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 conve ...
in a
magnetic field
A magnetic field is a vector 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 to its own velocity and t ...
. It is used for accelerating ions in a
cyclotron
A cyclotron is a type of particle accelerator invented by Ernest O. 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: J ...
, 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 u ...
, 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. ...
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 physics (specifically in electromagnetism) the Lorentz force (or electromagnetic force) is the combination of electric and magnetic force on a point charge due to electromagnetic fields. A particle of charge moving with a velocity in an ele ...
. The
angular frequency
In physics, angular frequency "''ω''" (also referred to by the terms angular speed, circular frequency, orbital frequency, radian frequency, and pulsatance) is a scalar measure of rotation rate. It refers to the angular displacement per unit ti ...
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 the electric charge carried by a single proton or, equivalently, the magnitude of the negative electric charge carried by a single electron, which has charge −1 . This elementary charge is a funda ...
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 corkscrew or spiral staircase. 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 formed as two intertwined hel ...
, 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 rolls along a straight line without slipping. A cycloid is a specific form of trochoid and is an example of a roulette, a curve generated by a curve rolling on another ...
.
Ion cyclotron resonance heating
Ion cyclotron resonance heating (or ICRH) is a technique in which
electromagnetic waves
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) lig ...
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 energy that it possesses due to its motion.
It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its a ...
. This technique is commonly used in the heating of
tokamak
A tokamak (; russian: токамáк; otk, 𐱃𐰸𐰢𐰴, Toḳamaḳ) is a device which uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being ...
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 upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the ...
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.
See also
*
Cyclotron resonance
*
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
Condensed matter physics
Electric and magnetic fields in matter
Ion source
Scientific techniques
Plasma physics
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