Technical innovations for ITER Edge Thomson scattering measurement system

Yatsuka, E.; Bassan, M.; Hatae, T.; Yamamoto, T.; Shimada, Takahiko; Torimoto, Kazuhiro; Itami, K.

doi:10.1016/j.fusengdes.2018.04.071

Cited by 8 publications

(6 citation statements)

References 10 publications

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“…They include special provisions for initial alignment and to maintain targeting after maintenance periods. These include secondary laser systems to paint targets on the first wall visible to passive survey cameras [5]; dedicated systems to image the edges of the laser beam dump [26] and radiation-hard stepper motors to provide for in-situ fine adjustment [6]. These solutions and alternatives (based for example on radiation-hard motors) should allow initial and maintainable alignment in a reactor optical module.…”

Section: Alignment and Calibrationmentioning

confidence: 99%

Laser and microwave instrumentation for ITER and future reactors

Vayakis

2024

J. Inst.

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ITER diagnostics include an extensive set of laser and microwave diagnostics to give access to a wealth of information on the core and edge plasma and to support high performance operation of ITER. For example, Core and Edge Thomson scattering systems build detailed density and temperature profiles on time scales much faster than τ E to follow transient events; ECE and reflectometry add time resolution to follow MHD events. Implementing these diagnostics is challenging, needing a panoply of technologies to keep them functioning reliably for thousands of hours despite extreme events such as disruptions and wall conditioning cycles. Shielding, shutters and cleaning systems protect the forward elements of most optical systems from the build-up of deposits and damage. Still, plasma-facing mirrors must survive laser loads and endure erosion, deposition and in-situ RF cleaning. Calibration and monitoring systems ensure accurate and drift-free operation. These support systems are also not straightforward and required specific R&D. Access also drives the design: to deal with the neutron and gamma sources yet allow maintenance of activated components, ITER uses large, multi-purpose ports that couple otherwise distinct systems into modules for maintenance. Machine movement requires provisions to maintain alignment and calibration, from these port plugs, shown in figure 1, to the accessible areas 10–50 m away. A final complication comes from the difficulty of employing electronics near the plugs. Extensive qualification for radiation resistance is needed. This paper examines design adaptations that ITER adopted for its near-reactor environment, consider the lessons learnt from the ITER design activity specifically for laser and microwave systems and lays out some possible evolution paths for the reactor diagnostician that must follow a more industrial approach.

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Section: Alignment and Calibrationmentioning

confidence: 99%

Laser and microwave instrumentation for ITER and future reactors

Vayakis

2024

J. Inst.

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“…The ETS is one of the primary optical diagnostic systems for measuring electron temperature Te and electron density ne profiles, employing high power Nd: YAG lasers 1064 nm in wavelength for probing beams and 694.3 nm in wavelength for calibration [13]. High-power pulsed laser beams are irradiated in-vessel through the ITER vacuum windows, which function as the confinement boundary for tritium, beryllium, etc., and is crucial to ensure safety.…”

Section: Etsmentioning

confidence: 99%

Progress of Gamma Ray Irradiation Experiments on ITER Diagnostics from JADA

Kitazawa

Yatsuka

Ishikawa

et al. 2023

Plasma and Fusion Research

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The Japan domestic agency (JADA) is responsible for procuring five diagnostic systems for ITER: the microfission chamber (MFC), poloidal polarimeter (PoPola), edge Thomson scattering (ETS), divertor impurity monitor (DIM), and divertor infrared thermography (IRTh) systems. Components of these systems that will be installed in high radiation zones must undergo radiation resistance tests to ensure reliability. The JADA diagnostic group has been conducting gamma ray irradiation experiments on diagnostic components at QST since 2018. The MFC is a neutron diagnostic system that uses uranium fission chambers, the mineral-insulated cables of which were evaluated for corrosion resistance. In-situ observations of the MFC preamplifier have been launched. The PoPola provides the plasma current profile by detecting the polarizations of far-infrared laser beams at their inlets and outlets. Irradiation tests confirmed the durability of PoPola piezo actuators. The ETS is a laser-aided diagnostic to measure electron temperature and density in plasmas from scattered spectra. Laser-induced damages to the optical elements caused by irradiation were investigated. The DIM is a spectroscopic system having a wavelength range of 200 nm to 1000 nm. The effects of irradiation on optical devices, metal mirrors, and radiation-resistant optical fibers were investigated. The IRTh is an infrared thermography system to observe the surface temperature of the divertor. The optical elements and electrical devices of the IRTh have undergone irradiation experiments. The progress of the gamma ray irradiation experiments on the ITER diagnostic systems from JADA are reported.

