1mm CMOD ECE System

There have been no changes in design goals of the CMOD ECE during the past year. The work is on schedule and will be ready for first CMOD operation later this year. Design and fabrication is nearing completion. The vacuum components will be installed with in a month, with the remaining components will be installed before operations start.

This system will provide high-resolution electron temperature profiles and fluctuation measurements with 32 channels covering from the edge to the center of the plasma at a toroidal field of 5.4T. Channels will be spaced approximately every 5mm with a flux surface radial resolution of 1cm. The small beam waist not only maximizes profile measurements, but also allows the system to be configured to use correlation radiometry to measure electron temperature fluctuations across the full radius. A schematic view is shown here with the vertical lines indicating the location of the 32 channels at 5.4T toroidal field. Details of the entire system were presented at the latest diagnostic conference.

The interior mirror components have been fabricated and are now being tested at Auburn. The beam waist is ~2cm with radial resolution of <1cm. Vacuum flanges are nearing completion. All the associated vacuum hardware is ready. Transmission measurements have been completed on the crystal quartz vacuum window and over sized waveguide. A test fitting of the mirror, flange and waveguide will be conducted by the end of this month at the FRC. When these tests are completed, all the vacuum related pieces will be shipped to CMOD for installation.

The RF/IF section was designed to minimize the cost per channels for a second harmonic heterodyne ECE system. Two separate optical systems cover the frequency bands, 234-270 and 270-306 GHz respectively. This allows a full radial profile to be measured at 5.4T. In the RF section the upper 20 GHz bands are down-shifted to 2-22 gHz. This means we have four identical IF subsections. These four IF bands are then split and filtered into 8 individual channels each for a total of 32 channels.

All RF and IF components have been received and are now being assembled into the final configuration. The video amplifiers and detectors modules are the only remaining pieces required for final assembly. These units are under construction at this time.

The system’s noise temperature of the lower 18 gHz portions of each RF section have been measured as 7 eV for the 234-270 gHz unit and 4 eV for the 270-306 GHz unit. Further characterization of the entire system now underway. A layout of the entire RF/IF design is shown in the associated diagram.

The data acquisition for this diagnostic will be fully integrated with the CMOD MDS system. CAMAC units from TEXT will be utilized. Six high speed CAMAC 6810s will record temperature measurements up to 1MHz for temperature fluctuations. These units will also provide fast temperature profile changes for MHD or other fast temperature perturbations. A slower, 32-channel system, will record profile measurements for the entire CMOD discharge. This system will be used in parallel with the fast system allowing full coverage of the plasma profile for the entire discharge with simultaneously investigation of other fast changing phenomenon. All the CAMAC units are now begin tested for installation at CMOD.