Study of beamlets extracted from a multi-aperture and five-stage acceleration system

Area of Science:

• Plasma Physics
• Accelerator Physics
• Fusion Energy Engineering

Background:

• ITER requires high-intensity negative ion beams for plasma heating.
• Initial beam optics studies showed significant divergence and deflection issues.
• Limited pulse length and beam energy were critical challenges.

Purpose of the Study:

• To experimentally and analytically study beam optics for ITER-relevant negative ion beams.
• To compensate for beamlet deflections and reduce divergence.
• To investigate and suppress beam halo components and reduce heat loads.

Main Methods:

• Utilized a multi-aperture, five-stage accelerator for 1 MeV, 200 A/m^2 beams.
• Implemented compensation methods for beamlet deflections.
• Employed a novel beam emittance measurement system for high-intensity beams and combined with simulations.

Main Results:

• Achieved ITER requirements: divergence <7 mrad and deflection <1 mrad.
• Extended beam pulse length from 1 to 100 seconds.
• Identified halo components originating within 1 mm of the aperture edge.

Conclusions:

• Compensation methods are effective for achieving ITER beam requirements.
• Beam pulse length has been significantly extended.
• The origin of beam halo components has been clarified, enabling targeted suppression strategies.