G. Turri

École Polytechnique Fédérale de Lausanne, Lausanne, VD, Switzerland

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Publications (37)24.8 Total impact

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    ABSTRACT: The Tokamak à Configuration Variable (TCV) tokamak is equipped with high-power (4.5 MW), real-time-controllable EC systems and flexible shaping, and plays an important role in fusion research by broadening the parameter range of reactor relevant regimes, by investigating tokamak physics questions and by developing new control tools. Steady-state discharges are achieved, in which the current is entirely self-generated through the bootstrap mechanism, a fundamental ingredient for ITER steady-state operation. The discharge remains quiescent over several current redistribution times, demonstrating that a self-consistent, 'bootstrap-aligned' equilibrium state is possible. Electron internal transport barrier regimes sustained by EC current drive have also been explored. MHD activity is shown to be crucial in scenarios characterized by large and slow oscillations in plasma confinement, which in turn can be modified by small Ohmic current perturbations altering the barrier strength. In studies of the relation between anomalous transport and plasma shape, the observed dependences of the electron thermal diffusivity on triangularity (direct) and collisionality (inverse) are qualitatively reproduced by non-linear gyro-kinetic simulations and shown to be governed by TEM turbulence. Parallel SOL flows are studied for their importance for material migration. Flow profiles are measured using a reciprocating Mach probe by changing from lower to upper single-null diverted equilibria and shifting the plasmas vertically. The dominant, field-direction-dependent Pfirsch–Schlüter component is found to be in good agreement with theoretical predictions. A field-direction-independent component is identified and is consistent with flows generated by transient over-pressure due to ballooning-like interchange turbulence. Initial high-resolution infrared images confirm that ELMs have a filamentary structure, while fast, localized radiation measurements reveal that ELM activity first appears in the X-point region. Real time control techniques are currently being applied to EC multiple independent power supplies and beam launchers, e.g. to control the plasma current in fully non-inductive conditions, and the plasma elongation through current broadening by far-off-axis heating at constant shaping field.
    Nuclear Fusion 09/2009; 49:104005. · 2.73 Impact Factor
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    ABSTRACT: Starting from a standard single null X-point configuration, a second order null divertor (snowflake (SF)) has been successfully created on the Tokamak à Configuration Variable (TCV) tokamak. The magnetic properties of this innovative configuration have been analysed and compared with a standard X-point configuration. For the SF divertor, the connection length and the flux expansion close to the separatrix exceed those of the standard X-point by more than a factor of 2. The magnetic shear in the plasma edge is also larger for the SF configuration.
    Plasma Physics and Controlled Fusion 03/2009; · 2.37 Impact Factor
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    ABSTRACT: Generation of a swing electron cyclotron current drive (swing ECCD), i.e. driving alternated, symmetric, positive or negative local ECCD, during a single discharge and at constant total input EC power, was performed at the Tokamak à Configuration Variable (TCV). The electron temperature is observed to be modulated inside the deposition radius, implying modulation of the electron transport properties. The modulation of ECCD is the only actuator for the observed modifications in the electron transport properties. These exhibit inverted behaviors depending on the deposition location of the co- and counter-ECCD. At more on-axis depositions, swing ECCD results in a higher electron temperature during the co-ECCD phase, whereas at more off-axis depositions, the electron temperature is higher during the counter-ECCD phase. Transport modeling of these discharges shows that the local electron tranport behavior depends on the value of the modulated magnetic shear. The results are transport model independent, confirming the robustness of the magnetic shear modeling, and indicating that the main contribution is due to the ECCD. Moreover, the results are consistent with predictions from gyrokinetic simulations, that the local electron confinement is proportional to the magnetic shear at low shear and inversely at high shear values, s gsim 1.
    Plasma Physics and Controlled Fusion 01/2009; · 2.37 Impact Factor
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    ABSTRACT: Starting from a standard single null X-point configuration, a second order null divertor (snowflake (SF)) has been successfully created on the Tokamak à Configuration Variable (TCV) tokamak. The magnetic properties of this innovative configuration have been analysed and compared with a standard X-point configuration. For the SF divertor, the connection length and the flux expansion close to the separatrix exceed those of the standard X-point by more than a factor of 2. The magnetic shear in the plasma edge is also larger for the SF configuration.
