Journal
SCIENCE
Volume 361, Issue 6406, Pages 1000-1003Publisher
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.aap8730
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Funding
- NASA MMS Mission
- NASA [NNG04EB99C]
- Japan Society for the Promotion of Science (JSPS) [17H06140, 15H05747, 15H05815, 17K14402, 16H06286, 15H03730]
- NASA MMS Mission Guest Investigators program
- CNES
- CNRS
- University of New Hampshire
- NASA
- SwRI
- Grants-in-Aid for Scientific Research [17K14402, 15H03730] Funding Source: KAKEN
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Particle acceleration by plasma waves and spontaneous wave generation are fundamental energy and momentum exchange processes in collisionless plasmas. Such wave-particle interactions occur ubiquitously in space. We present ultrafast measurements in Earth's magnetosphere by the Magnetospheric Multiscale spacecraft that enabled quantitative evaluation of energy transfer in interactions associated with electromagnetic ion cyclotron waves. The observed ion distributions are not symmetric around the magnetic field direction but are in phase with the plasma wave fields. The wave-ion phase relations demonstrate that a cyclotron resonance transferred energy from hot protons to waves, which in turn nonresonantly accelerated cold He+ to energies up to similar to 2 kilo-electron volts. These observations provide direct quantitative evidence for collisionless energy transfer in plasmas between distinct particle populations via wave-particle interactions.
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