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Magnetically imploded tubes called liners, intended to help produce controlled nuclear fusion at scientific "break-even" energies or better within the next few years, have functioned successfully in preliminary tests, according to a Sandia research paper accepted for publication by Physical Review Letters (PRL).

To exceed scientific break-even is the most hotly sought-after goal of fusion research, in which the energy released by a fusion reaction is greater than the energy put into it -- an achievement that would have extraordinary energy and defense implications.

That the liners survived their electromagnetic drubbing is a key step in stimulating further Sandia testing of a concept called MagLIF (Magnetized Liner Inertial Fusion), which will use magnetic fields and laser pre-heating in the quest for energetic fusion.

In the dry-run experiments just completed, cylindrical beryllium liners remained reasonably intact as they were imploded by huge magnetic field of Sandia's Z machine, the world's most powerful pulsed-power accelerator. Had they overly distorted, they would have proved themselves incapable of shoveling together nuclear fuel -- deuterium and possibly tritium -- to the point of fusing them. Sandia researchers expect to add deuterium fuel in experiments scheduled for 2013.

"The experimental results -- the degree to which the imploding liner maintained its cylindrical integrity throughout its implosion -- were consistent with results from earlier Sandia computer simulations," said lead researcher Ryan McBride."These predicted MagLIF will exceed scientific break-even."

A simulation published in a 2010 Physics of Plasmas article by Sandia researcher Steve Slutz showed that a tube enclosing preheated deuterium and tritium, crushed by the large magnetic fields of the 25-million-ampere Z machine, would yield slightly more energy than is inserted into it.

A later simulation, published last January in PRL by Slutz and Sandia researcher Roger Vesey, showed that a more powerful accelerator generating 60 million amperes or more could reach "high-gain" fusion conditions, where the fusion energy released greatly exceeds (by more than 1,000 times) the energy supplied to the fuel.

These goals -- both the near-term goal of scientific break-even on today's Z machine and the long-term goal of high-gain fusion on a future, more powerful machine -- require the metallic liners to maintain sufficient cylindrical integrity while they implode.

The liner is intended to contain fusion fuel like a can holds peanut butter, and push it together in nanoseconds like two semicylindrical shovels compacting snow together.

An element of drama is present because the metallic liner doing the compressing is also being eaten away as it conducts the Z machine's enormous electrical current along its outer surface. This electrical current generates the corresponding magnetic field that crushes the liner, but under the stress of passing that current, the outer surface of the liner begins to vaporize and turn into plasma, in much the same way as a car fuse vaporizes when a short circuit sends too much current through it. As this happens, the surface begins to lose integrity and becomes unstable. This instability works its way inward, toward the liner's inner surface, throughout the course of the implosion.

"You might say: The race is on," said McBride. "The question is, can we start off with a thick enough tube such that we can complete the implosion and burn the fusion fuel before the instability eats its way completely through the liner wall?

"A thicker tube would be more robust in standing up to this instability, but the implosion would be less efficient because Z would have to accelerate more liner mass. On the flip side, a thinner tube could be accelerated to a much higher implosion velocity, but then the instability would rip the liner to shreds and render it useless," he continues. "Our experiments were designed to test a sweet spot predicted by the simulations where a sufficiently robust liner could implode with a sufficiently high velocity."

By following the dimensions proposed by the earlier simulations, the physical test proved successful and the liner walls maintained their integrity throughout the implosion. Radiographs taken at nanosecond intervals depicted the implosion of the initially solid beryllium liner through to stagnation -- the point at which an implosion stops because the liner material has reached the cylinder's central axis. The images show the outer surface of the imploding liner distorting until it resembles threads on a bolt. However, the more crucial inner surface remains reasonably intact all the way through to stagnation.

Said McBride's manager Dan Sinars, "When Magnetized Liner Inertial Fusion was first proposed, our biggest concern was whether the instabilities would disrupt the target before fusion reactions could occur. We had complex computer simulations that suggested things would be OK, but we were not confident in those predictions. Then McBride did his experiments, using liners with the same dimensions as our simulations, and the outcomes matched. We are now confident enough to take the next steps on the Z facility of integrating in the new magnetic field and laser preheat capabilities that will be required to test the full concept. Consequently, we intend to take those first integration steps in 2013."

Slated for December are the first tests of the final two components of the MagLIF concept: laser preheating to put more energy into the fuel before magnetic compression begins, and the testing of two secondary electrical coils placed at the top and bottom of the can. Their magnetic fields are expected to keep charged particles from escaping the hot fuel horizontally. This is crucial because if too many particles escape, the fuel could cool to the point where fusion reactions cease.

Sandia researchers intend to test the fully integrated MagLIF concept by the close of 2013.

"This work is one more step on a long path to possible energy applications," said Sandia senior manager Mark Herrmann.

The liner implosion experiments also served to verify that simulation tools like the popular LASNEX code are accurate within certain parameters, but may diverge when used beyond those limits -- information of importance to other labs that use the same codes. McBride will give an invited talk on his work this fall at the American Physical Society's annual Division of Plasma Physics meeting in Providence, RI. He is also preparing an invited paper for Physics of Plasmas to explain the PRL results in greater depth.

The work was funded by Sandia's Laboratory Directed Research and Development program and the National Nuclear Security Administration.

