Summary of ECE Presentations at EC-17

At the EC-17 workshop there were 12 presentations in the topic of diagnosing plasmas by measuring radiative emissions, mainly by ECE with one talk on EBW imaging. The number of ECE imaging systems on plasma devices has increased and new discoveries are being made from the expanded data set they provide. Technology continues to improve with some significant advances in receiver capabilities and clever designs for coupling to the plasma. A wide variety of ECE systems on many machines are providing crucial information on electron temperature and other plasma parameters, particularly on fluctuations related to MHD modes, their temporal and spatial structures. The ITER ECE system design is well along with the recent successful completion of the conceptual design review. 1 Imaging measurements The number of imaging measurements of plasma waves continues to grow with new systems planned or coming online on several machines. G. Yun presented results of ECE imaging from KSTAR, showing poloidal rotation of modes, dual flux tubes, and structures propagating near the plasma edge. First results from MAST were shown from a microwave imaging system that was looking at EBW emission (R. Vann). The 2-D imaging is accomplished with a novel phased array antenna system that is capable of both passive and active operation. A summary of measurements from the ECE imaging diagnostic on ASDEX-Upgrade was presented (A. Bogomolov) focusing on ELM observations. Rotating filaments associated with the type-I ELM precursor are seen and type-II ELMs show a broadband MHD fluctuation. 2 EC emission and radiation transport A number of papers addressed the basics of electron cyclotron emission and transport. S. Rathgeber presented analysis of radiation temperature from ECE edge emission on ASDEX-Upgrade. A key result is that the bump in Trad associated with ECE resonances just outside the LCFS in H-mode discharges has been shown to be due to emission from inside the steep gradient region in the plasma. This is extremely important for the ECE imaging diagnostics that are trying to interpret Te structures associated with the edge. A. White gave a talk on a statistical comparison of Thomson Scattering (TS) and ECE Te measurements up to 8 keV on C-MOD, looking for the TS/ECE discrepancy seen at high Te on other tokamaks. No discrepancy was found which motivates a need for modelling to interpret the multi-machine observations. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. EPJ Web of Conferences DOI: 10.1051/ C © Owned by the authors, published by EDP Sciences, 2012 , epjconf 201232 / 03001 (2012) 32 03001 Article available at http://www.epj-conferences.org or http://dx.doi.org/10.1051/epjconf/20123203001 A couple of papers addressed non-thermal emission. A new vertical viewing ECE system has been set up on TCV to study the electron distribution function in this tokamak’s high power density ECH discharges (W. Eshetu). On the T-10 tokamak, a number of cases of non-thermal emission have been noted with apparent invariant distribution function shape, implying a persistent turbulent state (V. Poznyak). Finally, a paper on the radiative transport of energy via cyclotron resonances was given by F. Albajar, discussing the importance of this effect on ITER for the case of suprathermal electrons. 3 ECE with heterodyne receivers A collection of presentations showed results from new or improved ECE heterodyne radiometer setups. First results from the line-of-sight ECE system incorporated into the ECRH launcher on ASDEX-Upgrade were presented by W. Bongers. This difficult engineering feat is necessary for feedback control of ECRH for NTM suppressing, and the early results are promising. L. Porte gave a talk on correlation ECE (CECE) measurements on TCV. Dramatic reductions in the turbulence correlation length were seen as collisionality was increased and surprising changes in fluctuation spectral content were observed for different z-height views. High frequency MHD modes were studied with the upgraded heterodyne radiometer on Tore Supra and differences in simultaneous half-radius low frequency modes were noted (D. Elbeze). The extensive suite of ECE instruments on T-10 was described by V. Poznyak where simultaneous measurements of 1st harmonic O-mode and 2nd harmonic X-mode are regularly made. Finally, R. Pavlichenko showed data from a heterodyne receiver measuring optically thin emission from the Uragnan-3M tokamak, demonstrating once again the broad range of usefulness of ECE measurements from magnetized plasmas.


Introduction
The ECE topics at EC-19 were presented in three talks and seven posters.The topics naturally divide themselves into the primary type of instrument involved, Michelson interferometer, heterodyne radiometer, and ECE-Imaging instruments, with a separate section for ITER ECE systems plus a special related topic of EBW heating.

Measurements with Michelson interferometers
Two papers dealt with the calibration of Michelson interferometers.A. Sinha reported on the calibration of the Michelson that will be used on the SST-1 tokamak.The system was calibrated at Culham before being sent to India.Two blackbody sources at 873 K and 77 K respectively were used, obtaining well-resolved response curves and verifying the stability of the instrument.M. Austin showed measurements of the variation of sensitivity of the Michelson instrument with humidity.For the DIII-D tokamak's system with the 18 m corrugated waveguide transmission line in air the results showed ignorable changes in response for low harmonic frequencies (70-300 GHz), less than 1% for relative humidity changes of 25% to 67%.But attenuation due to water vapor increases strongly with frequency such that the changes brought about at high frequency (300-1000 GHz) can be 5% or greater and hence need to be taken into account for data used in this range.

