Long pulse H- ion beam acceleration in MeV accelerator.

Area of Science:

• Plasma Physics
• Accelerator Technology
• Fusion Energy Engineering

Background:

• The International Thermonuclear Experimental Reactor (ITER) requires a robust neutral beam injection (NBI) system.
• High-power negative hydrogen ion (H-) beams are crucial for efficient plasma heating in fusion devices.
• Existing MeV accelerators faced limitations in pulse length due to grid heating and melting.

Purpose of the Study:

• To enhance the performance of the MeV accelerator for ITER's NBI system.
• To investigate the impact of water-cooled grids on long-pulse H- ion beam acceleration.
• To increase the energy density achievable in high-current, long-pulse ion beams.

Main Methods:

• Development and implementation of a MeV accelerator with new water-cooled grids.
• Experimental acceleration of H- ion beams with extended pulse durations.
• Measurement of beam parameters including energy, current, and pulse length.
• Analysis of energy density and grid behavior under high-power operation.

Main Results:

• Pulse length extended to 5 seconds for 750 keV, 221 mA beams.
• Pulse length extended to 10 seconds for 600 keV, 158 mA beams.
• Energy density increased by over an order of magnitude compared to non-cooled grids.
• Grid melting observed at higher energy/current due to beam deflection, limiting pulse length.
• Breakdowns between grids occurred, further limiting pulse duration.

Conclusions:

• Water-cooled grids are effective in extending the pulse length of H- ion beams.
• Beam deflection remains a critical issue causing grid damage and limiting performance.
• Future experiments will focus on compensating beam deflection via aperture displacement to overcome current limitations.