Dependence of phantom current in a metal vapor laser on electrode geometry

Abstract

It is observed that the discharge current in a copper vapor laser rises prior to the voltage breakdown. This current, which appears almost 50 ns before the discharge breakdown and is equivalent to almost 70% of the peak current at the time of breakdown, is termed the phantom current. It is reported that by reducing the residual electron density (phantom current) in a metal vapor laser (MVL), its performance can be significantly improved. Metallic pins are used in the electrode to facilitate discharge in the long discharge tube. Besides augmenting the discharge during the initial stage, it has a significant impact on the laser performance. In this paper, we find out the correlation between the phantom current and the electrode pin geometry and then present the optimum electrode geometry for improved laser performance. It was observed that the number of pins in the electrode affects the localized electric field in the nearby region and plays a dominant role in the quantum of the phantom current in the discharge tube of the laser. The MVL system was tested with electrodes that had a different number of pins (zero, eight and 36) and it was found that the phantom current is minimum when the electrode has zero pins and highest with an eight-pin electrode.

Analysis of the discharge plasma impedance of copper vapor laser

“…A CVL discharge tube (36 mm and 1.8 m long) in leakfree condition delivers an average output power of 30 W (plane-plane resonator configuration) and serves as the load to the pulse power supply. The complete details of the PGU, the laser head and the measurement setup are reported in detail in our previous publications [14][15][16][17]. A schematic of the pulse discharge circuit and the laser head is shown in figure 1.…”

“…The PGU consists of a resonant charging circuit, pulse transformer, Insulated Gate Bipolar Transistor (IGBT) and the magnetic pulse compression (MPC) stages [15]. The pulse voltage across the laser head is 13 kV and the pulse current through the laser head is in the order of 450-500 A, depending on the laser head discharge condition [14,17].…”

“…The pins facilitate the discharge during initial condition due to the sharp edges, which intensify the electric field; thus, pins are used in the laser electrodes. In previous reports [14,15], we presented the impact of different pin configurations on the laser performance. It has been shown that the electrode pin configuration has an immense impact on the phantom current in the metal vapor laser [14].…”

“…In previous reports [14,15], we presented the impact of different pin configurations on the laser performance. It has been shown that the electrode pin configuration has an immense impact on the phantom current in the metal vapor laser [14]. In this paper we studied the impact of pin configurations on the laser resistance.…”

“…The discharge pins were of diameter 3 mm, having a total length of 18 mm, and a cone length of 5 mm with a sharp edge (tip) diameter of nearly 0.01 mm. The purpose of choosing specifically 0, 8 and 36 pins is to exhibit maximum variation in the electric field enhancement, as explained in detail in [14].…”