Betatron

The betatron is an accelerator that whirls electrons in circles instead of spirals, effectively accelerating beta particles without incurring mass increases that would cause the accelerating pulse to go out of sync. This innovation made useful electron bombardment possible.
 Donald William Kerst United States 1940 Betatron

The betatron is an accelerator that whirls electrons in circles instead of spirals, effectively accelerating beta particles without incurring mass increases that would cause the accelerating pulse to go out of sync. This innovation made useful electron bombardment possible.