	float	maximum allowed timestep (in s) when using adaptive solver
loop_length	float	Loop half-length (in cm)
saturation_limit	float	Flux limiter, $f$ in section 2.1 of Barnes et al. (2016)
force_single_fluid	bool	if True, electron and ion populations forced into equilibrium
use_c1_loss_correction	bool	use correction in Eq. 16 of Cargill et al. (2012a)
use_c1_grav_correction	bool	use correction in Eq. 12 of Cargill et al. (2012a)
use_flux_limiting	bool	impose a flux limiter according to Eq. 22 of Klimchuk et al. (2008)
calculate_dem	bool	if True, do the TR and coronal DEM calculation; increases compute time significantly
save_terms	bool	if True, save heat flux, $c_1$ parameter, and radiative loss to a separate file <output_filename>.terms
use_adaptive_solver	bool	if True, use adaptive timestep; significantly smaller compute times. In both cases, a Runge-Kutta Cash-Karp integration method is used (see section 16.2 of Press et al. (1992))
output_filename	string	path to output file
adaptive_solver_error	float	Allowed truncation error in adaptive timestep routine
adaptive_solver_safety	float	Refinement factor, between 0 and 1, used if timestep becomes too large and solution contains NaNs. Especially important for short, infrequently heated loops. Also controls decreases in timestep due to thermal conduction timestep. Suggested value is 0.5
c1_cond0	float	Nominal value of $c_1$ during the conduction phase; see Appendix A of Barnes et al. (2016)
c1_rad0	float	Nominal value of $c_1$ during radiative phase; see Eq. 16 of Cargill et al. (2012a)
helium_to_hydrogen_ratio	float	Ratio of helium to hydrogen abundance; used in correction to ion mass, ion equation of state
surface_gravity	float	Surface gravity in units of solar surface gravity; should be set to 1.0 unless using for extra-solar cases

Heating

The time dependent heating is configured in a separate node. It includes the following parameters,

Parameter	Type	Description
partition	float	partition of heating between electrons and ions, between 0 and 1; 1 is pure electron heating, 0 pure ion heating
background	float	constant background heating (in ergs cm$^{-3}$ s$^{-1}$)

The heating function is constructed by a list of discrete events and should be specified in the following way,

<events>
  <event magnitude="0.1" rise_start="0.0" rise_end="50.0" decay_start="50.0" decay_end="100.0"/>
  <event magnitude="0.05" rise_start="1000.0" rise_end="1250.0" decay_start="1350.0" decay_end="1450.0"/>
</events>

Here, we've configured two separate heating events. The first starts at 0 seconds, rises linearly to a maximum heating rate of 0.1 erg cm$^{-3}$ s$^{-1}$ in 50 seconds, and then immediately falls off with the event concluding at 100 seconds, i.e. a triangular heating profile. The second starts at 1000 seconds, rises to a maximum heating rate of 0.05 erg cm$^{-3}$ s$^{-1}$ in 250 seconds, is sustained at 0.05 for 100 seconds and then the event concludes at 1450 seconds.

Using this format, it is easy to specify either symmetric or asymmetric events of many different shapes. For more examples, see the example configuration file or the included examples.

Differential Emission Measure

Optionally, ebtel++ can can also calculate the differential emission measure (DEM) in both the transition region and the corona. See sections 2.2 and 3 of Klimchuk et al. (2008) for the details of this calculation. To enable this calculation, set calculate_dem to True in the configuration file (as described above). Note that this will result in much longer computation times.

If calculate_dem is set to True, ebtel++ will read in the dem node from the configuration file which should be structured as follows,

<dem>
  <use_new_method>True</use_new_method>
  <temperature bins="451" log_min="4" log_max="8.5"/>
</dem>

If use_new_method is set to True (False), the transition region DEM is calculated using the method outlined in section 3 (the appendix) of Klimchuk et al. (2008). The temperature node configures the range and number of bins used when calculating the DEM. Here, for example, there are 450 bins of equal width between $10^4$ and $10^{8.5}$ K.

If you do not need to calculate the DEM, set the calculate_dem parameter to False and this section of the configuration file need not be included.

Output

Once the EBTEL run has finished, the results are printed to the file specified in output_filename in the configuration file (as described above). Several examples of how to parse the results in Python can be found here. In general, the results file follows the structure,

$t_0$	$T_e(t_0)$	$T_i(t_0)$	$n(t_0)$	$p_e(t_0)$	$p_i(t_0)$	$v(t_0)$	$h(t_0)$
...	...	...	...	...	...	...	...
$t_i$	$T_e(t_i)$	$T_i(t_i)$	$n(t_i)$	$p_e(t_i)$	$p_i(t_i)$	$v(t_i)$	$h(t_i)$
...	...	...	...	...	...	...	...
$t_{N-1}$	$T_e(t_{N-1})$	$T_i(t_{N-1})$	$n(t_{N-1})$	$p_e(t_{N-1})$	$p_i(t_{N-1})$	$v(t_{N-1})$	$h(t_{N-1})$

Here $t$ is the time, $T_e$ is the electron temperature, $T_i$ is the ion temperature, $p_e$ is the electron pressure, $p_i$ is the ion pressure, $n$ is the density, $v$ is the velocity, and $h$ is the heating rate.

If calculate_dem is set to True, the TR and coronal DEM results are printed to <output_filename>.dem_tr and <output_filename>.dem_corona, respectively. These output files are structured in the following way,

$T_0$	...	$T_j$	...	$T_{M-1}$
DEM$(t_0,T_0)$	...	DEM$(t_0,T_j)$	...	DEM$(t_0,T_{M-1})$
...	...	...	...	...
DEM$(t_i,T_0)$	...	DEM$(t_i,T_j)$	...	DEM$(t_i,T_{M-1})$
...	...	...	...	...
DEM$(t_{N-1},T_0)$	...	DEM$(t_{N-1},T_j)$	...	DEM$(t_{N-1},T_{M-1})$

where $M$ is the number of temperature bins and $N$ is again the number of timesteps.