Impact of calibration technique on measurement accuracy for the JET core charge-exchange system

Giroud, C.; Meigs, A.; Negus, C. R.; Zastrow, K.‐D.; Biewer, T. M.; Versloot, T. W.; Contributors, Jet‐Efda

doi:10.1063/1.2974806

Cited by 44 publications

(50 citation statements)

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“…[20], from charge exchange recombination spectroscopy (CXRS) [21,22] and, from the observed frequency of MHD modes [17]. These three methods of diagnosing the toroidal rotation, give comparable angular rotation velocities.…”

Section: Iia -Tools For Measuring Intrinsic Rotationmentioning

confidence: 99%

“…The so called subtracted spectra are analysed by fitting them to only one Gaussian component. Statistical errors, determined from the error in the least square fit [22], are shown as shaded areas in the plots below. CXRS intrinsic rotation measurements have been routinely compared with the observed frequency of MHD modes [1,12,17] .…”

Section: Iia -Tools For Measuring Intrinsic Rotationmentioning

confidence: 99%

“…Results of both analyses are presented here. The first method uses multi-Gaussian fit to the C +6 emission line [22]. Two Gaussian fit function accounts for: (i) the 'warm' component, which is due to charge exchange between C +6 ions and thermal deuterium at the edge and (ii) the 'hot' component which arises from the interaction of the C +6 with the fast neutral beam.…”

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confidence: 99%

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JET intrinsic rotation studies in plasmas with a high normalized beta and varying toroidal field ripple

Nave

Eriksson

Giroud

et al. 2012

Plasma Phys. Control. Fusion

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Understanding the origin of rotation in Ion Cyclotron Resonance Frequency (ICRF) heated plasmas is important for predictions for burning plasmas sustained by alpha particles, being characterized by a large population of fast ions and no external momentum input. The angular velocity of the plasma column has been measured in JET H-mode plasmas with pure ICRF heating for both the standard low toroidal magnetic ripple configuration, of about ~ 0.08% and, for increased ripple values up to 1.5 % [1]. These new JET rotation data were compared with the multi-machine scaling of ref. [2] for the Alfven-Mach number and with the scaling for the velocity change from L-mode into H-mode. The JET data do not fit well any of these scalings that were derived for plasmas that are co-rotating with respect to the plasma-current.With the standard low ripple configuration, JET plasmas with large ICRF heating power and normalized beta, βN ≈1.3, have a very small co-current rotation, with Alfven-Mach numbers significantly below those given by the rotation scaling of ref. [2]. In some cases the plasmas are actually counter-rotating. No significant difference between the H-mode and L-mode rotation is observed. Typically the H-mode velocities near the edge are lower than in Lmodes. With ripple values larger than the standard JET value, between 1% and 1.5%, H-mode plasmas were obtained where both the edge and the core counter rotated. I -IntroductionIntrinsic rotation can play a key role in the performance of future tokamak power plants where the momentum input will be small [3]. In present day tokamak experiments, rotation is mostly driven by the torque coming from the neutral beam injection (NBI). However, in reactors with high NBI power at high beam energy, the torque is expected to be small. The central toroidal rotation velocity for ITER H-mode plasmas with NBI power of 34 MW, was predicted to be in the range of 10-170 km/s [4]. This is lower than currently observed at JET for the same Prandtl number (ratio between momentum and ion heat diffusivity) and with NBI power less than 20 MW [5]. It is important to note that ITER simulations depend on options of momentum transport whose theory is still evolving. For instance, the ITER simulations of ref.[4] do not include any contribution from a momentum pinch which is found to exist in JET NBI discharges [6,7] and other tokamaks [8,9]. This inward pinch will modify the rotation profile in ITER, in particular the peaking of the rotation profile will increase. Understanding of momentum transport is crucial in order to reliably model rotation profiles in ITER and other future devices, however, this is not the scope of this paper. A good overview of momentum transport theory, covering also aspects like residual stress and up-down asymmetry that may affect significantly the rotation profile in ITER, is given in reference [10].As the NBI driven rotation in future machines is presumed to be small, the intrinsic plasma rotation, which occurs in the absence of momentum sources such as NBI, has...

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Section: Iia -Tools For Measuring Intrinsic Rotationmentioning

confidence: 99%

Section: Iia -Tools For Measuring Intrinsic Rotationmentioning

confidence: 99%

mentioning

confidence: 99%

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JET intrinsic rotation studies in plasmas with a high normalized beta and varying toroidal field ripple

Nave

Eriksson

Giroud

et al. 2012

Plasma Phys. Control. Fusion

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“…Beam-into-gas measurements without and with toroidal field have three primary functions for main-ion CER: (i) determination of the shape of the neutral beam emission spectrum for a "beam profile" used for Stark analysis, [18][19][20] (ii) evaluation of the accuracy of the spatial calibration through Doppler line shifts of all viewchords for a single beam neutral injector voltage, 21 and Stark splitting of the beam emission for beam into gas with toroidal field, and (iii) evaluation of the dynamic and steady-state mix of fractional current injected for the full, half and third energy components extracted from the beam ion source. 22 Photoemission from thermal deuterium charge exchange is more sensitive to the fractional density of full, half and third energy components because the cross-section peaks at lower relative velocity than carbon, which is sensitive to the full energy.…”

