Generation of Noninductive Current by Electron-Bernstein Waves on the COMPASS-D Tokamak

Shevchenko, V.; Baranov, Y.; O’Brien, M.R.; Saveliev, A. N.

doi:10.1103/physrevlett.89.265005

Cited by 74 publications

(66 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…EBW start-up: A short pulse (∆t ≤ 90 ms) 100 kW f ECRH = 28 GHz ECRH system was commissioned to study plasma start-up with EBW current drive [59]. The waves are launched in O-mode (n cut−off ≈ 10 19 m −3 ) from the LFS and converted to X-mode using a grooved tile at the mid-plane of the centre column as a mirror-polariser.…”

Section: Current Drive and Start-upmentioning

confidence: 99%

Overview of physics results from MAST

Raman¹,

Ahn²,

Allain³

et al. 2011

Nucl. Fusion

Self Cite

View full text Add to dashboard Cite

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...

show abstract

Section: Current Drive and Start-upmentioning

confidence: 99%

Overview of physics results from MAST

Raman¹,

Ahn²,

Allain³

et al. 2011

Nucl. Fusion

Self Cite

View full text Add to dashboard Cite

show abstract

“…Finally, it is worth mentioning that Bernstein waves should also be useful to drive current in a high temperature plasma, which makes them especially attractive to be used in configurations that need internal currents to sustain the configuration such as STs or RFPs. The predicted CD efficiency is higher than that of conventional ECCD [14] and this has been demonstrated in the inside launch experiment in COMPASS-D [12]. We note here that a third scheme, the direct X-B conversion exists for low field devices where the width of the evanescent region between the two layers can be comparable to the wave length and thus tunneling is possible in principle.…”

Section: O-x-b Conversionmentioning

confidence: 61%

“…This has been successfully demonstrated in COMPASS-D [12]. However, high field side launch is usually technically not easy in toroidal fusion experiments and in addition, ν sc must be smaller than the wave frequency along the whole path up to the UHR layer, so that the use of this scheme is restricted to below the cutoff density.…”

Section: O-x-b Conversionmentioning

confidence: 99%

Recent Experimental Progress in Electron Cyclotron Resonance Heating and Electron Cyclotron Current Drive in Magnetically Confined Fusion Plasmas

Zohm

2007

Fusion Science and Technology

View full text Add to dashboard Cite

A review of recent experimental results in the area of ECRH and ECCD is given. Special emphasis is put on the recent developments of new schemes in which EC waves can heat and drive current in magnetically confined fusion plasmas. These comprise scenarios to overcome the density cutoff experienced in application of the classical O1 and X2 scheme as well as to increase the current drive efficiency of EC waves while maintaining their good localization. In particular, we discuss recent experimental progress in tokamaks, stellarators and spherical tori in the areas of the O2, X3 and EBW schemes (mostly OXB scheme) as well as experiments in which the combination of ECCD with Lower Hybrid Current Drive (LHCD) leads to a synergetic increase of the ECCD efficiency. A particular application of ECCD that has recently received a lot of attention and is therefore reviewed in this paper is the suppression of Neoclassical Tearing Modes (NTMs) by ECCD. We show that the theoretically predicted requirements for ECCD in terms of deposition (maximising the ECCD driven current density) and injection in phase with the O-point of the magnetic island associated with the NTM (which is needed when the island width falls below the deposition width) have been verified experimentally. Also, many of the elements needed for constructing a reliable, feedback controlled NTM suppression system for ITER based on ECCD have now been demonstrated experimentally and the next step, which is their integration into a reliable scheme, is well within reach.

show abstract

“…Thus, EBWs are strong candidates for delivering external energy and momentum to electrons in regions of a plasma inaccessible to the X and O modes [1] [2]. Coupling to EBWs via mode conversion has been demonstrated in stellarators [3] and tokamaks [4]. The same experiments have also seen effective interaction of EBWs with electrons.…”

Section: Introductionmentioning

confidence: 94%

Relativistic description of electron Bernstein waves

Decker

Ram

2006

Physics of Plasmas

View full text Add to dashboard Cite

The application of the extraordinary and ordinary electron cyclotron waves for heating and current drive in overdense, magnetized plasmas is restricted. For frequencies near low harmonics of the electron cyclotron frequency these waves are cutoff near the edge of the plasma. For higher frequencies the interaction of the waves with electrons is weak leading to very low absorption of wave power. However, electron Bernstein waves provide means for heating and current drive in overdense plasmas since they have no density cutoffs and are strongly damped near harmonics of the electron cyclotron resonance. This paper discusses properties of electron Bernstein waves that make them an attractive means for delivering energy and momentum to electrons. An approximate analytical model for electrostatic waves in the weakly relativistic and weak damping limits is developed. From this model the propagation and damping characteristics of electron Bernstein waves and their dependence on plasma parameters are derived. It is found that relativistic effects are necessary to properly describe the resonant interaction of electron Bernstein waves with electrons. The characteristics of electron Bernstein wave propagation and damping are very different depending on whether the electron cyclotron harmonic resonance is approached from the low-or the high-field side. The results from the analytical model and the associated analysis agree well with the results from the exact numerical calculations. This validates the physics of the simplifying assumptions on which the model is based. The electron Bernstein waves are completely damped well before the electron cyclotron resonance due to the Doppler shift. Within the damping region the waves interact with suprathermal electrons thereby having the potential for efficient current drive.

show abstract

Generation of Noninductive Current by Electron-Bernstein Waves on the COMPASS-D Tokamak

Cited by 74 publications

References 4 publications

Overview of physics results from MAST

Overview of physics results from MAST

Recent Experimental Progress in Electron Cyclotron Resonance Heating and Electron Cyclotron Current Drive in Magnetically Confined Fusion Plasmas

Relativistic description of electron Bernstein waves

Contact Info

Product

Resources

About