CT ball tubes are mainly composed of tube cores, tube sleeves, heat sinks, insulating oil and some accessory parts, etc. Among them, the core is the central component of the tube, which is composed of an anode and a cathode.

I. Buffer Tube (Expansion Bellow

When the ball tube is in operation and generates heat, the volume of the oil increases, acting as a buffer.

Ii. Boom (Horn

It contains a socket for connecting high-voltage cables to supply power to the X-line.

Iii. Filament /Focal Spots (Filaments/Focal Spots)

At present, almost all X-ray tubes use tungsten as the filament material. Because tungsten has a certain emission capacity at high temperatures; It has a relatively high melting point (3370℃) and is not easy to evaporate into gas at high temperatures. It has good ductility and tensile strength, is easy to process, and can be drawn into fine wires to form certain shapes. It is not prone to deformation under the absorption of a strong electric field.

Due to the limitation of the specific capacity of the anode target surface (the power dissipated on a focal area of 1mm ²), the filament cannot be made too small. As the practical focal area of the X-ray tube with a fixed anode is very small, a too small focal area will reduce the amount of emitted X-rays. To obtain a large amount of X-rays, the filament must be thickened. Although this increases the focus and improves the geometric ambiguity, the increase in X-ray quantity should shorten the exposure time to prevent ambiguity caused by the movement of the illuminated object.

At present, many X-ray tubes achieve focal points of different sizes by equips two filaments of different sizes on the same cathode

It is called a bifocal X-ray tube. Its filament has three leads. One is the common lead, and the other two are the leads of the large and small focus filaments respectively.
Vii. Yin Extremes (-)

When the filament temperature rises to a certain value, it begins to emit electrons, and the number of emitted electrons depends on the temperature of the filament.

It can be seen from the figure that when the filament temperature is low, the density of the emitted electron current is relatively small. However, when the temperature rises to a certain value (2600°K), the emission current density increases extremely rapidly. Therefore, when adjusting the X-ray tube current, special attention should be paid to this characteristic. That is, when the filament voltage increases to a value close to the maximum, a slight change in the filament voltage will cause a significant change in the tube current.

Iv. CT Tube Port

The exit of the X-ray, and the sight of the X-ray is also installed here.

V. Glass Core Rod (Tube Insert)

Glass mandrel: The X-ray glass casing is used to support the anode and cathode and maintain the vacuum degree inside the tube. Boric acid hard glass with silicon as the main component, which can withstand high temperatures, has high insulation strength and a small shrinkage coefficient, is usually adopted. The vacuum degree in the X-ray tube should be maintained below 133.322×10-7Pa(10-7 MMHG) to ensure the normal heating of the filament and the speed at which electrons fly towards the anode.

Vi. Stator

The heavy anode disc is firmly mounted on the rotating shaft in the bearing. On the same shaft, there is also a copper cylinder serving as the rotor for the induced electron motion. The stator of the motor is sleeved outside the glass shell of the X-ray tube. The current flowing through the stator winding creates a rotating magnetic field, driving the rotor to rotate and thus the anode to rotate. The cathode of the tube is equipped with a tungsten filament wound into a spiral tube shape. Its position deviates from the central axis of the pipe. Therefore, when the anode rotates, the practical focus rotates along its surface, and its trajectory is a circular ring, which causes the generated heat to be distributed over a continuously moving circular surface. When the heat mass received per unit area at the focus becomes smaller, the power of the X-ray tube is significantly increased. Although the actual focus area is larger, the effective focus is very small, which improves the clarity of the X-ray image.

Cathode: The cathode of an X-ray tube is composed of a filament, a focusing cover, etc. Its function is to emit electrons and focus them to bombish the anode.

"Yang Extreme (+

Anode: The function of the anode target is to withstand electron bombardment and radiation X-rays while distributing heat in. Tungsten is commonly used as the material for the anode target surface. It has the advantages of high atomic number, high melting point and low vapor pressure at high temperatures.

This end is the part close to the cathode installation. This is the part at the end of the frame close to the anode installation

Viii. Trunnion Area

The ball tube suppliers (such as Siemens, Pique, GE, etc.) specially provide an ear shaft ring around the ball tube for the clamping frame. This ring enables the tube frame to be placed flat and fixed at the location where the CT tube is placed.

Ix. Target

The function of the anode target is to withstand the electron bombardment and radiation X-rays while distributing heat in. Tungsten is commonly used as the material for the anode target surface. It has the advantages of high atomic number, high melting point and low vapor pressure at high temperatures.

The tungsten target surface is generally square or rectangular, with a thickness of 1.5mm to 3mm, and is inlaid on an oxygen-free copper column with good thermal conductivity. This not only ensures high radiation performance but also enables heat to be conducted in a timely manner.

The area of the anode target bombarded by an electron beam is called the practical focus. To reduce geometric ambiguity in order to obtain a clear image, it is requested to decrease the effective focus of X-rays, which can be achieved by reducing the inclination Angle of the anode target surface. Of course, from the perspective of projection requirements, the smaller the effective focal area, the better. This inevitably requires a reduction in the actual focal area. However, under a certain anode load power condition, the specific capacity of the target surface is increased, which is not conducive to heat diffusion. Therefore, the inclination Angle should not be too small. However, it should not be too large either. If the anode tilt Angle is too large, it will increase the effective focal area, making the image blurry.

The secondary electrons generated on the anode target surface not only pose a threat to the filament and glass shell but also scatter in all directions, causing X-rays to be produced in the center outside the anode target surface. These non-focal X-rays can affect the clarity of the image. Therefore, a metal cover made of oxygen-free copper is added to the anode, which is called a rebound cover. The axial opening of the cover is for the cathode electrons to pass through at high speed. The opening on the side is the X-ray outlet.

In this way, the tungsten target surface of the anode, the copper column and the rebound cover are integrated into one unit. After being sealed with an iron-nickel-drill alloy with a shrinkage coefficient similar to that of glass and a glass shell, they are connected to the outside of the tube.