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“…This is especially important for systems with relatively large optical apertures and large mirrors dimensions where the risk of mirror contamination is higher. Plasma cleaning systems based on RF capacitively coupled plasma are considered as candidate systems for large diagnostics of the ITER tokamak such as Ultra-Wide Angle Viewing System [1,2], Infrared Thermography [3], Visible Spectroscopy Reference System [4,5] and Edge Thomson Scattering [6][7][8][9]. The current level of plasma cleaning technology is not mature enough to be implemented in the design of the diagnostic systems.…”

Section: Introductionmentioning

confidence: 99%

“…To maintain the performance of the ETS front-end collection mirrors, a cleaning system based on a capacitively coupled plasma discharge is foreseen, with the mirror surfaces being used as the powered electrodes. The ETS system provides measurements of the electron temperature and density profiles at the periphery plasma of the ITER tokamak for physics studies and advanced plasma control [6,7]. The performance of the front-end optical mirrors is critical for the whole system operation as the diagnostics will be used for advanced machine control.…”

Section: Introductionmentioning

confidence: 99%

Radio-frequency plasma to clean ITER front-end diagnostic mirrors in geometry of Edge Thomson Scattering system

Ushakov¹,

Veldhoven²,

Rijnsent³

et al. 2022

Phys. Scr.

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The ITER Edge Thomson scattering (ETS) system provides electron temperature and density profile measurements in the ITER tokamak for plasma control. In collection optics, the front-end metallic first and second mirrors are expected to experience contamination with beryllium and tungsten degrading performance. Plasma cleaning based on a low-pressure radiofrequency discharge is expected to sputter contaminants. In the ETS, a water-cooled first mirror is combined with a powered electrode. Water cooling was realized as a notch filter for the driving frequency, and the electrode was grounded for a DC- voltage. A new breadboard reproducing the ETS mirror geometry was developed for experimental modelling. The notch filter uses equivalent cables. To understand the cleaning effect, ion energies and fluxes were measured in 40-50 MHz discharges in argon and helium at 1-10 Pa with and without the notch filter. Without a notch filter with minimum power losses, 2-4·1018 ions·m-2s-1 ion fluxes with energies of 100-140 eV were produced. With the notch filter, the peak ion energies were 30-50 eV. The power in the plasma was lower than 50 W with ion fluxes of – 1.5-1.9 1018 ions·m-2s-1. 53-m-long cable feeds equivalent to those of a real system were studied at 13-50 MHz and produced significant power loss: more than 95% at 40-50 MHz. A pre-matching element is essential to reduce power losses. A lower radiofrequency may be less sensitive to pre-matching and may be considered for mirrors without water cooling. A 40 MHz discharge is proposed for cleaning due to better stability, higher ion energies and possibly better uniformity. Powers in plasma in the range of hundreds of Watts may be needed to achieve ion fluxes suitable for cleaning. This requires more powerful components and shall be addressed in later experiments. The results are important for plasma cleaning in ETS and in other diagnostics where water-cooled first mirrors are used.

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Technical innovations for ITER Edge Thomson scattering measurement system

Cited by 8 publications

References 10 publications

Laser and microwave instrumentation for ITER and future reactors

Laser and microwave instrumentation for ITER and future reactors

Progress of Gamma Ray Irradiation Experiments on ITER Diagnostics from JADA

Radio-frequency plasma to clean ITER front-end diagnostic mirrors in geometry of Edge Thomson Scattering system

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