The figure below illustrates the history of nuclear fusion.

These projects have explored the best way to contain the plasma and to heat it to a temperature at which the fusion reaction can start place. The favoured solution is a Tokamak with plasma confinement in a magnetic toroid The main method for heating the plasma is by inducing a circulating current in the machine with polar magnetic fields which vary with time. Collisions in the plasma then cause resistive heating. 

Tokamak schematicMagnetic fields for induction 

Taken from Future Of Fusion Energy, J. Parisi, J. Ball 


ITER 

The ITER project is the latest in the long series of increasingly large magnetic containment devices. Construction started in 2007 and was 77% complete by the end of March 2022. The ITER machine is described in detail on the official website: Machine .

The objectives of ITER are 

  1. Produce 500 MW of fusion power
  2. Demonstrate the integrated operation of technologies for a fusion power plant
  3. Achieve a deuterium-tritium plasma in which the reaction is sustained through internal heating
  4.  Test tritium breeding
  5.  Demonstrate the safety characteristics of a fusion device

ITER will never send electricity to the grid because there is no system to make the heat from the plasma work a turbine.


DEMO

The objective of the next phase of fusion R&D, is to construct prototype fusion power plants with the extraction of energy from the fusion reactor to generate electricity.

While ITER is an international collaboration project, the next stage to build an actual prototype fusion reactor will consist of separate machines in different countries. Most use the word "DEMO" in their description but have different designs. 

The illustrations below show the principal components of a fusion reactor.

Nuclear Fusion ReactorFunctions of critical components

The enormous flux of neutrons from the Deuterium-Tritium reactions in the hot plasma are stopped in the "Blanket" in which coolant is circulated to drive a turbine for electricity generation. The blanket also has the essential task to breed tritium fuel which is one of the most difficult developments necessary for a successful commercial fusion reactor ( Challenges for Nuclear Fusion Reactors ).

Beyond, the shield must reduce as much as possible the neutron flux escaping the blanket to avoid radiation damage and activation in the components outside the vacuum vessel.