freeofcharge.stopping
Beam-stopping cross sections of fast hydrogen atoms in a plasma.
A neutral beam is attenuated as dI/ds = -n_e sigma_s I, with the effective
stopping cross section sigma_s of all ionising channels (ionisation by
electrons and ions, charge exchange, and their multi-step paths through excited
states). A stopping model is a callable
sigma_s(energy_per_amu, ne, te, ion_densities, ion_masses, ion_charges)
of the beam energy per nucleon [eV], the electron density [m^-3] and
temperature [eV], and the density [m^-3], mass number and charge number of
each ion species, returning sigma_s [m^2] on the broadcast shape of the
arrays.
Classes
| Name | Description |
|---|---|
ConstantStopping | A constant stopping cross section, for tests and estimates. |
StoppingModel | The call signature of a beam-stopping model. |
SuzukiStopping | Suzuki's fit of the stopping cross section of H, D, T beams. |
ConstantStoppingclassdataclass#
class ConstantStopping(sigma: float)A constant stopping cross section, for tests and estimates.
StoppingModelclass#
class StoppingModel(Protocol)Bases: Protocol
The call signature of a beam-stopping model.
SuzukiStoppingclassdataclass#
class SuzukiStopping(blend: float = 1.1)Suzuki’s fit of the stopping cross section of H, D, T beams.
Valid for 10 keV/amu to 10 MeV/amu, plasmas of H, D or T with He, B, C, N, O or Fe impurities in the Z_eff ranges of the fit. A hydrogen species is picked by its mass number (1 to 3); with several, their cross sections are averaged with their densities.
The paper fits 10 to 100 and 100 to 10000 keV/amu separately (its tables 3
and 2), and the two fits do not meet at 100 keV/amu: they differ there by a
few per cent, with a sign that depends on T_e (+1.7 % at 1 keV and -4.4 %
at 10 keV, for 5e19 m^-3). The coefficients agree with ASCOT5 and STELLOPT,
so the step is in the published fit. Within a factor blend of 100
keV/amu, log sigma is interpolated linearly in log E between the
two fits, which makes the cross section continuous; blend=1 gives the
fits as published.