Breakdown in high vacuum: Contribution of dark current emission

Summary form only given. Under high electric field and vacuum conditions, cathode electronic emission phenomena result in a low intensity current, the so-called dark current. Such conditions can be encountered in circuit breakers and in the planned neutral beam injector heating systems for fusion power plants (ITER and DEMO). Apart from energy losses, the main risk posed by this dark current is a runaway phenomenon leading to breakdown and failure of the injector.