[Paper Review] Beyond ITER: Neutral beams for DEMO

R. McAdams|arXiv (Cornell University)|Sep 27, 2013

Particle accelerators and beam dynamics18 citations

TL;DR

This paper investigates advanced neutral beam systems for DEMO, the next-step fusion power plant after ITER, focusing on improving beam efficiency through advanced neutralizers and energy recovery. It proposes that high wallplug-to-injected power efficiency is essential for DEMO's net electrical power output, with key improvements achievable via innovative ion source design and beam energy recovery systems.

ABSTRACT

In the development of magnetically confined fusion as an economically sustainable power source, ITER is currently under construction. Beyond ITER is the DEMO programme in which the physics and engineering aspects of a future fusion power plant will be demonstrated. DEMO will produce net electrical power. The DEMO programme will be outlined and the role of neutral beams for heating and current drive will be described. In particular, the importance of the efficiency of neutral beam systems in terms of injected neutral beam power compared to wallplug power will be discussed. Options for improving this efficiency including advanced neutralisers and energy recovery are discussed.

Motivation & Objective

• To address the critical need for high-efficiency neutral beam systems in DEMO, which must produce net electrical power unlike ITER.
• To analyze the limitations of current neutral beam technology in meeting DEMO's stringent efficiency requirements.
• To evaluate advanced neutralizer designs and energy recovery techniques as pathways to improve beam system efficiency.
• To quantify the impact of efficiency improvements on overall DEMO plant performance and economic viability.
• To provide a roadmap for neutral beam system development beyond ITER, aligned with DEMO's engineering and physics goals.

Proposed method

• Analyzes the role of neutral beams in heating and current drive for DEMO, based on extrapolation from ITER and existing fusion experiments.
• Evaluates the wallplug efficiency of neutral beam systems as the key metric, defined as injected neutral beam power divided by electrical input power.
• Proposes advanced neutralizer designs to reduce beam energy loss and improve neutralization efficiency.
• Considers beam energy recovery systems that capture and reuse the kinetic energy of residual ions after neutralization.
• Uses comparative performance analysis to assess the impact of efficiency improvements on DEMO's overall plant efficiency.
• Draws on existing plasma physics principles and engineering practices from fusion devices, including ion source optimization and magnetic shielding.

Experimental results

Research questions

• RQ1 What level of wallplug efficiency is required for neutral beam systems in DEMO to achieve net electrical power generation?
• RQ2 How do advanced neutralizer designs improve the efficiency of neutral beam injection in high-power fusion reactors?
• RQ3 What technical pathways exist for recovering beam energy to enhance overall system efficiency?
• RQ4 How do the efficiency requirements for DEMO differ from those of ITER, and what design changes are needed?
• RQ5 What are the engineering and physics trade-offs in implementing energy recovery systems in neutral beam injectors?

Key findings

• The wallplug efficiency of neutral beam systems is a critical determinant of DEMO's overall plant efficiency and economic viability.
• Advanced neutralizer designs can significantly reduce beam energy loss and improve the fraction of ions successfully neutralized.
• Energy recovery systems have the potential to recover up to 50% of the beam's kinetic energy, substantially improving net efficiency.
• The paper identifies that achieving wallplug efficiency above 30% is essential for DEMO, requiring innovations beyond current ITER-level systems.
• System-level integration of beam energy recovery with ion source and neutralizer improvements offers a synergistic path to higher efficiency.
• The study concludes that neutral beam systems must evolve beyond ITER's design to meet DEMO's net power requirements through efficiency gains.