Design of the 48, 57 μm Poloidal Polarimeter for ITER

Pavlichenko, R. O.; Kawahata, K.; Donne, T.

doi:10.1585/pfr.2.s1040

Cited by 7 publications

(4 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Even if from a physics point of view, the accuracy of the polarimeter should increase with the number of wavelengths, from an engineering/technological perspective, it is expected that two wavelengths are the best trade-off between performances and technological complexity/costs. Besides that, next tokamaks will be implemented with a dualwavelength interferometer, like the Density Interferometer Polarimeter (DIP) of ITER [7], so this proposed approach could be taken into consideration to increase the performances.…”

Section: Discussionmentioning

confidence: 99%

A multi-wavelength approach to increase polarimeter diagnostic performance in nuclear fusion reactors

Wyss¹,

Rossi²,

Gaudio³

2022

J. Inst.

View full text Add to dashboard Cite

In future tokamaks, the huge variation of the plasma parameters during a discharge (ramp up, flat top, and ramp down) may involve that a diagnostic suitable for the flat top is not suitable for transients, and vice versa. Moreover, future reactors will start the experimental campaigns in safe scenarios, where events like disruptions are not critical, and they will increase their parameters gradually. Also in this case, a diagnostic optimised for the final target scenario may fail at the beginning of the experimental campaign. Laser-based polarimetry, a plasma diagnostic used in magnetized plasma to measure quantities that are related to the electron density, the magnetic field, and the electron temperature (in the case of relativistic effects), is a typical diagnostic that must be optimised for specific scenarios, since it is affected by several issues (refraction, type-I approximation, noise sensitivity) that limit its range of applicability. The aim of this work is to present a method to solve, or at least alleviate, this type of problem by using a multi-wavelength approach. The main idea consists of measuring the polarisation effects (Faraday rotation and Cotton-Mouton phase shift) with more than one wavelength and then calculating the plasma parameters by a weighted average of the measurements, where the weights are derived from the theory of polarimetry. The analysis is performed simulating the process of measurement introducing a casual error. The outcomes demonstrate that the adoption of a multi-wavelength polarimeter system brings a more accurate measurement in a wider range. Considering that next tokamaks will be implemented with a dual-wavelength interferometer, like the dispersion interferometer-polarimeter of ITER, this proposed approach could be taken into consideration to increase the performances of polarimetry.

show abstract

Section: Discussionmentioning

confidence: 99%

A multi-wavelength approach to increase polarimeter diagnostic performance in nuclear fusion reactors

Wyss¹,

Rossi²,

Gaudio³

2022

J. Inst.

View full text Add to dashboard Cite

show abstract

“…The information provided by the JET polarimeter is relevant for the next class of future machines such as ITER, DTT, DEMO and future tokamaks [23]. For example, the toroidal dispersion interferometer of ITER will have a dual interferometer-polarimeter channel when polarimetry data will be used for real-time fringe jump correction errors [24], while the poloidal polarimeter of ITER will have a retroreflector similar to the lateral channels of JET diagnostics [31], which will involve systematic errors, and the new calibration method may be used to correct these issues.…”

Section: Conclusion and Further Developmentsmentioning

confidence: 99%

First measurements of line-integrated electron density in an ITER-like configuration using the JET far infrared polarimeter diagnostic

Rossi

Boboc

Orsitto

et al. 2021

Plasma Phys. Control. Fusion

View full text Add to dashboard Cite

Polarimetry exploits the optical activity and birefringent properties of thermonuclear plasmas to calculate some important quantities for their control like the line-integrated electron density and magnetic field distribution. The Joint European Torus (JET) far infrared polarimeter shares the same probing laser beams of the interferometer, with eight channels, four vertical and four lateral. While the vertical channels were already optimised to provide accurate measurements of the Faraday rotation angle, Cotton–Mouton (CM) phase shift and ellipticity, the lateral channels had been only optimised for Faraday rotation angle alone. By setting the initial polarisation angle of the lateral channel at zero degrees the CM effect is minimised, the ellipticity is almost zero, and the CM phase shift angle is impossible to measure. During the recent JET experimental campaign (C38 in 2019–2020), the input polarisation for the lateral channels was altered for a class of pulses to analyse the possibility to measure the CM phase shift angle and the ellipticity, and, more important, to assess if it is possible to provide information of line-integrated electron density using the lateral channels of JET polarimetry in an ITER-like configuration. As a note, ITER will have only tangential channels with reflectors buried deep inside the first wall, so this setup was truly an ITER-like configuration. The results clearly show huge improvements, which can be achieved by just changing the input polarisation. Moreover, the analysis of the measurements shows that the polarimetric measurements have a systematic error, which is probably due to the effect of refraction and to the in-vessel mirrors, which was only partially taken into account during the calibration phase before the plasma. Thus, a new calibration method was developed and the results presented on a statistical basis. It has been demonstrated that, varying the input polarisation of the polarimeter and using the new calibration method, it is possible to measure the line-integrated electron density, using the CM phase shift (or the ellipticity) of the lateral channels, with good accuracy with respect to the electron density measured by the interferometer that was considered the reference.

show abstract

“…Polarimetry is an important diagnostic for ITER, measuring line integrated Faraday rotation angle (∝< n e B || > L p ) on poloidal sightlines, L p is the plasma size [5]. Retro-reflecting mirrors are required for polarimetry.…”

Section: Pulsed Polarimetry Measurements On Itermentioning

confidence: 99%

Excess noise in Lidar Thomson scattering methods

Smith¹,

Drake²,

Lestz³

2012

J. Inst.

View full text Add to dashboard Cite

Fundamental detection limits for the Lidar Thomson scattering technique and in particular pulsed polarimetry are presented for the first time for the long wavelength limit of incoherent Thomson scattering. Pulsed polarimetry generalizes Lidar Thomson scattering to include local magnetic field sensing. The implication for these techniques is explored for two experimental regimes where shot limited detection no longer applies: tokamaks of ITER size and cm-size wire Z pinch plasmas of High Energy Density (HED) science. The utility and importance of developing Lidar Thomson scattering at longer wavelengths for the magnetic fusion program is illustrated by a study of sightline (local) polarimetry measurements on a 15MA ITER scenario. Polarimetric measurements in the far infrared regime are shown to reach sensitivities that are instructive and useful but with a complex behaviour that make spatially resolved measurements all but mandatory.

show abstract

Design of the 48, 57 μm Poloidal Polarimeter for ITER

Cited by 7 publications

References 11 publications

A multi-wavelength approach to increase polarimeter diagnostic performance in nuclear fusion reactors

A multi-wavelength approach to increase polarimeter diagnostic performance in nuclear fusion reactors

First measurements of line-integrated electron density in an ITER-like configuration using the JET far infrared polarimeter diagnostic

Excess noise in Lidar Thomson scattering methods

Contact Info

Product

Resources

About