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• A second 1.2 MW/53 keV high-energy neutral beam (NBI-2) procured, manufactured and installed on TCV. • NBI-2 is designed to probe plasma physics issues of higher plasma density, fast ion plasma interactions with static and dynamic fields and plasma rotation. • The higher NBI-2 energy together with NBI-1 (1.3 MW/28 keV) greatly enhances the operational space for fast ion studies and plasma heating with up to 2.5 MW NBH power. The TCV tokamak continues to leverage its unique shaping capabilities, flexible heating systems and modern control system to provide a stepladder approach for extrapolations of experimental results from different machines to ITER and DEMO. TCV's configurational flexibility has recently been enhanced by the installation of two heating neutral beams, new dual frequency gyrotrons, removable divertor gas baffles together with upgrades of its diagnostic infrastructure. Plasma regimes with high plasma pressure, a wider range of temperature ratios and significant fast-ion population are now attainable on TCV. A 1.3 MW/28 keV heating beam (NBI-1) has been operated on TCV from 2015 introducing the direct ion auxiliary heating. A second 1MW/50–60 keV high-energy neutral beam (NBI-2) has since been procured, manufactured and installed on TCV in July 2021. NBI-2 injected near anti-co-linearly to NBI-1 is designed to probe plasma physics issues of higher plasma density, fast ion plasma interactions with static and dynamic fields and plasma rotation. The higher NBI-2 energy greatly enhances the operational space for fast ion studies. NBI-2 commissioning is presently ongoing in parallel with TCV experiments using both NBIs. This paper summarises the experience with intensive use and improvements of the NBI-1, together with the status of NBI-2 commissioning. [ABSTRACT FROM AUTHOR]

Experiments on TCV are designed to complement the work at large integrated tokamak facilities (such as JET) to provide a stepwise approach to extrapolation to ITER and DEMO in areas where medium-size tokamaks can often exploit their experimental capabilities and flexibility. Improving the understanding and control requirements of burning plasmas is a major scientific challenge, requiring access to plasma regimes and configurations with high normalized plasma pressure and a wide range of ion to electron temperature ratios, including T e / T i ∼ 1. These conditions will be explored by adding a 1 MW neutral heating beam to TCV's auxiliary for direct ion heating (2015) and increasing the ECH power injected in X-mode at the third harmonic (2 MW in 2015–2016). The manufacturing of the neutral beam injector was launched in 2014. [ABSTRACT FROM AUTHOR]

Abstract: The TCV tokamak contributes to the physics understanding of fusion plasmas, broadening the parameter range of reactor relevant regimes, by investigations based on an extensive use of the existing main experimental tools: flexible shaping and high power real time-controllable electron cyclotron heating (ECH) and current drive (ECCD) systems. A proposed implementation of direct ion heating on the TCV by the installation of a 20–35keV neutral beam injection (NBI) with a total power of 1–3MW would permit an extension of the accessible range of ion to electron temperatures (T i/T e ∼0.1–0.8) to well beyond unity, depending on the NBI/ECH mix and the plasma density. A NBI system would provide TCV with a tool for plasma study at reactor relevant T i/T e ratios ∼1 and in investigating fast ion and MHD physics together with the effects of plasma rotation and high plasma β scenarios. The feasibility studies for a NBI heating on TCV presented in this paper were undertaken to construct a specification for the neutral beam injectors together with an experimental geometry for possible operational scenarios. [Copyright &y& Elsevier]

Abstract: The diagnostic neutral beam injector (DNBI) together with a charge exchange recombination spectroscopy (CXRS) system has been used on the TCV Tokamak as a diagnostic tool for local measurements of plasma ion temperature, velocity and carbon impurity density based on analysis of the beam induced impurity radiation emission since 2000. To improve the performance of the CXRS diagnostic, several upgrades of both the optical system and the neutral beam were performed. An increase of the plasma source size together with beam optimization in 2003 resulted in a twofold increase the beam current. The RF plasma generator was replaced by an arc-discharge plasma source together with a new ion optical system (IOS) in 2006 and subsequent beam optimization is presented herein. This was designed to increase the line brightness of the beam in the CXRS observation region without increasing of the injected power (to avoid plasma perturbation by the beam). The beam characteristics are measured by a multi-chord scanning of Doppler-shifted emission, thermal measurements on a movable calorimeter and visible optical measurements inside the Tokamak vessel. [Copyright &y& Elsevier]

Experimental apparatus and data analysis techniques used in neutral particle analyzer (NPA) diagnostics on the Tokamak à Configuration Variable (TCV) are described. Two NPAs are used on TCV to measure the energy spectrum of neutral particle fluxes from the plasma. The “five-channel energy analyzer of atomic particles” used in double electrical analysis mode with fast voltage sweeping detect particles without atomic mass discrimination in the energy range of 0.6–8.0 keV with a time resolution of 0.5–2.0 ms and an energy resolution of 7%–20%. The 28-channel “compact neutral particle analyzer” (CNPA) is an EIIB spectrometer with mass and energy separations designed for medium sized fusion machines featuring a carbon neutral stripping foil, a permanent magnet for dispersion, and channel-electron multiplier detectors. The CNPA simultaneously detects two mass species [hydrogen (H) and deuterium (D) or D and helium (He)] in the 0.5–50 keV energy range with a resolution of 60%–10% and a time resolution of 0.5–4.0 ms. The CNPA views the plasma across the path of the diagnostic neutral beam and can perform active charge-exchange NPA measurement. Data analysis procedures and numerical algorithms developed for NPA measurement are routinely used on TCV to obtain information on the plasma ion temperature, ion energy distribution function, plasma isotope ratios, and other plasma characteristics. [ABSTRACT FROM AUTHOR]

A diagnostic neutral beam injector (DNBI) [CRPP report LRP 710/01, CRPP-EPFL, 2001; EPS Conf. Contr. Fusion Plasma Phys., 25A (2001) 365] has been installed on tokamak à configuration variable (TCV) [Plasma Phys. Control Fusion, 36 (1994) B277; Plasma Phys. Control Fusion, 43 (2001) A161; Plasma Phys. Control Fusion, to be published] for the purpose of providing local measurements of plasma ion temperature, velocity and impurity density by Charge eXchange recombination spectroscopy (CXRS) [EPS Conf. Contr. Fusion Plasma Phys., 25A (2001) 365]. The system recently underwent a technical upgrade, which allowed to increase the full neutral beam current density by a factor of two (from 0.5 to 1 A at 52 keV injection energy) and to extend the operational range of the diagnostic. This was achieved by means of a new, larger ion source, with an increased extraction area and corresponding enhancements of the power supplies. [Copyright &y& Elsevier]

The 1MW power of the neutral beam injector (NBI) enters the plasma of the Tokamak à Configuration Variable (TCV) through a duct. The original beam propagation model predicted a maximal heat flux on the internal faces of the duct below 350 kW/m2, leading to an acceptable temperature rise for the 2 s nominal pulse duration. During commissioning, the NBI showed unacceptable overheating in the duct, the beam divergence being higher than expected. Several ion source grids have been tested to mitigate the beam divergence however the overheating of the duct is still problematic. Since then, the NBI operates with reduced power and duration to avoid damaging the beam duct. This paper describes the design and thermal analysis of a new beam duct capable of withstanding NBI shots at nominal regime for a range of modeled neutral beam divergences. The design drivers are the high heat flux protection and the accumulated heat dissipation. The concept features a thermal shield composed of a smooth elliptical castellated layer surrounded by an actively cooled structure. [ABSTRACT FROM AUTHOR]