Samonavigace laserových svazků na termonukleární pelety Lukáš Matěna

Hypothetical inertial confinement fusion power plant Spherical evacuated target chamber 10 m in diameter Spherical cryogenic fuel pellet is injected at high speed The pellet is irradiated by lasers when in the center of the chamber and ignites Released neutrons are absorbed in the walls of the chamber and the heat is removed by coolant This all has to be repeated few times a second

Problems of inertial fusion High requirements on irradiation symmetry Insufficient laser repetition rate Very precise injection system is needed The target position has to be tracked in order to ensure required irradiation precition

Problems of inertial fusion High requirements on irradiation symmetry Insufficient laser repetition rate Very precise injection system is needed !The target position has to be tracked in order to ensure required irradiation precition Tracking the target and adjusting the optics for each shot might be possible, but also difficult to do, considering the precision needed is in the order of tens of micrometers. Alternative approach was therefore proposed.

Self-navigation method Instead of tracking the target, the whole area in the middle of the target chamber is illuminated by low- energy laser light which reflects off the target This light is collected, amplified and after a reflection on SBS phase conjugating mirror is sent back to the target and ignites it

Self-navigation method - stages

Proof of concept

Unconverted first harmonic removal Because the higher harmonic conversion is never perfect, the unconverted first harmonic has to be filtered out Possible way to do this is by Faraday rotator

Parameters of reflected light Structure of amplitude on collecting windows is important in order to check whether the light can be properly amplified It is important to realize, that light on a given window is in fact a superposition of light from many illuminating beams reflected off the target A numerical simulation was developed to find out the parameters of reflected light

Numerical model A random ray from the beam is selected, followed to the target and reflected In case it hits the specified window, the distance travelled and polarization are calculated The process is repeated until enough information is gathered

Wavefront shape after reflection

Phase and amplitude structure Phase is easy to calculate from travelled distance Amplitude is affected by the polarizer in the window In case the beam is circularly polarized, the amplitude is the same for all the windows

Superposition from many beams What needs to be calculated is amplitude structure after superposition of light from many beams Considering the polarizers in the window, the superposition means only adding waves of the same frequency However, a way to position arbitrary number of beams has to be found – another simulation was developed to accomplish this

Amplitude structure 5 beams 400 beams

Amplitude dependence on number of beams used

Conclusion Amplitude after superposition varies rapidly across the window. A way to even the structure will probably have to be found. So far only circular polarization was used. Linearly polarized light would make a difference. Deviances from the ideal situation studied so far have to be considered.

Conclusion 2 There is a lot of loose ends and matters that have not been studied so far (TDC and FR construction). Even is self-navigation method worked, there are very serious issues with ICF itself (ignition not yet achieved, lasers, injection system), that might (and likely will) render the self-navigation method needless. Magnetic confinement fusion (tokamaks) is more promising candidate for nuclear fusion power plant than ICF.