Plasma Performance Optimization in ASDEX Upgrade

Mertens, V.; Aubanel, C.; Gruber, O.; Kaufmann, Michael; Neu, G.; Raupp, G.; Richter, H.; Treutterer, W.; Zasche, D.; Zehetbauer, T.; ASDEX-Upgrade-Team,; NBI-Team,; ICRH-Team,

doi:10.13182/fst97-a8

Cited by 11 publications

(9 citation statements)

References 2 publications

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“…Passive measures involve direct intervention to mitigate the underlying cause of the disruption, for example, by reducing the plasma density if approach to a density limit threshold occurs, or by the addition of auxiliary power if an edge power balance condition develops. Preset operation of the feedback control loops provided in the plasma control system for 'control' of such operation parameters (see Section 2 of Chapter 8) constitutes a first level of implementation of such avoidance techniques [340]; with the further addition of making the set points of such control loops plasma state [342] or event (e.g. disruption onset predictor) dependent (e.g.…”

Section: Avoidance Methodsmentioning

confidence: 99%

“…In the same vein, provision of plasma control systems incorporating feedback algorithms to control sensitive scenario parameters (plasma density, radiation fraction, etc.) makes reliable achievement of the desired scenario parameters without occurrence of disruption a matter of closed loop control rather than open loop setting of parameters on a beforethe-pulse basis [340].…”

Section: Disruption Avoidancementioning

confidence: 99%

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Chapter 3: MHD stability, operational limits and disruptions

Plasma¹

1999

Nucl. Fusion

296

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The present physics understandings of magnetohydrodynamic (MHD) stability of tokamak plasmas, the threshold conditions for onset of MHD instability, and the resulting operational limits on attainable plasma pressure (beta limit) and density (density limit), and the consequences of plasma disruption and disruption related effects are reviewed and assessed in the context of their application to a future DT burning reactor prototype tokamak experiment such as ITER. The principal considerations covered within the MHD stability and beta limit assessments are (i) magnetostatic equilibrium, ideal MHD stability and the resulting ideal MHD beta limit; (ii) sawtooth oscillations and the coupling of sawtooth activity to other types of MHD instability; (iii) neoclassical island resistive tearing modes and the corresponding limits on beta and energy confinement; (iv) wall stabilization of ideal MHD instabilities and resistive wall instabilities; (v) mode locking effects of non-axisymmetric error fields; (vi) edge localized MHD instabilities (ELMs, etc.); and (vii) MHD instabilities and beta/pressure gradient limits in plasmas with actively modified current and magnetic shear profiles. The principal considerations covered within the density limit assessments are (i) empirical density limits; (ii) edge power balance/radiative density limits in ohmic and L-mode plasmas; and (iii) edge parameter related density limits in H-mode plasmas. The principal considerations covered in the disruption assessments are (i) disruption causes, frequency and MHD instability onset; (ii) disruption thermal and current quench characteristics; (iii) vertical instabilities (VDEs), both before and after disruption, and plasma and in-vessel halo currents; (iv) after disruption runaway electron formation, confinement and loss; (v) fast plasma shutdown (rapid externally initiated dissipation of plasma thermal and magnetic energies); (vi) means for disruption avoidance and disruption effect mitigation; and (vii) 'integrated' modelling of disruptions and fast shutdown and of the ensuing effects. In each instance, the presentation within a given topical area progresses from a summary of present experimental and theoretical understanding to how this understanding projects or extrapolates to an ITER class reactor regime tokamak. Examples of extrapolations to the specific ITER design concept developed during the course of the ITER EDA are given, and assessments of the degree of adequacy of present understanding are also provided. In areas where present understanding is identified to be less than fully adequate, areas in which continuing or new research is needed are identified.

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Section: Avoidance Methodsmentioning

confidence: 99%

Section: Disruption Avoidancementioning

confidence: 99%

Chapter 3: MHD stability, operational limits and disruptions

Plasma¹

1999

Nucl. Fusion

296

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“…The first example of an expert intelligent control in an existing tokamak scenario has been provided on ASDEX Upgrade [264]. In this scheme, the plasma control system has been given the ability to recognize the current operating mode (H-mode or L-mode).…”

Section: Demonstration Of Intelligent Control In Steady State Scenariosmentioning

confidence: 99%

Chapter 6: Steady state operation

Gormezano¹,

et al. 2007

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Significant progress has been made in the area of advanced modes of operation that are candidates for achieving steady state conditions in a fusion reactor. The corresponding parameters, domain of operation, scenarios and integration issues of advanced scenarios are discussed in this chapter. A review of the presently developed scenarios, including discussions on operational space, is given. Significant progress has been made in the domain of heating and current drive in recent years, especially in the domain of off-axis current drive, which is essential for the achievement of the required current profile. The actuators for heating and current drive that are necessary to produce and control the advanced tokamak discharges are discussed, including modelling and predictions for ITER. The specific control issues for steady state operation are discussed, including the already existing experimental results as well as the various strategies and needs (qψ profile control and temperature gradients). Achievable parameters for the ITER steady state and hybrid scenarios with foreseen heating and current drive systems are discussed using modelling including actuators, allowing an assessment of achievable current profiles. Finally, a summary is given in the last section including outstanding issues and recommendations for further research and development.

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“…The inventory of the storage cryostate is sufficient to deliver about 100 pellets, the reliability of the system (injected pellets/requested pellets) was found to be above 0.9. Feedback density (n e ) control was performed by pellet injection initiated by the fast (cycle time 2 ms) ASDEX Upgrade control system [17]. The density ne was taken from a suitable bremsstrahlung signal calibrated to the DCN interferometer (maximum sample rate 1 kHz) in the early plasma phase before pellet injection started.…”

Section: Experimental Set-up and Technical Equipmentmentioning

confidence: 99%

High density operation in H mode discharges by inboard launch pellet refuelling

et al. 2000

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Operating a tokamak at plasma densities near the empirical Greenwald limit n̄eGw in H mode could yield significant advantages for a fusion reactor. Trying to avoid the strong confinement degradation observed with gas puff refuelling, pellet injection from the magnetic high field side was applied. Sufficient pellet particle flux was supplied to achieve persistent density rampup and to enable density control in H mode at a level beyond n̄eGw for the first time. The pellet induced density increase decays in a fast phase with τ = 10 ms until about half of the latest pellet inventory remains, and decays thereafter to the base density on the particle confinement timescale with τ = 120 ms. The fast decay is the result of strong ELM events following each injected pellet, accompanied by a loss of energy, causing a transient reduction of the plasma energy content by convective heat flux. Recovery of the plasma energy after the ELM sequence takes place with τ = 25 ms, enabling transient operation at appropriately high densities without significant confinement degradation. To reach this scenario, however, confinement degradation caused by other factors must be inhibited. Other factors causing confinement degradation were found to be the increase of neutral gas pressure by pellet born gas puff at insufficient pumping speed or the occurrence of neoclassical tearing modes triggered by pellets when the temperatures close to rational surfaces were reduced too strongly.

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Plasma Performance Optimization in ASDEX Upgrade

Cited by 11 publications

References 2 publications

Chapter 3: MHD stability, operational limits and disruptions

Chapter 3: MHD stability, operational limits and disruptions

Chapter 6: Steady state operation

High density operation in H mode discharges by inboard launch pellet refuelling

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