Derby and District Astronomical Society

DDAS Visit to the Culham Centre for Fusion Energy in Oxfordshire - Saturday 20th May 2017

Article by Mike Lancaster

How do you build a star on Earth? On Saturday 20th May 2017 a group of 12 DDAS members headed down to Culham in Oxfordshire to find out. It might be usual for astronomical societies to visit observatories, and places of space and astronomy research etc., and indeed looking through our past trips on this website that has been the case. But on this occasion our secretary Brian Dodson had arranged something a little bit different. We were not disappointed. Awe struck would be good term. Fusion is the process that powers the stars including our own Sun. Nature has done this trillions of times across the universe but to our own species this presents something of a challenge. We've already done it in the apocalyptic power of the H-bomb but to release this source of energy in a sustained and peaceful fashion to provide power for the grid is something else entirely. As science presenter Brian Cox has said, it would be a 'get out of jail card' for the future of our energy needs.

In short as we were reminded at Culham, fusion has the following benefits:

Our day began with 2 hours of fossil fuel burning from Derby to Abingdon on the south side of Oxford, where we stopped off at The Spread Eagle pub for an excellent lunch. Having replenished our own energy levels we drove over to the Culham Centre for Fusion Energy, which is operated by the UK Atomic Energy Authority. This was in fact an open day and we were one of four groups touring the site this afternoon. After receiving our security passes at the main gate we headed over to the centre itself where after tea and biscuits we were given a lecture on fusion energy and the work being carried out at Culham. The centre operates two main experiments - MAST (Mega Amp Spherical Tokamak) and JET (Joint European Torus).

In The Spread Eagle, Abingdon.  Image © Brian Dodson

Our visit began with a talk on fusion and the work being done at Culham.  Image © Tony Barker

Following the talk the four groups split up to tour the facility and the DDAS party were taken to see the MAST experiment (Mega Amp Spherical Tokamak). A tokamak is a device that uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being developed to contain the hot plasma needed for producing controlled thermonuclear fusion power. MAST uses a spherical shaped containment vessel rather than the more conventional torus used by JET, and is one of the world's two leading spherical tokamaks (the other being at Princeton in the USA). We were shown around MAST by a very enthusiastic and enganging scientist. Having originally begun operating in 1999 the device is currently undergoing a major upgrade (MAST-U). It is designed to study the physics of plasmas and investigate the potential of the spherical tokamak route to fusion power. In particular the results from MAST-U will be used to shape the design of ITER (International Thermonuclear Experimental Reactor), the next generation of fusion reactor being built in the south of France. Our guide showed us video footage of the plasma inside MAST and the site of what will become the MAST-U control centre. Next we got up close to MAST itself before being shown a number of components from it, and also a scale model of the device.

The Mega Amp Spherical Tokamak - Upgrade (MAST-U). The cabinet at left with the horizontal pipe leading into the reactor is the off axis neutral beam which, as well as powerful electromagnets inside the reactor, is used to heat the plasma.  Image © Mike Lancaster

We were shown video footage of the plasma inside MAST.  Image © CCFE & Bill Miles

A central column that was used in MAST. The column generates a toroidal magnetic field which is used to confine and heat the plasma inside the tokamak. It takes a current of 50,000 amps! MAST-U will employ an even more powerful version.  Image © Mike Lancaster

A central column from MAST cut lengthways showing the helical copper windings in cross section.  Image © Mike Lancaster

A copper element from one of the electromagnets used in MAST.  Image © Mike Lancaster

A scale model of MAST-U in cross section. The various electromagnets that are used to confine and shape the plasma inside the tokamak are labelled. the central column is also visible. Graphite blocks cover some of the surfaces. The circular trench running around the base of the device is a diverter used to channel and cool exhaust plasma - an important requirement for future reactor design.  Image © Mike Lancaster

TOSCA (Toroidal Shaping and Compression Assembly). This device operated from 1974 to 1986 and was designed to investigate plasma performance. This is not a model - it was one of the smallest tokamaks to be used.  Image © Tony Barker

I spotted this piece of graffiti on the ceiling of the MAST building!  Image © Mike Lancaster

