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Access Success Stories

Ever since the beginning of LASERLAB-EUROPE, one of its most important features has been the Transnational Access Programme. Up to now, about 1,200 scientists from institutions outside LASERLAB-EUROPE had access to LASERLAB facilities to perform their experiments. Proposals for Transnational Access are reviewed by an external and independent Access Selection Panel on the basis of scientific merit. Access to LASERLAB facilities is free of charge; travel and accommodation expenses of visits with a typical duration of two to six weeks are covered by the Programme.

Each access project has its unique history and benefits. In many cases, the host researchers are not only involved in assisting their guests, but form an integral part of the research project. As a result, the host institutions benefit directly from the programme. Through the years, many long-term research collaborations have been formed as a result of Transnational Access. On the following pages, we highlight a few particularly successful access projects. Tom Jeltes

Plasma interferometry diagnostic studies (PALS)

One of the longest-running and most productive access related collaborations is situated at the Prague Asterix Laser System (PALS). Starting more than a decade ago, Tadeusz Pisarczyk from the Institute of Plasma Physics and Laser Microfusion (IPPLM, Warsaw, Poland) has used his multi-frame laser interferometry system to study plasmas in numerous experiments at PALS. For this purpose, he developed a modular optical system which allows quick assembly of the interferometer, depending on the experimental requirements. Several other researchers have since used the Polish system, benefiting from PALS facilities and Pisarczyk’s expertise.

The idea of constructing multi-frame interferometric diagnostics has its origin in Pisarczyk’s first LASERLAB Access project at PALS, some ten years ago. In this experiment he adapted an automated single-frame polaro-interferometer to study plasma parameters. The experience gained during the installation of this system and the results obtained turned out to be sufficiently useful and convincing to encourage extension of this method to a multi-frame approach. This led to the construction of an interferometric system with the capability to record three independent interferometric images with an adjustable time delay in the range of 1-3 nanoseconds. Each channel was equipped with a high-resolution, high dynamic range CCD camera. All cameras were connected to a computer, which allowed for easy control of the data acquisition process and maximally automated the work required to process the recorded data. The successful implementation of a three-frame interferometer on PALS was expensive and included a great deal of complex technical work, and would not have been possible without strong support from the management of both PALS and IPPLM. The reason for this was that the components of this system had to be installed in the experimental chamber in such a way that they would not obstruct access to the chamber and could be used in parallel with other important diagnostic tools. For example, to this end a unique custom-designed lead-out of the diagnostic laser beams from the experimental chamber for different recording channels had to be constructed, using a system of prisms mounted on the window in the chamber door; when the door was opened, the prisms were removed, providing an unobstructed access to the chamber. Furthermore, the main subsystems of the interferometer (e.g., the delay line and the recording system) were designed as independent modules, with permanently mounted components, which allows for a quick assembly and disassembly of the interferometer, depending on the experimental requirements. Over the time sufficient experience was gained with the multi-frame interferometer for it to become a routine diagnostic tool, which had the advantage that it could also be used for training of undergraduate and postgraduate students. Presently two students – one Czech and the other from Pisarczyk’s Polish team – are working on PhD theses which rely on the multi-frame interferometry as a basic source of information on the parameters of the laser plasma.

www.laserlab-europe.eu

June marks the 30th anniversary of JET’s first plasma – the moment commemorated in the photo above. Amazingly JET at thirty years old is still at the forefront of fusion research, these days as a test bed for its successor, ITER – hence the theme for the celebrations: JET – Paving the Way to ITER’s Take-Off.

During celebrations people involved in JET from the very early days through to the present will assemble at Culham, to hear tales of JET and ITER’s early days, and their entertwined futures.

There will also be a reenactment of JET’s original pulse, using equipment from 30 years ago, juxtaposed with a modern pulse – hopefully more successful and clean than the original pulse’s extremely brief life.

And of course, to toast the success of toroidal geometry, doughnuts will be served.

Interviews with people present at JET’s first pulse

Source: EFDA

It sounds like a kind of gothic torture – being put in a large bucket and lowered into a 9m deep hole at the centre of a huge machine. But it’s all in a day’s work for JET’s inspection team, as part of maintenance of JET’s central magnet, the P1 solenoid.

