Speaker
Description
Ten-thousand-fold enhancements of $^3$He abundance in impulsive solar energetic particle (SEP) events indicate that $^3$He ions, before accelerated to high energies (~ 1 MeV/nucleon) in solar flares, should have been preferentially heated significantly ($T_{^3He}/T_{^4He} ~ 10 - 100$). The best mechanism developed so far for preferential heating of $^3$He is the first or second harmonic resonances of $^3$He with current-driven electrostatic $^4$He or H-cyclotron waves. This mechanism for minor ionic species to be strongly heated by major ionic species cyclotron waves may also play an important role in the heating of laboratory plasmas for nuclear fusion. It is well known that nuclear fusion is a high-energy reaction in which two extremely energized lighter atomic nuclei, after overcoming the sturdy Coulomb barrier, fuse tightly into a heavier one via the nuclear force. For the fusion to occur among nuclei in labs such as in a tokamak, the plasma must be heated to or above 100 million Kelvins (MK) with sufficient confinement time and sufficient plasma density. Efforts on experiments of plasma fusion conducted in the past decades indicate numerous mysteries and difficulties surrounding how to control heat bursts and confine plasmas of extreme temperatures. Based on our previous work for $^3$He-rich SEP events, we propose a new general mechanism for plasma fusion of minor ionic species extremely heated with major ionic species at only about 10 MK in order to reduce difficulties of fusion technology and engineering in the plasma confinement and control. We consider multi-ion plasmas composing of various major and minor ionic species with a current drive. As an electric current is driven through, a plasma can be ohmically heated by the current up to 10 MK, at which the resistivity in the plasma is too low for the current to be significantly dissipated further and the entire plasma saturates its temperature at this level in this first-stage of the heating process. When the current is continuously driven up to a critical point, e.g. thirty percent of the electron thermal current, electrostatic ion-cyclotron waves of the major ionic species are destabilized, which can have frequencies at around a multiple of the ion-cyclotron frequencies of the minor ionic species and thus can further heat the minor ionic species via particular harmonic resonances to 100 MK and higher, at which the nuclear fusion between the extremely heated minor ionic species and the relatively cold major ionic species can occur. In this second-stage of the heating process, only the minor ionic species are preferentially heated. This mechanism of plasma fusion, because temperatures of the major ionic species and electrons are only around 10 MK, can greatly reduce difficulties of technology and engineering in confinement and control of the fusing plasma.
| Eligible for student paper award? | No |
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