Measurements with heterodyne radiometers
Three papers showed results from heterodyne systems.V. Siju summarized the radiometer diagnostics on the IPR tokamaks.The SST-1 system, eight channels covering 75-85 GHz, is providing well resolved Te data.The ADITYA-U system is under construction; it will consist of 16 channels covering 75-94 GHz. S. Denk gave a talk discussing measurements in ASDEX-U of non-thermal ECE in the edge channels of that tokamak's 60 channel system.Forward modeling of the edge emission data has provided valuable information about the non-thermal distribution.Finally, M. Fontana presented data from the TCV tokamak heterodyne radiometer suite.TCV has multiple systems with a variety of flexible configurations.A highlight of the data was from TCV's Correlation-ECE system, that showed a strong reduction in Te fluctuations for plasma discharges with a negative triangularity shape over an equivalent positive triangularity shape, indicating a causal relationship between the reduced turbulence and the improved confinement in the "backwards-D" configuration.

Measurements with ECE-Imaging
Results were presented from the ECE-Imaging system on KSTAR by M. Choi.The 2-D system was used to observe the onset of m/n=2/1 magnetic islands with various actuators.In the case of a density ramp actuation the 2-D contours closely resemble ballooning mode simulations.Mode structure was mapped out during the growth, crash, and recovery phases of both small and large minor disruptions.KSTAR now has a second ECE-I system located 22.5 degrees toroidally from the first system; this permits 3-D imaging of plasma Te structures.This capability made possible observation of the modes of major disruption where the 2/1 magnetic island was seen to interact with a cold bubble which affected its growth.This could be one explanation for the explosive 2/1 island growth in a major disruption.

ITER ECE systems
There were three papers discussing ECE systems related to ITER. S. Danani gave a talk on the testing of a prototype receiver for the ITER high frequency radiometer.The receiver, which covers the 200-300 GHz range, was put through noise temperature and sensitivity checks and subsequently measured plasma signals at the DIII-D facility.The instrument met ITER requirements of 20,000 K noise temperature and 500 V/W sensitivity and was shown to make linear, frequency resolved measurements of plasma Te when compared to simultaneous data from the DIII-D Michelson interferometer.R. Kumar presented data from the characterization of a high temperature blackbody source intended to be used in the ITER instrument room.IR measurements at 500 ˚C validated the high emissivity and good thermal conductivity of the silicon carbide source element.
G. Taylor gave an overview talk on the status ITER ECE diagnostic system.Good progress has been made in the design of interlocking systems that are shared between the US and IN-DA groups.The front end optics design is nearly final; recent changes were made to redirect the oblique view away from the ECH launchers and to accommodate improved neutron shielding.The hot calibration source (1000 K operating temperature) has been through several design iterations in order to meet tough requirements for shock loads, radiation loads, and overall robustness.The path of the transmission line (~45 m length) and the beam modification units (splitter boxes) are designed.The final details of the transmission line waveguide are awaiting testing of the two candidate options, smooth wall

EBW heating
A. Koehn presented a paper on electron Bernstein wave (EBW) heating on the TJ-K stellarator.EBW techniques are a way to launch and receive waves in over-dense plasmas and in this case the heating and current drive aspects were investigated.Using a novel phased array antenna that steers via small frequency changes, heating was observed as the density was increased to the point where the O-X-B mode conversion for 2nd harmonic took place.Additionally, reduction of broadband turbulence was obtained when heating at high harmonic frequencies.

Conclusions
ECE continues to be a major diagnostic for Te measurements in magnetically confined high temperature plasmas.Heterodyne radiometers and Michelson interferometers are still the major contributors for most experiments.Advanced versions of heterodyne instruments, such as correlation radiometers and 2-and 3-D imaging systems are exploring the finest details of electron temperature structures in plasmas.The design of the ITER-ECE diagnostic system is well along.Challenges are being found due to the machine size and nuclear aspects of ITER, particularly in the areas of hot source development, transmission line design.These challenges are being met and it is expected that the ECE diagnostic will be an important contributor to ITER plasma physics understanding.
dielectric wall, both which would be in circular metal tubing.The layout of the ITER ECE instrument hall, containing two Michelson interferometers (70-1000 GHz), a low frequency radiometer (122-230 GHz) and a high frequency radiometer (220-340 GHz) has been decided. or