The solenoid itself is made up of 1440 turns of copper, separated into 14 “pancakes” – sections of coils stacked on top of each other. During the course of experiments these carry up to 60 000 amps, and are subjected to huge magnetic forces, which causes them to shift around slightly. A set of spring-loaded keys pull the pancakes back into alignment, but over the course of thousands of plasma pulses you would expect these to wear and lose their precision.

“Actually no refurbishment was needed, even though this procedure was last done 8 years ago,” says project leader Michael Porton.

“In the intervening time, a number of key staff had retired, so we were partly re-learning how to do the work,” says Mr Porton. “It was very interesting – it’s not often you get to peer down the insides of JET!”

Not surprisingly pulling the large iron core out of the heart of JET and accurately measuring the rotation of the pancakes was a complex task, which involved cooperation from many different areas, such as the lifting team, and the photogrammetry team, whose expertise in locating and surveying the exact positions of the components was vital.

There were also safety contingencies developed – rescue plans, in case the gothic horror tale came true. But there was a happy ending to this tale, no rescues were needed and JET’s central solenoid is in great shape ready for another busy experimental campaign, beginning mid-July.

Source: EFDA

Experts believe that fusion energy - which would never run out and is environmentally-friendly - could one day form 50% of the energy market, although it may not come into use for another few decades.

Source: CNBC

The last open seam on the steel outer cover of the Wendelstein 7-X fusion device was closed last week. The core of the research device is thus ready as basic skeleton and can go into operation at the Greifswald branch institute of Max Planck Institute of Plasma Physics (IPP) in 2014

The objective of fusion research is to derive energy from fusion of atomic nuclei, just as happens in the sun. To ignite the fusion fire, the hydrogen plasma fuel in a future power plant has to be confined in magnetic fields and heated to temperatures exceeding 100 million degrees. Wendelstein 7-X, the world's largest fusion device of the stellarator type when completed, is intended to investigate the suitability of this configuration for a power plant. With 70 large superconducting magnet coils in continuous operation it is then to produce a highly stable and thermally insulating magnetic cage confining the plasma.

The ring-shaped device is being installed as five almost structurally identical modules: Each of the five sections of the plasma vessel, along which 14 magnet coils are strung, is enclosed by a steel outer sheath, weighing altogether 120 tons. Assembled like slices of cake on the machine's foundation, the five modules form a steel ring from which numerous connection ports protrude. These link the apertures of the plasma chamber through the coil region with the outer vessel. Later, measuring instruments, pumps and heating facilities will be affixed here.

The 254th and last port was brazed in between the plasma vessel and outer vessel with millimetre precision on 28 May 2013. The elaborate port installation lasted a good two years. This was preceded by an equally long test phase – "a huge training session" as installation head Dr. Lutz Wegener put it – during which the methods for exact placement and connection of the variously configured ports to the bizarrely shaped plasma vessel were developed. One of the many challenges: As stainless steel inevitably shrinks at the seam when it is brazed, the components are distorted and change position. This had also to be allowed for when brazing the five modules of the device together: Calculations and tests during installation planning had predicted here up to eight millimetres shift per seam, this being intolerable since the ports and the subsequently connected measuring instruments would be looking at the wrong place in the plasma.

The solution: The module to be brazed, exactly monitored by laser tracker measurements, was shifted on sliding bearings about eight millimetres away from its firmly attached component opposite. Then, to prevent anything shifting, several welders began together to close the two brazing gaps of both the plasma chamber and the outer sheath. For the multi-layered seams with a total length of 40 metres the specialists of the MAN Diesel Turbo company took several weeks, during which the heavy module – in keeping with the shrinkage – slowly returned to its initial position in tenths of a millimetre steps. "It is a veritable work of art to guide in the right direction such a big and heavy component during brazing", states Karsten Liesenberg, who is responsible for the vessel installation concept: "If the laser trackers showed that the module was not being shifted exactly parallel, the brazing crew had to change over to the opposite side of the seam so that the component was again put on the right track". This precision work was repeated on the other four module boundaries. The ring is meanwhile closed and all five modules are in place with the required two millimetre precision.

Till installation of Wendelstein 7-X is completed in 2014, there are still a few tasks to be done, such as linking the magnets to their power and helium supplies and doing the interior of the plasma vessel. This will be accompanied by provision of the systems for heating the plasma, the supply facilities for electric power and cooling, machine control and finally the numerous measuring instruments for diagnosing the behaviour of the plasma.

Source:  phys.org