    01/2009;
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    ABSTRACT: A TCV plasma with high power density (up to 8MW/m%^3) core deposited ECR heating at significant plasma densities (<=7 x10^19 m-3) is analyzed for the electron thermal transport. The discharge has four distinct high confinement mode (H-mode) phases, an ohmic H-mode with type III edge localized modes (ELMs), a type I ELMy H-mode with the ECRH on, two quasi-stationary ELM-free H-modes, one of which without magneto-hydrodynamics (MHD) and one with. For all four phases both large-scale TEM and ITG modes and small-scale ETG modes are analyzed. For easy comparison of the results, a dimensionless error measure, the so-called average relative variance (ARV) is introduced. According to this method the ETG model explains 70% of the variation in the electron heat diffusivity whereas the predictive capabilities of the TEM-ITG models are poor. These results for TCV support the conclusion that the ETG model is able to explain a wide range of anomalous electron transport data, in addition to existing evidence from ASDEX, Tore Supra and FTU.
    11/2008;
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    ABSTRACT: A Tokamak a Configuration Variable (TCV) [G. Tonetti, A. Heym, F. Hofmann et al., in Proceedings of the 16th Symposium on Fusion Technology, London, U.K., edited by R. Hemsworth (North-Holland, Amsterdam, 1991), p. 587] plasma with high power density (up to 8 MW/m{sup 3}) core deposited electron cyclotron resonance heating at significant plasma densities ({<=}7x10{sup 19} m{sup -3}) is analyzed for the electron thermal transport. The discharge distinguishes itself as it has four distinct high confinement mode (H-mode) phases. An Ohmic H-mode with type III edge localized modes (ELMs), which turns into a type I ELMy H-mode when the ECRH is switched on. The ELMs then vanish, which gives rise to a quasistationary ELM-free H-mode. This ELM-free phase can be divided into two, one without magnetohydrodynamics (MHD) and one with. The MHD mode in the latter case causes the confinement to drop by {approx}15%. For all four phases both large-scale trapped electron (TEM) and ion temperature gradient (ITG) modes and small-scale electron temperature gradient (ETG) modes are analyzed. The analytical TEM formulas have difficulty in explaining both the magnitude and the radial profile of the electron thermal flux. Collisionality governs the drive of the TEM, which for the discharge in question implies it can be driven by either the temperature or density gradient. The TEM response function is derived and it is shown to be relatively small and to have sharp resonances in its energy dependence. The ETG turbulence, predicted by the Institute for Fusion Studies electron gyrofluid code, is on the other hand driven solely by the electron temperature gradient. Both trapped and passing electrons add to the ETG instability and turbulent thermal flux. For easy comparison of the results of the above approaches and also with the Weiland model, a dimensionless error measure, the so-called average relative variance is introduced. According to this method the ETG model explains 70% of the variation in the electron heat diffusivity whereas the predictive capabilities of the TEM-ITG models are poor. These results for TCV support the conclusion that the ETG model is able to explain a wide range of anomalous electron transport data, in addition to existing evidence from ASDEX [F. Ryter, F. Leuterer, G. Pereverzev, H.-U. Fahrbach, J. Stober, W. Suttrop, and the ASDEX Upgrade Team, Phys. Rev. Lett. 86, 2325 (2001)], Tore Supra [G. T. Hoang, W. Horton, C. Bourdelle, B. Hu, X. Garbet, and M. Ottaviani, Phys. Plasmas 10, 405 (2003)] and the Frascati Tokamak Upgrade [A. Jacchia, F. D. Luca, S. Cirant, C. Sozzi, G. Bracco, A. Brushi, P. Buratti, S. Podda, and O. Tudisco, Nucl. Fusion 42, 1116 (2002)].
    Physics of Plasmas 08/2008; · 2.38 Impact Factor
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    ABSTRACT: Advanced scenarios exhibit improved confinement properties, which make them attractive candidate for ITER. For these to be achieved, the sustainment of transport barriers and therefore high pressure gradients is inherent. Their stability properties both in the transient and steady state phases is a major issue [1], because of the relationship between high performances and proximity to a stability limit. Core MHD modes are one of the key issues in the development and sustainment of transport barriers, as they degrade the confinement properties and, in the worse case, disrupt the plasma. The understanding of the underlying physics can provide the means of finding regimes without modes. In TCV (Tokamak à Configuration Variable) H-mode and electron internal transport barriers (eITBs) have been obtained with different schemes, usually accompanied by various types of MHD phenomenon [2, 3, 4]. In this paper we focus on the low-shear Quasi-Stationary ELM free H-mode (QSEFHM) scenarios [4], which displays infrequent sawteeth and/or NTMs. In addition to that, high-performance eITBs shots are discussed, during which a variety of resistive to ideal modes are observed and ascribable to the infernal stability limit [3, 5]. Analysis of data from TCV highest performance discharges can clarify the potential threats of MHD modes in advanced scenarios. MHD core analysis of the QSEFHM [4], and of eITBs is presented, focusing on the existence of stability windows.
