Improving spatial and spectral resolution of TCV Thomson scattering

Hawke, J.; Andrèbe, Y.; Bertizzolo, R.; Blanchard, P.; Chavan, R.; Decker, J.; Duval, B. P.; Lavanchy, P.; Llobet, X.; Marlétaz, B.; Marmillod, P.; Pochon, G.; Toussaint, M.

doi:10.1088/1748-0221/12/12/c12005

Cited by 23 publications

(29 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The black lines in the left panel of figure 1 correspond to the lines of sight of a multi-chord spectrometer called DSS (Divertor Spectroscopy System) [34]. The blue dots indicate the locations of the Thomson Scattering measurements [35], and the cyan areas show the field-of-views of the two infrared cameras [36]. The right panel of figure 1 plots the 64 lines of sight of the gold foil bolometers, used to estimate the radiated power.…”

Section: Methodsmentioning

confidence: 99%

Nitrogen-seeded divertor detachment in TCV L-mode plasmas

Février

Theiler

Harrison

et al. 2020

Plasma Phys. Control. Fusion

View full text Add to dashboard Cite

Most of the detachment experiments done to date on the Tokamak a Configuration Variable (TCV), both in standard and alternative divertor geometries, focused on L-mode integrated core density ramps. In view of extending these studies to high-power, high-confinement regimes, where impurity seeding will be necessary for detachment, the properties of nitrogen seeded L-mode detachment in TCV are assessed here with the extensive set of edge and divertor diagnostics and similarities and differences with integrated core density (ne) ramp detachment experiments are elucidated. It is found that in high current, reversed field plasmas, detachment at the outer target is achieved with N 2-seeding and density ramps, with target heat flux reductions of up to 90%, while the inner target only detaches with seeding. The Scrape-Off Layer radiation fraction reaches values of 60-80% and in all situations, a stable radiator can form around the Xpoint. The most striking difference between seeding and density ramp is the behavior of the upstream quantities. During the ne-ramp, a broadening of the upstream density profile (density "shoulder") occurs, concurrent with the outer target ion flux roll-over, while no such behavior occurs during nitrogen seeded detachment. Separatrix density, electron temperature and pressure also evolve strongly with increasing density, and are largely unaffected by the injection of nitrogen. Comparison of upstream and target pressures reveals that, in all cases, the outer target ion flux reduction coincides with the development of a parallel gradient of the total pressure. Common to all cases is also a reduction of energy confinement time with detachment, although this effect is weak for seeding at relatively high density. Studying the impact of the ∇B-drift direction in both nitrogen seeding and core density ramps reveals that drifts mainly affect the behavior at the inner strike point, highlighting the need to include drift in edge transport simulations.

show abstract

Section: Methodsmentioning

confidence: 99%

Nitrogen-seeded divertor detachment in TCV L-mode plasmas

Février

Theiler

Harrison

et al. 2020

Plasma Phys. Control. Fusion

View full text Add to dashboard Cite

show abstract

“…To analyse the spectrum, we employed one of the polychromators developed for the divertor TS diagnostic on TCV (tokamak à configuration variable) (Arnichand et al 2019). The technique is based on the fast collection of light during ∼2 s plasma shots (Pitzschke 2011;Hawke et al 2017). The polychromator collects Thomson scattered photons in a few spectral intervals and consists of a set of interference filters and avalanche photodiodes (APDs).…”

