Status, scientific results and technical improvements of the NBH on TCV tokamak

Abstract

The TCV tokamak contributes to physics understanding in fusion reactor research by a wide set of experimental tools, like flexible shaping and high power ECRH. A 1 MW, 25 keV deuterium heating neutral beam (NB) has been installed in 2015 and it was operated from 2016 in SPC-TCV domestic and EUROfusion MST1 experimental campaigns (~50/50%). The rate of failures of the beam is less than 5%. Ion temperatures up to 3.5 keV have been achieved in ELMy H-mode, with a good agreement with ASTRA predictive simulations. The NB enables TCV to access ITER-like β N values (1.8) and T e /T i ~1, allowing investigations of innovative plasma features in ITER relevant ELMy H-mode. The advanced Tokamak route was also pursued, with stationary, fully non-inductive discharges sustained by ECCD and NBCD reaching β N~1 .4-1.7. Real-time control of the NB power has been implemented in 2018 and presented together with the statistics of NB operation on the TCV. During commissioning, the NB showed unacceptable heating of the TCV beam duct, indicating a higher power deposition than expected on duct walls. A high beam divergence has been found by dedicated measurement of 3-D beam power density distribution with an expressly designed device (IR measurement on tungsten target).

Excitation of toroidal Alfvén eigenmodes with counter-current NBI in the TCV tokamak

“…TCV is a medium-size device (R 0 /a = 0.88 m/0.25 m) capable of flexible plasma shaping due to 16 independent poloidal field coils and an over-sized vacuum chamber. Available heating systems include ERCH and two tangential NBIs with 1 MW-1.3 MW in deuterium and energies ⩽28 keV and ⩽42 keV [4,12,13] arranged anti-collinearly at the TCV midplane (see figure 1(a)). The width of the beam (computed as the size with 1/e intensity of the interpolated beam footprint on the calorimeter) is 21.6 cm × 9.4 cm at the port entrance (horizontal × vertical).…”

“…The Tokamak á Configuration Variable (TCV) [3]) is a flexible device equipped with two tangential neutral beam (NB) injectors [4], both with a nominal injected power of ⩾1 MW. The study on the fast ion population injected by such beams and on the interaction with MHD modes has been explored in [5][6][7].…”

Physics research on the TCV tokamak facility: from conventional to alternative scenarios and beyond

“…Since 2015, NBH has also been employed on TCV, using a 15-25 keV beam of maximum 1 MW power (at the highest energy), in a tangential geometry affording a double pass through the plasma cross-section [5,6]. A second 1 MW injector, directed in the opposite direction and featuring an energy of 50-60 keV, is currently being planned for the 2020 horizon.…”

Extension of the operating space of high-b N fully non-inductive scenarios on TCV using neutral beam injection

“…However, such a process is notoriously complicated due to the exigent physics requirements: high input power and plasma confinement, current alignment between bootstrap current and current drive and MHD control. In order to assess the difficulties found on such scenarios and to extend previous steady-state plasmas obtained with only Electron Cyclotron Resonance Heating (ECRH), steady-state regimes have been explored at the Tokamak à Configuration Variable (TCV) using the newly available Neutral Beam Injection (NBI) system [1,2]. This system supplies up to 1MW (25keV) to the plasma by accelerating positive deuterium ions.…”

“…This system supplies up to 1 MW (25 keV) to the plasma by accelerating positive deuterium ions. Due to machine protection constraints [2,3], the maximum NB injected energy was initially limited to 0.5 MJ and relaxed to 0.8 MJ after NBI optim izations for experiments presented in this work. Since the beam duct port is installed on the torus middle plane, offaxis NBI is obtained on TCV by vertically shifting the plasma magnetic axis (z).…”