    Journal of Physics Conference Series 07/2008;
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    ABSTRACT: Predicting intrinsic plasma rotation and its shear, which often help stabilize plasma instabilities affecting plasma performance, is important for prospective fusion grade devices. Although rotation in ITER-like scenarios has been extrapolated from measured experimental plasma rotation data, little is understood about the underlying mechanisms governing either the generation or dissipation of momentum in a tokamak plasma. This paper reports on studies of intrinsic toroidal and poloidal plasma rotation from charge exchange spectroscopy using a low power diagnostic beam on the TCV tokamak [Tonetti et al., in Proceedings of the Symposium on Fusion Technology (1991), p. 587] that drives negligible toroidal velocity. In TCV, plasma behavior can be separated by the core and edge regions. In limited configurations, the core rotates in the counter-current direction and can reverse to the co-current direction with a <10% increase in the plasma density. This is different for diverted configurations where the core rotates in the co-current direction reversing to the counter-current direction at higher plasma densities. For all these situations, core toroidal momentum is strongly transported by plasma sawteeth oscillations. In contrast, the toroidal edge rotation is close to stationary for limited discharges but evolves with plasma density for diverted configurations. Theoretical models that predict a change in momentum transport from turbulence have previously been suggested to provide a mechanism that might explain these phenomena. In this paper, mode activity that changes at the toroidal velocity reversal, is identified as a new possible candidate. In the absence of an available model that can explain these basic phenomena, this paper presents observations and, where possible, scaling of the rotation profiles with some of the major plasma parameters such as current, density and shape to guide the development of a physics model for use in improving the extrapolation of the rotation amplitude and profiles to future devices.
    Physics of Plasmas 05/2008; · 2.38 Impact Factor
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    ABSTRACT: Global plasma oscillations, involving electron temperature, plasma density and current, have been observed during electron cyclotron current driven ECCD discharges on TCV (Tokamak à Configuration Variable; R/a = 0.88 m/0.25 m, k ≤ 2.8, BT < 1.54 T). This is confirmed by multiple diagnostics operating on different physical principles: electron cyclotron emission radiometer, soft x-ray, far-infrared reflectometer, bolometer and magnetic probes. The oscillations develop in the presence of electron internal transport barriers and reversed magnetic shear. They are reminiscent of the central electron temperature oscillations (the so-called O-regime) seen in low-loop voltage or fully non-inductive lower-hybrid current driven plasmas with reversed central magnetic shear on Tore Supra (Giruzzi et al 2003 Phys. Rev. Lett. 91 935001). The oscillations have m/n = 0/0 periodicity and are not the manifestation of a magnetohydrodynamic (MHD) instability in itself, but they are invariably linked to the presence of MHD modes on TCV. In fact, no plasma discharge has been obtained so far displaying oscillations in the absence of MHD activity. The interaction of the oscillations with MHD can play a strong role in the coupled dynamics of heat and current transport, as the modes can significantly perturb the q profile. More generally the presence of MHD modes can aid in the correct identification of rational q-surfaces [4]. The interplay between MHD and the plasma oscillations, with the first being the cause for the development of the second, is the main focus of this paper. It is also shown that the global oscillations can be removed by adding an Ohmic current perturbation and therefore by modifying the current density profile.
