Enhanced edge Thomson scattering on MAST

Scannell, R.; Walsh, Mike; Carolan, P. G.; Conway, N. J.; Darke, A.; Dunstan, M. R.; Hare, Donald G.; Prunty, S. L.

doi:10.1063/1.2237488

Cited by 45 publications

(39 citation statements)

References 5 publications

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“…In previous studies α BP P has been measured directly 6,7,9 by applying an external voltage sweep to the BPP, however this is not possible in the present implementation. Instead α BP P will be constrained by a detailed cross-diagnostic comparison with the Thomson scattering system on MAST 23 . The BPP has been compared favourably with potential measurements from an emissive probe 7 and a self-emitting Langmuir probe 15 .…”

Section: Figmentioning

confidence: 99%

Profile measurements in the plasma edge of mega amp spherical tokamak using a ball pen probe

Walkden

Adámek

Allan

et al. 2015

Review of Scientific Instruments

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The ball pen probe (BPP) technique is used successfully to make profile measurements of plasma potential, electron temperature, and radial electric field on the Mega Amp Spherical Tokamak. The potential profile measured by the BPP is shown to significantly differ from the floating potential both in polarity and profile shape. By combining the BPP potential and the floating potential, the electron temperature can be measured, which is compared with the Thomson scattering (TS) diagnostic. Excellent agreement between the two diagnostics is obtained when secondary electron emission is accounted for in the floating potential. From the BPP profile, an estimate of the radial electric field is extracted which is shown to be of the order ∼1 kV/m and increases with plasma current. Corrections to the BPP measurement, constrained by the TS comparison, introduce uncertainty into the ER measurements. The uncertainty is most significant in the electric field well inside the separatrix. The electric field is used to estimate toroidal and poloidal rotation velocities from E × B motion. This paper further demonstrates the ability of the ball pen probe to make valuable and important measurements in the boundary plasma of a tokamak.

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Section: Figmentioning

confidence: 99%

Profile measurements in the plasma edge of mega amp spherical tokamak using a ball pen probe

Walkden

Adámek

Allan

et al. 2015

Review of Scientific Instruments

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“…Using the better NdYag edge TS system on the low field side (LFS) [7] in conjunction with the high field side (HFS) data from the Ruby system earlier studies on the comparison of LFS and HFS pedestals with the Ruby system alone [8,9] were revisited. The study covered a wide data set with 0.5 MA ≤ I p ≤ 1.2 MA, 0.2 ≤ n e /n G ≤ 0.9 (n G : Greenwald density), 3 ≤ q 95 ≤ 7, 0.45 T ≤ B t ≤ 0.55 T, triangularity of 0.3 ≤ δ ≤ 0.5, elongation of 1.6 ≤ κ ≤ 2.1 and auxiliary heating power of 1.0 MW ≤ P NBI ≤ 3.8 MW in double null (DN) and single null (SN) configurations [10].…”

Section: Elms and Pedestalmentioning

confidence: 99%

Overview of physics results from MAST

Raman¹,

Ahn²,

Allain³

et al. 2011

Nucl. Fusion

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Several improvements to the MAST plant and diagnostics have facilitated new studies advancing the physics basis for ITER and DEMO, as well as for future spherical tokamaks. Using the increased heating capabilities P NBI ≤ 3.8 MW H-mode at I p = 1.2 MA was accessed showing that the energy confinement on MAST scales more weakly with I p and more strongly with B t than in the ITER IPB98(y,2) scaling. Measurements of the fuel retention of shallow pellets extrapolate to an ITER particle throughput of 70% of its original design value. The anomalous momentum diffusion, χ φ , is linked to the ion diffusion, χ i , with a Prandtl number close to P φ ≈ χ φ /χ i ≈ 1, although χ i approaches neoclassical values. New high spatially resolved measurements of the edge radial electric field, E r , show that the position of steepest gradients in electron pressure and E r are coincident, but their magnitudes are not linked. The T e pedestal width on MAST scales with the β pol rather than ρ pol . The ELM frequency for type-IV ELMs, new in MAST, was almost doubled using n = 2 resonant magnetic perturbations from a set of 4 external coils (n = 1, 2). A new internal 12 coil set (n ≤ 3) has been commissioned. The filaments in the inter-ELM and L-mode phase are different from ELM filaments, and the characteristics in L-mode agree well with turbulence calculations. A variety of fast particle driven instabilities were studied from 10 kHz saturated fishbone like activity up to 3.8 MHz compressional Alfvén eigenmodes (CAE). The damping rate of ellipticityinduced AE was measured to be 4% using the new internal coils as antennae. Fast particle instabilities also affect the off-axis NBI current drive and lead to fast ion diffusion of the order of 0.5 m 2 /s and reduce the driven current fraction from 40% to 30%. EBW current drive start-up is demonstrated for the first time in a spherical tokamak generating plasma currents up to 55 kA. Many of these studies contributed to the physics basis of a planned upgrade to MAST. Introduction: MAST [1]is one of the two leading tight aspect ratio (A = ε −1 = R/a = 0.85 m/0.65 m ∼ 1.3, I p ≤ 1.5 MA) tokamaks in the world. The hot T ≤ 3 keV, dense n e = (0.1 − 1) × 10 20 m −3 and highly shaped (δ ≤ 0.5, 1.6 ≤ κ ≤ 2.5) plasmas are accessed at moderate toroidal field B t (R = 0.7 m) ≤ 0.62 T and show many similarities to conventional aspect ratio tokamaks. Detailed physics studies using the extensive array of state of the art diagnostics and access to different physics regimes help to consolidate the physics basis for ITER and DEMO [2,3], and explore the viability of future devices based on the spherical tokamak (ST) concept such as a component test facility (CTF) [4] or an advanced power plant [5]. The challenge for today's experiments is to find an integrated scenario that extrapolates to these future devices, in particular to develop plasmas with reduced power load on plasma facing components, notably from edge localised modes (ELM), but high confinement facilitated by internal or edge transport ba...

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“…The new edge Thomson scattering system [13] provides T e and n e information at the probe tip, on which the SX/Bs depend. These have been compared with the number of photons observed by the visible spectrometer.…”

Section: Erosion Rate Calculationsmentioning

confidence: 99%