Precautions for using hydrogen thyratron

Cecelia Qiu Cecelia Qiu 10 January
Precautions for using hydrogen thyratron

Hydrogen Thyratron is a hot cathode low pressure gas (hydrogen or deuterium) discharge device. It has the advantages of high working voltage, large pulse current, rapid and stable ignition, low trigger voltage, high repetition frequency, high reliability, high efficiency, light weight, small body, and convenient use. Widely used in scientific research, military, medical fields and high-tech civilian products, including lasers, radars, pulse modulators, medical linear accelerators, crowbar protection and other electronic instruments and equipment.

Precautions for using hydrogen thyratron

(1) Preheating time (usually 5min to 15min, 15min is easy): The hydrogen thyratron needs enough preheating time to make the cathode temperature rise and fully emit electrons. If the preheating time is not enough, it will cause a positive tube. If the pressure drop is too large, positive ions bombard the cathode and spark in the tube.

(2) Cooling: The hydrogen thyratron emits a lot of heat when it is working, and the tube wall is very hot, so attention should be paid to cooling (the fan or cold air conditioner cannot be stopped, otherwise it will reduce the life or damage the hydrogen thyratron). Do not touch the tube immediately to avoid burns. Note: After cooling, hydrogen is adsorbed on the hydrogen generator again (equivalent to recovery).

(3) Hydrogen generator voltage adjustment (to adjust the hydrogen concentration of the hydrogen generator): After the hydrogen thyratron is used for a certain period of time, the internal hydrogen pressure will drop, and the heating voltage of the gas accumulator needs to be increased to increase the hydrogen concentration. When the DC high voltage of the modulator is normal and the charging high voltage drops, and the charging current and the average tube current also drop, it can be suspected that the hydrogen pressure of the hydrogen thyratron is insufficient.

The method of adjusting the heating voltage: adjust the resistance value of the series resistance wire, so that the voltage of the hydrogen generator increases in steps of 0.2VDC each time. After the arc is the working upper limit of the hydrogen thyratron), the voltage is reduced in turn until no arcing occurs (the voltage of the hydrogen generator voltage at this time is the appropriate working voltage of the hydrogen generator).

(4) If the startup is always over-current and the hydrogen thyratron makes a loud sound, you should first judge whether the hydrogen thyratron is faulty (before judging, you should first check the front stage of the hydrogen thyratron, the small modulator part , look at its waveform and various parameters), if it is, replace it (if there is no new tube, you can take off the hydrogen thyratron to check whether the resistance wire is burnt and stuck, if so, you can store the bad hydrogen thyratron. The resistance wire on the top can be removed and replaced.) If all parts of the hydrogen thyratron are checked, the method of reducing the filament voltage of the hydrogen thyratron (normally 6.2VDC-6.4VDC) can be adopted: in the primary of the filament transformer Connect a 5W (20Ω) resistor in series to reduce it to about 5.8VDC. If it is not enough, connect another same resistor in series until it can work normally. This will temporarily solve the problem, but you will need to buy a new tube to replace right away.

In addition, there is a degassing device. Since a layer of adsorbent material (like activated carbon) is coated on the inner wall of a section of the new tube, it mainly absorbs ions in the air to increase the vacuum in the hydrogen thyratron, thereby improving the the service life of the tube.

(5) Due to the self-discharge phenomenon of vacuum devices such as hydrogen thyratrons, the vacuum degree is reduced, so the vacuum devices cannot be stored for a long time, and the spare tubes should be used alternately to improve the vacuum degree of the tubes and further improve the service life.

(6) Reasons for the overcurrent of the hydrogen thyratron: ignition and aging of the magnetron; too high repetition frequency; too high internal pressure of the hydrogen thyratron.

(7) A hydrogen generator is installed inside the hydrogen thyratron. The heating wire of the hydrogen generator is connected in parallel with the hydrogen thyratron filament of the heating cathode. When heating, hydrogen gas is emitted, and the voltage of the heating wire of the hydrogen generator can be adjusted (adjust the bottom Resistance method) can make the hydrogen thyratron work stably.

(8) Whether the hydrogen thyratron works normally: it mainly depends on whether the filament voltage is normal, which is related to whether the charging/discharging is normal (the charging inductance is mainly judged by the charging current waveform). Although there is a measuring hole on the M machine, the signal line is not connected. Connect the line from the back of the main unit to display the charging waveform on the console (if you see a peak sparking waveform in the waveform on the oscilloscope, you can confirm the The reason for the fire is caused by the internal ignition of the charging inductor).

Summarized by Easybom.

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