Source: sciencedaily.com

The snowflake is not usually associated with extremely high temperatures – yet this image from the latest issue of Fusion in Europe is from the hottest part of a tokamak, the divertor. The snowflake divertor is a new approach to managing the intense heat loads generated by fusion experiments, based on a complex magnetic field configuration. The success of this approach earned a prestigious “R & D 100″ award for the team that developed it, from the EFDA’s Swiss Associate CRPP, and the Lawrence Livermore National Laboratory, US and Princeton University, US.

The full story is in the Autumn Issue of Fusion in Europe, along with novel tritium recovery methods, how industry benefits from Wendelstein 7-X, a new negative ion source and models of the future global energy market. There is also a round up of JET’s latest progress and future plans – and the interest they are attracting from ITER – and much more.

Follow the link to the right to read the articles online or download the complete issue as a PDF. If you would prefer to get your hands on a hard copy use the subscribe link at the bottom of this page.

Fusion in Europe online

Source: EFDA

It’s a well known fact that the fusion of tritium and deuterium produces helium. However, a fusion power plant also uses helium – it is a vital coollant which, while not actually consumed, is inevitably lost during operation in quantities that far outweigh the amount produced – and in recent years it has become apparent the future supply of helium is not assured.

This week former Cryogenic Section Leader at JET, Richard Clarke, is presenting a paper about the world’s helium market at the Cryogenics 2012 international conference in Dresden. In 2005, while working at Culham, Richard was prompted by uncertainties in the helium supply to begin investigating the situation, which led to a global exploration of the technological, economic and political factors influencing the helium market. Teaming up with William J Nuttall and Bartek A Glowacki from Cambridge University Richard has recently co-edited a book, entitled “The Future of Helium as a Natural Resource” (Routledge 2012). The book is the first in-depth book on the noble gas since 1968.

Helium is produced in the ground by alpha decay of naturally radioactive minerals, and then comes to the surface as a by-product of natural gas production. “The big challenge now is for the natural gas industry to better preserve known geological helium reserves,” says Richard Clarke. Although the global helium market turns over around $1 billion per year and demand is predicted to double by 2030, this is a pittance compared with the $1 trillion natural gas market – there is little incentive for natural gas producers to invest in additional processing to extract helium.

In a recent comment published in Nature, the three authors added their voices to those calling for global arrangements to oversee helium resources: “A global agency is urgently needed to address the long-term issues facing the supply and demand of this precious element.”

In the meantime JET has been doing its bit towards preserving this scarce resource: the cryogenics plant has recently been upgraded, which has reduced the helium losses by up to £10,000-worth per month.

Source: EFDA

In the story of “The Princess and the Pea”, as told by Hans Christian Andersen, a princess is able to detect a pea in the bed she is lying on, despite a large pile of mattresses and feather quilts on top of it. However physicist Katharina Dobes can do much better: she can detect single layers of atoms, weighing a billionth of a milligram – around 10^-12 of a pea.  She does this not by lying on them, but by using a device known as a quartz crystal microbalance (QCM).

Ms Dobes is doing a PhD at the Institute of Applied Physics at the Vienna University of Technology, and the layers that she is studying are the surfaces of plasma facing materials, such as tungsten, carbon and beryllium. In her experiments these materials are bombarded with ions, which knocks off atoms, in a process known as sputtering. This process happens to plasma-facing materials in a fusion vessel – with the QCM Katharina can measure exactly how much sputtering occurs with each combination of wall material and plasma ion. This in turn gives vital information about how much of the wall material will contaminate the plasma.

Recent experiments have explored bombarding a tungsten wall with argon or nitrogen, because these have been used in JET to cool the edge of the plasma. These gases are much heavier than deuterium and so were expected to cause more sputtering of tungsten, which these measurements confirmed. “It was not a particularly disappointing result for fusion,” says Head of the Atomic and Plasma Physics Research Group, Professor Friedrich Aumayr. “but you don’t need bad surprises!”

The quartz crystal microbalance consists of a quartz crystal on to which layers are deposited. A vibration is then electronically induced in the crystal and the resonant frequency of the crystal measured. When atoms are sputtered off the crystal the resonant frequency changes, as it gets lighter. Although QCMs are not uncommon in the thin film manufacturing industry – for measuring deposition, not erosion – this particular experiment has achieved outstanding results. “QCMs can usually measure less than a micrometer,” says Professor Aumayr, “but thanks to a carefully controlled lab environment and specially built electronics we can detect less than one thousandth of a monolayer – fractions of a nanometer”

The next set of measurements will use beryllium as the wall material, however the Vienna University of Technology does not have a beryllium handling facility. This means, in keeping with the fairytale theme, to complete her quest Katharina Dobes will need pack the QCM up into a truck and journey to a faraway kingdom  – the Institute for Plasma Physics in Garching, Germany.

The Institute of Applied Physics at the Vienna University of Technology is a signatory to EFDA through the Austrian Fusion Research Programme ÖAW-EURATOM. The Max-Planck-Institute for Plasma Physics in Garching is one of three German signatories to EFDA.

Source: EFDA

After more than a half a century addressing the scientific challenges of controlled nuclear fusion, the research focus is moving from plasma physics to engineering. Chris Warrick from the Culham Centre for Fusion Energy explains how remote handling, materials and superconducting magnets are taking fusion energy into the reactor era.

Read the whole story:  INGENIA ISSUE 52 SEPTEMBER 2012