The plasma experiments in the Wendelstein 7-X fusion device at Max Planck Institute for Plasma Physics (IPP) in Greifswald have now been resumed after a 15-month conversion break. The ex

tension has made the device fit for higher heating power and longer pulses. This now allows experiments in which the optimised concept of Wendelstein 7-X can be tested. Wendelstein 7-X, the world’s largest fusion device of the stellarator type, is to investigate this type’s suitability for application in a power plant.

Besides new heating and measuring facilities, over 8,000 graphite wall tiles and ten divertor modules have been installed in the plasma vessel since March last year, i.e. the scheduled end of the first experimentation phase. This cladding is to protect the vessel walls and allow higher temperatures and plasma discharges lasting 10 seconds in forthcoming experiments.

A special function is exercised here by the ten sections of the divertor: As broad strips on the wall of the plasma vessel, the divertor tiles conform exactly to the twisting contour of the plasma edge. They thus protect especially those wall areas to which particles escaping from the edge of the plasma ring are specifically directed. Along with unwanted impurities the impinging particles are neutralised and pumped off. The divertor is thus an important tool for regulating the purity and density of the plasma.

The smaller predecessor, the Wendelstein 7-AS stellarator at IPP in Garching, had already yielded encouraging results in divertor tests. But not till the much larger successor, Wendelstein 7-X at Greifswald, did the geometry conditions come up to power plant size, particularly the ratio of the divertor area to the plasma volume. “We are therefore very excited that we are now able for the first time to investigate whether the divertor concept of an optimised stellarator can really work properly”, says Project Head Professor Thomas Klinger. These tests will play a major role: Many detailed investigations will carefully check how to guide the plasma and what magnetic field structures and heating and replenishing methods are most successful.

Newly enlisted measuring instruments will also allow observation of turbulence in the plasma for the first time: The small eddies entailed influence how successful magnetic confinement and thermal insulation of the hot plasma are, these being important parameters for a future power plant, because they determine the size of the plant and hence its economical merit. “We shall be able for the first time to check whether the promising predictions of theory for a completely optimised stellarator are correct. In comparison with previous devices, Wendelstein 7-X is expected to yield quite new, possibly even better, conditions”, says Thomas Klinger.

As all ten microwave transmitters for the microwave heating of the plasma are meanwhile ready for use, this will allow a higher energy throughput and plasmas of higher density. It will now be possible to raise the energy to 80 megajoules once all versions of the microwave heating have been tackled and tested, as compared with 4 megajoules in 2016. The rather low plasma density hitherto can now be more than doubled to attain values meeting power plant requirements.

This has significant consequences: First the density of the plasma has to be sufficient to allow electrons and ions to exchange energy effectively. Previously, the microwave heating had only been able to heat essentially just the electrons. Instead of hot electrons with 100 million degrees and cold ions with 10 million degrees as hitherto the electrons and ions in the new plasma will have almost equal temperatures of up to 70 million degrees. This should also enhance the thermal insulation of the plasma. Whereas it was hitherto just upper average in relation to the size of the device, the effect of optimising Wendelstein 7-X should now become visible: “It’s getting very exciting”, states Thomas Klinger.

Background

The objective of fusion research is to develop a power plant favourable to the climate and environment. Like the sun, it is to derive energy from fusion of atomic nuclei. As the fusion fire does not ignite till temperatures exceeding 100 million degrees are attained, the fuel, viz. a low-density hydrogen plasma, ought not to come into contact with cold vessel walls. Confined by magnetic fields, it levitates inside a vacuum chamber with hardly any contact.

The magnetic cage of Wendelstein 7-X is formed by a ring of 50 superconducting magnet coils about 3.5 metres high. Their special shapes are the result of sophisticated optimisation calculations. Although Wendelstein 7-X is not meant to produce energy, the device should prove that stellarators are suitable for power plants. For the first time the quality of the plasma confinement in a stellarator is to attain the level of competing devices of the tokamak type. 

For this purpose, further stages of modification are being planned. For example, the graphite tiles of the divertor are to be replaced in a few years by carbon-fibre-reinforced carbon elements that are additionally water-cooled. This will allow discharges lasting up to 30 minutes in which it can be tested whether Wendelstein 7-X will achieve its optimisation targets in the long run: In this way the device is to demonstrate the essential advantage of stellarators, viz. their capability for continuous operation.

