Plasma Physics and Fusion Energy Research

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1 Coláiste na hollscoile Corcaigh University College Cork Plasma Physics and Fusion Energy Research Plasma Data Analysis Group: Graduate Student: Paddy Mc Carthy Sean Knott (PhD) (Group Leader) (Co-supervisor: Andy Ruth) Recent graduates: Diarmuid Curran (PhD, 2015) Cormac McAuliffe (MSc, 2014) Mike Dunne (PhD, 2013) Funders: EuroFusion Consortium, Max Planck Institut für Plasmaphysik P.J. Mc Carthy Final Year Project Talk, UCC Oct 10 th

2 Coláiste na hollscoile Corcaigh University College Cork Activity and Projects: MHD Equilibrium reconstruction from tokamak and stellarator diagnostic data Development of temperature and density diagnostic for MAST Upgrade spherical tokamak Monte Carlo generation of large equilibrium databases for predictive aaequilibrium recovery and diagnostic sensitivity studies Double Plasma experiment for student training and He line ratio studies P.J. Mc Carthy Final Year Project Talk, UCC Oct 10 th

3 Coláiste na hollscoile Corcaigh University College Cork What is a plasma? Plasmas are conductive assemblies of charged particles and neutrals whose behaviour is dominated by collective effects. Plasmas carry electrical currents and generate magnetic fields. Plasmas (dubbed the fourth state of matter ) are the most common form of visible matter, comprising more than 99% of the visible universe. P.J. Mc Carthy Final Year Project Talk, UCC Oct 10 th

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5 jxb p Fluid pressure gradient (outward force/m 3 ) p Axisymmetry: jxb = p simplifies to: Force Balance in a Tokamak jxb = p balances inward pinch force/m 3 : jxb % 2 ψ R 2 1 ψ R R + 2 ψ ( ' & Z 2 * = µ 0 R 2 p'(ψ) + FF'(ψ) µ 0 R j φ ) - Grad-Shafranov equation: scalar, weakly nonlinear PDE

6 Blick in das Plasmagefäß von ASDEX Upgrade

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8 The Wendelstein 7-X Stellarator, Greifswald, Germany Construction completed 2014; in operation since December 2015 B (T) P.J. Mc Carthy 12 m Final Year Project Talk, UCC Oct 10 th 2016

9 Double Plasma Experiment (Physics Dept. UCC) Axisymmetric Magnetic Mirror Configuration Magnetic field lines P.J. Mc Carthy Final Year Project Talk, UCC Oct 10 th Cross-section showing contours of constant magnetic flux.

10 Exposed probe tip Ceramic insulation

11 Incandescent Tungsten Filaments

12 n e =3.0e16 m -3 T e =2.4eV P He =3.0e-3mb

13 n e =8.4e16 m -3 T e =0.9eV P He =6.0e-3mb

14 n e =1.1e17 m -3 T e =0.6eV P He =9.6e-3mb

15 n e =1.5e17 m -3 T e =0.4eV P He =1.2e-2mb

16 Inverse Problems Frequently, we are faced with a problem of inferring parameter values that characterise the state of a physical system from experimental data which may be indirect, noisy and/or incomplete. This is known as an Inverse Problem and can be loosely expressed as: Given the effect (the measurements), find the cause (the parameters describing the system state that gave rise to the measurements). Unknown radial profile of emissivity (for a given He I line) P.J. Mc Carthy A common and important inverse problem is that of tomographic reconstruction. In 2D tomography, we seek the reconstruction of a 2D object from a 1D projection consisting of a series of line integrals along many lines of sight. For a fan of lines (see diagram) the intensity at a given angle θ is given by: I(θ ) = ε( x(s), y(s), E) α(e) ds where ε(x,y) is the emissivity, α(e) is the detector sensitivity to photons of energy E and s is the coordinate along the line of sight. With certain caveats, the 2D profile ε(x,y) can be reconstructed from the 1D projection I(θ). Final Year Project Talk, UCC Oct 10 th 2016

17 Final Year Project 2016/2017 < 10eV electrons and ions Conventional divertor design MAST Upgrade Super X design P.J. Mc Carthy Final Year Project Talk, UCC Oct 10 th

18 Final Year Project 2016/2017 Tomographic reconstruction of He I emissivity profiles from line-of-sight measurements. Using the mirror plasma experiment in the plasma physics laboratory, the student will become familiar with basic plasma measurement techniques and explore the plasma parameters achievable in a magnetic mirror configuration. He I line emission spectra will be recorded for multiple lines of sight using an Ocean Optics spectrometer with continuously controllable orientation. The student will learn the concept of Tikhonov regularization for optimal information retrieval from noisy or incomplete data and, using regularized inversion techniques, s/he will invert the line-integrated data to obtain the unknown radial* emissivity profile for each of 15 significant He I lines. These results will form an important part of an ongoing project to develop an electron temperature and density diagnostic based on He I line ratios in the divertorleg region of the Mega Ampere Spherical Tokamak (MAST) Upgrade experiment which is planned to start operating in 2017 at the Culham Centre for Fusion Energy, Oxfordshire. *For axisymmetric emissivity, the profiles will be 1D functions of the magnetic flux surface radius. The analysis will include significance tests for possible departures from axisymmetry. P.J. Mc Carthy Final Year Project Talk, UCC Oct 10 th 2016