Electron cyclotron resonance

Electron cyclotron resonance is a phenomenon observed both in SI units^[1]) by

$\omega_{ce}=\frac{eB}{m}$ .

where $e$ is the elementary charge and $m$ is the mass of the electron. For the commonly used T.

In plasma physics

An ionized diagnostic of the radial electron temperature profile.

ECR Ion Sources

Since the early 1980's, following the award-winning pioneering work done by Dr. Richard Geller^[2], Dr. Claude Lyneis, and Dr. H. Postma ^[3]; respectively from French Atomic Energy Commission, Lawrence Berkeley National Laboratory and the Oak Ridge National Laboratory, the use of electron cyclotron resonance for efficient plasma generation, especially to obtain large numbers of multiply charged ions, has acquired a unique importance in various technological fields. Many diverse activities depend on electron cyclotron resonance technology, including

advanced cancer treatment, where ECR proton therapy,
advanced semiconductor manufacturing, especially for high density DRAM memories, through plasma processing technologies,
electric propulsion devices for spacecraft propulsion, where a broad range of devices (HiPEP, some electrodeless plasma thrusters),
for particle accelerators, on-line mass separation and radio-active ion charge breeding ^[4].
and, as a more mundane example, painting of plastic bumpers for cars.

The ECR ion source makes use of the Electron Cyclotron Resonance to heat a plasma. Microwaves are injected into a volume, at the frequency corresponding to the Electron Cyclotron Resonance defined by a magnetic field applied to a region inside the volume. The volume contains a low pressure gas. The microwaves heat free electrons in the gas which in turn collide with the atoms or molecules of the gas in the volume and cause ionization. The ions produced correspond to the gas type used. The gas may be pure, a compound gas or can be a vapour of a solid or liquid material.

ECR ion sources are able to produce singly charged ions with high intensities (e.g H⁺ and D⁺ ions of more than 100 mA (electrical) in DC mode ^[5] using a 2.45 GHz ECR ion source).

For multiply charged ions, the ECR ion source has the advantage that it is able to confine the ions for long enough for multiple collisions to take place (leading to multiple ionization) and that the low gas pressure in the source avoids recombination. The VENUS ECR ion source at Lawrence Berkeley National Laboratory has produced in intensity of 0.25 mA (electrical) of Bi²⁹⁺ ^[6].

Some of these industrial fields would not even exist without the use of this fundamental technology, which makes electron cyclotron resonance ion and plasma sources one of the enabling technologies of today's world.

In condensed matter physics

Within a solid the mass in the cyclotron frequency equation above is replaced with the Fermi surface cross-section in solids. In a sufficiently high magnetic field at low temperature in a relatively pure material

$\begin{matrix}\omega_{ce} > 1/\tau \\ \hbar \omega_{ce} > k_B T \\ \end{matrix}$

where $τ$ is the carrier scattering lifetime, $k B$ is Boltzmann's constant and $T$ is temperature. When these conditions are satisfied, an electron will complete its cyclotron orbit without engaging in a collision, at which point it is said to be in a well-defined Landau level.

References

^ In SI units, the elementary charge e has the value 1.602×10^-19 second.
^ R. Geller, Peroc. 1st Int. Con. Ion Source, Salcay, p537, 1969
^ H. Postma, Phys. Lett. A, 31, p196, 1970
^ Handbook of Ion Source, B. Wolf, ISBN 0-8493-2502-1, p136-146
^ R. Gobin et al, Saclay High Intensity Light Ion Source Status The Euro. Particle Accelerator Conf. 2002, Paris, France, June 2002, p1712
^ VENUS reveals the future of heavy-ion sources CERN Courier, 6 May 2005

Electron cyclotron resonance

In plasma physics

ECR Ion Sources

In condensed matter physics

References

See also