    Plasma Physics and Controlled Fusion 04/2008; 50(6):065010. · 2.37 Impact Factor
  • Plasma Physics and Controlled Fusion 02/2008; · 2.37 Impact Factor
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    ABSTRACT: This overview highlights the progress accomplished on tokamak à configuration variable (TCV) during the past two years, along five research avenues: particle, energy and momentum transport, edge physics, H-mode physics under strong electron heating, electron cyclotron (EC) heating and electron cyclotron current drive physics, scenarios with internal transport barriers and large non-inductive current fractions. Peaked density profiles are measured in the absence of a Ware pinch or a core particle source. Decreasing the plasma triangularity leads to a significant reduction in χe. Measurements of the plasma toroidal rotation in the absence of external torque are inconsistent with diffusion of toroidal momentum from the edge. Scrape-off layer fluctuation measurements and the relevant modelling using a fluid turbulence code indicate radial interchange motion of plasma filaments as the cause of cross-field transport. Third harmonic EC heating (1.5 MW) applied to ELMy H-modes leads to βN ~ 2, large ELMs and peaked density profiles, significant ion heating (Ti ~ 1 keV, with Ti/Te ~ 0.4) and to quasi-stationary ELM-free H-modes lasting for many energy confinement times. Supra-thermal electrons produced during strong EC heating and following sawtooth crashes are shown to undergo rapid cross-field transport. Electron Bernstein wave heating is demonstrated in the O–X–B conversion scheme. Electron internal transport barriers are generated in a variety of scenarios, leading to significant confinement improvement and bootstrap current fractions in excess of 70%.
    Nuclear Fusion 01/2008; 48:034001. · 2.73 Impact Factor
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    ABSTRACT: In the Tokamak a Configuration Variable (TCV) (Hofmann F et al 1994 Plasma Phys. Control. Fusion 36 B277), global plasma oscillations have been discovered in fully non-inductively driven plasmas featuring electron internal transport barriers (ITB) with strong ECRH/ECCD. These oscillations are linked to the destabilization and stabilization of MHD modes near the foot of the ITB and can lead to large oscillations of the total plasma current and line-averaged density, among others. They are intrinsically related to the fact that ITBs have large pressure gradients in a region of low magnetic shear. Therefore, the ideal MHD limit is relatively low and infernal modes can be unstable. Depending on the proximity to the ideal limit, small crashes or resistive modes can appear which affect the time evolution of the discharge. Being near marginal stability, the modes can self-stabilize due to the modification of the pressure gradient and local q-profile. The plasma recovers good confinement, reverses shear and the ITB builds up, until a new MHD mode is destabilized. TCV results show that this cycling behaviour can be controlled by modifying the current density or the pressure profiles, either with Ohmic current density perturbation or by modifying the ECH/ECCD power. It is demonstrated that many observations such as q >= 2 sawteeth, beta collapses, minor disruptions and oscillation regimes in ITBs can be assigned to the same physics origin: the proximity to the infernal mode stability limit.
    01/2008;
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    ABSTRACT: In the Tokamak àConfiguration Variable (R/a = 0.88 m/ 0.24 m, BT < 1.54 T), global plasma oscillations are found to exist in fully non-inductive plasmas featuring eITBs with strong ECRH/ECCD. This phenomenon is akin to the so-called Oscillatory, or O-regime, first observed in LHCD plasmas on Tore Supra. In TCV, the O-regime is linked to the evolution of the MHD modes in the reversed magnetic shear plasmas. It is demonstrated that the O-regime can be effectively suppressed by ECCD-induced local cur-rent density perturbation or by adding an Ohmic current perturbation. In these experiments MHD activity is modified through current density profile tailoring rather than local deposition within an island. The suppression of the O-regime usually leads to improved energy confinement, which is characterized by exceeding the Rebut-Lallia-Watkins scaling, to obtain HRLW above 3.5. The detection of the MHD modes by various diagnostics (ECE, SXR, Mirnov coils etc) has aided in the correct identification of rational q-surfaces and in understanding their role in the evolution of the O-regime. The evolution of the safety factor during the O-regime has been studied by means of CQL3D/ASTRA simulations and will be presented.
