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High-frequency discharge is a form of discharge caused by the presence of a high-frequency alternating electric field between two electrodes. When an alternating voltage is applied across the discharge tube, electrons and positive ions in the gas generate additional harmonic motion under the action of an alternating electric field. Since the positive ion mass is much larger than the electron, the harmonic amplitude is small. When the frequency is low and the amplitude of the harmonic vibration is much larger than the distance between the two poles, the electrons undergo the whole process of collapse, discharge and extinction in each half cycle, and the discharge condition is the same as the DC condition. When the frequency is higher, the amplitude of the harmonic motion is much smaller than the distance between the two poles, and as the electrons move back and forth continuously, the ionization ability will be greatly enhanced. Since the amplitude of the electronic resonance is small, the amount of electrons entering the electrode will be greatly reduced. This ensures that the self-sustained discharge of the gas will no longer be provided by the secondary electrons generated by the electrode, but by the electrons generated by the ionization when the electron moves back and forth. At this time, although a small amount of positive ions and photon bombardment electrodes generate secondary electrons, since the polarities of the two electrodes constantly change, the direction of vibration of the secondary electrons may be the same as the direction of electron flow into the electrodes, and may be reversed. Therefore, it is not advantageous for guaranteeing self-sustaining conditions.

This kind of high-frequency discharge can be formed as long as there is a high-frequency electric field, and it is not necessarily a secluded electrode, so it is generally called an electrodeless discharge. The electrodeless discharge can be formed not only under an alternating electric field but also under an alternating magnetic field. Since the alternating magnetic field can generate a scorching electric field, electrons generated in the gas due to residual ionization accelerate the movement around the magnetic lines under the action of the vortex electric field, thereby generating a large amount of ionization. When the direction of the magnetic field is along the axis of the discharge tube, the vortex electric field will gradually weaken along the radial direction, and the ionization ability of the electron will also decrease in the radial direction, thus forming a concentration gradient of electrons and ions along the radial direction. Under the action of the concentration gradient, electrons and ions diffuse from the axis to the tube wall. Since the electron diffusion is faster than the ions, the diffusion results in a positive potential at the axis and a negative potential at the tube wall, which in turn creates an electrostatic field directed by the axis toward the tube wall. Therefore, there are two kinds of electric fields in the discharge tube, one is the vortex electric field around the magnetic lines of force, and the other is the electrostatic field from the axis to the tube wall. At the same time of the two electric fields, the electrons move around the axis and expand toward the tube wall, resulting in a series of concentric rings. Since the energy of electrons on different radii is the most different, the level and number of excitations are different, so the auras with different radii have different colors.

The ignition voltage at the time of high-frequency discharge is the amplitude of the alternating potential difference applied to the electrodes at the time of discharge. The amplitude of this voltage is lower than the ignition voltage of the DC discharge. The high frequency breakdown electric field strength is related to the air pressure. The higher the air pressure, the greater the breakdown electric field strength and the higher the frequency of breakdown. High frequency discharge has a wide range of applications in radar and pulse technology.

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