Editing Electron cyclotron resonance (section)

== ECR ion sources ==
The use of electron cyclotron resonance for efficient plasma generation, especially to obtain large numbers of multiply charged ions,<ref>Geller, R. "ECRIS sources for highly charged ions." Europhysics News 22.1 (1991): 8-11.</ref><ref>{{cite journal|author=H. Postma|journal=Physics Letters A|volume=31|issue=4|page=196|year=1970|title=Multiply charged heavy ions produced by energetic plasmas|doi=10.1016/0375-9601(70)90921-7|bibcode=1970PhLA...31..196P}}</ref> has been applied in diverse fields:
* advanced cancer treatment, where ECR [[ion sources]] are crucial for [[proton therapy]],{{cn|date=February 2025}}
* advanced [[Semiconductor fabrication|semiconductor manufacturing]], especially for high density [[DRAM]] memories, through [[plasma etching]] or other [[plasma processing]] technologies,{{cn|date=February 2025}}
* [[Electrically powered spacecraft propulsion|electric propulsion]] devices for [[spacecraft propulsion]], where a broad range of devices ([[HiPEP]], some [[Electrostatic ion thruster|ion thruster]]s, or [[electrodeless plasma thruster]]s),{{cn|date=February 2025}}
* for [[particle accelerator]]s, on-line mass separation and radioactive ion charge breeding,<ref>''Handbook of Ion Source'', B. Wolf, {{ISBN|0-8493-2502-1}}, pp. 136–146</ref>
* and, as a more mundane example, painting of plastic bumpers for cars.{{cn|date=February 2025}}

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 the magnetic field applied to a region inside the volume. The volume contains a low pressure gas. The alternating electric field of the microwaves is set to be synchronous with the gyration period of the free electrons of the gas, and increases their perpendicular kinetic energy. Subsequently, when the energized free electrons collide with the gas in the volume they can cause ionization if their kinetic energy is larger than the ionization energy of the atoms or molecules. The ions produced correspond to the gas type used, which may be pure, a compound, or vapour of a solid or liquid material.

ECR ion sources are able to produce singly charged ions with high intensities (e.g. [[Hydrogen|H]]<sup>+</sup> and [[Deuterium|D]]<sup>+</sup> ions of more than 100&nbsp;[[milliampere|mA]] (electrical) in DC mode<ref>R. Gobin et al., [http://accelconf.web.cern.ch/AccelConf/e02/PAPERS/THPRI003.pdf Saclay High Intensity Light Ion Source Status] The Euro. Particle Accelerator Conf. 2002, Paris, France, June 2002, p. 1712</ref> using a 2.45&nbsp;GHz ECR ion source).

For multiply charged ions, the ECR ion source has the advantages that it is able to confine the ions for long enough for multiple collisions and multiple ionization to take place, and 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&nbsp;mA (electrical) of [[Bismuth|Bi]]<sup>29+</sup>.<ref>[http://cerncourier.com/cws/article/cern/29329 VENUS reveals the future of heavy-ion sources] CERN Courier, 6 May 2005</ref>

Some important industrial fields would not 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.