It is 25 years since JET landed on a large plot of farmland near Culham. The arrival of this mighty machine brought with it jobs and international prestige for the region, but also, more importantly, hope for a world just starting to come to terms with the fact that fossil fuels have only a limited life.

Back in 1983, when JET began its operations, the nation certainly had energy concerns.

Only back then, they were rather more short term - focusing on Arthur Scargill and the prospect of a national miners' strike, rather than anything to do with global warming and climate change.

The dangers facing the planet and energy priorities have certainly changed. Yet the massive device located a couple of miles outside Abingdon is still there, providing work for 500 people and attracting scientists from across Europe.

And, most remarkably, it continues its pursuit of one of science's last holy grails - always maddeningly within grasp but ultimately always another couple of decades and a billion euros away - the quest for fusion.

Nuclear fusion is the process that provides the sun's energy and for decades it has held the promise of cheap, clean energy.

In simple terms, what we have at Culham is a man-made sun on earth.

In fact, as the world's largest and most powerful fusion research experiment, JET can claim to be the hottest place in the Solar System.

Numerous records have been set, with gases routinely heated to 200m degrees celsius, far hotter than the sun's core, which is 'only' about 15m degrees.

More significantly, in 1991 it achieved the first controlled release of fusion power.

Computer technology, the Internet and the genetic revolution mean scientific breakthroughs seem to come on a monthly basis.

But JET has stood the test of time, albeit with the network of buildings looking a little shabbier these days and the headlines it attracts tending to be about its eventual closure.

JET (Joint European Torus) is due to close in 2010, with the nuclear fusion torch being passed to the international project known as ITER, a massive experimental reactor that is being build in southern France.

On Wednesday, a party will bring together past and present JET staff.

It might have had all the makings of a wake rather than a birthday celebration. Except, while nothing has yet been formally announced, Dr Francesco Romanelli, the associate leader of JET, is confident that JET is to be given an extended lease of life after all.

The construction of JET's replacement in Cadarache, costing an estimated 5bn Euros, is due to start later this year and will take ten years to complete.

Dr Romanelli believes that JET's research will be given the job of preparing the way for its planned successor.

He told The Oxford Times: "Yes, we have been discussing the extension of JET beyond 2010. Within the science community there is a willingness to go beyond the date of 2010 at least to 2014 in order to allow JET to complete a number of research activities, which are essential to ITER.

"It is work that can only be done here. JET has the capability to go beyond 2014."

As well as scientists, it is now looking like the European Commission has been won over.

Few guests at the party will be more relieved by the news than guest of honour Dr Paul-Henri Rebut, the Frenchman who built JET. Construction started in 1978, with operations beginning in 1983.

Run by UKAEA on behalf of its European partners, it was a pioneering example of a Euro-scientific collaboration.

Ask Dr Romanelli to explain the importance of JET and he will immediately refer you to the sun and the stars.

In a fusion reaction, energy is produced when light atoms are fused together to form heavier atoms, he explained.

This is the same process that provides the energy in the sun and the other stars. The sun is, in fact, a giant fusion reactor, fusing 600bn kg of hydrogen every second to release the energy that powers all life on earth.

For fusion to work in the laboratory, much higher temperatures are needed than in the sun.

In case you are wondering why the good people of Culham and most of the northern hemisphere are not fried, it should be explained that the hot plasma is held in a vacuum chamber, with strong magnets keeping it from the walls of the machine while fusion occurs.

If the plasma hits the wall of the machine, it goes out immediately (we are assured).

At these temperatures the particles deuterium and tritium, both heavy forms of hydrogen, fuse together to form helium and high-speed neutrons, which carry significant amounts of energy.

Experimental physicist Phil Morgan was one of 30 or so scientists to witness the first day of operations who is still working at JET.

"It felt like a groundbreaking event", he recalls.

"Nobody had previously built or operated such a large fusion reactor. Walkie-talkie radios were used to keep the various groups in touch with each other.

"There was an air of hushed expectancy as the countdown for the first plasma attempt progressed. A suppressed gasp was heard as, on one of the TV screens, the machine appeared to tilt when the magnetic field was switched on. Loud laughter followed as people realised that the field was distorting the image recorded by the TV camera."

Clear evidence that plasma had been created was provided by an oscilloscope which recorded a flash of light lasting about a tenth of a second.

"I remember polaroid pictures were taken of the oscilloscope trace and handed around to an eager audience. There was much smiling and animated discussion with confirmation that a peak plasma current of about 16,000 amps had been achieved."

In the years that followed, JET has has allowed scientists to study fusion in conditions approaching those needed for a fusion power plant.

Ironically, the JET anniversary comes just days after the Government set out its plans to expand nuclear power in the coming years.

Fusion scientists continue to talk up the potential of fusion to provide a source of fuel with no carbon emissions, greenhouse gases, or long-lived radioactive waste - a clean energy to literally save the planet.

But no one is pretending it offers a fuel for today or even tomorrow.

After 25 years, with JET soaking up £40m of funding a year, there is no prospect of commercial energy production from fusion for many decades.

Press Dr Romanelli to set out his road map towards fusion energy production and he speaks of it perhaps providing 20 per cent of the world's energy by the year 2100.

Polar bears have little cause to relax as the polar ice cap melts under their feet.

But the world simply cannot give up on fusion.

ITER, a scaled-up version of JET, will become the world's largest international co-operative research and development project, after the international space station.

Its participants will represent more then half the world's population. But the best hope is that it will have a demonstration power plant in operation within 30 years "if successful".

You start to realise just how far away fusion is from powering homes and industry on being told that ITER aims to become the first fusion experiment to actually produce a net power gain.

But that's not to denigrate what has been achieved at JET, the European research programme par excellence. The scientists who will be gathering there next week have succeeded in showing it is possible to create the temperatures needed for fusion, and to hang on to them.

For scientists like Dr Romanelli, the potential prize means the abandonment of JET cannot be contemplated.

"What we have in fusion is an unlimited energy source.

"We need a portfolio of options when we are dealing with energy policy. We need to continue with nuclear power. We need to develop renewables. But in the long term I thinks fusion has the best chance."

A public consultation about the future use of the site last summer showed 70 per cent of respondents wanting to see the JET experimental facilities being retained, with less than ten per cent in favour of removing the buildings and returning the site to farmland.

Even if its role from now on is to prepare the way for a £5bn experiment in France, the good news this summer is that a corner of Culham looks set to remain the hottest place in the solar system.

Just don't start hoping JET is going to rescue us from the consequences of global warming.