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MIR on DIII-D

 

 

Research and development of the first generation MIR system on DIII-D is currently underway. It will share the same 270 degree midplane port with the existing ECEI system, eventually allowing for both temperature and density fluctuation measurements of the same plasma volume. Ultimately, the array will consist of 16 imaging channels (stacked poloidally), each consisting of 16 probing frequencies. With this eventual 16 x 16 channel array, poloidal and radial density correlation lengths can be measured. The feasibility of the DIII-D MIR optics design is being assessed [1,2] through synthetic diagnostic simulations utilizing a full-wave code FWR2D [3] coupled to an optical ray tracing platform that models realistic imaging components.

 

 

 

Above: Schematic of a combined ECEI/MIR system

 

Above: Schematic showing representative probing microwave beam incident on the cutoff surface (top) and the associated scattered signal collected and refocused by imaging optics (bottom).

 

 

Above: Schematic of synthetic MIR diagnostic. The horn antenna launches a microwave beam into the plasma (top) which reflects at the cutoff surface (left). The reflected beam propagates toward the receiver (bottom). The convolution of the EM fields are collected and analyzed by optical ray-tracing software.

 

 

Above: I/Q plots of receiver signal from a microwave beam propagating through a representative plasma modeled by FWR2D coupled to synthetic imaging optics. As the density fluctuation amplitude is increased, the amplitude and phase modulations of the detected signal increase.

 

 

 

 

Coherent fluctuation simulation

 

Above: Results from MIR synthetic diagnostic simulations for a DIII-D relevant plasma. Density layer at the cutoff is perturbed with an ensemble of spectra that each have a Gaussian distribution of wavenumbers centered at the values specified by the abscissa (each Gaussian distribution has a variance of 0.1 /cm). Various perturbation amplitudes are studied specified by the ordinate values. Linear correlation coefficients between the density fluctuations and the measured phase fluctuations are plotted in parameter space as the contour plots above for a sightline at the midplane. Results obtained for a sightline -19cm below the midplane are forthcoming.

 

 

 

Broadband fluctuation simulation

 

 

Above: Results from a MIR synthetic diagnostic simulation for a DIII-D relevant plasma. Density layer at the cutoff is perturbed with an ensemble of spectra that each have a Gaussian distribution of wavenumbers centered at the 0.0 /cm and varying widths specified by the abscissa. Various perturbation amplitudes are studied specified by the ordinate values. Linear correlation coefficients between the density fluctuations and the measured phase fluctuations are plotted in parameter space as the contour plot above for a sightline at the midplane. Similar results are obtained with a sightline -19cm below the midplane.

 

 

 

 

 


 


 

[1] Ren X., et al, “Evaluation of the operating space for density fluctuation measurements employing 2D imaging reflectometry” (to be published in Rev. Sci. Instrum.).

[2] Lei L., et al, “A synthetic diagnostic for the evaluation of new microwave imaging reflectometry diagnostics for DIII-D and KSTAR” Rev. Sci. Instrum. 81 (2010) 10D904.

[3] Kramer G.J., et al, “Simulation of optical and synthetic imaging using microwave reflectometry” Plasma Phys. Control. Fusion 46 (2004) 695.

 

·         MIR on KSTAR

·         MIR on NSTX


 Comments to: Calvin Domier