Section: A Beam Into Gasmentioning

confidence: 99%

Active spectroscopic measurements of the bulk deuterium properties in the DIII-D tokamak (invited)

Grierson

Burrell

Chrystal

et al. 2012

Review of Scientific Instruments

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The neutral-beam induced D α emission spectrum contains a wealth of information such as deuterium ion temperature, toroidal rotation, density, beam emission intensity, beam neutral density, and local magnetic field strength magnitude |B| from the Stark-split beam emission spectrum, and fast-ion D α emission (FIDA) proportional to the beam-injected fast ion density. A comprehensive spectral fitting routine which accounts for all photoemission processes is employed for the spectral analysis. Interpretation of the measurements to determine physically relevant plasma parameters is assisted by the use of an optimized viewing geometry and forward modeling of the emission spectra using a Monte-Carlo 3D simulation code.

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“…In the convention used here, positive rotation means rotation in the cocurrent direction. The difference in toroidal rotation speeds of the D main ion and the C impurity [15] are estimated to be smaller than the CXRS measurement uncertainty [16], which is showed in the figures as shaded areas. The charge exchange measurements in the plasma core were found to be consistent with the observed frequency and direction of propagation of MHD modes, that is the main ion frequency Doppler shifted by the frequency of the MHD instability.…”

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confidence: 99%

Influence of Magnetic Field Ripple on the Intrinsic Rotation of Tokamak Plasmas

Nave¹,

Johnson

Eriksson

et al. 2010

Phys. Rev. Lett.

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Using the unique capability of JET to monotonically change the amplitude of the magnetic field ripple, without modifying other relevant equilibrium conditions, the effect of the ripple on the angular rotation frequency of the plasma column was investigated under the conditions of no external momentum input. The ripple amplitude was varied from 0.08% to 1.5% in Ohmic and ion-cyclotron radio-frequency (ICRF) heated plasmas. In both cases the ripple causes counterrotation, indicating a strong torque due to nonambipolar transport of thermal ions and in the case of ICRF also fast ions. Plasma rotation is one of the central topics for toroidal plasma confinement and it is considered to play a key role in tokamak plasma performance. Plasma rotation can have a strong impact on plasma stability and confinement of fusion plasmas, through its ability to stabilize MHD modes [1], affect the strength of transport barriers [2], affect turbulence stabilization due to E Â B shear [3], and reduce the profile stiffness in the presence of anomalous transport [4]. In present day experiments, rotation is often driven by the torques of neutral beam injection (NBI), while in an alpha-heated reactor the momentum input is expected to be small [5]. In reactors with high NBI power, the torque is still expected to be small due to the high injection energy needed for the beam to penetrate deep into the plasma, which reduces the torque per MW of injected power. Thus, there has been a growing interest in the intrinsic rotation of the plasma, which is observed to occur in the absence of momentum sources such as NBI. Besides its relevance for fusion reactors, the residual plasma rotation in confinement configurations, without momentum injection, is an interesting, and not yet understood, problem from a basic physics point of view that has attracted great theoretical and experimental interest in recent years. The extrapolation from intrinsic plasma rotation data observed in several machines suggests that a substantial rotation in the cocurrent direction, i.e., in the direction parallel to the plasma current, will occur in ITER [6]. However, an effect that is still to be accounted for when extrapolating intrinsic rotation observations to ITER comes from the toroidal ripple in the magnetic field, which appears in tokamaks due to the finite number of toroidal magnetic field coils. ITER will have 18 toroidal magnetic field coils and, a ripple amplitude ¼ B=B of 0.5% to 1.2% at the edge (depending on the configuration of ferritic inserts) [7] where B is the averaged toroidal magnetic field and B is the Fourier amplitude of the toroidal ripple. Since the ripple breaks the toroidal symmetry, the motion of individual particles may lead to nonambipolar transport that can affect the plasma rotation through the neoclassical toroidal viscosity [8][9][10].The effect of ripple on plasma rotation during NBI has been reported from and JET [12]. Evidence that ripple transport of fast ions induces edge counterrotation in plasmas with no external momentum input wa...

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Impact of calibration technique on measurement accuracy for the JET core charge-exchange system

Cited by 44 publications

References 5 publications

JET intrinsic rotation studies in plasmas with a high normalized beta and varying toroidal field ripple

JET intrinsic rotation studies in plasmas with a high normalized beta and varying toroidal field ripple

Active spectroscopic measurements of the bulk deuterium properties in the DIII-D tokamak (invited)

Influence of Magnetic Field Ripple on the Intrinsic Rotation of Tokamak Plasmas

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