CO_2 Laser Collective Thomson Scattering Diagnostics on the HT-7 Tokamak

A CW CO2 laser collective Thomson scattering diagnostics was developed to measure plasma density fluctuations on the HT-7 tokamak. The design and construction of CO2 laser scattering apparatus is described. The laser source is a continuous-wave CO2 laser with a cavity length of 1.9 m and a power output of about 10 W at 10.6 μm. The k-resolution of the system is △k ≈ 3.2 cm-1. The preliminary data from the diagnostic is presented.

Development of the HCN heterodyne collective scattering system on J-TEXT

A heterodyne collective scattering system has been designed and developed to investigate the turbulent transport of core plasma on J-TEXT.A dual-HCN laser which consists of two separately pumped HCN gas lasers at 337μm has been developed as the laser source of the scattering system.The intermediate frequency(IF)is~1 MHz when there is a 4μm cavity length difference and capable to maintain stability more than 5 h without manual operation.Detection channels at three different angles(2≤k_(⊥)≤12 cm^(-1))have been installed with Schottky barrier diode mixers of 893 GHz.The sampling frequency of the acquisition system is6 MHz to observe low-frequency density fluctuations.Initial experimental results have been detected and more results can be expected in future experiments.

Investigation of gyrotron-based collective Thomson scattering for fast ion diagnostics in a compact high-field tokamak

As a promising method for fast ion diagnostics,collective Thomson scattering(CTS)can measure the one-dimensional velocity distribution of fast ions with high spatial and temporal resolution.The feasibility of diagnosing fast ions in a compact high-field tokamak by CTS was studied in this work,and the results showed that a wide range of probing frequencies could be applied.A high-frequency case and a low-frequency case were mainly considered for fast ion diagnostics in a compact high-field tokamak.The use of a high probing frequency could effectively avoid the refraction effect of the beams,while the application of a low probing frequency allows greater flexibility in the selection of scattering angle which may help to improve the spatial resolution.Based on typical plasma conditions(B_(0)=12.2 T,n_(e0)=4.3×10^(20)m^(-3),T_(e0)=22.2 keV,T_(i0)=19.8 keV)for a compact high-field tokamak,a220 GHz CTS diagnostic that utilizes a small scattering angle ofθ=30°and a 160 GHz CTS diagnostic that utilizes an orthogonal geometry were proposed.Further study showed that the high-frequency case could operate in a wider range of plasma conditions and provide more information on fast ions while the low-frequency case could achieve higher spatial resolution of the poloidal direction.

Statistical Study on the HF Radar Multi-Frequency Autocorrelation Functions

To fit the autocorrelation functions (ACFs) of HF radar ionospheric backscattered signal to an analytical function, which is obtained theoretically by introducing a Lagrangian description of turbulent motion, can estimate directly the turbulent parameters of the scatters. We use this method to analyze the HF radar ACFs. A statistical study has been performed with the multi-frequency data, and shown that the statistical results are not the same in different frequency bands. We found that the influences of the limit radar time resolution and the received noise played the important roles in causing this inconsistency, both of them result in an additional expansion to the spectral width, and cause more Lorentzian behavior to ACFs; these two limitations affect the form of ACFs more seriously in the higher frequency band. We verified this by a simple simulation.

The influence of the characteristics of a collection of particles on the scattered spectral density and its applications

The far-zone scattered spectral density of a light wave on the scattering from a collection of particles is investigated, and the relationship between the character of the collection and the distribution of the scattered spectral density is discussed. It is shown that both the number of particles and their locations in the collection play roles in the distribution of the far-zone scattered spectral density. This phenomenon may provide a potential method to reconstruct the structure character of a collection of particles from measurements of the far-zone scattered spectral density.