NSE

Important

NSE is only supported with the simplified-SDC method for coupling hydrodynamics and reactions. We do not support operator-splitting (Strang) coupling with NSE.

The reaction networks in Microphysics have the ability to use NSE instead of integrating the entire network when the conditions are appropriate. There are 2 different implementations of NSE in Microphysics, that have slightly different use cases.

• Tabulated NSE and aprox19 : this uses a table of NSE abundances given $(\rho ,T,Y_e)$ generate from a large network (96 isotopes). The table also returns $d{Y}_e/dt$ resulting from electron-captures, to allow for the NSE state to evolve. This is meant to be used in the cores of massive stars and works only with the aprox19 reaction network.

  Furthermore, since the table can achieve $Y_e$ and $\overline{A}$ that are not representable by the 19 isotopes in aprox19, this table requires that we use the auxiliary composition and advect $Y_e$, $\overline{A}$, and $⟨B/A⟩$. All of the EOS calls will work with these quantities.

  This algorithm was described in [36].

  This is enabled via USE_NSE_TABLE

• Self-consistent NSE : this adds an NSE solver to the network that can be called to find the equilibrium abundances of each of the species defined in the network. It works with any of the pynucastro-generated networks. Unlike the tabulated NSE, there is no need to advect the auxiliary composition, since this only deals with the isotopes defined in the main reaction network.

  This is enabled via USE_NSE_NET

Both solvers define a number of preprocessor variables, and both will provide a function in_nse() that can be used to determine if a state is currently in NSE.

make option	preprocessor variables set
USE_NSE_TABLE	NSE, NSE_TABLE, AUX_THERMO
USE_NSE_NET	NSE, NSE_NET

The directive NSE should be used whether the specific implementation of NSE does not matter.

These two NSE solvers are in the next sections.