Anode Current Density Distribution Measurements for Different Vacuum Arc Modes Subjected to Axial Magnetic Field

Abstract

We report our measurements of anode current density distributions for different modes in vacuum arc discharge using a split-anode and a cup-shaped axial magnetic field cathode configuration system. The modes investigated included the diffuse arc and anode spot. The anode surface was divided into four regions: one central region and three symmetricaldisposed peripheral annular-arc regions. Three different-sized central regions were selected with diameters of 12, 18, and 20 mm. The contact material was CuCr25 (25% Cr). The arc current in the tests ranged from 6 to 14 kA (rms) at 50 Hz. The opening velocities were 1.8 and 2.4 m/s, respectively. The currents of the four areas on the anode contact were measured by four Rogowski coils situated outside the vacuum chamber. The experimental results show the current density distribution in different arc modes. For the diffuse arc mode with arc currents of 6 and 8 kA (rms), the average current density in the central region at current peak ranged from 8.5 to 15.9 A/mm 2 . The anode spot current density ranged from 31.9 to 37.7 A/mm 2 , estimated from the current density in the eroded region caused by the anode spots covering the entire central region of diameters 12 and 18 mm, at currents of 12 and 14 kA, respectively, regarded as the lower limit current density of the anode spot. Moreover, the dependence of the current density distribution on opening velocity in diffuse arcs was slight. For the anode spots, the current density distribution with higher opening velocity was more concentrated.

Study of axial double layer in helicon plasma by optical emission spectroscopy and simple probe

“…The results of the plasma potential along the Z-axis are shown in figure 3(a) under RF powers of 200, 800, 1000, 1200 and 1500 W. The helicon plasma was operated in a capacitively coupled mode (the E-mode at a lower power of 200 W), an inductive coupled mode (H-mode) at a higher power of 800 W, and finally enters wave-coupled mode (W-mode) at high powers of 1000, 1200 and 1500 W, as seen in figure 3(b); details of the mode transition can be found in [30]. In the first mode at low power, the plasma potential data (noted as stars in figure 3(a)) acquired by the RF-compensated probe (RFCP) is also presented for comparison with the current method (noted as open diamonds in figure 3(a)).…”

“…The rate coefficients are the function of the cross-sections and the electron energy distribution function, which are related to the electron temperature and assumed to be a Maxwellian distribution of energies in this paper. The rate coefficients and other parameters are listed in reference [29] and [30]. Here, we selected the argon emission lines 750.39 nm and 811.53 nm.…”

Characteristics of inductively coupled plasma (ICP) and helicon plasma in a single-loop antenna

“…Generally, the coupled TG mode and H mode will heat electrons both in the center and in the radial edge, since a TG wave with a short radial wavelength is highly damped near the radial boundary [14], and an H wave with a longer wavelength can reach the center of the plasma [15]. As is well known [16][17][18][19], helicon plasma will undergo three discharge modes, namely the E, H, and W modes, which can be characterized by density jumping, spectral line intensity variation, and intensified chargecoupled device discharge images.…”

Axial profiles of argon helicon plasma by optical emission spectroscope and Langmuir probe

“…Experimental measurement is usually a direct and best way to obtain information of the helicon plasma. Langmuir RF-compensated probe [14], for example, is a commonly used method to determine the plasma density at low pressure.…”