gyrofrequency

plasmapy.formulary.gyrofrequency(B: Unit(‘T’), particle: plasmapy.particles.particle_class.Particle, signed=False, Z=None, to_hz=False)

Calculate the particle gyrofrequency in units of radians per second.

Aliases: oc_, wc_

Parameters

  • B (Quantity) – The magnetic field magnitude in units convertible to tesla.

  • particle (Particle) – Representation of the particle species (e.g., ‘p’ for protons, ‘D+’ for deuterium, or ‘He-4 +1’ for singly ionized helium-4). If no charge state information is provided, then the particles are assumed to be singly charged.

  • signed (bool, optional) – The gyrofrequency can be defined as signed (negative for electron, positive for ion). Default is False (unsigned, i.e. always positive).

  • Z (float or Quantity, optional) – The average ionization (arithmetic mean) for a plasma where the a macroscopic description is valid. If this quantity is not given then the atomic charge state (integer) of the ion is used. This is effectively an average gyrofrequency for the plasma where multiple charge states are present, and should not be interpreted as the gyrofrequency for any single particle. If not provided, it defaults to the integer charge of the particle.

Returns

omega_c – The particle gyrofrequency in units of radians per second.

Return type

Quantity

Raises

  • TypeError – If the magnetic field is not a Quantity or particle is not of an appropriate type.

  • ValueError – If the magnetic field contains invalid values or particle cannot be used to identify an particle or isotope.

Warns

UnitsWarning – If units are not provided, SI units are assumed.

Notes

The particle gyrofrequency is the angular frequency of particle gyration around magnetic field lines and is given by:

\[ω_{ci} = \frac{Z e B}{m_i}\]

The particle gyrofrequency is also known as the particle cyclotron frequency or the particle Larmor frequency.

The recommended way to convert from angular frequency to frequency is to use an equivalency between cycles per second and hertz, as Astropy’s dimensionles_angles equivalency does not account for the factor of \(2π\) needed during this conversion. The dimensionless_angles equivalency is appropriate when dividing a velocity by an angular frequency to get a length scale.

Examples

>>> from astropy import units as u
>>> gyrofrequency(0.1*u.T, 'e-')
<Quantity 1.7588...e+10 rad / s>
>>> gyrofrequency(0.1*u.T, 'e-', to_hz=True)
<Quantity 2.79924...e+09 Hz>
>>> gyrofrequency(0.1*u.T, 'e-', signed=True)
<Quantity -1.75882...e+10 rad / s>
>>> gyrofrequency(0.01*u.T, 'p')
<Quantity 957883.32... rad / s>
>>> gyrofrequency(0.01*u.T, 'p', signed=True)
<Quantity 957883.32... rad / s>
>>> gyrofrequency(0.01*u.T, particle='T+')
<Quantity 319964.5... rad / s>
>>> gyrofrequency(0.01*u.T, particle='T+', to_hz=True)
<Quantity 50923.9... Hz>
>>> omega_ce = gyrofrequency(0.1*u.T, 'e-')
>>> print(omega_ce)
1758820... rad / s
>>> f_ce = omega_ce.to(u.Hz, equivalencies=[(u.cy/u.s, u.Hz)])
>>> print(f_ce)
279924... Hz
Other Parameters

to_hz (bool) – Set True to to convert function output from angular frequency to Hz