The space charge effect limits the functional milliamperage (mA) of the x-ray tube to approximately:

The space charge effect refers to a phenomenon that occurs in x-ray tubes during the process of thermionic emission, where electrons are emitted from the cathode and form a cloud around it. As more electrons are emitted, the increasing negative charge of this electron cloud repels additional electrons, thus limiting the number of electrons that can be drawn towards the anode to produce x-rays.

The functional milliamperage (mA) that an x-ray tube can effectively utilize is constrained by this space charge effect. For standard x-ray tubes, the limit is set at around 1,000 mA. This means that while the tube might be designed to operate at higher levels, in practical terms, the space charge effect imposes restrictions that prevent efficient operation beyond this threshold, typically maxing out around 1,000 mA under normal operating conditions.

Understanding this limit is important for radiographers as it affects the choice of exposure settings and ultimately the quality of the resultant image. Using milliamperage higher than what the tube can accommodate effectively due to the space charge effect could lead to decreased image quality and longer exposure times. Thus, recognizing that 1,000 mA is the typical upper limit of functional milliamperage in the context