Maintaining the alignment of electric and magnetic fields in an x-ray tube operated in a magnetic field

摘要

A new technique for maintaining the alignment of electric and magnetic fields in an x-ray tube so the tube can be operated in the presence of a static external magnetic field without being negatively affected thereby. Deflection of the electron beam of the x-ray tube by the high magnetic field is reduced or eliminated by modifying or canceling, at a location near the electron beam, the magnetic field components transverse to the beam. In a preferred embodiment, a set of electromagnet coils are positioned on or near the tube and oriented in a way that when current is applied internal magnetic fields are produced in a direction opposite to the transverse magnetic fields, thereby causing cancellation. In one implementation, one or more sensors are used to detect the transverse magnetic fields. The sensor is positioned near the electron beam, either inside or outside the x-ray tube. The sensor produces a signal dependent on a static magnetic field component transverse to the desired direction of the electron beam. This signal is used to control the amount of current applied to the coils. A controller and a feedback circuit may be included to adjust in real time the amount of current being applied.