Source: http://www.ipp.mpg.de/4254576/08_17

The scientist in charge of Europe’s drive to harness a revolutionary new form of energy has accused Theresa May of risking its development by putting up a “new political wall” between researchers. Professor Tony Donné said Brexit and the UK’s decision to withdraw from the EU’s atomic agency would mean a “strong negative impact” on ground-breaking nuclear fusion research.

UK and EU scientists are collaborating under his programme to be the first to make a major breakthrough on fusion technology, which mimics processes at the core of the sun and promises a new era of clean, safe and cheap energy.

Speaking exclusively to The Independent, Prof Donné said Brexit had “only losers in fusion research” and went on to put up a staunch defence of EU free movement as a way of harnessing the collective knowledge needed to make its success a reality. His intervention follows attacks from other scientists and doctors arguing withdrawal from the Euratom agency risks the UK’s power supply, life-saving cancer treatments and plans to make all cars on British roads electric. A survey of specialists said retaining links to the agency should be a high priority.

Prof Donné is the programme manager for EuroFusion, the umbrella organisation of Europe’s fusion research laboratories. He said: “Brexit has only losers, as it will have a strong negative impact on European, UK and international fusion research.” Currently nuclear reactors produce power by fission, splitting uranium atoms and harnessing the energy released to drive turbines and generate electricity. But scientists know it would be more efficient to actually force hydrogen atoms together through fusion, producing four times as much energy, with helium the only by-product, and removing the toxic waste created by fission.  

At the international ITER project in France, EuroFusion and other scientists are trying to build a huge magnetic ring that can force heavy hydrogen isotopes to fuse together at temperatures up to 150 million degrees Celsius, for operation in 2025.

Prof Donné set out how fusion scientists during the Cold War helped inspire Ronald Reagan and Mikhail Gorbachev to start ITER and more recently brought Russian and Ukrainian academics together despite the problems between those countries. He said: “Unfortunately, almost at the same time when Ukraine became associate member of Euratom, Theresa May announced a new political wall, Brexit. “This causes a new hurdle for the fusion scientists as the United Kingdom is one of the key players in European and international fusion research.”

Days after immigration data revealed the number of EU nationals coming to the UK plummeted, he argued free movement is critical to gain and retain skilled scientists and engineers. One project Prof Donné claims is immediately threatened when the UK falls out of Euratom and the EU is the Joint European Torus scheme hosted in the UK at Culham near Oxford. JET, commissioned by Euratom, is Europe’s main ongoing nuclear fusion experiment and is integral research for making Iter a success in proving fusion energy can work on an industrial scale.

The decision to leave Euratom is believed to be largely driven by Ms May’s desire to remove the UK from all areas of jurisdiction of the European Court of Justice, which oversees the nuclear agency. But under pressure from MPs, including enough on the Conservative benches to cause an upset in the Commons, it has signalled a potential softening, emphasising a “strong, mutual interest” in ensuring the UK work closely with Euratom. Brexit Secretary David Davis has said that an “association agreement” may even be possible, but has been clear the UK will not sign up to any mechanism which gives the ECJ oversight over UK affairs. A Government spokesperson said: “We have been clear that we want the UK to remain the best place for science and innovation.  As a key contributor to the EU’s nuclear fusion research programme, we will be working closely with our EU partners to ensure international collaboration in this field continues. “That’s why the Government has pledged to meet its fair share of funding for the JET project until the end of 2020, should the EU extend the contract to host the Oxfordshire-based JET facility beyond 2018.” But UK Atomic Energy Agency chair Professor Roger Cashmore has warned leaving Euratom will leave no framework for transporting nuclear materials between Britain and the EU, with a risk the UK could run out of fuel within two years – just as Britain increases its reliance on nuclear energy.

Professor Martin Freer, one of Britain’s leading nuclear physicists, told The Independent earlier this month the “shortsighted” decision to quit Euratom would also hit the UK’s nuclear-driven power supply, just as demand for electricity explodes due to a soaring number of battery-powered cars – the Government wants to ban all petrol cars by 2040. Martin McKee, professor of European public health at the London School of Hygiene and Tropical Medicine, warned in July that quitting would make it harder for the UK to access the isotopes for cancer treatments and medical imaging.

