Reaction Networks
Summary of available nets
This is an incomplete summary of the nets included for use with
mesa/net. See $MESA_DIR/data/net_data/nets
for the full list.
This lists the isotopes that are included in each net, but not the
reactions. To check on those, it is best to have the code list them .
In mesa/star you can do this by setting the star_job options
show_net_reactions_info = .true.
; similarly, you can get a list of
the isotopes by setting show_net_species_info = .true.
.
“no frills” hydrogen and helium burning
- basic
h1, he3, he4, c12, n14, o16, ne20, mg24
Assumes T is low enough so can ignore advanced burning and hot cno issues.
more complete coverage for hydrogen and helium burning
- c13
basic + c13
- o18_and_ne22
basic + o18 and ne22
- o18_to_mg26
o18_and_ne22 + mg26
- hot_cno
basic + c13, n13, n15, o15, o17, o18, f17, f18
for high temperatures where cno becomes beta limited.
- cno_extras
hot_cno + o14, f19, ne18, ne19, mg22
for high temperatures where start to breakout of hot cno.
- pp_and_cno_extras
pp_extras + cno_extras
- pp_cno_extras_o18_ne22
pp_and_cno_extras + o18_and_ne22
extensions of the basic net for C/O burning and alpha chains
- co_burn
basic + si28
- alpha_s32
co_burn + s32
- alpha_ar36
alpha_s32 + ar36
- alpha_ca40
alpha_ar36 + ca40
- alpha_ti44
alpha_ca40 + ti44
- alpha_cr48
alpha_ti44 + cr48
- alpha_fe52
alpha_cr48 + fe52
- alpha_ni56
alpha_fe52 + fe54, ni56, neut, and prot
- approx19
same isotopes as alpha_ni56; similar to Frank Timmes’ APPROX19
- approx20
approx19 + fe56
- approx21
approx20 + cr56
- ns_he
approx21 + (a,p)*(p,g) intermediates for alpha links + “bypass” for c12
Creating a custom net
If you don’t find what you need here, it is fairly easy to create new nets. First, study o18_and_ne22.net to see how it works. The idea is to start from a net that is close to what you need, then add isotopes and reactions as needed; you may also need to remove some reactions. You can put your new net file in your work directory; mesa/net looks in the current directory before it checks data/net_data/nets. Before using your new net, get a list of isotopes and reactions and carefully check them.
For reference, the current set of isotopes is in mesa/data/chem_data/isotopes.data. The format of that file is described in a README file in the same directory. The current set of reactions is in mesa/net_data/reactions.list. The reaction names in net files must be defined in the reactions.list file. Those reactions are implemented by the mesa/rates module.
Description of net format
A net is defined by a set of isotopes and a set of reactions. These sets are specified in a net definition file.
A net definition file contains a sequence of commands. It can have any number of the following commands in any order.
- include 'net_filename'
This lets you break up a definition into several files (e.g., one net can defined as an extension of another). This first tries to open ‘net_filename’ in current directory. If that fails, it tries in mesa/data/net_data/nets/.
- add_isos(isos_list)
For each iso in isos_list, add it to the current set of isos in the net. It really is a set, so multiple adds are okay.
- remove_isos(isos_list)
For each iso in isos_list, remove it from the current set of isos in the net.
- add_reactions(reactions_list)
For each reaction in reactions_list, add it to the current set of reactions in the net. It really is a set, so multiple adds are okay.
- remove_reactions(reactions_list)
For each reaction in reactions_list, remove it from the current set of reactions in the net.
- add_isos_and_reactions(isos_list)
For each iso in isos_list, add the iso to the current set, and add reactions linking it to other isos in current set.
The reactions (see below for descriptions of the reaction handle format) that automatically added by the add_isos_and_reactions command are:
p,a,n capture reactions and photodisintegrations (e.g., r_x_pg_y)
p,a,n exchanges (e.g., r_x_ap_y)
standard 1-to-1 weak reactions (e.g., r_x_wk_y)
other weak reactions (e.g., r_x_wk_h1_y)
It also checks if there are special cases to be added. Here’s an incomplete list.
