Journal Article

Direct measurements of two-way wave-particle energy transfer in a collisionless space plasma

Hasegawa, H., Pollock, C. J., Katoh, Y., Gershman, D. J., Burch, J. L., Saito, Y., Kitamura, N., Miyoshi, Y., Vinas, A. F., Kitahara, M., Paterson, W. R., Strangeway, R. J., Fuselier, S. A., Giles, B. L., Shoji, M., Yokota, S., Moore, T. E., Russell, C. T., Nakamura, S.

2018

Overview

Plasmas are ionized gases that contain negative electrons, positive ions, and electromagnetic fields. These constituents can oscillate in position over time, carrying energy as plasma waves. In principle, such waves could transfer energy between two different ion populations. Kitamura et al. analyzed data from the Magnetospheric Multiscale mission, a group of four spacecraft that are flying in tight formation through Earth's magnetosphere. They discovered an event in which energy was transferred from hydrogen ions to plasma waves and then from the waves to helium ions. This energy transfer process is likely to occur in many other plasma environments. Science , this issue p. 1000 Energy transfer between H + ions, plasma waves, and He + ions is observed in a space plasma. 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 ~2 kilo–electron volts. These observations provide direct quantitative evidence for collisionless energy transfer in plasmas between distinct particle populations via wave-particle interactions.

• Publisher: The American Association for the Advancement of Science
• Subject: Collisionless plasmas / Cyclotron resonance / Data processing / Earth magnetosphere / Electromagnetic fields / Energy / Energy transfer / Gases / Helium / Helium ions / Hydrogen ions / Ions / Magnetic fields / Magnetic resonance / Multiscale analysis / Particle acceleration / Particle energy / Particle interactions / Plasma / Plasma waves / Populations / Positive ions / Protons / Quantitative analysis / Space plasmas / Spacecraft / Wave generation / Wave-particle interactions