Plasma normal modes in ion-beam–plasma systems were experimentally investigated previously only for the waves propagating in the downstream（along the beam） direction. In this paper, the ion wave excitation and prop...Plasma normal modes in ion-beam–plasma systems were experimentally investigated previously only for the waves propagating in the downstream（along the beam） direction. In this paper, the ion wave excitation and propagation in the upstream（against the beam） direction in an ion-beam–plasma system were experimentally studied in a double plasma device. The waves were launched by applying a ramp voltage to a negatively biased excitation grid. Two kinds of wave signals were detected, one is a particle signal composed of burst ions and the other is an ion-acoustic signal arising from the background plasma. These signals were identified by the dependence of the signal velocities on the characteristics of the ramp voltage. The velocity of the burst ion signal increases with the decrease of the rise time and the increase of the peak-to-peak amplitude of the applied ramp voltage while that of the ion-acoustic signal is independent of these parameters.By adjusting these parameters such that the burst ion velocity approaches to the ion-acoustic velocity, the wave–particle interaction can be observed.展开更多
In this paper, we study the electromagnetic instability driven by ion beams and plasmainhomogeneity in the plasma sheet boundary layer and for the first time obtain the growthrate spectrum of electromagnetic waves in ...In this paper, we study the electromagnetic instability driven by ion beams and plasmainhomogeneity in the plasma sheet boundary layer and for the first time obtain the growthrate spectrum of electromagnetic waves in a broad frequency range (Ω<sub>i</sub>【【0.1ω<sub>LH</sub>?|ω<sub>r</sub>|≤Ω<sub>e</sub>,Ω<sub>i</sub> and Ω<sub>e</sub> are respectively the ion and electron cyclotron frequencies, ω<sub>LH</sub>=（Ω<sub>i</sub>Ω<sub>e</sub>）<sup>1/2</sup> is thelower hybrid frequency). The peak of the growth rate spectrum is near |ω<sub>r</sub>|≈ω<sub>LH</sub> and thesecond peak is near |ω<sub>r</sub>|?Ω<sub>e</sub>. The fundamental characteristics of the growth rate spectrumare in agreement with the satellite observations of the magnetic noise bursts in the magneto-tail.展开更多
Earlier we reported an ion current jump which was observed at a fixed negative biased disc potential in the 6.4GHz ECR ion source at VECC,Kolkata.In a recent experiment with neon ions,we measured the time spectra of t...Earlier we reported an ion current jump which was observed at a fixed negative biased disc potential in the 6.4GHz ECR ion source at VECC,Kolkata.In a recent experiment with neon ions,we measured the time spectra of the ion current and observed the presence of a burst frequency in the kilohertz range.This frequency shows a correlated jump with the ion current jump described above.Another interesting feature is that the observed burst frequency shows a good linear correlation with the extracted ion current.The higher the ion current,the higher is the burst frequency.This means that current per burst is a constant factor;when there are more number of bursts,the current also increases.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11575183 and 11705201)
文摘Plasma normal modes in ion-beam–plasma systems were experimentally investigated previously only for the waves propagating in the downstream（along the beam） direction. In this paper, the ion wave excitation and propagation in the upstream（against the beam） direction in an ion-beam–plasma system were experimentally studied in a double plasma device. The waves were launched by applying a ramp voltage to a negatively biased excitation grid. Two kinds of wave signals were detected, one is a particle signal composed of burst ions and the other is an ion-acoustic signal arising from the background plasma. These signals were identified by the dependence of the signal velocities on the characteristics of the ramp voltage. The velocity of the burst ion signal increases with the decrease of the rise time and the increase of the peak-to-peak amplitude of the applied ramp voltage while that of the ion-acoustic signal is independent of these parameters.By adjusting these parameters such that the burst ion velocity approaches to the ion-acoustic velocity, the wave–particle interaction can be observed.
基金Project supported by the National Natural Science Foundation of.China.
文摘In this paper, we study the electromagnetic instability driven by ion beams and plasmainhomogeneity in the plasma sheet boundary layer and for the first time obtain the growthrate spectrum of electromagnetic waves in a broad frequency range (Ω<sub>i</sub>【【0.1ω<sub>LH</sub>?|ω<sub>r</sub>|≤Ω<sub>e</sub>,Ω<sub>i</sub> and Ω<sub>e</sub> are respectively the ion and electron cyclotron frequencies, ω<sub>LH</sub>=（Ω<sub>i</sub>Ω<sub>e</sub>）<sup>1/2</sup> is thelower hybrid frequency). The peak of the growth rate spectrum is near |ω<sub>r</sub>|≈ω<sub>LH</sub> and thesecond peak is near |ω<sub>r</sub>|?Ω<sub>e</sub>. The fundamental characteristics of the growth rate spectrumare in agreement with the satellite observations of the magnetic noise bursts in the magneto-tail.
文摘Earlier we reported an ion current jump which was observed at a fixed negative biased disc potential in the 6.4GHz ECR ion source at VECC,Kolkata.In a recent experiment with neon ions,we measured the time spectra of the ion current and observed the presence of a burst frequency in the kilohertz range.This frequency shows a correlated jump with the ion current jump described above.Another interesting feature is that the observed burst frequency shows a good linear correlation with the extracted ion current.The higher the ion current,the higher is the burst frequency.This means that current per burst is a constant factor;when there are more number of bursts,the current also increases.
