| Clean and controlled fusion energy is in pursuit of human's ideal energy,and laser driven inertial confinement fusion would be the most efficient way to realize this goal.Giant research budget have been spent to carry out the studies in this field in many countries all over the world,and large laser facilities has been co nstructed or being built such as the National Ignition Facility(NIF)in USA,Laser Megajoule(LMJ)in Franch and SG-III facility in China.To realize laser driven ignition,uniformly implosion of the compressed fuel capsule should be satisfied by symmetrical distributed X-rays which are emerged from laser beam.So that hundreds of laser beams must be precisely focused into the hohlraum according to fixed spatial distribution,which is the so-called 'Laser drive target'.Therefore,the high precise pointing and positioning problem with multi-beams turns to be one of the most important issues concerning to the success of laser fusion.The laser-target coupling precision is commonly required to be less than 1'' so that the non-uniformity of implosion can be prior to 1%.By theoretical analysis,numerical simulation and experimental investigation,several principle problems have been systematically studied,such as the mech anism of laser-target coupling and positioning for fusion-class laser facilities,the parallel beam guidance strategy of multi-beams,and the influence of positioning accuracy caused by the structure stability of the long-term optical transport system.The beam-target coupling and positioning system was constructed and applied to the laser facility,and the laser-target coupling precision has achieved to be superior to 1''.In this paper,the target positioning technique with "off-line target character measurement" and "on-line matching positioning" was proposed.With modified SIFT algorithm and Halcon image processing method,off-line target character library was established.In on-line reset stage,the spatial position of the target can be recognized with character matching by scanning the target image in standard positions and the basic feature.By making the target position and adjuster to be closed loop,high precision recognition and rapid positioning of super complex target can be intelligently realized.Parallel beam guidance technique based on space-time coding was proposed.By this method,the recognition of overlap spot caused by multi-beams can be solved,and the rapid alignment and guidance of multi-beams can be realized.Moreover,the pointing drift of laser beam due to structure stability can be reduced to a bare minimum,so that the 48 laser beams can be pointed to the target rapidly and precisely.To make sure the pointing stability of hundreds of high energy laser beams during laser-target coupling,the positioning accuracy should be strictly controlled and reasonably assigned to the laser chain all over the hundreds of meters long transport distance.For this purpose,the response mechanism of beam pointing stability with environment vibration,temperature radiation was established,and the characterization method based on the characteristic parameter of environmental load was also proposed for the structure stability design and control of the laser facility.The theoretical and experimental results manifest that,when the PSD spe ctral due to environmental vibration is less than 10-10g2/Hz,and the fundamental vibration frequency attributed to optical supporting system is large than 10 Hz,as well as the temperature variation during one shot period is less than 3?,the structure stability of the optical transportation system can be controlled to be 0.9?rad/5h to meet the demand of positioning accuracy.The results have been successfully applied to SG-III laser facility. |
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