ECEI on EAST

The ECE imaging system for EAST was successfully installed in June 2012, and has 384 individual channels (24 poloidal, 16 radial). The typical parameters of the ECE-Imaging system can be found in Fig 2. The ultra-wide radial observation range is almost able to cover the entire q=1 surface. The real-time temperature imaging has helped EAST scientists to measure energy deposition, magnetic axis, and understand sawtooth physics more clearly over the past five years

Fig 1: 384-channel ECE Imaging system layout on EAST tokamak for 2016 campaign (credit to Yilun Zhu)

Fig 2: Typical parameters of the ECE-Imaging system on EAST (credit to Yilun Zhu)

Highlight Innovations

Shielding crate (survived from Megawatts LHCD)

Electron cyclotron emission imaging (ECEI) diagnostic system with 384 channels was installed on EAST tokamak. Since EAST was equipped with 4MW ICRF system, 4MW LHCD system and NBI system, the ECEI diagnostic system on EAST was heavily interfered, especially by the lower hybrid wave. The optimization of the electromagnetic shielding is presented, which help to reduce the interference to 40dB. Appropriate copper mesh shield and the correct ground connection are the key solutions. The comparisons of the ECEI raw signals before and after the optimization clearly show that the shielding performance is greatly improved.

Artificial Remote-control Technology (A.R.T.)

An intelligent remote control system based on a power distribution unit (PDU) and Arduino has been designed for the electron cyclotron emission imaging (ECEI) system on Experimental Advanced Superconducting Tokamak (EAST). This intelligent system has three major functions: ECEI system reboot, measurement region adjustment and signal amplitude optimization. The observation region of ECEI can be modified for different physics proposals by remotely tuning the optical and electronics systems. Via the remote adjustment of the attenuation level, the ECEI intermediate frequency signal amplitude can be efficiently optimized. The remote control system provides a feasible and reliable solution for the improvement of signal quality and the efficiency of the ECEI diagnostic system, which is also valuable for other diagnostic systems.

Flow chart of the attenuation remote regulation system:

The number of attenuators in the ECEI system is huge, 48 on the IF modules and 384 on the video modules. So when it comes to the IF modules, 288 bits (48 modules × 6 bits) of voltage signals have to be provided and the regulation system must maintain high integration in order to fit into the current ECEI system. If one Arduino chip is only utilized for one attenuator, the number of Arduino chips will be the same. Correspondingly, the number of IP addresses is also huge and the time spent on the state changing is too long. Thus the shift operation technique is applied to reduce the number of Arduino chips.

Physics Results:

Many exciting physics results in the past five years ultilizing ECE-Imaging system on EAST have been observed, like m/ n = 1/ 1 and higher harmonic modes during sawtooth oscillation in ICRF heating plasmat, and the partial and large full collapses in compound sawtooth etc.

Fig 3: The ICRF power deposition profile during the H-mode phases is confirmed by ECE imaging (ECEI) diagnostic. (source: Nuclear Fusion 53.2 (2013): 023004)

The ECE data clearly show that the electron temperature increase during the ICRF heating pulse is peaked near the magnetic axis

Fig 4: Estimation of the position of the magnetic axis using ECE-Imaing (credit to Yilun Zhu)

Fig 5: Higher Harmonic Modes during Sawtooth Oscillation in ICRF Heating Plasma on EAST (source: Physics of Plasmas 23, 042504 (2016))

Fig 6:Time-sequenced 2D ECE images of the compound sawtooth are demonstrated in the ELM H-mode ICRF plasma (source: Physics of Plasmas 23, 042504 (2016))

Selected Publications/ Presentations:

Yilun Zhu invited talk on High Temperature Plasma Diagnostic 2016 conference
H. AZAM, "Observations of compound sawteeth in ion cyclotron resonant heating plasma using ECE imaging on experimental advanced superconducting tokamak", Physics of Plasmas 23, 042504 (2016)
H. AZAM, "Electron Cyclotron Emission Imaging Observations of 𝑚/𝑛 = 1/1 and Higher Harmonic Modes during Sawtooth Oscillation in ICRF Heating Plasma on EAST *", CHIN. PHYS. LETT. Vol. 32, No. 6 (2015) 065201
Ming Xu, "Internal Magnetic Configuration Measured by ECE Imaging on EAST Tokamak", Plasma Science and Technology 15.12 (2013): 1189

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