spectral_density_model

plasmapy.diagnostics.thomson.spectral_density_model(wavelengths, settings, params)

Returns a lmfit.model.Model function for Thomson spectral density function.

Parameters:

• wavelengths (numpy.ndarray) – Wavelength array, in meters.

• settings (dict) –

  A dictionary of non-variable inputs to the spectral density function which must include the following keys:

  • "probe_wavelength": Probe wavelength in meters

  • "probe_vec" : (3,) unit vector in the probe direction

  • "scatter_vec": (3,) unit vector in the scattering direction

  • "ions" : list of particle strings, Particle objects, or a ParticleList describing each ion species. All ions must be positive. Ion mass and charge number from this list will be automatically added as fixed parameters, overridden by any ion_mass or ion_z parameters explicitly created.

  and may contain the following optional variables:

  • "electron_vdir" : (e#, 3) array of electron velocity unit vectors

  • "ion_vdir" : (e#, 3) array of ion velocity unit vectors

  • "instr_func" : A function that takes a wavelength Quantity array and returns a spectrometer instrument function as an ndarray.

  • "notch" : A wavelength range or array of multiple wavelength ranges over which the spectral density is set to 0.

  These quantities cannot be varied during the fit.

• params (Parameters object) –

  A Parameters object that must contain the following variables:

  • n: Total combined density of the electron populations in m^-3

  • T_e_e# : Temperature in eV

  • T_i_i# : Temperature in eV

  where where i# and where e# are replaced by the number of electron and ion populations, zero-indexed, respectively (e.g., 0, 1, 2, …). The Parameters object may also contain the following optional variables:

  • "efract_e#" : Fraction of each electron population (must sum to 1)

  • "ifract_i#" : Fraction of each ion population (must sum to 1)

  • "electron_speed_e#" : Electron speed in m/s

  • "ion_speed_ei" : Ion speed in m/s

  • "ion_mu_i#" : Ion mass number, \(\mu = m_i/m_p\)

  • "ion_z_i#" : Ion charge number

  • "background" : Background level, as fraction of max signal

  These quantities can be either fixed or varying.

Returns:

model – An lmfit.model.Model of the spectral density function for the provided settings and parameters that can be used to fit Thomson scattering data.

Return type:

lmfit.model.Model

Notes

If an instrument function is included, the data should not include any numpy.nan values — instead regions with no data should be removed from both the data and wavelength arrays using numpy.delete.