A systematic methodology for structured design of feedback controllers for the sawtooth period is presented, based on dedicated identification of the sawtooth dynamics. Therefore, a combined Kadomtsev–Porcelli model of a sawtoothing plasma actuated by an electron cyclotron current drive system has been set-up. This is used to derive the linearized input–output relations (transfer functions) from the varying deposition location of the electron cyclotron waves (ECW) to the sawtooth period. These transfer functions are derived around a large collection of operating points. Assessment of these control-relevant transfer functions shows that a sawtooth period controller requires an integral (I) action to guarantee closed-loop stability with zero steady-state error. Additional proportional-integral (PI) action can be applied to further increase the closed-loop performance. The parameters of both the I and PII controllers have been optimized in terms of stability, performance and robustness. Moreover, the effect of the mechanical ECW launcher on the closed-loop performance is studied for realistic cases. It is shown that the launcher dynamics seriously affects the achievable closed-loop performance in present-day experiments.
In this Letter we report measurements of collective Thomson scattering (CTS) spectra with clear signatures of ion Bernstein waves and ion cyclotron motion in tokamak plasmas. The measured spectra are in accordance with theoretical predictions and show clear sensitivity to variation in the density ratio of the main ion species in the plasma. Measurements with this novel diagnostic demonstrate that CTS can be used as a fuel ion ratio diagnostic in burning fusion plasma devices. Waves and particle dynamics in the frequency range of ion cyclotron motion (ICM), ! ci ¼ q i B=m i , play important roles for diagnostic of ion composition in magnetized plasmas. Under certain conditions collective Thomson scattering (CTS) spectra are distinctively sensitive to ion Bernstein waves (IBWs) and the ICM. The combined effect of IBWs and ICM gives rise to an ion cyclotron structure (ICS) in CTS spectra which depend on the ion species densities and their ratios. Measurements of the ICS in CTS spectra can thus demonstrate basic plasma and wave physics as well as provide great diagnostic potential for characterizing the composition of magnetized plasmas.We present in this Letter the first measurements of CTS spectra with signatures of intrinsic IBWs and ICM in a multispecies tokamak plasma. In experiments on multispecies plasmas containing, e.g., hydrogen, deuterium, and 3 He, we demonstrate that we resolve changes in the ICS in CTS spectra caused by variations in the isotope ratios. In addition, calculations and experimental results agree. This indicates that the relevant physics of CTS and the interaction with IBWs and ICM are well represented by our kinetic, fully electromagnetic model.While our results are of general interest and have application in plasma physics, there is a particular implication on the field of fusion energy research. The issue of measuring the fuel ion ratio in future burning plasma magnetic confinement devices has recently received increasing attention. The fuel ion ratio in burning plasmas is the ratio of the number densities of the main ion species. On ITER it is not clear if this ratio can be determined in the plasma center (normalized radius < 0:3) with the diagnostic set currently included in the ITER baseline design [1]. As measurements of the fuel ion ratio are of high priority for machine protection and basic control, it is of great interest to develop alternative diagnostic methods capable of measuring the tritium-deuterium ratio. Our results represent a key step for developing a novel CTS-based fuel ion ratio diagnostic which can fulfill the measurement needs for ITER and future devices.IBWs are electrostatic hot plasma waves generally present in magnetized plasmas [2,3]. IBWs are weakly damped for propagation near perpendicular to the magnetic field (k k % 0) while the damping of the waves increases strongly as k k increases. The frequencies of propagating IBWs lie between the harmonics of the cyclotron frequency for each ion species in the plasma, ! ci . The frequencies of IBWs with wave vectors...
Corroborating evidence is presented that the sawtooth period can follow the modulation frequency of an externally applied high power electron cyclotron wave source. Precise, fast and robust open loop control of the sawtooth period with a continuously changing reference period has been achieved. This period locking is not associated with the crash, but with the phase evolution of the inter-crash dynamics. This opens new possibilities of open loop control for physics studies and maybe for reactor performance control.
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