'Shock Ignition' is the selected physics scheme for HiPER. This scheme requires a target design which meets the following criteria:

  1. Directly engaged by lasers to compress the fuel into dense matter, followed by shock pulse(s) which coalesce at the core of the fuel, increasing its density and producing heat to ignite it.
  2. Sufficiently robust to survive the acceleration of injection (1000g) into the chamber (velocity will be ~1000ms-1) with the chamber environment (reactor) operating at ~700°C and a pressure of 10-3 mbar(a).
  3. Capable of achieving fusion at nominal target chamber centre under a reactor operating temperature range between ~181°C to ~700°C (the lower temperature range allowing for reactor start-up, with primary coolant (lithium) is in liquid form).
  4. With maximised energy gain combined with due regard to target robustness. (Design compromises will be required to satisfy both criteria)
  5. Capable of being mass produced in high volume at an appropriately low cost.

The simplest form of shock ignition target used for experiments is a ~2mm diameter sphere with an external layer of Glow Discharge Polymer (GDP) shell enclosing a central void filled with tritium and deuterium fuel held at a temperature corresponding to the fuel’s triple point (equilibrium point between ice, liquid and vapour forms).

Before use, the target is “layered” to deposit a thin fuel ice layer on the internal surface of the GDP.

Although the simplest form of fuel target is likely to meet the requirements for acceleration to injection velocities, it cannot maintain capability to be fused in the reactor environment. This would require a heat shield to protect it from the thermal radiation within the chamber as well as a debris shield to prevent damage from interaction with molecules present in the reactor following the previous fusion event.

Design of a suitable target is a significant balancing act, requiring sophisticated supercomputer modelling to assess the effect of small changes on target performance.

Validation of the model can only be obtained through experimentation. Designing a target will require a significant experimental programme to validate results before a design can be completed.

In conjunction with modelling of a target design, production engineers consider whether that design is appropriate for mass production an important consideration, as over a million targets per day will be required to fuel each Laser Energy plant.

 

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