What happens when an x-ray tube is space charge limited?

When an X-ray tube is space charge limited, the emission of electrons from the cathode is restricted by the accumulation of negative charge around it, which repels additional electrons. This results in a saturation of electron flow, limiting the tube current despite increasing the applied voltage. Consequently, the X-ray output becomes less efficient, as the tube cannot produce more X-rays even with higher potentials, leading to a maximum achievable current known as the space charge limit. This phenomenon typically occurs at lower voltages and is more pronounced in tubes with high cathode temperatures.