Evolution of Lower-Hybrid-Driven Current during the Formation of an Internal Transport Barrier

Naito, O.; Z, Cui; Ide, S.; Suzuki, Takahiro; Oikawa, T.; Seki, M.; Hatae, T.; Fujita, T.; Kondoh, T.; Shirai, Hiroshi; Ikeda, Yoshitaka; Ushigusa, K.

doi:10.1103/physrevlett.89.065001

Cited by 9 publications

(6 citation statements)

References 21 publications

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“…Error bars in T e and n e measured by YAG Thomson scattering diagnostics are evaluated considering error bars in similar discharges. Since the NB and LH heating powers are almost constant during t = 12-13 s, as shown in figures 2(b) and (c), the increase in the central T e could be attributed to the ITB formation by the q profile change [17] through the q min control. Since the ion temperature and electron density are increased inside ρ = 0.5, increase in the bootstrap current also contributes to the change in the q profile.…”

Section: Real-time Control Of Q Min and Dynamic Response Of The Self-...mentioning

confidence: 88%

“…Moreover, the off-axis NBCD is taken into consideration in JT-60SA for the control of the current profile and for the formation and sustainment of reversedshear plasmas [12]. Although the LHCD was studied well in various devices ( [13] and section 4.4 of [14]), for example JT-60U [15][16][17] and JET [18,19], the study on the off-axis NBCD is still under way. Although the off-axis NBCD has been successfully used in the JT-60U experiment in order to modify the current profile, detailed measurement of the off-axis NBCD 'profile' has not yet been done.…”

Section: Introductionmentioning

confidence: 99%

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Off-axis current drive and real-time control of current profile in JT-60U

et al. 2008

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Aiming at optimization of current profile in high-β plasmas for higher confinement and stability, a real-time control system of the minimum of the safety factor (q min) using the off-axis current drive has been developed. The off-axis current drive can raise the safety factor in the centre and help to avoid instability that limits the performance of the plasma. The system controls the injection power of lower-hybrid waves, and hence its off-axis driven current in order to control q min. The real-time control of q min is demonstrated in a high-β plasma, where q min follows the temporally changing reference q min,ref from 1.3 to 1.7. Applying the control to another high-β discharge (βN = 1.7, βp = 1.5) with m/n = 2/1 neo-classical tearing mode (NTM), q min was raised above 2 and the NTM was suppressed. The stored energy increased by 16% with the NTM suppressed, since the resonant rational surface was eliminated. For the future use for current profile control, current density profile for off-axis neutral beam current drive (NBCD) is for the first time measured, using the motional Stark effect diagnostic. Spatially localized NBCD profile was clearly observed at the normalized minor radius ρ of about 0.6–0.8. The location was also confirmed by multi-chordal neutron emission profile measurement. The total amount of the measured beam driven current was consistent with the theoretical calculation using the ACCOME code. The CD location in the calculation was inward shifted than the measurement.

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Section: Real-time Control Of Q Min and Dynamic Response Of The Self-...mentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Off-axis current drive and real-time control of current profile in JT-60U

et al. 2008

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“…One approach to estimating the driven current profile is by measuring the current profile and the loop voltage profile from sequences of equilibrium reconstructions constrained by internal measurements of the magnetic field [59]. For example, profiles of LH current density have been inferred in an LHCD dominant JT-60U plasma [132]. In this analysis, the total current (J TOT ) was inferred from MSE measurements; the bootstrap (J BS ) and NB currents (J NBI ) were computed numerically [130].…”

Section: Progress In Numerical Modellingmentioning

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 mid-plane current density profiles obtained from the MSE + ECE constrained EFIT method are shown by the solid lines in figure 4(a). A similar approach was used by Naito et al [6]. The mid-plane current density profile can also be obtained from the MSE pitch angle data directly using an analytic formula derived by Petty et al [7].…”

Section: Local Measurements Of Current Drive and Comparison With Mode...mentioning

confidence: 99%

Lower hybrid heating and current drive on the Alcator C-Mod tokamak

Wilson¹,

Parker²,

Bitter³

et al. 2009

Nucl. Fusion

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Abstract.On the Alcator C-Mod tokamak, lower hybrid current drive (LHCD) is being used to modify the current profile with the aim of obtaining advanced tokamak (AT) performance in plasmas with parameters similar to those that would be required on ITER. To date, power levels in excess of 1 MW at a frequency of 4.6 GHz have been coupled into a variety of plasmas. Experiments have established that LHCD on C-Mod behaves globally as predicted by theory. Bulk current drive efficiencies, n 20 I lh R/P lh ~ 0.25, inferred from magnetics and MSE are in line with theory. Quantitative comparisons between local measurements, MSE, ECE and hard x-ray bremsstrahlung, and theory/simulation using the GENRAY, TORIC-LH CQL3D and TSC-LSC codes have been performed. These comparisons have demonstrated the off-axis localization of the current drive, its magnitude and location dependence on the launched n || spectrum, and the use of LHCD during the current ramp to save volt-seconds and delay the peaking of the current profile. Broadening of the x-ray emission profile during ICRF heating indicates that the current drive location can be controlled by the electron temperature, as expected. In addition, an alteration in the plasma toroidal rotation profile during LHCD has been observed with a significant rotation in the counter current direction. Notably, the rotation is accompanied by peaking of the density and temperature profiles on a current diffusion time scale inside of the half radius where the LH absorption is taking place. PACS: 52.50.Sw, 52.55.Wq IntroductionThe Alcator C-Mod program has as one of its goals the aim of producing advanced tokamak (AT) discharges. In order to provide the current profile control required for obtaining reduced or reverse shear a lower hybrid (LH) rf power system [1] has been installed on the tokamak. One of the advantages of exploring the applicability of LH current drive on Alcator C-Mod is the equivalence of many of the important parameters, such as plasma density, magnetic field, and rf frequency to those required for a reactor, and in particular ITER. In addition, C-Mod uses heating sources that provide low torque to the plasma, as would be true for a reactor, and the time constants involved allow for relaxation of the relevant profiles. Initial experiments [2,3] have demonstrated that the system behaves as expected with bulk current drive efficiencies η = n 20 I lh R/P lh ~ 0.25 in line with theory and expectations from previous experiments. Recent work, reported in this paper, concentrates on detailed measurements of the spatial location of the driven current, the role of fast electron diffusion in spreading the current and other effects of applying LH power to the plasma. In addition, to extrapolate the application of LHCD for use in future devices a program of model development and validation is underway. The plan of this paper is as follows. The local measurements of fast electrons and CD derived from hard x-ray measurements and MSE along with comparisons to modeling will be

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Evolution of Lower-Hybrid-Driven Current during the Formation of an Internal Transport Barrier

Cited by 9 publications

References 21 publications

Off-axis current drive and real-time control of current profile in JT-60U

Off-axis current drive and real-time control of current profile in JT-60U

Chapter 6: Steady state operation

Lower hybrid heating and current drive on the Alcator C-Mod tokamak

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