Real-time diamagnetic flux measurements on ASDEX Upgrade

Abstract

Author(s)Giannone, L.; Geiger, B.; Bilato, R.; Maraschek, M.; Odstrčil, T.;Fischer, R.; Fuchs, J. C.; McCarthy, Patrick J.; Mertens, V.; Schuhbeck, K. H. Publication date 2016-05-24Original citation Giannone, L., Geiger, B., Bilato, R., Maraschek, M., Odstrčil, T., Real-time diamagnetic flux measurements are now available on ASDEX Upgrade. In contrast to the majority of diamagnetic flux measurements on other tokamaks, no analog summation of signals is necessary for measuring the change in toroidal flux or for removing contributions arising from unwanted coupling to the plasma and poloidal field coil currents. To achieve the highest possible sensitivity, the diamagnetic measurement and compensation coil integrators are triggered shortly before plasma initiation when the toroidal field coil current is close to its maximum. In this way, the integration time can be chosen to measure only the small changes in flux due to the presence of plasma. Two identical plasma discharges with positive and negative magnetic field have shown that the alignment error with respect to the plasma current is negligible. The measured diamagnetic flux is compared to that predicted by TRANSP simulations. The poloidal beta inferred from the diamagnetic flux measurement is compared to the values calculated from magnetic equilibrium reconstruction codes. The diamagnetic flux measurement and TRANSP simulation can be used together to estimate the coupled power in discharges with dominant ion cyclotron resonance heating.[http://dx

Note: Internal diamagnetic flux measurements on ASDEX Upgrade

“…The diamagnetic flux integrator can also be initiated in the flat top of the toroidal field current to make digital compensation of the signal possible [5,9]. In earlier research work, the details and the theoretical background of external diamagnetic flux measurements were described [10]. It has a limited bandwidth of operation owing to the low pass filtering e↵ect of the vacuum vessel.…”

Measurements and modelling of diamagnetic flux in ASDEX Upgrade

“…Knowledge of the fast-ion contribution to the pressure profile is an important input for magnetic equilibrium reconstruction with pressure constraints. Earlier modelling of diamagnetic flux measurements on ASDEX Upgrade [17,18,31] used IDE equilibrium reconstruction [32] and TRANSP [33,34] for fast-ion pressure profiles. Real-time simulations of the NBI fast-ion distribution can also be calculated by the time-dependent solution of the Fokker-Planck equation (2D in velocity) based on analytic expressions by the RABBIT code [35].…”

“…The diamagnetic flux therefore provides a continuous measure of the perpendicular poloidal beta without requiring density and temperature profiles of the ions or electrons. It can be seen that β p⊥ , as determined from diamagnetic flux measurements using equation (17), is related to the perpendicular pressure, whereas the poloidal beta determined from magnetic equilibrium from equation (21) in TRANSP is related to the perpendicular, parallel and flow components of pressure [40,41]. Thus magnetic equilibrium measurements together with diamagnetic measurements may be used to determine the plasma anisotropy.…”

“…A number of tokamaks and stellarators have demonstrated the measurement of diamagnetic flux [4][5][6][7][8][9][10][11][12][13][14][15][16]. The time evolution of internal and external diamagnetic flux is routinely measured on ASDEX Upgrade [17,18]. A comparison of diamagnetic flux measurements and calculation from equilibrium reconstruction and transport simulations can identify discharge conditions where plasma anisotropy, fast-ion losses or transport are strong enough to lead to a discrepancy between measurements and modelling.…”

Propagating transport-code input parameter uncertainties with deterministic sampling

“…A commonly used method for modeling fusion plasma properties, such as fuel ion distributions [1] confinement time [2], or diamagnetic flux [3], is the transport code TRANSP [4], developed at Princeton Plasma Physics Laboratory. It is often used together with the code NUBEAM [5] which models the slowing down of the beam ions.…”