Allison Hayley J, Shprits Yuri Y, Zhelavskaya Irina S, Wang Dedong, Smirnov Artem G
GFZ German Centre for Geosciences, Potsdam, Germany.
Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany.
Sci Adv. 2021 Jan 29;7(5). doi: 10.1126/sciadv.abc0380. Print 2021 Jan.
The Van Allen Probes mission provides unique measurements of the most energetic radiation belt electrons at ultrarelativistic energies. Simultaneous observations of plasma waves allow for the routine inference of total plasma number density, a parameter that is very difficult to measure directly. On the basis of long-term observations in 2015, we show that the underlying plasma density has a controlling effect over acceleration to ultrarelativistic energies, which occurs only when the plasma number density drops down to very low values (~10 cm). Such low density creates preferential conditions for local diffusive acceleration of electrons from hundreds of kilo-electron volts up to >7 MeV. While previous models could not reproduce the local acceleration of electrons to such high energies, here we complement the observations with a numerical model to show that the conditions of extreme cold plasma depletion result in acceleration up to >7 MeV.
范艾伦探测器任务提供了对超相对论能量下最具能量的辐射带电子的独特测量。对等离子体波的同步观测使得能够常规推断总等离子体数密度，这是一个很难直接测量的参数。基于2015年的长期观测，我们表明，底层等离子体密度对加速到超相对论能量具有控制作用，这种加速仅在等离子体数密度下降到非常低的值（约10厘米）时才会发生。如此低的密度为电子从数百千电子伏特到超过7兆电子伏特的局部扩散加速创造了优先条件。虽然以前的模型无法再现电子到如此高能量的局部加速，但在这里我们用一个数值模型对观测结果进行补充，以表明极端冷等离子体耗尽的条件导致加速到超过7兆电子伏特。
