Development in the DIII-D tokamak of advanced operating scenarios and associated control techniques for ITER

Abstract

Abstract. Significant progress has been made on the DIII-D tokamak in the capability to control key plasma features and using such control to expand the operational limits of stationary and steady-state tokamak operation. Recent experiments have demonstrated the capability to suppress the key plasma instabilities of concern for ITER, including edge localized modes, neoclassical tearing modes, and resistive wall modes. In addition, the ability to regulate the rotation and current density profiles through feedback control has been demonstrated. The use of these control techniques has allowed an expansion of the envelope of viable, stationary tokamak operation, highlighted by the demonstration of sustained (~2 s) operation of ! N_ 4 (50% above the no-wall stability limit) as well as fully noninductive operation with !_ 3.5%. This development is supported by a vigorous basic physics program, which has provided new insights into turbulence dynamics over a large range in spatial scales, new measurements of the structure of fast-ion instabilities and their effect on the fast ion population, and important information on the transport of carbon and associated tritium co-deposition on plasma facing surfaces.

Real-time measurement and feedback control of ion temperature profile and toroidal rotation using fast CXRS system in JT-60U

“…In these high performance plasmas, the pressure, rotation and current profiles play the critical roles in determining transport [1][2][3] and MHD stability [4][5][6][7] interacting with each other [8]. Therefore, the development of the real-time control system [9][10][11][12][13][14] for these parameters is essentially important in sustaining high performance plasmas. For example, it is generally accepted that the control of pressure and current profiles is useful to stabilize the neoclassical tearing mode (NTM) [4] and the edge localized mode (ELM) [15].…”

“…However, because the response of current profile is about one order magnitude longer than that of pressure profile, the control of pressure is more useful for fast MHD feedback control. It is also reported that the toroidal rotation velocity (V t ) plays an important role for the NTM stabilization [13] and ELM behavior [16][17][18]. And V t profile can also be changed on a time scale comparable to the change in the pressure profile.…”

Time–frequency analysis of fusion plasma signals beyond the short-time Fourier transform paradigm: An overview

“…The need for time-frequency (t-f) analysis [1,2] in nuclear fusion research, when processing data coming from dedicated high-temperature plasma diagnostics, has always been strongly felt [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Indeed, fusion plasmas are an incredibly rich source of physical phenomenology whose spectral content changes in time, as often seen in plasma turbulence and MHD instabilities.…”

“…This gives rise to signals exhibiting, in general, time-varying spectra that can range from a few to hundreds of kHz, and can change as fast as in some hundredths of ms. The basic, almost universal approach to process and analyse such signals has been the short-time Fourier transform (STFT), from which the spectrogram (SPEC) has emerged as the ancestor of modern t-f distributions [1][2][3][4][5][6][7][8][9][10][11]13,[16][17][18][19][20]. Sometimes, more sophisticated versions of time-local Fourier spectra, like wavelets [12,17], or alternative yet equivalent techniques, such as complex demodulation [14], have been used, but always within a framework that can be called the STFT paradigm.…”

“…The authors' basic motivation has been the divulgation of these less-known t-f tools to as broader a nuclear fusion audience as possible, so fellow researchers can get well acquainted with and take full advantage of them. The worthiness of such a task can be easily justified by the significant fraction of reports monitoring the recent progress on controlled thermonuclear research in which t-f analysis is actually present, although always within the realm of the STFT paradigm [6][7][8][9][10][11][12].…”