Section: Relative Calibration Of the Polychromatorsmentioning

confidence: 99%

Application of Thomson scattering to helicon plasma sources

et al. 2020

Self Cite

View full text Add to dashboard Cite

The possibility of performing electron density and temperature measurements in a high power helicon plasma is a crucial issue in the framework of the AWAKE (Advanced WAKefield Experiment) project, which demonstrates acceleration of particles using $\text{GeV}~\text{m}^{-1}$ electric fields in plasmas. For AWAKE, a helicon is currently envisaged as a candidate plasma source due to its capability for low electron and ion temperature, high electron density and production of an elongated plasma column. A plasma diagnostic to accurately determine the electron density in AWAKE regimes would be a valuable supporting tool. A demonstration Thomson scattering (TS) diagnostic was installed and successfully tested on the resonant antenna ion device (RAID) at the Swiss Plasma Center of Ecole Polytechnique Fédérale de Lausanne. RAID produces a helicon plasma column with characteristics similar to those of the AWAKE helicon source, and is therefore an optimal testbed for application to the AWAKE device. The spectrometer employed in RAID is based on polychromators which collect the light scattered by plasma electrons in spectrally filtered wavelength regions. Results from TS on RAID demonstrate conditions of electron density and temperature respectively of $n_{e}=1.10\,(\pm 0.19)\times 10^{19}~\text{m}^{-3}$ and $T_{e}=2.3\,(\pm 0.6)~\text{eV}$ in a steady-state discharge in an Ar plasma with 5 kW of RF power. If the same polychromator system is used for AWAKE, where the electron density attained is $2\times 10^{20}~\text{m}^{-3}$ , the contribution to measurement error due to coherent scattering is ${\sim}2.5\,\%$ . Presented here are details of the TS diagnostic and the first tests in RAID, and the expectations for the system when employed on the AWAKE device.

show abstract

“…Specifically, the experimental island widths (w exp ) presented in this paper are estimated by fitting the helical flux perturbations to the measurements from the probes [28,29] and have an error bar of about 20%. The plasma equilibrium is reconstructed by the Grad-Shafranov equilibrium solver LIUQE [30] while the local electron density and temperature are measured by a Thomson scattering system [31]. The measured and reconstructed data are then used by the transport code ASTRA [32] that solves relevant profiles such as q, magnetic shear and bootstrap current density consistently.…”

Section: Plasma Scenario and Experimental Setupmentioning

confidence: 99%

Control of neoclassical tearing modes and integrated multi-actuator plasma control on TCV

et al. 2019

View full text Add to dashboard Cite

The control of 2/1 neoclassical tearing modes (NTMs) with electron cyclotron (EC) waves has been studied both experimentally and numerically on TCV. Dynamic evolutions of NTMs along with time-varying deposition locations of the control beam have been studied in detail. The prevention of NTMs by means of preemptive EC (i.e. the control beam is switched on before the mode onset) has also been explored. A small sinusoidal sweeping with full amplitude of 0.07 (normalized to the minor radius) has been added to the control beam in two of the experiments to facilitate the comparison between NTM stabilization and prevention. It is shown that the prevention of NTMs is more efficient than NTM stabilization in terms of the minimum EC power required. Interpretative simulations with the Modified Rutherford Equation (MRE) have been performed to better quantify various effects, with coefficients well defined by dedicated experiments. Specifically, in order to obtain more insight on the dominant dependencies, a simple ad-hoc analytical model has been proposed to evaluate the time-varying classical stability index ∆ in the test discharges, based on the ∆ -triggered nature of these 2/1 NTMs. This allows simulating well the entire island width evolution with the MRE, starting from zero width and including both NTM stabilization and prevention cases for the first time. The exploration of NTM physics and control has facilitated the development of an NTM controller that is independent of the particular features of TCV and has been included in a generic plasma control system (PCS) framework. Integrated control of 2/1 NTMs, plasma β (the ratio of plasma pressure to magnetic pressure) and model-estimated safety factor q profiles has been demonstrated on TCV.

show abstract

Improving spatial and spectral resolution of TCV Thomson scattering

Cited by 23 publications

References 3 publications

Nitrogen-seeded divertor detachment in TCV L-mode plasmas

Nitrogen-seeded divertor detachment in TCV L-mode plasmas

Application of Thomson scattering to helicon plasma sources

Control of neoclassical tearing modes and integrated multi-actuator plasma control on TCV

Contact Info

Product

Resources

About