3D diagnostic of complex plasma

Summary form only given. Complex plasmas have been the focus of increasing interest over the years due to its application which cover a wide range of scientific fields. These include astrophysics, technological plasmas and energy research. Respective examples within each field are planetary rings, surface processing and dust in fusion reactors. A micro-particle (dust) component is the defining feature of complex plasmas. The self-organization of dust in dusty plasmas leads to the formation of plasma structures, examples are two-dimensional(2D) lattices and three-dimensional (3D) clusters. The characteristically slow system dynamics allow for the study of phase transitions, waves and molecular dynamics. The dust serves as both a diagnostic probe for plasma parameters and a tool by which facilitates the characterization of coupled systems. Previous 3D diagnostic techniques include, stereoscopy, high speed tomography, and colour gradient laser illumination [14]. Tomographic imaging can miss fast processes during its scanning procedure. The computational requirement and difficulty with larger clouds limits the stereoscopic techniques. The colour gradient method with laser illumination relies on knowing the exact particle size, since the intensity of the scattered light strongly depends on the particle diameter. Therefore a large vertical position error is introduced if the particles have random sizes or a wide size distribution when they are illuminated with monochromatic light (less than 1 nm). The effect of a change in scattered intensity over a size range of particles has been calculated for light sources with a varying spectral width using Mie scattering theory. It was found that the variations of the scattered light intensity have been significantly reduced for sources with wide spectral band. Using broadband light sources (with the bandwidth of 10 nm or more) will significantly reduce the vertical position error. Light emitting diodes (LEDs) provide a bandwidth o- 10-30 nm and can be used for the colour gradient illumination. The experimental setup consists of two LED light sources with line generators, which produce a colour gradient illumination of the sample. We use a glass cube with laser-etched dots in the volume as well as a moving screen in order to characterize the distribution of the colours and calibrate the system.