Types of X-ray Tubes and High-voltage Power Supplies

A simple X-ray tube consists of a filament (cathode), which generates thermal electrons, and an anode, which generates X-rays when electrons collide, fixed in a glass tube and vacuumed. Many of these tubes are relatively small, and are used at voltages ranging from 20 kV to 130 kV. They are used for non-destructive inspection using X-rays, foreign object inspection, analysis and medical applications. They are usually placed in a special metal case (housing for X-ray tubes) filled with insulating oil to reduce X-ray leakage and make them safe and easy to handle. In some cases, the surface is covered with resin or other material. In non-destructive testing of infrastructure, etc., X-ray shield cases filled with insulating gas are used instead of insulating oil to reduce the weight of the X-ray unit. The high-voltage power supply can be connected to anode grounding, cathode grounding, or bipolar.

A Beryllium-Window X-Ray Tube is an X-ray tube with beryllium (element symbol Be, atomic number 4) attached to the output portion of the X-ray. X-ray tube voltage ranges from a few kilovolts to 80 kV, and is mainly used for X-ray analysis. They are generally more expensive than standard X-ray tubes due to the specialized window material.

A rotating anode X-ray tube is an X-ray tube in which the anode, which generates X-rays when hit by an electron beam, rotates. By rotating the anode, heat can be dispersed, and the tube current can be increased to increase the intensity of X-rays. It is mainly used in medical applications such as CT scans and X-ray imaging. Due to their complex mechanical structure, these tubes are typically higher in cost compared to stationary anode tubes.

A ceramic X-ray tube is a vacuum tube in which the insulating part of the X-ray tube is made of ceramics instead of glass. They are resistant to heat and shock and are mainly used for non-destructive testing and XRD. Other small X-ray tubes made of ceramics are also used in handheld X-ray fluorescence analyzers and soft X-ray ionization tubes.

An end-window X-ray tube is an X-ray tube in which the beryllium window is located at the end face of the X-ray tube. Since the anode, which generates X-rays, is located near the end of the beryllium window, the distance to the analysis sample can be shortened and more X-rays can be emitted. The power supply for X-ray tubes is a cathode-grounded high-voltage power supply, with tube voltages ranging from 50 kV to 80 kV and power from 50 W to 4 kW.

Manufacturers

MICRO X-RAY: https://microxray.com/

VAREX IMAGING: https://www.vareximaging.com/products/industrial/vf-series-x-ray-tubes/

X-ray tubes for XRD are X-ray tubes used in X-ray diffractometers (XRD), which are designed to be easily interchangeable since different target materials are used depending on the analysis target. X-ray tubes for XRD are sold by various companies, and they are highly interchangeable and can be used by different manufacturers. However, it is important to note that there are two types: short anode and long anode. There are also glass and ceramic tube types available on the market. The voltage can be up to 60kV, but the power of the X-ray tube is large, ranging from 1kW to 4kW, and water cooling is required. X-ray tubes for XRD are anode-grounded type.

Manufacturers

Philips/Panalytical: https://www.malvernpanalytical.com/en/products/category/x-ray-tubes/xrdtubes

Siemens/Bruker: https://www.bruker.com/en/products-and-solutions/diffractometers-and-x-ray-microscopes/x-ray-diffractometers/davinci-components/sources.html

PROTO: https://www.protoxrd.com/products/x-ray-tubes/overview

AXT Pty Ltd (AXT): https://www.axtxraytubes.com/ceramic-xrd-tubes/

A microfocus X-ray tube is an X-ray tube in which the X-ray emitting area is very small, ranging from a few micrometers to several tens of micrometers. Electrons generated from the filament are focused onto the anode (target) to generate X-rays. The area where X-rays are generated is called the focal point, and by reducing the size of the focal point to the micrometer size, sharp X-ray images with little blur can be obtained even when X-ray images are magnified. For this reason, microfocus X-ray tubes are used for non-destructive inspection of electronic devices with fine structures.
Microfocus X-ray tubes require multiple electrodes in addition to a high-voltage power supply for acceleration in order to focus the electrons. Acceleration voltages of 90kV to 150kV are used. There are two types of microfocus X-ray tubes: open X-ray tubes and sealed microfocus X-ray tubes.

Open-type X-ray tubes feature replaceable filaments and targets, requiring continuous evacuation by a vacuum pump during operation. These tubes typically offer micro-focus or nano-focus capabilities, enabling high-magnification imaging of minute details with minimal blur.

There are two main configurations:
Reflection Target Type: Similar to standard X-ray tubes, X-rays are emitted from the same side that the electron beam strikes. Due to target thickness, X-ray emission from the back is minimal.
Transmission Target Type: A target material (e.g., tungsten) is deposited on a thin window material like beryllium or diamond. Electrons strike the target, and X-rays are emitted through the window. This allows the sample to be placed extremely close to the focal point, achieving high geometric magnification. Note that target current is limited by the thermal capacity of the thin target.
Open X-ray tubes are commercially available with acceleration voltages ranging from 100 kV to 300 kV.