Following our tour of MAST we headed over to the viewing gallery by the control room of the Joint European Torus (JET). We viewed footage of previous experiment runs or 'pulses' of JET and our guide explained a little of what goes on in the control room. Today however all was quiet with the device shut down and the control room empty except for a lone engineer keeping an eye on things. JET has been in operation since 1983. It is the world's largest and most powerful tokamak and holds the world record for fusion power of 16 mega-watts, which it attained in 1997. After viewing the control room we were given a more detailed overview of how JET works and its place in fusion research. Like MAST it is also very much involved in testing the physics and engineering to be used for ITER. Suitably briefed we donned hard hats and headed over to the JET building for an encounter with the machine itself. First off we viewed a test rig version of JET which is not a working device but it is used to test equipment and concepts before installation on the real thing. Then we were privileged to be allowed access to the holy of holies itself, which members of the public do not often get the chance of doing, as currently the device was fully powered down.

Fresh from our encounter with MAST our group heads over to JET.  Image © Mike Lancaster

The JET control room.  Image © Mike Lancaster

We were shown video footage of the plasma inside JET.  Image © CCFE & Bill Miles

Our guide explains the inner workings of JET with the aid of this poster. This is a view of the inside of the tokamak. The central column is coated with beryllium plates. With its thermal stability low atomic mass beryllium is less likely to contaminate the plasma inside the reactor than other materials. The ring shaped trench in the floor of the reactor is the diverter which is made of tungsten due to its high melting point. The four radiator like panels on the right hand side of the chamber are radio frequency antennas used to heat the plasma - using essentially the same principle as a microwave oven.  Image © Tony Barker

Our guide shows how JET fits into future of fusion along with ITER and DEMO (DEMOnstration Power Station).  Image © Mike Lancaster

A scale model of JET. Take a look at the left-hand cross section of the reactor. At the bottom of that cross-section are two grey blobs lying horizontally together. These are some of the electromagnets used in the reactor. To get a sense of scale a piece of the full size actual version of these electromagnets is visible to the right of the model.  Image © Mike Lancaster

Our group ascends to view the mockup rig used to design and verify components used on JET including diagnostic equipment.  Image © Tony Barker

View inside the torus of the JET test rig. TV documentaries which show presenters inside JET will actually use this mockup rather than the real machine!  Image © Mike Lancaster

These giant doors close to shield the outside world from JET while the device is operating. The JET reactor itself is hidden behind the mass of girders, walkways, pipes and cables visible through the doors.  Image © Tony Barker

A closer view of JET. When operating no one is allowed inside this room due to the shower of neutrons emitted by the reactor and the intense and varying magnetic fields used to contain and shape the plasma. Indeed after one run or 'pulse' engineers entered the room to discover a hammer embedded in the wall of the building - hurled there by the strong magnetic fields! Nevertheless a fusion reactor is far less hazardous than a conventional fission reactor, and neutron radiation is easily stopped by concrete, certain plastics and even water.   Image © Mike Lancaster

Up close and personal with JET - our guide explains what we can see of the machine. Blue pipes carry cooling water. Red pipes contain dielectric fluid and act as waveguides transferring radio frequency energy (microwaves) into the reactor from sources beneath the floor level. The light blue 'Lego' like object visible immediately behind the horizontal girder near the middle of the picture is one of several variable resistors.  Image © Mike Lancaster

Our group close to JET. The reactor itself is out of picture to the right.  Image © Mike Lancaster

Things get a bit hotter inside JET than the liquid in this cup, several hundred million degrees in fact. That's hotter than the centre of the sun.  Image © Bill Miles

Fusion converts.  Image © Brian Dodson

After having toured JET we returned to the reception area where we had a chance for further refreshments, to purchase souvenirs and to chat to the enthusiastic staff a while longer. I must admit that despite all the troubles we are facing in the world today to feeling a great sense of optimism after visiting CCFE. The future can be bright if we so choose. The future is fusion.

Our thanks go to CCFE and especially our guides for the excellent tour they gave us, and for giving up a Saturday afternoon to do so! Also many thanks to DDAS secretary Brian Dodson for organising an enthralling day out.

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