The operating frequency range of the thyratron does not exceed tens of kilohertz and is mainly determined by the recovery time of the control action of the grid. The recovery time depends on the deionization time. After termination of the discharge, the concentration of ions in the discharge gap decreases due to deionization in the volume and their withdrawal to the anode and grid. At the same time, a large volume of the ion shell is required to compensate for the grid charge. As the ion concentration decreases, the width of the ion shells surrounding the coils of the grid increases, and at the moment when they overlap, the grid restores its control action.
If a positive voltage is applied to the anode of the thyratron before the grid restores its control action, the thyratron will light up at a lower voltage at the anode, which will disrupt its normal operation. Reducing the limiting resistance in the grid circuit increases its ion current, which reduces the deionization time and increases the operating frequency.
The development time of an avalanche discharge is an order of magnitude shorter than the deionization time and therefore practically does not affect the frequency properties of ion devices. Deionization occurs faster on the surface than in the volume, so the inclusion of an additional shielding grid in the thyratron, mounted on a base or connected to a cathode, reduces the deionization time. In this regard, the shielded thyratron has a higher cut-off frequency.
The presence of an additional grid allows you to change the ignition voltage by changing its potential. The positive potential of the shielding grid improves the arc conditions, and the negative potential makes it difficult, so in the first case, the ignition potential along the anode decreases and the starting characteristic shifts to the left, and in the second case, the potential increases and the characteristic shifts to the right. In addition, the shield partially protects the anode from ion bombardment, which increases the reverse ignition voltage.
For the thyratron, there is a limit positive voltage at the anode U, at which the ignition voltage depends on the voltage across the grid. With a higher voltage at the anode, a glow discharge occurs between it and the grid, the resulting ions compensate for the negative charge of the control grid, and a working arc is ignited between the anode and the cathode.
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