ECR Ion Sources
Since the early 1980s, following the award-winning pioneering work done by Dr. Richard Geller, Dr. Claude Lyneis, and Dr. H. Postma; 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 ion sources are crucial for proton therapy,
- advanced semiconductor manufacturing, especially for high density DRAM memories, through plasma etching or other plasma processing technologies,
- electric propulsion devices for spacecraft propulsion, where a broad range of devices (HiPEP, some ion thrusters, or electrodeless plasma thrusters),
- for particle accelerators, on-line mass separation and radioactive ion charge breeding,
- and, as a more mundane example, painting of plastic bumpers for cars.
The ECR ion source makes use of the electron cyclotron resonance to ionize 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 alternating electric field of the microwaves being synchronous with the gyration period of the free electrons of the gas, it increases their perpendicular kinetic energy. When in turn the energized free electrons collide with the atoms or molecules of the gas in the volume and cause ionization, if their kinetic energy is larger than the molecule or atom ionization energy. The ions produced correspond to the gas type used. The gas may be pure, a compound gas, or can be a vapor 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 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+.
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.
Read more about this topic: Electron Cyclotron Resonance
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