宽电磁束有效加热薄圆柱靶I
Efficient Heating of Thin Cylindrical Targets by Broad Electromagnetic Beams I
摘要：
在核聚变和短波长激光器的活性介质泵浦等重要应用中，需要在目标中实现电磁束的高比功率输入。衍射为电磁束的横向尺寸设定了下限，并且代表了对小区域或不可接近区域进行电磁加热的基本障碍。然而，人们发现，它是可能的，以实现有效的加热的圆柱形目标的电磁束的横向尺寸是几个数量级大于那些圆柱体。这些反直觉的结果具有以下物理机制：圆柱体中的吸收导致场分布的深度下降，并且这种下降导致场从大体积的光束朝向轴的衍射扩散。热效率是严格计算使用的问题的精确解衍射一个无限均匀的圆柱体（J.R.等等，1955年）。几个非共振域的参数被发现，提供了有效的吸收的能量的一个广泛的光束在一个薄的导电圆柱。对于非常薄的圆柱体，典型的渐近效率是（2-5）/L，其中L=ln（w/d），其中d是圆柱体的直径，w是纵向几何形状中的束腰宽度或横向几何形状中的波长。即使光束比圆柱体宽几个数量级，这种效率也很高。相关条件不是太严格，并且可以在许多重要应用中用于将圆柱形靶加热到高温。外部磁场可进一步放宽有效加热的条件。
英文摘要：
In many high-profile applications, such as nuclear fusion and pumping of active media of short-wavelength lasers, it is necessary to achieve high specific input of power of an electromagnetic beam in a target. Diffraction sets the lower limit to the transverse dimensions of electromagnetic beams and represents a fundamental obstacle for electromagnetic heating of small or inaccessible regions. It was found, however, that it is possible to achieve efficient heating of cylindrical targets by electromagnetic beams with transverse dimensions that are several orders of magnitude greater than those of the cylinder. These counter-intuitive results have the following physical mechanism: the absorption in the cylinder causes a deep fall in the field distribution, and this fall causes diffractive diffusion of the field towards the axis from a large volume of the beam. The heating efficiency was rigorously calculated using the exact solution of the problem of diffraction on an infinite homogeneous cylinder (J.R. Wait, 1955). Several non-resonant domains of parameters were found that provide efficient absorption of the energy of a broad beam in a thin conducting cylinder. The typical asymptotic efficiency for very thin cylinders is (2-5)/L, where L=ln(w/d), where d is the diameter of the cylinder and w is the width of the beam waist in the longitudinal geometry or the wavelength in the transverse geometry. This efficiency is high even if the beam is several orders of magnitude broader than the cylinder. The relevant conditions are not too rigid and may be used to heat cylindrical targets to high temperatures in a number of important applications. External magnetic field may further relax the conditions of efficient heating.
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