mass_density¶

plasmapy.formulary.parameters.mass_density(density: [Unit("1 / m3"), Unit("kg / m3")], particle: Union[plasmapy.particles.particle_class.Particle, str], z_ratio: Optional[numbers.Real] = 1) -> Unit("kg / m3")¶

Calculates the mass density from a number density.

\[\rho = \left| \frac{Z_{s}}{Z_{particle}} \right| n_{s} m_{particle} = | Z_{ratio} | n_{s} m_{particle}\]

where \(m_{particle}\) is the particle mass, \(n_{s}\) is a number density for plasma species \(s\), \(Z_{s}\) is the integer charge of species \(s\), and \(Z_{particle}\) is the integer charge of particle. For example, if the electron density is given for \(n_s\) and particle is a doubly ionized atom, then \(Z_{ratio} = -1 / 2\).

Aliases: rho_

Parameters:	density (`Quantity`) – Either a particle number density (in units of \(m^{-3}\) or equivalent) or a mass density (in units of \(kg/m^3\) or equivalent). If `density` is a mass density, then it will be passed through and returned without modification. particle (`Particle`) – The particle for which the mass density is being calculated for. Must be a `Particle` or a value convertible to a `Particle` (e.g., `'p'` for protons, `'D+'` for deuterium, or `'He-4 +1'` for singly ionized helium-4). z_ratio (`int`, `float`, optional) – The ratio of the integer charges corresponding to the plasma species represented by `density` and the `particle`. For example, if the given `density` is and electron density and `particle` is doubly ionized `He`, then `z_ratio = -0.5`. Default is `1`.
Raises:	`UnitTypeError` – If the `density` does not have units equivalent to a number density or mass density. `TypeError` – If `density` is not of type `Quantity`, or convertible. `TypeError` – If `particle` is not of type or convertible to `Particle`. `TypeError` – If `z_ratio` is not of type `int` or `float`. `ValueError` – If `density` is negative.
Returns:	The mass density for the plasma species represented by `particle`.
Return type:	`Quantity`

Examples

>>> import astropy.units as u
>>> mass_density(1 * u.m ** -3, 'p')
<Quantity 1.67262...e-27 kg / m3>
>>> mass_density(4 * u.m ** -3, 'D+')
<Quantity 1.33743...e-26 kg / m3>
>>> mass_density(2.e12 * u.cm ** -3, 'He')
<Quantity 1.32929...e-08 kg / m3>
>>> mass_density(2.e12 * u.cm ** -3, 'He', z_ratio=0.5)
<Quantity 6.64647...e-09 kg / m3>
>>> mass_density(1.0 * u.g * u.m ** -3, "")
<Quantity 0.001 kg / m3>