Observation of fast ion behaviour with a neutron emission profile monitor in MAST

Cecconello, M.; Sangaroon, Siriyaporn; Turnyanskiy, M.; Conroy, S.; Wodniak, I.; Akers, R.; Ericsson, Göran

doi:10.1088/0029-5515/52/9/094015

Cited by 21 publications

(26 citation statements)

References 34 publications

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“…This new observation in turn leads to Alfvénic mode destabilization. The low-frequency modes are consistent with non-resonant internal kinks [89,90], destabilized by pressure gradient, whose saturation and nonlinear evolution are modified by fast ions. Full-orbit particle-following code (SPIRAL [91]) calculations have been performed with an ideal kink radial mode structure (PEST code) and validated by soft X-ray data.…”

Section: Fast Ion Phase Space Redistribution and Effects On Low And Hsupporting

confidence: 55%

Overview of physics results from the conclusive operation of the National Spherical Torus Experiment

Sabbagh¹,

Ahn²,

Allain³

et al. 2013

Nucl. Fusion

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Research on the National Spherical Torus Experiment, NSTX, targets physics understanding needed for extrapolation to a steady-state ST Fusion Nuclear Science Facility, pilot plant, or DEMO. The unique ST operational space is leveraged to test physics theories for next-step tokamak operation, including ITER. Present research also examines implications for the coming device upgrade, NSTX-U. An energy confinement time, τ E , scaling unified for varied wall conditions exhibits a strong improvement of B T τ E with decreased electron collisionality, accentuated by lithium (Li) wall conditioning. This result is consistent with nonlinear microtearing simulations that match the experimental electron diffusivity quantitatively and predict reduced electron heat transport at lower collisionality. Beam-emission spectroscopy measurements in the steep gradient region of the pedestal indicate the poloidal correlation length of turbulence of about ten ion gyroradii increases at higher electron density gradient and lower T i gradient, consistent with turbulence caused by trapped electron instabilities. Density fluctuations in the pedestal top region indicate ion-scale microturbulence compatible with ion temperature gradient and/or kinetic ballooning mode instabilities. Plasma characteristics change nearly continuously with increasing Li evaporation and edge localized modes (ELMs) stabilize due to edge density gradient alteration. Global mode stability studies show stabilizing resonant kinetic effects are enhanced at lower collisionality, but in stark contrast have almost no dependence on collisionality when the plasma is off-resonance. Combined resistive wall mode radial and poloidal field sensor feedback was used to control n = 1 perturbations and improve stability. The disruption probability due to unstable resistive wall modes (RWMs) was surprisingly reduced at very high β N /l i > 10 consistent with low frequency magnetohydrodynamic spectroscopy measurements of mode stability. Greater instability seen at intermediate β N is consistent with decreased kinetic RWM stabilization. A model-based RWM state-space controller produced long-pulse discharges exceeding β N = 6.4 and β N /l i = 13. Precursor analysis shows 96.3% of disruptions can be predicted with 10 ms warning and a false positive rate of only 2.8%. Disruption halo currents rotate toroidally and can have significant toroidal asymmetry. of this phenomenon in designing future RF systems. The snowflake divertor configuration enhanced by radiative detachment showed large reductions in both steady-state and ELM heat fluxes (ELMing peak values down from 19 MW m −2 to less than 1.5 MW m −2 ). Toroidal asymmetry of heat deposition was observed during ELMs or by 3D fields. The heating power required for accessing H-mode decreased by 30% as the triangularity was decreased by moving the X-point to larger radius, consistent with calculations of the dependence of E × B shear in the edge region on ion heat flux and X-point radius. Co-axial helicity injection reduced the induct...

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Section: Fast Ion Phase Space Redistribution and Effects On Low And Hsupporting

confidence: 55%

Overview of physics results from the conclusive operation of the National Spherical Torus Experiment

Sabbagh¹,

Ahn²,

Allain³

et al. 2013

Nucl. Fusion

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“…They move around a helical drift axis, positioned on the opposite side of the magnetic axis inside the kinked core. That behaviour is in part responsible for off-axis redistribution of NBI fast particles, evidenced by MAST neutron camera traces [17] and illustrated using a guiding-centre drift approach in slowing-down simulations [4]. In a full-orbit formulation, particles can develop small gyro-motion even if their pitch-variable is initially equal to unity (zero Larmor radius) depending on the bending of field-lines.…”

Section: Deeply-passing Particlesmentioning

confidence: 99%

Hybrid guiding-centre/full-orbit simulations in non-axisymmetric magnetic geometry exploiting general criterion for guiding-centre accuracy

