Enhanced recombination in low-temperature magnetized plasmas

The ion-electron recombination process in cold magnetized plasmas is currently intensively studied both experimentally and theoretically. Recent storage ring experiments show a dramatic enhancement of the recombination rate for high Z ions relative to what standard radiative recombination rates predict. The aim of proposal is to understand the fundamental mechanism of this recombination process and the origin of the enhancement. We will investigate the role of classical chaotic dynamics and unstable periodic orbits which may bring an electron to multiple visits to the target ion and enhance the recombination. In addition, a role of stochastic perturbations in the dilute electron gas will be considered.

Radiative recombination of electron and ion is one of the most fundamental processes in quantum physics. Its rate coefficients are useful for understanding of cosmic plasmas in astrophysics and for fusion plasmas which can be used as one of the possible energy supplies in the future. In the present context rate coefficients provide the information on how many ions are lost in ion storage rings when an ion beam is cooled by an electron beam to keep the ion beam from being heated up during circulations in the storage ring. The rate coefficient of radiative recombination has been measured using ion storage rings assuming that ion loss during the electron cooling is caused by radiative recombination. However, recent measurements were found to overestimate the theoretical estimates which have been developed in 1920`s and recognized nowadays as a fundamental and well-understood theory. This discrepancy has been unexplained for more than a decade. In this project, we focused to solve this unexplained mystery. We have found out that the enhanced measured rate coefficients have contributions not only from radiative recombination but also another recombination mechanism. At the entrance of an electron cooler in ion storage rings the electron beam is guided by a magnetic field and merged with an ion beam. The interaction between the magnetic field and the ion beam induces a motional (time- dependent) electric field, which provides an additional path for recombination. Theoretical estimates including contributions from radiative and motional recombination are found to agree with the measured rate coefficients. The scaling of the coefficient in the magnetic field or in the charge of ion is also proven to follow the measured scaling law.