Spectroscopic Measurements of Temporal and Spatial Profiles of Electric Fields in a Discharge Plasma Fusion Neutron Source

为了利用激光诱导荧光（LIF）方法对电场进行高精度测量，提高了空间分辨率，介绍了一个7毫米见方、256 × 256像素的CCD。此外，我们还介绍了一种将光束的横向形状从圆形变为直线的转换器，即片状光束。为了利用这些设备进行高空间分辨率的测量，还需要开发一种基于斯塔克效应的激光诱导荧光法的方法，以适应放电等离子体聚变中子源中电场强度的宽动态范围。在2000年的研究中，为了获得更高的灵敏度，我们研究了n = 4禁跃迁（4^1D→2^1P, 492.2nm）的LIF，理论上预计其跃迁概率比以前使用的n = 3跃迁高10倍，并且适用于0.05 ~ 0.5 kV/cm的更低的电场范围。为了验证该方法的有效性，将该方法应用于已知电场分布的u型空心阴极放电等离子体中，发现该方法在检测0.1 kV/cm以下的弱场时具有很高的精度。在2001年，我们将上述高灵敏度的LIF方法应用于放电等离子体聚变中子源，同时使用光倍增器和CCD。特别是CCD，然而，发现信噪比太小，无法识别电场的存在，完全是因为它的空间和时间分辨率高于光倍增器。较差的信噪比也被发现是由于2^1S状态（约为2^1S）的一小部分过小造成的。（高出地面20.6 eV）中子源中的氦原子，特别是在高压模式下。因此，为了克服这一问题，我们开始了在LIF观测点上开发2^1S态氦原子束注入器的研究。CCD具有极高的分辨率，可以很好地测量放电等离子体自发发射强度的空间分布，以及利用多普勒频移光谱测量快中性氦原子的能量分布，精度也很高。此外，通过改进中子源的设计，我们实现了1.1 x 107 n/sec的中子产率提高，并提高了高压保持能力。少

For a highly accurate measurement of electric field with an improved spatial resolution by the laser-induced fluorescence (LIF) method, a CCD of 7 mm square with 256 x 256 pixels has introduced. Also, we have introduced a converter of transverse shape of optical beam from a circle to a line, i.e. a sheet beam. For the measurements with a high spatial resolution by making use of these equipments, it is also necessary to develop a method based on the laser-induced fluorescence method by use of Stark effect, to adapt the wide dynamic range of the electric field strength in the discharge plasma fusion neutron source.In 2000 in this study, for a higher sensitivity, we studied an LIF for n = 4 forbidden transition (4^1D →2^1P, 492.2nm), which is theoretically expected to have 10 times higher transition probability, and adaptable to a much lower electric field range of 0.05〜0.5 kV/cm, as well, than the n = 3 transition previously we used. For verification, the present method was applied to a … More U-shaped hollow cathode discharge plasma, within which the electric field profile is well known, and was found to show a excellent accuracy in detecting a weak field of around 0.1 kV/cm or less.In 2001, we applied the above highly sensitive LIF method to the discharge plasma fusion neutron source with both a photo-multiplier and, then, the CCD. Particularly with the CCD, however, the S/N ratio was found too small to identify the existence of electric field, exclusively due to its higher spatial and temporal resolution than the photo-multiplier. The poor S/N ratio is found to result, also, from a too small fraction of 2^1S state (approx. 20.6 eV above the ground level) helium atoms in the neutron source, especially at high-voltage mode operations. To overcome this problem, we, thus, started a study to develop an injector of 2^1S state helium atom beam into the LIF observation point.The CCD with an extremely high resolution, on the other hand, was found to be very efficient in measuring the spatial profile of the spontaneous emission intensity from the discharge plasma, and the energy distribution of the fast neutral helium atoms by use of Doppler shift spectroscopy, as well, with a high accuracy. Also, we achieved an enhanced neutron yield of 1.1 x 107 n/sec with an improved high-voltage holding capability with a design refinement of the neutron source. Less