Pfefferlé

Graves

Cooper

2015

Plasma Phys. Control. Fusion

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To identify under what conditions guiding-centre or full-orbit tracing should be used, an estimation of the spatial variation of the magnetic field is proposed, not only taking into account gradient and curvature terms but also parallel currents and the local shearing of field-lines. The criterion is derived for general three-dimensional magnetic equilibria including stellarator plasmas. Details are provided on how to implement it in cylindrical coordinates, and in flux coordinates that rely on the geometric toroidal angle. A means of switching between guiding-centre and full-orbit equations at first order in Larmor radius with minimal discrepancy is shown. Techniques are applied to a MAST (Mega Amp Spherical Tokamak) helical core equilibrium in which the inner kinked flux-surfaces are tightly compressed against the outer axisymmetric mantle and where the parallel current peaks at the nearly rational surface. This is put in relation with the simpler situation B(x, y, z) = B0[sin(kx)ey + cos(kx)ez], for which full orbits and lowest order drifts are obtained analytically. In the kinked equilibrium, the full orbits of NBI fast ions are solved numerically and shown to follow helical drift surfaces. This result partially explains the off-axis redistribution of NBI fast particles in the presence of MAST Long-Lived Modes (LLM).

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“…Neutron camera systems have been demonstrated on a variety of different machines: Single camera systems were employed on TFTR [37,59,60], JT-60U [57], and MAST [61]; a two camera system has been used on JET [62]; and a three camera system is being designed for ITER [31]. JET's nine-collimator vertical array and twelve-collimator horizontal array allow for 2D tomographic reconstructions [63] of the plasma and wide imaging coverage of a poloidal cross-section.…”

Section: Neutron Camera Systemmentioning

confidence: 99%

“…Each collimator is 90 cm long and 1 cm in diameter. These dimensions were chosen based on the dimensions used in JET and MAST [64,61]. The upper camera is rotated ∼60 degrees above the horizontal camera in the same poloidal plane and has only five collimator channels (∼20 cm resolution) to minimize its size and interference with a possible upper divertor.…”

Section: Neutron Camera Systemmentioning

confidence: 99%

Neutron diagnostics for the physics of a high-field, compact, Q ≥ 1 tokamak

Tinguely

Rosenthal

Simpson

et al. 2019

Fusion Engineering and Design

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Advancements in high temperature superconducting technology have opened a path toward high-field, compact fusion devices. This new parameter space introduces both opportunities and challenges for diagnosis of the plasma. This paper presents a physics review of a neutron diagnostic suite for a SPARC-like tokamak [Greenwald et al 2018 doi:10.7910/DVN/OYYBNU]. A notional neutronics model was constructed using plasma parameters from a conceptual device, called the MQ1 (Mission Q ≥ 1) tokamak. The suite includes time-resolved micro-fission chamber (MFC) neutron flux monitors, energy-resolved radial and tangential magnetic proton recoil (MPR) neutron spectrometers, and a neutron camera system (radial and off-vertical) for spatially-resolved measurements of neutron emissivity. Geometries of the tokamak, neutron source, and diagnostics were modeled in the Monte Carlo N-Particle transport code MCNP6 to simulate expected signal and background levels of particle fluxes and energy spectra. From these, measurements of fusion power, neutron flux and fluence are feasible by the MFCs, and the number of independent measurements required for 95% confidence of a fusion gain Q ≥ 1 is assessed. The MPR spectrometer is found to consistently overpredict the ion temperature and also have a 1000× improved detection of alpha knock-on neutrons compared to previous experiments. The deuterium-tritium fuel density ratio, however, is measurable in this setup only for trace levels of tritium, with an upper limit of n T /n D ≈ 6%, motivating further diagnostic exploration. Finally, modeling suggests that in order to adequately measure the self-heating profile, the neutron camera system will require energy and pulse-shape discrimination to suppress otherwise overwhelming fluxes of low energy neutrons and gamma radiation.

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Observation of fast ion behaviour with a neutron emission profile monitor in MAST

Cited by 21 publications

References 34 publications

Overview of physics results from the conclusive operation of the National Spherical Torus Experiment

Overview of physics results from the conclusive operation of the National Spherical Torus Experiment

Hybrid guiding-centre/full-orbit simulations in non-axisymmetric magnetic geometry exploiting general criterion for guiding-centre accuracy

Neutron diagnostics for the physics of a high-field, compact, Q ≥ 1 tokamak

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Observation of fast ion behaviour with a neutron emission profile monitor in MAST

Cited by 21 publications

References 34 publications

Overview of physics results from the conclusive operation of the National Spherical Torus Experiment

Overview of physics results from the conclusive operation of the National Spherical Torus Experiment

Hybrid guiding-centre/full-orbit simulations in non-axisymmetric magnetic geometry exploiting general criterion for guiding-centre accuracy

Neutron diagnostics for the physics of a high-field, compact, Q ≥ 1 tokamak

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Product

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Neutron diagnostics for the physics of a high-field, compact, Q ≥ 1 tokamak