Which of the following describes an unwanted surge of electrical current in CT equipment?

The term that best describes an unwanted surge of electrical current in CT equipment is tube arcing. Tube arcing specifically refers to the phenomenon where an electrical discharge occurs in the x-ray tube, often due to high voltage leading to unstable currents. This can result in performance issues or damage to the tube itself, disrupting the normal operation of a CT scanner.

Power fluctuations refer to variations in the power supply that may not necessarily involve a sudden surge and could occur without impacting equipment directly. Voltage spikes signify a brief increase in voltage that can affect electronic devices but may not specifically describe the context of CT equipment such as the x-ray tube. Grid failure refers to a complete loss of electrical supply, which is a broader issue that affects all electrical equipment and is not limited to surges in current. Thus, the specificity of tube arcing in relation to CT equipment makes it the most appropriate description of an unwanted surge of electrical current.