Research

Sustainable Energies from Plasmas

Energy management seems certain to be a central problem in the twenty-first century. Fossil fuel reserves are limited, and may be exhausted in the foreseeable future. Even if new reserves are found, fossil fuels are environmentally damaging. Such fuels essentially must be burned, and combustion produces green house gases. Moreover, the parts of the world where new reserves are most likely to be found are environmentally sensitive regions such as Alaska and the Antarctic, where exploration and extraction will inevitably be destructive. These difficulties occur against a background of rising demand for energy, because of accelerating economic development, especially in the populous countries of South-East Asia, such as China and India. The twin issues of the impending exhaustion of fossil fuels (especially oil) and continuing environmental damage caused by present consumption of the same fuels have made it seem imperative to pursue alternative energy sources and reductions in energy usage. Many options are under consideration, but an important long-term possibility is fusion energy. The sun and other stars produce energy by burning hydrogen to produce helium. This is an attractive process both because the fuel is widely available (essentially it is water) and the residue is innocuous.

However, the conditions required to induce a self-sustaining fusion reaction are almost unbelievably extreme: A temperature of millions of degrees must be produced. This is very hard, but it seems to be close to realisation. In the last few months, the "Iter" project has been launched with the aim of demonstrating a burning fusion reaction. This international project will be focused at a site in the south of France where the test reactor will be built. Inside the reactor will be a very hot plasma where the fusion process occurs. The NCPST is a partner in this effort, and will be committed with our collaborators elsewhere in Europe to help in the development of the heating systems for the Iter reactor. These heating systems are used to ignite the plasma at the start of the reaction, and subsequently to help maintain the burning fusion reaction. NCPST expertise in plasma measurement, modelling and related technologies will be committed to the Iter project.

List of projects within programme

Association Euratom & DCU

This is a long standing (since 1996) collaborative programme that incorporated a large number of projects. An annual work plan, submitted and approved by a steering committee, outlines the project being undertaken, the major milestones and deliverables and the resources associated with the project. It is anticipated that this project will continue through FP7.

Projects

• JET NBI Neutraliser MMT
• Development and commissioning of a laser photodetachment technique in an RF system
• Optical Emission Spec
• Laser Photdetachment studies on the Kamaboko III
• External Cavity Technique
• Development and commisioning of a B-Dot probe
• Long pulse operation with the Kamaboko III
• Langmuir Probe studies : EEFD Measurements W / UKAEA
• Power Balance on the Mantis Test bed
• RF Ion Source and Collab with IP

Technical Outline

The NCPST energy research programme is primarily concerned with the development of fusion power through participation in the international .Iter. project. NCPST is the leader and coordinator of the Irish Fusion Association, which is funded by the pan European EURATOM authority, the vehicle for European participation in the .Iter. project. The NCPST fusion research effort is thereby directed towards support of the .Iter.. The focus of the NCPST programme is plasma heating systems. As indicated above, a burning fusion plasma must reproduce conditions of plasma density and temperature comparable with those found in the Sun. Ideally, once the fusion reaction is ignited, the plasma will be self-sustaining . it will produce enough power to maintain itself while delivering a substantial excess that may be used to heat water to drive steam turbine generators, for example, as in a conventional power station. However, there clearly must be an initial phase where the plasma is first formed and then heated to a temperature where the fusion reaction can begin. Powerful auxiliary heating systems are required during this initial phase of the fusion burn. Important elements of these heating systems are so-called neutral beam injectors. The burning plasma is confined using magnetic fields, and these magnetic fields are necessarily strong enough to prevent charged particles from diffusing significantly. These same magnetic fields make it impractical to heat the plasma by injecting energetic beams of charged particles, since the beam particles cannot penetrate the confining field. Beam heating systems are therefore required to use neutral particles. This technique entails first accelerating a beam of charged particles to a suitable high energy, typically using an accelerating voltage of a few MV. The energetic charged particle beam is then passed through a tenuous gas where neutralization occurs. This process is not specially efficient, and minimizing the power loss at this stage is an important aim of beam heating technology development. The present generation of fusion experiments . such as the JET tokamak . utilize positive ion beams in the acceleration stage. However, has been established that the neutralization step is appreciably more efficient if negative ions are used, and this difference is important in large scale devices such as Iter. An important challenge here is to develop sources of negative ions that are reliable enough and large enough in scale to meet the Iter specifications. Negative ion sources are essentially low-temperature plasma discharges, and NCPST's technical expertise is highly focused on the problems that arise in this area. NCPST staff are expert in radio-frequency techniques, and are developing diagnostic techniques and models to push forward our basic understanding of the physics of high performance negative ion sources. This work is collaborative with the French nuclear energy laboratory at Cadarache, and a substantial fraction of the work is conducted on site in France. A typical pattern is that a diagnostic is demonstrated first on small scale experiments in Dublin, before being deployed to Cadarache. Recent and forthcoming on-site experiments include a new plasma density probe and a novel spectroscopic technique for measuring negative ion density. The latter work involves collaboration with the Open University laboratory at Milton Keynes. A second challenge for beam heating systems is the neutralization step. This affects negative and positive ion beam systems equally, and is therefore an issue for present and future experiments. As a side effect of neutralization, a low-temperature plasma forms in the neutralization cell, and this plasma transfers much of its energy to the background gas as an increase in temperature. The result is a decrease in the neutral gas density in the neutralizer, and a corresponding reduction in the neutralizer efficiency. In collaboration with JET, NCPST is investigating the physics of this effect. This is a modelling activity at NCPST and an experimental programme at JET. The immediate aim is to improve the efficiency of the JET beam heating system, but there are expected to be implications for the design of the Iter neutralizers in the future.

The potential long-term significance and commercial possibilities of the research programme to which NCPST is here contributing are obvious. Less obvious is that the scale and structure of the Iter project invites participation from small and medium sized enterprises. The managers of the Iter project envisage subcontracting much of the technology development and hardware construction. They are anxious to encourage the development of companies able to contribute to this effort. This could conceivably involve construction of such things as negative ion sources, or the development and installation of diagnostics, on ion sources or the tokamak itself.

Educationally, the impact of Iter on the plasma physics community is likely be profound. The present fusion community is much smaller than the team expected to be needed to support Iter, and many members of the community are nearing retirement age. Consequently, a large number (thousands) of qualified individuals will need to be educated in relevant scientific and technical disciplines in the next decade or so. In the longer term, and in the event of a large scale deployment of fusion technology, the implications will be still larger.