Microwave tube needs high vacuum environment: microwave tube is a kind of electric vacuum device that amplifies microwave signal, mainly including electron gun, slow wave system, beam system, energy transmission device and collector, which are five basic functional components.
The function of electron gun is to generate electron beam from cathode, and then use focusing pole and anode to converge and accelerate the electron beam to form electron injection of a certain cross-section shape, size and energy.
Slow wave system is a device used to slow down the propagation speed of electromagnetic wave along the tube, so that the interaction between electron injection and high frequency electromagnetic field can convert the energy of electron beam into high frequency microwave energy, so that the microwave tube can complete signal amplification.
The beam clustering system USES magnetic field to restrain the divergence of electron injection and make it pass through the slow wave system smoothly. The energy transfer device is the inlet and outlet of the amplified microwave signal.
The collector is used to collect the electron injection current after energy exchange through the slow wave system.
It can be seen that the microwave tube USES electric field and magnetic field to control the electron beam’s internal movement, so that the electron beam can generate, accelerate, move, collect and interact with signals, so as to achieve the purpose of signal amplification. Therefore, it is absolutely necessary to avoid the collision of electrons to gas molecules, to prove the movement rule of electrons inside the microwave tube, to stop the cathode oxidation poisoning of emitting hot electrons, and to pump the microwave tube to a certain vacuum degree to ensure the normal operation of the microwave tube. The whole life of microwave tube requires the maintenance of high vacuum or ultra-high vacuum. The good vacuum ring directly affects the reliability of microwave tube.
2. To obtain a high vacuum environment and maintain the vacuum degree in the microwave tube, the gas in the tube is extracted through the exhaust process, so as to obtain a certain vacuum degree. Because microwave tube structure is complex, many parts, are generally more than 100 kinds; Vacuum gas tightness weld, there are generally dozens of weld. Therefore, the exhaust needs to be heated to a high temperature for the metal parts and welding areas for air treatment. So in the microwave tube working state, the temperature of the internal parts will be high, will not vent, so in the working state will still ensure a high vacuum.
Common exhaust system for oil diffusion pump and exhaust system and turbo molecular pump and exhaust system, the main components for the first stage pump, mechanical pump, roots pump, etc.) thick smoke, then use the main pump (oil diffusion pump, molecular pump etc.), the configuration necessary vacuum piping, must have high vacuum valve, the vacuum gauge, resistance vacuum gauge, ionization gauge, B – A vacuum gauge, etc.) the vacuum to high vacuum. When the oil diffusion pump is used, an oil well should be added to prevent the oil from contaminating the internal system of the vacuum device.
After exhaust, the vacuum can reach 106Pa, which can meet the requirements of microwave tube. In order to improve the vacuum degree of the microwave tube exhaust, reduce the put gas in the process, we use xie beam ion pump to the exhaust of microwave tube, exhaust after vacuum degree can reach 2 x10-7 pa. After the exhaust, microwave tube cold sealing and exhaust system, in the process of sealing from mechanical squeeze deflated, metal parts and microwave tube in place after a period of time, because of its high vacuum itself, internal material will be deflated, thus reducing the vacuum tube. At this time, we used a small ion pump (commonly known as titanium pump) to ensure the internal vacuum degree. At the same time, in microwave tube aging, testing and other processes, the parts in the tube will be released after the bombardment of high-speed electron beam, and titanium pump is needed for extraction. The current of the titanium pump also has the function of detecting the vacuum inside the microwave tube.
After the microwave tube aging and testing, the vacuum in the tube generally remains stable. Because titanium pump itself volume is larger, affect the appearance of the microwave tube size, generally we will be removed (no requirements on the appearance can not be removed).
However, microwave tube and other electrical vacuum devices generally need a certain long life, the general index requirements for 3 years (space microwave tube requirements for 20 years). In this long time of work, the parts of the material itself defects (pores, cracks, etc.) and the dead space welding may produce chronic leakage or air, destroy the internal vacuum, we here water machine supporting soft water hardness testing agent, and some domestic soft water manufacturers prepared hardness testing agent. One of their common features is that they serve only as indicators. That is, it can only qualitatively indicate whether the hardness of the water sample is within a specified value (e.g. 0.03mmol/L). Several indicators have been tested by the author, and the error is relatively large, one of which is up to 300%. 4 the use of KS soft water hardness tester has the advantages of fast test speed, high efficiency, only a few seconds to determine a water sample.
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Under the same exhaust technology, we calculated the vacuum degree of five microwave tubes after exhaust.
Inhalation. Absorb the residual gas in the tube and the gas re-released from the parts in the tube to maintain the vacuum degree in the tube.
The principle of absorption vacuum pump can be seen that in the manufacture of microwave tubes, the absorption vacuum pumps like coupler, titanium pump and getter are used. Here’s how they work.
(d) the mistle ion pump and titanium pump: a honeycomb anode is installed between two cathode plates. A magnetic field is applied perpendicular to the cathode plate and parallel to the honeycomb axis. The electrons produced during ionization continue to separate from other gas molecules. During ionization, electrons surrender energy and gradually reach the anode, while the positive ions are accelerated to the negative electrode made of titanium. Ions and titanium metal interact with each other, and there are three pumping methods: (1) the ion (xie xie) removes the titanium cathode material, plays the role of deposition of degassy film, adsorption reaction gas (nitrogen, hydrogen and oxygen); Some ions have enough energy to be buried in the electrode and thus absorbed by ion implantation, which is effective against all ions, including noble and noble gases. (3) titanium ejected from the cathode can bury the gas atoms on the target electrode and improve the pumping speed of the inert gas. The main application of getter in microwave tubes is non-evapotranspiration getter, which USES zirconium and Zr – V – Fe alloys to form porous sintering structure. Activated after normal baking of the microwave tube at 400-500°C, it has a strong inspiratory capacity to CO2, 2, N2 and water vapor with its porous structure.
(4) the effect of a certain suction suction on absorption curve of CO2 and H2 for u4 adsorption vacuum pump (coupe) The figure below is our comparison of two vacuum systems. System 1 is mechanical pump + molecular pump, and system 2 is mechanical pump + molecular pump + ion pump.
It can be seen that the application of couplet pump improves the vacuum degree of the microwave tube and reduces the air discharge in the process of aging and testing, etc. The current drops to almost zero when the vacuum degree is detected by the following small titanium pump, which reduces the time of these processes and improves the production efficiency and the reliability of the pipe.
Microwave tube in the exhaust pipe to increase small ion pump, titanium pump) and an increase in the electron gun getter, exhaust with microwave tube, exhaust system high temperature baking process requirement, to activate the getter, exhaust process of titanium pump at the same time also has carried on the exhaust, after the cold sealing off the residual gas pipe and tube parts to release gas, titanium, and getter pump suction as well as maintain the vacuum tube. In the following licensing process, the current of the titanium pump can also help detect the micro-leakage point in the case of microdew, which facilitates the production and reduces the scrap rate of the microwave tube. In the microwave tube that increases inspiratory agent, the probability that electron gun high pressure ignites reduces greatly, after long time is stored, add electricity to microwave tube directly and do not appear to let off air or everybody phenomenon.
It can be seen that the absorption vacuum pumps such as coupler pump, titanium pump and getter can improve and maintain the high vacuum degree in the production of microwave tube, thus improving the reliability of microwave tube and increasing its service life.