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  • 2015-2019  (2)
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  • 2015-2019  (2)
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  • 1
    In: Physics of Plasmas, AIP Publishing, Vol. 26, No. 1 ( 2019-01-01)
    Abstract: Experimental investigation of lower hybrid fast wave (LHFW) coupling and propagation is carried out by wave measurements utilizing magnetic probes in Versatile Experiment Spherical Torus. Coupling experiments are conducted in marginal (ne≥nconfluence) and prohibited (ne≫nconfluence) regimes for fast wave coupling. In the marginal regime of Ip = 25 kA, about two folds of n∥-upshift are observed. The propagation path of the fast wave is largely modified compared to that of full wave simulation, and more fast waves are detected inside the last-closed-flux surface despite the unsatisfied accessibility condition. Since spectral broadening is measured to be narrow and linearly proportional to coupled wave power with a high density fluctuation of about 20% in the frequency range (ω0/ωlh∼15), it is thought to be crucially correlated with wave scattering rather than parametric decay instabilities. Consequently, the spectral broadening implicates that n∥-upshift can take place via a wave scattering mechanism. In the prohibited regime of Ip = 100 kA, more enhanced coupling of up to 90% is observed with similar density fluctuation to that of the marginal regime, which is explained with intensified wave scattering due to the high dielectric constant of spherical torus plasmas. It is concluded that practical windows for propagation and coupling of LHFW are widened with the aid of n∥-upshift via wave scattering even though the accessibility condition is not satisfied right in front of the antenna.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2019
    detail.hit.zdb_id: 1472746-8
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  • 2
    Online Resource
    Online Resource
    AIP Publishing ; 2018
    In:  Review of Scientific Instruments Vol. 89, No. 10 ( 2018-10-01)
    In: Review of Scientific Instruments, AIP Publishing, Vol. 89, No. 10 ( 2018-10-01)
    Abstract: High current regulations are widely required in tokamaks to generate a specific magnetic field for plasma confinement which is challenging for power electronics. For high current regulation, the stray inductance will cause high noise and surge voltage that may damage the power electronics. In addition, it is difficult to ensure both a fast response and a steady evolution. In this paper, a power supply based on a buck converter for high current regulation in an inductive load is described, in which insulated gate bipolar transistors are used as switches and two capacitor banks are used for energy storage. The first stage capacitor bank at a higher voltage ensures the fast current growth rate at the beginning of discharge and plays the role of wave filter later to reduce the noise. The second stage capacitor bank at a lower voltage provides the main energy required during discharge. A microcontroller is used to regulate the current by a feedback mechanism. This power supply can regulate the high current in an inductive load with low noise and fast response, which has been applied to the poloidal field coils and the ultrafast reciprocating probe system in the SUNIST (Sino-UNIted Spherical Tokamak) spherical tokamak.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2018
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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