Observation of multi-mode ion waves in electron cyclotron resonance plasma

Abstract

In this paper, ion waves were experimentally investigated in a microwave electron cyclotron resonance plasma. By applying a ramp voltage to a negatively biased excitation grid, multimode ion waves were excited. It was found through the time-of-flight method that the velocities of the excited ion waves are independent of the excitation signals, suggesting that the waves are eigenmodes of the plasma. Plasma potential, electron temperature, and electron density decrease from the source chamber to the target chamber, which establishes a spatial electrostatic field for ion acceleration. There exists a broad and multimodal ion distribution function along the magnetic field axis, which was observed using a retarding-field-energy-analyzer. Applying the model of an ion-beam-background-plasma system, three kinds of ion waves were identified as fast and slow ion-beam modes and an ion acoustic mode. In addition, the dependence of the amplitudes of the excited ion waves on the rise time of the ramp signal was presented, which is correlated with the difference in the times that the beam ions and background ions take to pass through the plasma sheath.

A dual-route optical emission spectroscopy diagnostic with wide spectral range and high wavelength resolution on HL-2A tokamak

“…The total D-OES diagnostic can be synchronized with the external trigger signal. The D-OES performance is tested with a DC hydrogen glow discharge [25]. As shown in the insert of figure 3(a), DC hydrogen plasma is generated between two plate electrodes at with a discharge current of 13 A.…”