X-ray devices used in the medical field contain an X-ray tube which typically includes a cathode which is heated to emit electrons, a (typically rotating) anode having a target surface facing the cathode, and a surrounding glass and/or metal frame containing an X-ray-transparent window secured by a window mount. Some emitted electrons strike the target surface at a focal point and produce X-rays, and some of the X-rays exit the frame as an X-ray beam through the X-ray-transparent window. Other emitted electrons do not produce X-rays and are backscattered when they strike the focal point on the target surface.
Many of the backscattered electrons go on to strike and heat the frame including the X-ray-transparent window and the window mount. It is known to place an electron collector between the focal point and the X-ray-transparent window to capture backscattered electrons that would otherwise strike and heat the X-ray-transparent window, wherein the electron collector has a central hole to permit passage of the X-ray beam. The heated frame is typically cooled by a liquid coolant, such as oil or water, located between the frame and a surrounding casing. The dissimilar coefficients of thermal expansion of the X-ray-transparent window and the window mount generate mechanical stresses which can cause tube failure. Additionally, high temperatures in the X-ray-transparent window itself can induce boiling of the adjoining liquid coolant. Such coolant boiling will degrade the quality of the X-ray beam which exits the frame through the X-ray-transparent window. Existing grounded metal frame tubes include those having high-cost components to mechanically join the window to the rest of the frame while reducing thermal stresses to acceptable levels. Some known tubes have enhanced cooling applied to the window region.
It is also known that the backscattered electrons can create a thermal hot spot on the frame and can burn a hole through a glass frame. Such hot spot is located on the frame apart from the X-ray-transparent window and the window mount. Reducing the power of the X-ray beam and/or increasing cooling to the thermal hot spot region are known techniques used to overcome this problem.
What is needed is an improved X-ray tube design which reduces heating of the X-ray-transparent window and the window mount from backscattered electrons.