    11/2007;
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    34th EPS Conference on Plasma Physics and Controlled Fusion; 07/2007
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    ABSTRACT: Electron internal transport barriers (eITBs) are generated in the TCV tokamak with strong electron cyclotron resonance heating in a variety of conditions, ranging from steady-state fully noninductive scenarios to stationary discharges with a finite inductive component and finally to transient current ramps without current drive. The confinement improvement over L-mode ranges from 3 to 6; the bootstrap current fraction is invariably large and is above 70% in the highest confinement cases, with good current profile alignment permitting the attainment of steady state. Barriers are observed both in the electron temperature and density profiles, with a strong correlation both in location and in steepness. The dominant role of the current profile in the formation and properties of eITBs has been conclusively proven in a TCV experiment exploiting the large current drive efficiency of the Ohmic transformer: small current perturbations accompanied by negligible energy transfer dramatically alter the confinement. The crucial element in the formation of the barrier is the appearance of a central region of negative magnetic shear, with the barrier strength improving with increasingly steep shear. This connection has also been corroborated by transport modelling assisted by gyrofluid simulations. Rational safety-factor (q) values do not appear to play a role in the barrier formation, at least in the q range 1.3-2.3, as evidenced by the smooth dependence of the confinement enhancement on the loop voltage over a broad eITB database. MHD mode activity is however influenced by rational q values and results in a complex, sometimes cyclic, dynamic evolution.
    01/2007;
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    ABSTRACT: The Fokker-Planck code CQL3D has been used to investigate the effect of radial particle diffusion on ECCD current density profiles in the TCV tokamak. For two discharges with electron internal transport barriers (eITB), the jcd and the resulting q-profile have been calculated and reconstructed. The studied eITBs are of two kinds: fully sustained non-inductive eITB with off-axis co-current ECCD, or with a large Ohmic current and on-axis counter ECCD. It is shown that different diffusion profiles do modify the ECCD current density profiles, but that the resulting q-profiles are less influenced due to the resulting necessary self-consistent inductive current contribution.
    11/2006;
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    ABSTRACT: Significant progress has been made on the Mega Ampere Spherical Tokamak (MAST) towards a fundamental understanding of transport, stability and edge physics and addressing technological issues for future large devices. Collaborative studies of the L–H transition with NSTX and ASDEX Upgrade confirm that operation in a connected double-null configuration significantly reduces the threshold power, Pthr. The MAST data provide support for a theory for the transition based on finite β drift wave turbulence suppression by self-generated zonal flows. Analysis of low and high field side density gradients in the H-mode pedestal provides support for an analytical model of the density pedestal width dependent on the neutral penetration depth. Adding MAST data to international confinement databases has enhanced confidence in scalings for ITER by significantly expanding the range of β and ε explored and indicates a slightly stronger ε dependence than in current scalings. Studies of core transport have been conducted for well-diagnosed L-mode, H-mode and internal transport barrier (ITB) discharges using TRANSP, and microstability and turbulence studies have been carried out using GS2. Linear micro-stability analysis indicates that ITG modes are typically unstable on all flux surfaces with growth rates that are comparable to the equilibrium E × B flow shearing rate. Mixing length estimates of transport coefficients from ITG (neglecting flow shear) give diffusion coefficients that are broadly comparable with observed thermal diffusivities. Non-linear, collisionless ETG calculations have been performed and suggest radially extended electrostatic streamers up to 100ρe across in radius. Transport from ITG could easily be suppressed in regions where the E × B shear flow rate, ωSE, exceeds the ITG growth rate, possibly contributing to ITBs. Toroidal rotation, driven by neutral beam torque, is the dominant contribution to ωSE via the vBθ term in the radial electric field. Early edge localized mode activity on MAST is associated with the formation of narrow filamentary structures following field lines in the edge. These filaments rotate toroidally with the edge plasma and, away from the X-points, accelerate radially outwards from the edge up to 20 cm. Studies of disruptions on MAST demonstrate a complex evolution of core energy loss and resultant divertor power loads, including phases where the target heat flux width is broadened by a factor of 8. Observations of energetic particle modes driven by super-Alfvénic beam ions provide support for a model for the non-linear evolution of toroidal Alfvén eigenmodes (AEs) forming Bernstein–Green–Krushal waves. The AE activity reduces to low levels with increasing β. Plasma start-up without a central solenoid and in a manner compatible with future large spherical tokamak (ST) devices has been demonstrated using breakdown at a quadrupole magnetic null. Closed flux surface plasmas with peak plasma currents up to 370 kA have been generated and sustained for 0.3 s. New error field correction coils have extended the operational space for low density plasmas and enabled scaling studies of error field induced locked mode formation in the ST.
