A)The UK Just Switched on an Ambitious Fusion Reactor – And It Works
First plasma has been achieved.
The UK’s newest fusion reactor, ST40, was switched on last week, and has already managed to achieve ‘first plasma’ – successfully generating a scorching blob of electrically-charged gas (or plasma) within its core.
The aim is for the tokamak reactor to heat plasma up to 100 million degrees Celsius (180 million degrees Fahrenheit) by 2018 – seven times hotter than the centre of the Sun. For this reactor, that’s the ‘fusion’ threshold, at which hydrogen atoms can begin to fuse into helium, unleashing near-limitless, clean energy in the process.
“Today is an important day for fusion energy development in the UK, and the world,” said David Kingham, CEO of Tokamak Energy, the company behind ST40.
“We are unveiling the first world-class controlled fusion device to have been designed, built and operated by a private venture. The ST40 is a machine that will show fusion temperatures – 100 million degrees – are possible in compact, cost-effective reactors. This will allow fusion power to be achieved in years, not decades.”
Nuclear fusion is the process that fuels our Sun, and if we can figure out a way to achieve the same thing here on Earth, it would allow us to tap into an unlimited supply of clean energy that produces next to no carbon emissions.
Unlike nuclear fission, which is achieved in today’s nuclear reactors, nuclear fusion involves fusing atoms together, not splitting them apart, and it requires little more than salt and water, and primarily produces helium as a waste product.
But as promising as nuclear fusion is, it’s something scientists have struggled to achieve.
The process involves using high-powered magnets to control plasma at ridiculous temperatures for long enough to generate useful amounts of electricity, which, as you can imagine, is far from simple.
Over the past year there have been some big wins. Scientists from MIT broke the record for plasma pressure back in October, and in December, South Korean researchers became the first to sustain ‘high performance’ plasma of up to 300 million degrees Celsius (540 million degrees Fahrenheit) for 70 seconds.
But we’re still a long way off being able to put all those pieces together – finding an affordable way to generate plasma at the temperatures required for fusion to occur, and then being able to harness it for long enough to generate energy.
The next step is for a full set of those magnetic coils to be installed and tested within ST40, and later this year, Tokamak Energy will use them to aim to generate plasma at temperatures of 15 million degrees Celsius (27 million degrees Fahrenheit).
In 2018, the team hopes to achieve the fusion threshold of 100 million degrees Celsius (180 million degrees Fahrenheit), and the ultimate goal is to provide clean fusion power to the UK grid by 2030.
Whether or not they’ll be able to pull off the feat remains to be seen.
But the company is now one step closer, and as they’re not the only ones with a tokamak reactor in development, it will hopefully only speed up the race to get a commercial fusion reactor online.
“We are excited by the opportunity to tackle the substantial engineering challenges in fusion and motivated by the global impact this technology will have.”
David Kingham, CEO
Tokamak Energy aims to accelerate the development of fusion energy by combining two emerging technologies – spherical tokamaks and high-temperature superconductors.
Tokamaks are the most advanced fusion concept in the world, but we take an innovative approach to develop fusion faster.
Our business model is based on agility and “open innovation” – working collaboratively with universities, research laboratories and businesses whilst ensuring that we retain the ownership of crucial intellectual property.
On the fusion triple product and fusion power gain of tokamak pilot plants and reactors
The energy confinement time of tokamak plasmas scales positively with plasma size and so it is generally expected that the fusion triple product, nTτ E, will also increase with size, and this has been part of the motivation for building devices of increasing size including ITER. Here n, T, and τE are the ion density, ion temperature and energy confinement time respectively. However, tokamak plasmas are subject to operational limits and two important limits are a density limit and a beta limit. We show that when these limits are taken into account, nTτ E becomes almost independent of size; rather it depends mainly on the fusion power, P fus. In consequence, the fusion power gain, Q fus, a parameter closely linked to nTτ E is also independent of size. Hence, Pfus and Q fus, two parameters of critical importance in reactor design, are actually tightly coupled. Further, we find that nTτ E is inversely dependent on the normalised beta, β N; an unexpected result that tends to favour lower power reactors. Our findings imply that the minimum power to achieve fusion reactor conditions is driven mainly by physics considerations, especially energy confinement, while the minimum device size is driven by technology and engineering considerations. Through dedicated R&D and parallel developments in other fields, the technology and engineering aspects are evolving in a direction to make smaller devices feasible.
Heat deposition into the superconducting central column of a spherical tokamak fusion plant
A key challenge in designing a fusion power plant is to manage the heat deposition into the central core containing superconducting toroidal field coils. Spherical tokamaks have limited space for shielding the central core from fast neutrons produced by fusion and the resulting gamma rays. This paper reports a series of three-dimensional computations using the Monte Carlo N-particle code to calculate the heat deposition into the superconducting core. For a given fusion power, this is considered as a function of plasma major radius R0, core radius rsc and shield thickness d. Computations over the ranges 0.6 m ≤ R0 ≤ 1.6 m, 0.15 m ≤ rsc ≤ 0.25 m and 0.15 m ≤ d ≤ 0.4 m are presented. The deposited power shows an exponential dependence on all three variables to within around 2%. The additional effects of source profile, the outer shield and shield material are all considered. The results can be interpolated to 2% accuracy and have been successfully incorporated into a system code. A possible pilot plant with 174 MW of fusion is shown to lead to a heat deposition into the superconducting core of order 30 kW. An estimate of 1.7 MW is made for the cryogenic plant power necessary for heat removal, and of 88 s running time for an adiabatic experiment where the heat deposition is absorbed by a 10 K temperature rise.
On the power and size of tokamak fusion pilot plants and reactors
It is generally accepted that the route to fusion power involves large devices of ITER scale or larger. However, we show, contrary to expectations, that for steady state tokamaks operating at fixed fractions of the density and beta limits, the fusion gain, Qfus, depends mainly on the absolute level of the fusion power and the energy confinement, and only weakly on the device size. Our investigations are carried out using a system code and also by analytical means. Further, we show that for the two qualitatively different global scalings that have been developed to fit the data contained in the ITER ELMy H-mode database, i.e. the normally used beta-dependent IPB98y2 scaling and the alternative beta-independent scalings, the power needed for high fusion performance differs substantially, typically by factors of three to four. Taken together, these two findings imply that lower power, smaller, and hence potentially lower cost, pilot plants and reactors than currently envisaged may be possible. The main parameters of a candidate low power (~180 MW), high Qfus (~5), relatively small (~1.35 m major radius) device are given.
Recent Advances on the Spherical Tokamak Route to Fusion Power
Stambaugh developed the Peng-Hicks concept of a fusion reactor based on a solid copper center-post spherical tokamak (ST). Using the promising results from the START experiment, they produced a vision for a path to fusion power. This path had two elements such as the ability to produce high fusion gain from an ST and of equal importance, the ability to demonstrate this in a small (and therefore relatively low cost) pilot plant device. In this paper, we review various attempts to pursue this vision, and try to elucidate the reason why success has not yet been achieved. However, we show that the advent of high temperature superconductors may overcome some of the problems, and we suggest a revised version of the small, low entry cost route to fusion power.