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Integrated data analysis of fast-ion measurements by velocity-space tomography

Mirko Salewski Technical University of Denmark

Department of Physics

M.Nocente, B.Geiger, A.S.Jacobsen, F.Binda, C.Cazzaniga, G. Gorini, G.Ericsson, J.Eriksson, W.W. Heidbrink, C.Hellesen, A.Hjalmarsson, V.G.Kiptily, S.B.Korsholm, T.Koskela, T.Kurki-Suonio, F.Leipold, J.Madsen, D.Moseev, S.K.Nielsen, J.Rasmussen, L.Stagner, M.Schneider, S.E.Sharapov, M.Stejner, M.Tardocchi, M.Weiland

2nd IAEA TM on Fusion Data Processing, Validation and Analysis 30 May - 2 June 2017, Cambridge, MA, USA

DTU Physics, Technical University of Denmark

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• Introduction to velocity-space tomography

• GRS/NES-based velocity-space tomography at JET

• FIDA-based velocity-space tomography at ASDEX Upgrade

• Summary and outlook

Outline

Mirko Salewski

Introduction to velocity-space tomography

Mirko Salewski

Forward problem

Salewski et al (2011,12,13,14,15,16,17) NF

Inverse problem

𝑊𝐹 = 𝑆

Distribution function F Measurements S Matrix W

Outline

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Neutron emission and gamma-ray spectrometry at JET

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Perpendicular view

Φ=90°(LOS, B)

Oblique view Φ=47°(LOS, B)

Eriksson et al (2015) NF

NES measurements

• 3 simultaneously measured spectra in JET #86459

• 4.5 MW NBI + 3 MW 3rd harmonic ICRF-heating

• Yellow: Used for inversion

6 Salewski et al (2017) NF

GRS measurements

• 2 GRS spectra in JET #86459

• High-resolution High-purity Germanium detector (1keV over 10 MeV)

• Two competing reactions

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Velocity-space observation regions

• Weight functions w:

• Signal/ion

• Discretize:

• Reject data if w is

1) is outside the target velocity space.

2) covers the velocity space below 120 keV.

Jacobsen et al (2014) RSI, Jacobsen et al (2015) NF

Heidbrink et al (2007) PPCF

• 5 detectors

• 3 typical Doppler shifts

GRS 2868 keV

GRS 3367 keV

Diamond

High Medium Low

NES: Jacobsen et al (2014) RSI, Jacobsen et al (2015) NF

GRS: Salewski et al (2015) NF, Salewski et al (2016a) NF

Inversion by 1st-order Tikhonov regularization

Mirko Salewski

• Forward problem:

• Inverse problem:

Velocity-space tomography vs. simulation

• Basic features agree: Tail length, tail width.

• Barrier region suggests low densities above 2 MeV.

• Velocity-space tomography confirms the barrier experimentally.

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[a.u.] [a.u.] [a.u.]

Salewski et al (2017) NF

What if we only use NES or GRS?

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• Inversions rely on integrated data analysis

• NES only or GRS only do not work well

Outline

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FIDA spectroscopy at ASDEX Upgrade

Weiland et al (2016) PPCF

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Prior information: What do we know?

• F is non-negative.

• Null-measurements of FIDA light • (E,p) position of NBI peaks at E, E/2, E/3

Mirko Salewski Salewski et al (2016b) NF

High-definition tomography: Inversion using prior information

Simulation

Without prior information

With prior information

Artifacts

No visible artifacts

Mirko Salewski

Salewski et al (2016b) NF

Tomography movie of a sawtooth crash

• Upper panel: Measurement of fast ion density

𝑛𝑓 = 𝑓𝑑𝐸𝑑𝑝

• Lower panel: tomographic inversion movie

• fit to 50.000 data points

–100 frames

–5 spectra per frame

–100 data points per spectrum

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Sawteeth: FIDA tomography vs. TRANSP

TRANSP

• Fairly good agreement

• Measured crashes smaller than simulated crashes.

• No measured crashes for |p|<0.25 in agreement with Kolesnichenko (1996) NF and disagreement with TRANSP.

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AUG #32323

For two-view FIDA systems: Numeric simulation as prior information

MUCH easier!

Not using TRANSP as prior information

Using TRANSP as prior information

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Reconstruction of differences from TRANSP

• Cases with and without TRANSP as prior information give consistent results for the 5-view case.

• Works for 2 FIDA views.

Mirko Salewski Salewski et al (2016b) NF

Optimal experimental design for fast-ion diagnostic sets

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• ASDEX Upgrade went from 3 to 5 FIDA views.

• Chose 2 viewing angles to best complement the other 3.

• Minimize quality parameter

• 85°and 50°are best.

Weiland et al (2016) PPCF

3 existing viewing angles

2-step GRS

1-step GRS

NPA: Heidbrink et al (2007) PPCF

CTS: Salewski et al (2011) NF

FIDA: Salewski et al (2014) PPCF

NES: Jacobsen et al (2015) NF

GRS-2: Salewski et al (2015) NF

GRS-1: Salewski et al (2016) NF

• W has vastly different forms for the different diagnostics.

• Known already.

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Summary

• Velocity-space tomography reveals new physics.

– Converts complex data to straightforward 2D images

– Combines diagnostics

– Accounts for nuisance parameters

• MeV range ion velocity-space tomography based on 5 NES/GRS spectra agrees well with simulations

• FIDA-based velocity-space movies at ASDEX Upgrade

• Velocity-space studies of sawtooth crashes confirm pitch selectivity

• Increase fast-ion measurement data at AUG and JET

• Use thermal ion signals

• Demonstrate approach on other machines

• Apply: Alfven modes, NTM, sawteeth, burning plasma

• Improve inversion methods

• Go 3D (spatial coordinate, constants-of-motion or EPmRm) Stagner (this conference)

Mirko Salewski

Outlook

Thank you for your attention!

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