Methods of Beam Emittance Measurements of High Power Negative Ion beams for NBIs.

A thermal beam emittance measurement method is developed specifically to measure high power density beams for the ITER neutral beam injection system (NBI)’s. A one-dimensional carbon-fiber composite (CFC) target is utilized to withstand the high current densities of the negative hydrogen beam making the beam emittance measurement possible. Schemes for the emittance measurement were discussed since beam instabilities are present in various stages of the beam phase. The allowable time for the measurement will be less than 2 seconds and it’s necessary to monitor the CFC temperature to not exceed 2000°C. The proposed measurement scheme to minimize beam instabilities is through the constant operation of the arc discharge and pulsed beam extraction. Mechanical structures are also being designed for rapid measurements to select different phases of the beam and for implementing the measurement system to long pulse beam operation. [ABSTRACT FROM AUTHOR]