r_h1_h1_wk_h2
r_h1_h1_ec_h2
r_h2_h2_to_h1_h3, r_h1_h3_to_h2_h2
r_he3_ec_h3
r_h2_h2_to_neut_he3, r_neut_he3_to_h2_h2
r_neut_neut_he4_to_h3_h3, r_h1_h1_he4_to_he3_he3
r_h3_he3_to_h2_he4, r_h2_he4_to_h3_he3
r_li6_to_neut_h1_he4, r_neut_h1_he4_to_li6
r_h1_li7_to_h2_li6, r_h2_li6_to_h1_li7
r_he4_he4_he4_to_c12, r_c12_to_he4_he4_he4
r_c12_c12_to_he4_ne20, r_he4_ne20_to_c12_c12
r_neut_mg23_to_c12_c12, r_c12_c12_to_neut_mg23
r_c12_ne20_to_h1_p31, r_h1_p31_to_c12_ne20
r_s27_wk_h1_h1_al25
r_he4_ca36_to_h1_h1_ca38, r_h1_h1_ca38_to_he4_ca36
r_pd89_to_h1_h1_ru87, r_h1_h1_ru87_to_pd89
The arguments to these commands have the following form:
- isos_list
A sequence of iso_spec values optionally separated by commas
- iso_spec
Either iso_name or element_name A_lo A_hi.
iso_name is something like h1 or he4 defined in chem.
element_name is something like h or he defined in chem. A_lo and A_hi define the range of A values to add for the element e.g., if iso_spec is he 3 4, then adds he3 and he4.
- reactions_list
A sequence of reaction_handle values optionally separated by commas.
- reaction_handle
A reaction name defined in reactions.list
or
A reaction name derived from the input and output isos as follows, where x and y are iso_names; e.g., r_c12_pg_n13.
p,a,n capture reactions and photodisintegrations
r_x_pg_y
r_y_gp_x
r_x_ag_y
r_y_ga_x
r_x_ng_y
r_y_gn_x
p,a,n exchanges
r_x_ap_y
r_y_pa_x
r_x_np_y
r_y_pn_x
r_x_na_y
r_y_an_x
standard 1-to-1 weak reactions
r_x_wk_y (positron emission or electron capture)
r_x_wk-minus_y (electron emission or positron capture)
other weak reactions (not in weaklib)
r_x_wk_h1_y (* beta decay with products h1 and y*)
r_x_wk_he4_y (beta decay with products he4 and y)
r_h1_h1_ec_h2 (electron capture)
r_h1_h1_wk_h2 (beta decay)
r_he3_ec_h3
r_be7_ec_li7
r_h1_h1_wk_h2
r_h1_he3_wk_he4
other reactions
r_<inputs>_to_<outputs>
where <inputs> and <outputs> are iso_name values separated by ‘_’ If the same iso appears 2 or more times, repeat the name that many times. e.g., triple alpha is r_he4_he4_he4_to_c12. iso values are ordered by increasing Z and N. e.g., r_h3_be7_to_neut_h1_he4_he4.
Changing/selecting reaction rates
Warning
This section needs work.
change rates for existing reactions
create a file of (T8, rate) pairs as in data/rates_data/rates add the file name to reactions.list (you can have a local copy of reactions.list as well as rates directory)
add a new reaction with rate give by table of (T8, rate) pairs
get a name for the reaction by calling reaclib_create_handle then proceed same as for changing rate of an existing reaction use the reaction in a net in same way as for existing reactions.
selecting rates for reactions
reactions in reactions.list have various rates available such as NACRE, REACLIB, or CF88. several reactions have other options as well: see rates_def.f for listing of choices
other reactions use rates from weaklib or reaclib.
also can provide a table of values for any reaction. arbitrarily many pairs of temperatures and rates; piecewise monotonic cubic interpolation. specify files for rate tables in rate_list.txt
Adding new reactions
advanced topics – experts only
- to add a reaction
add to reactions.list
add to rates_def
add to rates_names
add to raw_rates
For a weak rate, add 1/2 life and Qneu to weak_info.list in weaklib_data. If possible, get 1/2 life = log(2)/exp(c1) with c1 from reaclib.
To get the reaction added automatically add it to init_special_case_reaction_info in net_initialize.
Inspect the temperature dependence of used rates
During a run, MESA will cache the data for individual reaction rates
in $MESA_DIR/data/rates_data/cache
. Whenever a nuclear reaction
whose rate has not yet been cached is used for the first time,
the terminal output will show a line similar to the following:
write $MESA_DIR/data/rates_data/cache/r34_pp2_1.bin
Each of the files in $MESA_DIR/data/rates_data/cache
contains
10000 lines listing temperature and corresponding rate for the
specific reaction. However, these are in binary format. Inside
$MESA_DIR/rates/test
you can find an executable called
show_rates
which can be used to to print the rates in a human
readable format. To do so, run it passing the path to a cache file as
argument. You can pipe the output of this executable to a file to
obtain a file that you can easily plot.
Example:
cd $MESA_DIR/rates/test/
./show_rates $MESA_DIR/data/rates_data/cache/r34_pp2_1.bin > rate_r34_pp2_1.txt
The file rate_r34_pp2_1.txt can now be opened with your text editor.
N.B.: you will need to explicitly give the full path name for
$MESA_DIR
in the second line.