A spinning mirror for fast angular scans of EBW emission for magnetic pitch profile measurements

Volpe, F.

doi:10.1063/1.3475786

Cited by 6 publications

(5 citation statements)

References 15 publications

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“…The calculated bootstrap current density appears to be somewhat smaller than that measured, with a narrower profile, the difference being more pronounced just after the ELM. At the time of the type-I ELM, ELITE calculations show the discharge to be close to the ballooning Edge current density evolution may also be inferred from electron Bernstein wave emission [36,37]. Initial measurements [38] indicate large variation in magnetic field line tilt angle over a very small region ( 2 cm) close to the LCFS, consistent with a local bidirectional radial current structure.…”

Section: Pedestal Physics and The L-h Transitionmentioning

confidence: 61%

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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Section: Pedestal Physics and The L-h Transitionmentioning

confidence: 61%

Overview of physics results from MAST

Raman¹,

Ahn²,

Allain³

et al. 2011

Nucl. Fusion

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“…This was confirmed by two-dimensional scans [115,116], including rapid scans performed during a single discharge by means of a spinning mirror [116], and eventually measurements simultaneously carried out with multiple sensors [117]. These initial demonstrations required the plasma to be overdense and emit Electron Bernstein (B) Waves (EBWs) that converted to the X-mode and eventually to the O-mode.…”

Section: Mode Conversion Based Techniquesmentioning

confidence: 87%

Prospects for a dominantly microwave-diagnosed magnetically confined fusion reactor

Volpe

2017

J. Inst.

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Compared to present experiments, tokamak and stellarator reactors will be subject to higher heat loads, sputtering, erosion and subsequent coating, tritium retention, higher neutron fluxes, and a number of radiation effects. Additionally, neutral beam penetration in tokamak reactors will only be limited to the plasma edge. As a result, several optical, beam-based and magnetic diagnostics of today's plasmas might not be applicable to tomorrow's reactors, but the present discussion suggests that reactors could largely rely on microwave diagnostics, including techniques based on mode conversions and Collective Thomson Scattering.

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“…16 . Warm plasma effects would be needed to model the BXO conversion used in radiometric techniques [9][10][11] , but not for the OX conversion invoked here.…”

Section: Full-wave Slab Modelmentioning

confidence: 99%

“…A related, earlier technique relies on partial transmission, though the O-mode cutoff, of internally emitted electron Bernstein (B) waves (EBW) undergoing BXO mode conversion [9][10][11] . However, not all fusion plasmas are over-dense EBW emitters.…”

Section: Introduction and Physical Principlementioning

confidence: 99%

Full-wave feasibility study of anti-radar diagnostic of magnetic field based on O-X mode conversion and oblique reflectometry imaging

Meneghini

Volpe

2016

Review of Scientific Instruments

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An innovative millimeter wave diagnostic is proposed to measure the local magnetic field and edge current as a function of the minor radius in the tokamak pedestal region. The idea is to identify the direction of minimum reflectivity at the O-mode cutoff layer. Correspondingly, the transmissivity due to O-X mode conversion is maximum. That direction, and the angular map of reflectivity around it, contains information on the magnetic field vector B at the cutoff layer. Probing the plasma with different wave frequencies provides the radial profile of B. Full-wave finite-element simulations are presented here in 2D slab geometry. Modeling confirms the existence of a minimum in reflectivity that depends on the magnetic field at the cutoff, as expected from mode conversion physics, giving confidence in the feasibility of the diagnostic. The proposed reflectometric approach is expected to yield superior signal-to-noise ratio and to access wider ranges of density and magnetic field, compared with related radiometric techniques that require the plasma to emit electron Bernstein waves. Due to computational limitations, frequencies of 10-20 GHz were considered in this initial study. Frequencies above the edge electron-cyclotron frequency (f > 28 GHz here) would be preferable for the experiment, because the upper hybrid resonance and right cutoff would lie in the plasma, and would help separate the O-mode of interest from spurious X-waves.

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A spinning mirror for fast angular scans of EBW emission for magnetic pitch profile measurements

Cited by 6 publications

References 15 publications

Overview of physics results from MAST

Overview of physics results from MAST

Prospects for a dominantly microwave-diagnosed magnetically confined fusion reactor

Full-wave feasibility study of anti-radar diagnostic of magnetic field based on O-X mode conversion and oblique reflectometry imaging

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