The following conditions are required to ignite the hollow cathode arc light:
- A hollow cathode gun made of tantalum tube is installed on the coating chamber wall and can be used to emit hot electron flow. The inner diameter of the flat tube is φ 6~ φ 15mm, with a wall thickness of 0.8-2mm.
- The power supply is composed of an arc starting power supply and an arc maintaining power supply in parallel. The voltage of the arc striking power supply is 800-1000V, and the arc striking current is 30-50A; The arc voltage is 40-70V, and the arc current is 80-300A.
The hollow cathode arc discharge process follows the process of converting from abnormal glow discharge to arc discharge in the “volt ampere characteristic curve”. Firstly, a power supply is required to provide an 800V starting voltage to generate glow discharge in the tantalum tube. The high-density argon ions inside the tantalum tube bombard and heat the tube to the temperature where hot electrons are emitted, resulting in a large amount of plasma electron flow and a sudden increase in the current of the hollow cathode arc. Then, a high current power supply is also needed to maintain the arc discharge. The process of converting from glow discharge to arc discharge is automatic, so it is necessary to configure a power supply that can output both high voltage and high current.
If these two requirements are concentrated on a single power source, the secondary output end of the power transformer must be wound with very thick wires for many turns in order to output high voltage and high current, which will be a large volume power source. After years of improvement, it is possible to parallelize a small arc starting power supply with a maintenance arc power supply. The arc starting power supply uses thin wires to wind multiple turns, which can output a high voltage of 800V to ignite tantalum tubes and generate glow discharge; The arc power supply can output tens of volts and hundreds of amperes of current by winding a thick wire with fewer turns to maintain the stability of the hollow cathode arc discharge. Due to the parallel connection of two power supplies on tantalum tubes, during the process of converting from abnormal glow discharge to arc discharge, the two power supplies will automatically connect and switch from high voltage and low current to low voltage and high current.
- Quickly adjust the vacuum level. The vacuum level for glow discharge in tantalum tubes is around 100Pa, and the deposited film structure under such low vacuum conditions is inevitably coarse. Therefore, after igniting the arc discharge, it is necessary to immediately reduce the amount of air flow and quickly adjust the vacuum level to 8×10-1~2Pa to obtain a fine initial film structure.
- The workpiece turntable is installed around the coating chamber, with the workpiece connected to the negative pole of the bias power supply and the vacuum chamber connected to the positive pole. Due to the high current density of the hollow cathode arc, the bias voltage of the ion coated workpiece does not need to reach 1000V, usually 50-200V.
5. Set a focusing electromagnetic coil around the Gan collapse, and the electromagnetic field generated by applying current to the coil can focus the electron beam at the center of the metal ingot, increasing the power density of the electron flow.
Post time: Jul-20-2023