Ion cyclotron resonance is a phenomenon related to the movement of
ions
An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
in a
magnetic field
A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...
. It is used for accelerating ions in a
cyclotron
A cyclotron is a type of particle accelerator invented by Ernest Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Januar ...
, and for measuring the masses of an ionized analyte in
mass spectrometry
Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used ...
, particularly with
Fourier transform ion cyclotron resonance
Fourier-transform ion cyclotron resonance mass spectrometry is a type of mass analyzer (or mass spectrometer) for determining the mass-to-charge ratio (''m''/''z'') of ions based on the cyclotron frequency of the ions in a fixed magnetic field. T ...
mass spectrometers. It can also be used to follow the
kinetics of chemical reactions in a dilute gas mixture, provided these involve charged species.
Definition of the resonant frequency
An ion in a static and uniform magnetic field will move in a circle due to the
Lorentz force
In electromagnetism, the Lorentz force is the force exerted on a charged particle by electric and magnetic fields. It determines how charged particles move in electromagnetic environments and underlies many physical phenomena, from the operation ...
. The
angular frequency
In physics, angular frequency (symbol ''ω''), also called angular speed and angular rate, is a scalar measure of the angle rate (the angle per unit time) or the temporal rate of change of the phase argument of a sinusoidal waveform or sine ...
of this ''cyclotron motion'' for a given magnetic field strength ''B'' is given by
:
where ''z'' is the number of positive or negative charges of the ion, ''e'' is the
elementary charge
The elementary charge, usually denoted by , is a fundamental physical constant, defined as the electric charge carried by a single proton (+1 ''e'') or, equivalently, the magnitude of the negative electric charge carried by a single electron, ...
and ''m'' is the mass of the ion. An electric excitation signal having a frequency ''f'' will therefore resonate with ions having a mass-to-charge ratio ''m/z'' given by
:
The circular motion may be superimposed with a uniform axial motion, resulting in a
helix
A helix (; ) is a shape like a cylindrical coil spring or the thread of a machine screw. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is for ...
, or with a uniform motion perpendicular to the field (e.g., in the presence of an electrical or gravitational field) resulting in a
cycloid
In geometry, a cycloid is the curve traced by a point on a circle as it Rolling, rolls along a Line (geometry), straight line without slipping. A cycloid is a specific form of trochoid and is an example of a roulette (curve), roulette, a curve g ...
.
Ion cyclotron resonance heating
Ion cyclotron resonance heating (or ICRH) is a technique in which
electromagnetic waves
In physics, electromagnetic radiation (EMR) is a self-propagating wave of the electromagnetic field that carries momentum and radiant energy through space. It encompasses a broad spectrum, classified by frequency or its inverse, wavelength, ran ...
with frequencies corresponding to the ion cyclotron frequency is used to heat up a
plasma. The ions in the plasma absorb the electromagnetic radiation and as a result of this, increase in
kinetic energy
In physics, the kinetic energy of an object is the form of energy that it possesses due to its motion.
In classical mechanics, the kinetic energy of a non-rotating object of mass ''m'' traveling at a speed ''v'' is \fracmv^2.Resnick, Rober ...
. This technique is commonly used in the heating of
tokamak
A tokamak (; ) is a device which uses a powerful magnetic field generated by external magnets to confine plasma (physics), plasma in the shape of an axially symmetrical torus. The tokamak is one of several types of magnetic confinement fusi ...
plasmas.
In the solar wind
On March 8, 2013, NASA released an article according to which ion cyclotron waves were identified by its solar probe spacecraft called WIND as the main cause for the heating of the
solar wind
The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...
as it rises from the Sun's surface. Before this discovery, it was unclear why the solar wind particles would heat up instead of cool down, when speeding away from the Sun's surface.
Magnetic confinement fusion
In
fusion devices, such as
tokamak
A tokamak (; ) is a device which uses a powerful magnetic field generated by external magnets to confine plasma (physics), plasma in the shape of an axially symmetrical torus. The tokamak is one of several types of magnetic confinement fusi ...
s and
stellarator
A stellarator confines Plasma (physics), plasma using external magnets. Scientists aim to use stellarators to generate fusion power. It is one of many types of magnetic confinement fusion devices. The name "stellarator" refers to stars because ...
s, ICRH antennas are installed in the machine vessel to heat the plasma using
radio wave
Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths g ...
s with frequencies in the range of the ion cyclotron resonance.
ICRH provides localized heating of ions in fusion plasmas, which can generate a large population of energetic particles typically inaccessible with other heating methods (such as
electron cyclotron resonance heating
A tokamak (; ) is a device which uses a powerful magnetic field generated by external magnets to confine plasma (physics), plasma in the shape of an axially symmetrical torus. The tokamak is one of several types of magnetic confinement fusi ...
or
neutral beam injection
Neutral-beam injection (NBI) is one method used to heat Plasma (physics), plasma inside a Tokamak, fusion device consisting in a beam of high-energy neutral particles that can enter the magnetic confinement field. When these neutral particles are i ...
). The confinement properties of fast ions in plasma is a major research topic in fusion plasma physics.
See also
*
Cyclotron resonance (disambiguation)
*
Electron cyclotron resonance
Electron cyclotron resonance (ECR) is a phenomenon observed in plasma physics, condensed matter physics, and accelerator physics. It happens when the frequency of incident radiation coincides with the natural frequency of rotation of electrons in ...
References
{{reflist
Condensed matter physics
Electric and magnetic fields in matter
Ion source
Scientific techniques
Plasma phenomena