A survey of over 1,500 energy and nuclear specialists published by Prospect today showed 86 per cent thought keeping links with EU energy agreements is a high priority for Brexit negotiations, while 82 per cent called for the Government to opt to stay in Euratom or retain “associate membership”.  

Source: Independent

Nuclear fusion is the process that powers the sun, but closer to home scientists are trying to develop fusion reactors that could provide immense amounts of energy. These reactors are big and (currently) inefficient, but a NASA-funded startup called Princeton Satellite Systems is working on a small-scale fusion reactor that could power advanced fusion rockets. Suddenly, other planets and even other star systems could be in reach.

All the forms of rocket propulsion we currently have involve accelerating propellant out of a nozzle. Then, physics takes over and the vessel moves in the opposite direction. Most spacecraft use chemical propulsion, which provides a large amount of thrust over a relatively short period of time. Some missions have been equipped with ion drives, which use electrical currents to accelerate propellant. These engines are very efficient, but they have low thrust and require a lot of power. A fusion rocket might offer the best mix of capabilities.

Princeton Satellite Systems is working on a small-scale fusion reactor that would only be 1.5 meters across and 4-8 meters long (4.9 by 13-26 feet). A experimental fusion power plant might cost $20 billion, but the smaller version being developed by Princeton Satellite Systems should only cost about $20 million. NASA seems interested in the idea, too. It’s given Princeton Satellite Systems three grants so far to pursue its research.

The goal is to generate 1 kilowatt per kilogram, so a 10-megawatt reactor would weight about 10 metric tons. This provides all the power a spacecraft would need, regardless of its distance from the sun, but what about propulsion? A fusion reactor uses magnetic fields and low-frequency radio waves to compress and heat matter until it becomes plasma that can undergo fusion (Princeton Satellite Systems uses a mix of deuterium and helium-3 in its reactor). As the plasma rotates, some of it can be directed out of a nozzle, and you’ve got a high-thrust, high-efficiency engine.

There are still issues to address with Princeton Satellite Systems’ design. For one, the reactor produces dangerous radiation that requires shielding from crew and computer systems. Additionally, helium-3 is rare on Earth. The company hopes to have a working prototype reactor by 2019 or 2020. From there, the sky’s the limit.

Source: ExtremeTech

The fusion world directed its applause to the east earlier this month as the Kazakh tokamak KTM started operations with a first plasma discharge.

"We are happy to report that the main objectives of the start-up have been achieved," reported lead scientist Irina Tazhibayeva at the World Scientific and Engineering Congress held this week in the Kazakh capital of Astana.

The KTM tokamak offers a unique feature among materials testing facilities: that is, a movable divertor and transport-sluice device allowing for the prompt replacement of the materials samples under investigation without the loss of vacuum in the vacuum chamber. A mobile receiving device inside the vacuum chamber is designed to manoeuvre all of the replacements through a gateway and to position the divertor plates through vertical and angle positioning.

In this way, 24 elements of the divertor (located at the bottom of the machine) can be replaced by remote control.

Last week it was finally time to count down to the start of machine operation. During the start-up, a plasma discharge pulse of 10 kA was achieved. The plasma discharge pulse time was 20 ms and a toroidal field of Bt ~ 0.35 T could be confirmed. Hydrogen, helium, and argon were used as working gases.

The ITER Organization has officially welcomed the National Nuclear Center of the Republic of Kazakhstan (NNC-RK) as a new technical collaborator.

On Sunday 11 June, a Cooperation Agreement was signed by ITER Director-General Bernard Bigot and the director of Kazakhstan's National Nuclear Center, Erlan Batyrbekov, calling for scientific and engineering cooperation between the two institutions. Agreement scope includes the technical exchange of experts, access to Kazakhstan's KTM tokamak for materials testing, and the development of diagnostics for ITER.

Kazakhstan also has an abundance of mineral resources that are of interest to ITER, some of which—like beryllium—are of great relevance to the project.

"We are very thankful to add today a new collaboration partner to the ITER Project," said Bernard Bigot. "It is a unique opportunity, enabling us to perform detailed material studies at the recently inaugurated KTM tokamak."