Modify Rates

It is natural to ask how the value of a particular reaction rate governs the results of a network calculation. This may be done via the –rate_mod option. To understand how this works, vary \((\alpha, \gamma)\) reaction rates from their values in the network data file.

Use a response file and a script. Choose a calculation similar to the default calculation but use an initial density of \(10^7\) g/cc. Thus, create a response file alpha_mod.rsp with the lines:

--t9_0 10 --tau 0.1 --rho_0 1.e7
--network_xml ../nucnet-tools-code/data_pub/my_net.xml
--nuc_xpath "[z <= 30]"
--iterative_solver gmres
--iterative_t9 2
--init_mass_frac "{h1; 0.5}" "{n; 0.5}"
--xml_steps 5
--t_end 10

You can create that file directly, download it from OSF, or type:

$ curl -o alpha_mod.rsp -J -L https://osf.io/snby3/download

Now create a script run_mod.sh with the lines:

./single_zone_network @alpha_mod.rsp --output_xml out_ref.xml
./single_zone_network @alpha_mod.rsp --rate_mod "{[(z = 2 and a = 4) or (z >= 10 and z <= 20)]; [reactant = 'he4' and product = 'gamma']; 10}" --output_xml out_mod.xml

As with the response file, you can create this file directly, download it from OSF, or type:

$ curl -o run_mod.sh -J -L https://osf.io/b25es/download

The first line is for the reference calculation that uses the default network data. The second line uses XPath to increase \((\alpha, \gamma)\) reaction rates (uniformly at all temperatures) on nuclear species in the subnetwork between Ne and Ca isotopes. The modification is entered as a triplet consisting of a nuclear XPath expression to choose the subnetwork, a reaction XPath to choose the reaction(s) to modify, and the factor by which to multiply the rate(s) at each temperature.

Make the script executable and run it:

$ chmod +x run_mod.sh
$ ./run_mod.sh

When the code runs with the modified rates, it first prints out the modification view, which shows the reactions whose rates are to be modified and the modification factor.

Check the effect of the rate modifications by typing in Python, for example:

>>> import wnutils.multi_xml as wm
>>> mx = wm.Multi_Xml(['out_ref.xml', 'out_mod.xml'])
>>> p_params = [{'label': 'Reference'}, {'label': 'Modified Rates'}]
>>> mx.plot_mass_fraction_vs_property('time', 'si28', xlabel = 'time (s)', xlim = [0,1], plotParams = p_params, use_latex_names=True, yscale = 'log', ylim = [1.e-10,1.e-2])

It is possible to have multiple modification views. To modify the \((\alpha, \gamma)\) rates, as above, and the rate for the triple-alpha reaction at the same time, type:

$ ./single_zone_network @alpha_mod.rsp --rate_mod "{[(z = 2 and a = 4) or (z >= 10 and z <= 20)]; [reactant = 'he4' and product = 'gamma']; 10}" "{[.]; [(count(reactant[.='he4']) = 3) and product = 'gamma']; 10}" --output_xml out_mod2.xml

The [.] selects all species, but the only reaction whose rate will be modified is he4 + he4 + he4 -> c12 + gamma, as verified in modification view 1. You can add the results of this calculation to your previous plot.

It is possible to have as many modification views as you want, although you will need to choose the views judiciously to explore the governing role of particular reaction rates.