Abstract
The TCV tokamak is augmenting its unique historical capabilities (strong shaping, strong electron heating) with ion heating, additional electron heating compatible with high densities, and variable divertor geometry, in a multifaceted upgrade program designed to broaden its operational range without sacrificing its fundamental flexibility. The TCV program is rooted in a three-pronged approach aimed at ITER support, explorations towards DEMO, and fundamental research. A 1 MW, tangential neutral beam injector (NBI) was recently installed and promptly extended the TCV parameter range, with record ion temperatures and toroidal rotation velocities and measurable neutral-beam current drive. ITER-relevant scenario development has received particular attention, with strategies aimed at maximizing performance through optimized discharge trajectories to avoid MHD instabilities, such as peeling-ballooning and neoclassical tearing modes. Experiments on exhaust physics have focused particularly on detachment, a necessary step to a DEMO reactor, in a comprehensive set of conventional and advanced divertor concepts. The specific theoretical prediction of an enhanced radiation region between the two X-points in the low-field-side snowflake-minus configuration was experimentally confirmed. Fundamental investigations of the power decay length in the scrape-off layer (SOL) are progressing rapidly, again in widely varying configurations and in both D and He plasmas; in particular, the double decay length in L-mode limited plasmas was found to be replaced by a single length at high SOL resistivity. Experiments on disruption mitigation by massive gas injection and electron-cyclotron resonance heating (ECRH) have begun in earnest, in parallel with studies of runaway electron generation and control, in both stable and disruptive conditions; a quiescent runaway beam carrying the entire electrical current appears to develop in some cases. Developments in plasma control have benefited from progress in individual controller design and have evolved steadily towards controller integration, mostly within an environment supervised by a tokamak profile control simulator. TCV has demonstrated effective wall conditioning with ECRH in He in support of the preparations for JT-60SA operation.
Highlights
The Tokamak à Configuration Variable (TCV) [1] is one of three national tokamak devices operating as European facilities within the medium-size tokamak work package (WPMST1) of the EUROfusion consortium [2]
This paper reports on scientific results primarily from the 2015–2016 campaign, which followed a nearly twoyear shutdown for neutral beam heating (NBH) installation and other upgrades and was dominated by the EUROfusion Consortium, and on the phased facility upgrade underway [4]
The X-point-target divertor (figure 4(e))— realized in TCV [16]—is topologically akin to the LFS SF−, with the secondary X-point close to the target. All these experiments have benefited from an extensive array of diagnostics, including a vertical and a horizontal infrared (IR) camera ensuring broad coverage of the floor and of the inner wall, 114 wall-mounted Langmuir probes (LPs), a fast reciprocating probe (RP—on loan from UCSD) [20], tomographic sets of foil and AXUV bolometers, a fast framing visible camera, a four-camera set with identical optics and viewline and different spectroscopic filters, and a visible-light divertor spectroscopy system (DSS)
Summary
The Tokamak à Configuration Variable (TCV) [1] is one of three national tokamak devices operating as European facilities within the medium-size tokamak work package (WPMST1) of the EUROfusion consortium [2]. TCV features a major radius of 0.88 m, a minor radius of 0.25 m, a vacuum toroidal field up to 1.5 T, and plasma cur rent up to 1 MA It has long been defined by its strong versatility in plasma shaping, made possible by 16 independently powered poloidal-field coils, supplemented by two internal coils to stem axisymmetric instabilities with high growth rates. This has motivated the allotment of a significant fraction of its recent experimental program to a determined search for alternative and unconventional configurations in view of meeting one of the primary challenges for a DEMO reactor, namely the need to handle higher heat fluxes than ITER.
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