    Nuclear Fusion 10/2005; 45(10):S157. · 2.73 Impact Factor
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    ABSTRACT: Low aspect ratio plasmas in devices such as the mega ampere spherical tokamak (MAST) are characterized by strong toroidicity, strong shaping and self fields, low magnetic field, high beta, large plasma flow and high intrinsic E × B flow shear. These characteristics have important effects on plasma behaviour, provide a stringent test of theories and scaling laws and offer new insight into underlying physical processes, often through the amplification of effects present in conventional tokamaks (e.g. impact of fuelling source and magnetic geometry on H-mode access). The enhancement of neoclassical effects makes MAST ideal for the study of particle pinch processes and neoclassical resistivity corrections, which can be assessed with unique accuracy. MAST data have an important influence on scaling laws for confinement and H-mode threshold power, exerting strong leverage on the form of these scaling laws (e.g. scaling with aspect ratio, beta, magnetic field, etc). The high intrinsic flow shear is conducive to transport barrier formation by turbulence suppression. Internal transport barriers are readily formed in MAST with both co- and counter-NBI, and electron and ion thermal diffusivities have been reduced to the ion neoclassical level. The strong variation in toroidal field (~ × 5 in MAST) between the inboard and outboard plasma edges, provides a useful test of edge models prompting, for example, a comparison of inboard and outboard scrape-off-layer transport to highlight magnetic field effects. Low aspect ratio plasmas are also an ideal testing ground for plasma instabilities, such as neoclassical tearing modes, edge localized modes (ELMs) and Alfvén eigenmodes, which are readily generated due to the supra-Alfvénic ion population. Examples of how MAST is providing new insights into such instabilities (e.g. ELM structure) are described.
    Plasma Physics and Controlled Fusion 11/2004; 46(12B):B477. · 2.37 Impact Factor
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    ABSTRACT: In MAST the appearance of a spontaneous snake in the plasma core has many of the properties of a full reconnection. Analysis of SXR and TS data indicates a strongly radiating core with high impurity levels forming before the onset of the snake. Following the appearance of an x-point (island on the q=1 surface) the former core is hypothesised to move off axis and shrink, appearing as a radiative region with flux-tube-like rotating helical structure (the snake). A code has been developed to compare this with a slow full Kadomtsev type reconnection process including effects of impurities, density and temperature perturbations, current profile evolution and transport. The code reproduces many of the trends and effects seen in the data, confirming the event as consistent with full reconnection. The time-scale of the event is also consistent with estimates of hybrid growth times for such a reconnection process. Further analysis will be presented exploring the physics of this process in more detail.
    01/2004;
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    ABSTRACT: The development of reliable H-modes on MAST, together with advances in heating power and a range of high spatial resolution diagnostics, has provided a platform to enable MAST to address some of the most important issues of tokamak stability. In particular the high beta potential of the spherical tokamak is highlighted with stable operation at beta(N) similar to 5-6, beta(T) similar to 16% and beta(p) up to similar to2. Magnetic diagnostic evaluation of the global beta parameters is independently confirmed by kinetic profile data. Calculations indicate that the beta(N) values are in the vicinity of no-wall stability limits. Studies of neoclassical tearing modes (NTMs) have been extended to explore their effects and develop avoidance strategies. Experiments have demonstrated that sawteeth play a strong role in triggering NTMs-by avoiding large sawteeth a much higher beta(N) value has been reached. The significance of NTMs is confirmed, with large islands observed using the 300 point Thomson scattering diagnostic, and locking of large n = 1 modes frequently leading to disruptions, which become more rapid at low q(95). The role of error fields has been explored. H-mode plasmas are also limited by edge localized modes (ELMs), with confinement degraded as the ELM frequency rises. However, in contrast to the conventional tokamak, the ELMs in high performing regimes on MAST (H-IPB98Y2 similar to 1) appear to be type III in nature. Modelling using the ELITE code, which incorporates finite n corrections, identifies instability to peeling modes, consistent with a type III interpretation. It also shows considerable scope to raise pressure gradients before ballooning type modes (perhaps associated with type I ELMs) occur. The calculations show that narrow pedestals can support much stronger pressure gradients than might be expected from simple n = infinity ballooning calculations. Finally sawteeth are shown to degrade confinement by similar to10-15% in particular cases examined. They are observed not to remove the q = 1 surface in the cases where snakes are present-various physics models of the sawteeth are now being explored. Thus research on MAST is not only demonstrating stable operation at high performance levels and developing methods to control instabilities; it is also providing detailed tests of the stability physics and models applicable to conventional tokamaks, such as ITER.
    01/2004;