6.46P Relate the conditions for fusion to the difficulty of making a…

The idea

Fusion needs extremely high temperature, so nuclei have enough kinetic energy to overcome electrostatic repulsion, and high pressure or density, so collisions are frequent. Reaching and holding those conditions is hard: plasmas at millions of kelvin must be confined, often by strong magnetic fields, and any contact with ordinary walls cools the plasma and damages materials. Keeping the plasma stable and confined long enough for net energy gain is difficult, and the energy used to heat and confine it can exceed the energy released. These engineering demands make a practical and economic fusion power station hard to build, because construction, fuel handling and maintenance costs are high while reliable continuous output is not yet achieved.

What earns the marks

• Links the need for very high temperature to the difficulty of heating and confining a plasma.
• Explains that high pressure or density must be sustained, which places severe demands on containment and materials.
• Identifies that energy supplied to heat and confine the plasma may exceed the energy released, undermining economic viability.
• Connects engineering complexity and cost of containment to the difficulty of building a practical power station.

Common mistakes and how to put them right

• Assumes fusion power stations already supply electricity economically.

  Put it right by noting that practical net-output stations are not yet established.

• Treats high temperature alone as sufficient.

  Put it right by including confinement and sustained pressure or density.

• Ignores the energy cost of running the device.

  Put it right by comparing input energy with energy released.

• Claims fusion produces no hazardous materials at all.

  Put it right by noting that activated materials and tritium handling still need management.

Exam tips

• Link each condition for fusion directly to a practical difficulty, for example high temperature to plasma confinement.
• Use the words 'practical' and 'economic' from the question to structure your answer.
• Refer to energy input versus energy output when discussing economic viability.
• Avoid claiming fusion is impossible; focus on why it is difficult and costly.