When Tokamak Energy was established by company founders Dr Mikhail Gryaznevich, Dr Alan Sykes and Dr David Kingham, they embarked on a unique mission: to recreate the process that powers the sun – on earth.
Mimicking the sun here on earth is an enormous scientific and engineering challenge.
The temperatures needed for efficient fusion to occur are over 100 million degrees and confining and controlling the immensely hot, sometimes unstable plasma, is a complicated task.
Very sophisticated systems are required to manipulate the plasma and after decades of research tokamaks can nearly produce and sustain the plasma conditions needed for efficient fusion to occur.
The company, which is named after the vacuum chamber that contains the fusion reaction inside powerful magnetic fields, announced the creation of the superhot plasma inside its experimental ST40 fusion reactor in early June.
The successful test – the highest plasma temperature achieved so far by Tokamak Energy – means the reactor will now be prepared next year for a test of an even hotter plasma, of more than 180 million degrees F (100 million degrees C).
That will put the ST40 reactor within the operating temperatures needed for controlled nuclear fusion; the company plans to build a further reactor by 2025 that will produce several megawatts of fusion power.
ST40 INSIDE VIEW
Our latest fusion device
All of the key components that are required for fusion are neatly packaged inside the tokamak.
TOROIDAL FIELD COILSConfining the plasma
The toroidal field (TF) magnets work with the poloidal field magnets to create a closed field pattern that confines the hot plasma and holds it away from the walls of the Inner Vacuum Chamber. The charged plasma particles follow the closed magnetic field lines, continuously spiralling around the tokamak.
The 250 000 amp current in the TF coil interacts with the magnetic fields to both expand the coils outwards and push them sideways. These large forces are transferred to the Outer Vacuum Vessel.
The strength of the toroidal field is about the same as an MRI
CENTRE COLUMN Confining the plasma
The centre column has two parts: the central wedges of the toroidal field magnets, and a large solenoid. The solenoid maintains a current flowing through the plasma, which is important for plasma stability, but the toroidal field magnets generate the magnetic field that keeps the plasma confined.
The solenoid stack is made up of 24 central wedges. Each wedge has a 15°
TWIST SO THEY CAN ALL BE JOINED UP IN A CIRCUIT.
POLOIDAL FIELD COILSControlling the plasma
The poloidal field coils control the shape and position of the hot plasma. The properties of plasma are heavily influenced by its shape so these coils help create optimum fusion conditions.
The divertor coils – centre, top and bottom – stretch the plasma vertically and guide the plasma exhaust to a dedicated region where it can be effectively removed.
Temperature gradients inside the tokamak are the largest in the universe. The coils will be cooled with liquid nitrogen to -196°
WHILE 40CM AWAY WILL BE A PLASMA THAT IS 10 TIMES HOTTER THAN THE CENTRE OF THE SUN
PLASMA START-UPGenerating the plasma
ST40 uses a novel technique to generate and heat the plasma – Merging Compression.
Normally start-up is the role of the solenoid. While ST40 still has a solenoid, it is used to maintain the plasma current rather than generate it.
Not relying on the solenoid is important in spherical tokamaks as there is only limited space in the centre of the machine.
The plasma inside the tokamak will reach more than 100 million degrees Celsius during the fusion process, which is 7X
HOTTER THAN THE CENTRE OF THE SUN
INNER VACUUM CHAMBER (IVC)Where the particles collide
To get the right conditions for fusion, you must create plasma – an electrically-charged gas. If the charged plasma particles that make up the plasma are moving fast enough (if the plasma is hot enough), the particles may overcome the repulsive force.
At the top and bottom of the IVC is the divertor region where the plasma exhaust is removed.
The divertor needs to handle heat loads that are larger than those experienced by the SPACE SHUTTLE
OUTER VACUUM CHAMBER (OVC)Supporting against strong magnetic fields
The OVC has an internal vacuum that provides thermal insulation for the liquid nitrogen-cooled copper field coils. It also has a vital role to play in supporting the toroidal and poloidal field coils against strong magnetic forces.
The tokamak needs to withstand huge forces and torque loads 5000
TIMES GREATER THAN THOSE IN AN F1 CAR
“It’s been really exciting,” said Tokamak Energy co-founder David Kingham.
“It was very good to see the data coming through and being able to get the high-temperature plasmas — probably beyond what we were hoping for.”
Tokamak Energy is one of several privately funded companies racing to create a working fusion reactor that can supply electricity to the grid, perhaps years before the mid-2040s, when the ITER fusion reactor project in France is expected to even achieve its “first plasma.”
It could be another decade after that before the experimental ITER reactor is ready to create sustained nuclear fusion — and even then, the reaction will not be used to generate any electricity.
“Fifty kilograms [110 lbs.] of tritium and 33 kilograms [73 lbs.] of deuterium would produce a gigawatt of electricity for a year,” while the amount of heavy hydrogen fuel in the reactor at any one time would be only a few grams, Kingham said.
That’s enough energy to power more than 700,000 average American homes, according to figures from the US Energy Information Administration.
Existing nuclear-fission plants generate electricity without producing greenhouse gas emissions, but they are fueled by radioactive heavy elements like uranium and plutonium, and create highly radioactive waste that must be carefully handled and stored.
In theory, fusion reactors could produce far less radioactive waste than fission reactors, while their relatively small fuel needs mean that nuclear meltdowns like the Chernobyl disaster or Fukushima accident would be impossible, according to the ITER project.
However, veteran fusion researcher Daniel Jassby, who was once a physicist at Princeton Plasma Physics Laboratory, has warned that ITER and other proposed fusion reactors will still create significant amounts of radioactive waste.
Road to nuclear fusion
The ST40 reactor and future reactors planned by Tokamak Energy use a compact spherical tokamak design, with an almost round vacuum chamber instead of the wider donut shape being used in the ITER reactor, Kingham said.
A critical advance was the use of high-temperature superconducting magnets to create the powerful magnetic fields needed to keep the superhot plasma from damaging the reactor walls, he said.
The 7-foot-tall (2.1 meters) electromagnets around the Tokamak Energy reactor were cooled by liquid helium to operate at minus 423.67 degrees F (minus 253.15 degrees C).
The use of advanced magnetic materials gave the Tokamak Energy reactor a significant advantage over the ITER reactor design, which would use power-hungry electromagnets cooled to a few degrees above absolute zero, Kingham said.
A Washington-based company, Agni Energy, has also reported early experimental success with yet a different approach to controlled nuclear fusion, called “beam-target fusion,” Live Science reported earlier this week.
One of the most advanced privately funded fusion projects is the compact fusion reactor being developed by U.S.-based defense and aerospace giant Lockheed Martin at its Skunk Works engineering division in California.
The company says a 100-megawatt fusion reactor, capable of powering 100,000 homes, could be small enough to put on a truck trailer and be driven to wherever it is needed.