Energy from nuclear fusion must surely be the answer to the majority of the world’s on-going energy headaches. The fuels used in nuclear fusion are plentiful and readily available across the world. There are absolutely no greenhouse gas emissions and - unlike even the most up-to-date nuclear energy programmes - not only are there no long-term radioactive wastes to deal with, but the reactors cannot “run out of control”.But a critical part of nuclear fusion requires the creation of extreme plasma conditions similar to those occurring on the sun. In many ways, to trace the path to nuclear fusion, is to follow the innovations associated with vacuum technology. The machinery, technology and know-how have only recently become available to elevate fusion to possible commercial viability.
Nuclear fusion occurs when two atoms combine to form a new atom, with the spare neutron “left over” providing the energy which can be harvested and re-used. To get such atoms to combine (and release their spare energy) they need to be fired into a plasma where the extreme high temperatures (approximately 150 million °C) overcomes their ion-repulsion and forces them together.
Indeed, one of the many challenges faced by fusion energy physicists is the ability to sustain controlled plasma ignition (magnetically or inertially) to enable a net energy gain. Whilst this fusion process occurs naturally in the sun, here on Earth, it must take place within a vacuum vessel.
To a large extent, nuclear fusion research involves understanding the behavior of plasma. As such, one of the major challenges faced by scientists is the ability to sustain plasma by maintaining the right pressure. Hence the need for large-scale, effective vacuum systems that ensure ultra-high vacuum in the large reactor vessels/cryogenic system surrounding the superconducting magnetic field coils, and which can withstand very high temperatures, ionizing radiation and high magnetic fields.
Working in a vacuum, these coils of superconducting wire have no electrical resistance and therefore can conduct much larger electric currents than ordinary wire, creating the required intense, high-density magnetic fields. This can only be achieved within an extreme vacuum.
Although the theory of nuclear fusion is understood by engineers and scientists, it’s “up-scaling” to a safe, commercial, practical, sustainable and long-term net supplier of energy, has been elusive. Therefore, in order to investigate and build a prototype fusion reactor, the International Thermonuclear Experimental Reactor (ITER) consortium was established to prove the feasibility of fusion as a large-scale and carbon-free source of energy.
ITER, with a budget of EUR 7.6 billion for the period 2007 to 2020, consists of a wide range of members, including China, India, Japan, South Korea, Russia, the United States, France, Germany, Italy, Spain and the United Kingdom, as well as many other European Union countries. The group is now nearing the end of its 35-year collaboration to build and operate the ITER experimental device.
ITER is a significant experimental step between today’s research machines, before committing wholeheartedly to tomorrow’s fusion power plants (i.e. the DEMO project). As such ITER aims to prove much of the technology, materials, methods, physics, regimes, procedures and practicalities of fusion physics.
Since the idea for an international joint collaboration in a fusion experiment was first launched in 1985, thousands of engineers and scientists have contributed to ITER, of which the most significant single item involves the designing and building of the world's largest vacuum vessel. This vacuum vessel, which weighs more than the Eiffel Tower, is ten times larger than previous models, and contains the world’s largest superconducting magnets.
ITER’s main vacuum pumping systems employ torus exhaust pumping, cryopumps for the neutral beam injection systems for plasma heating, and cryopumps for the ITER cryostat. All customised cryosorption pumps are force-cooled with supercritical helium and share a similar modular design of cryosorption pumping panels. For regeneration of the cryopumps, as well as for roughing down the system volumes prior to operation, four identical sets of forepump trains are used. These complex pumps have all been tailored to be tritium compatible.
Large-scale construction of the various buildings and the assembly of the components is well underway with over 2000 personnel involved in building and assembling the various components at ITER’s construction site at St Paul-lez-Durance in France. These various parts include those associated with superconducting magnets, cryogenic tanks, robotic remote handling and the neutral beam heating systems.
In addition, an inner-vertical target (IVT) prototype has just been completed and shipped to St Petersburg for trials. This prototype unit weight 0.5 t and measures about 1.5 m with 1104 tungsten tiles laid in 12 rows along its length. Its “plasma facing component” is designed to sustain high heat fluxes.
Once this work is completed in 2025, it will pave the way for the fusion power plants of tomorrow.
Quite simply, ITER is without doubt one of the most ambitious experimental energy projects that the world has ever seen…. which is only now possible due to the advances being made in vacuum technology and vessels.
If you're curious to know more about how the vacuum technology used in the ITER project works in on much broader scale, check our eBook that explores the foundations of vacuum generation to its concepts and parameters and much more.
Dr Andrew Chew has worked in the Vacuum Industry since 1993 in a variety of technical, marketing and sales roles and is now Applications Manager for Leybold, Edwards and Gamma Vacuum brands globally. He currently serves on the UK Institute of Physics Vacuum Group Committee and is an IOP delegate to the British Vacuum Council.
Learn more about Dr Andrew Chew on our contributor's page by clicking here.
Image Source: Oak Ridge National Laboratory, Flickr