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High-power TCV scenario for conventional and alternative divertor studies
Authors:
K. Lee,
C. Theiler,
M. Carpita,
M. Zurita,
P. Sintre,
O. Février,
F. Pastore,
H. Reimerdes,
K. Verhaegh,
M. Winkel,
D. Brida,
B. Y. K. Brown,
M. J. H. Cornelissen,
R. Ducker,
G. Durr-Legoupil-Nicoud,
D. Hamm,
R. I. Morgan,
A. Perek,
O. Sauter,
E. Tonello,
Y. Wang,
the TCV Team,
the EUROfusion Tokamak Exploitation Team
Abstract:
Alternative divertor configurations (ADCs) must be evaluated under boundary plasma conditions approaching reactor-level values to be considered a reliable, physics-based solution for tokamak power exhaust. Most ADC experiments performed to date were at relatively low exhaust power. This work presents a high-power scenario on the TCV tokamak enabling the study of a wide variety of divertor magnetic…
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Alternative divertor configurations (ADCs) must be evaluated under boundary plasma conditions approaching reactor-level values to be considered a reliable, physics-based solution for tokamak power exhaust. Most ADC experiments performed to date were at relatively low exhaust power. This work presents a high-power scenario on the TCV tokamak enabling the study of a wide variety of divertor magnetic shapes under an expanded SOL and power exhaust parameter space. The scenario is characterized by high power levels of electron cyclotron resonance heating ($2.5\,\text{MW}$ fully absorbed in a $\sim1\,\text{m}^{3}$ plasma) at high plasma current (edge safety factor $q_{95}\approx 2.5$), and low upstream separatrix densities ($n_{e,\text{u}}\approx1\times10^{19}\,\text{m}^{-3}$, Greenwald fraction $f_{\text{G}}\approx 0.1$). Stationary parallel heat fluxes up to $100\,\text{MW m}^{-2}$ are measured at the divertor target, an order of magnitude above previous TCV power exhaust studies. The obtained SOL collisionality and Lengyel detachment scaling metric lie within range of values expected in future reactors (SPARC, ITER, ARC).
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Submitted 19 August, 2026;
originally announced August 2026.
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Infrared Thermography in the Tokamak à Configuration Variable
Authors:
M. Zurita,
H. Reimerdes,
C. Colandrea,
H. Elaian,
M. Pedrini,
Y. Andrebe,
F. Crisinel,
S. Koncewiez,
J. -D. Landis,
D. Mykytchuk,
U. Sheikh,
the TCV team
Abstract:
In the Tokamak à Configuration Variable (TCV), infrared thermography (IR) is currently composed of the horizontal, vertical, and tangential infrared systems (HIR, VIR, TIR), which all use Equus 81k M cameras. The IR diagnostics obtain the surface temperature of TCV's graphite tiles for post-discharge analysis. Target heat flux profiles are inferred from the tile temperature with the THEODOR (Therm…
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In the Tokamak à Configuration Variable (TCV), infrared thermography (IR) is currently composed of the horizontal, vertical, and tangential infrared systems (HIR, VIR, TIR), which all use Equus 81k M cameras. The IR diagnostics obtain the surface temperature of TCV's graphite tiles for post-discharge analysis. Target heat flux profiles are inferred from the tile temperature with the THEODOR (Thermal Energy Onto Divertor) code. Fast transient analysis is possible in reduced frame mode, with acquisition frequencies above 10kHz. The main views are the lower inner wall for HIR, the floor for VIR, and the lower outer wall for TIR. The HIR camera can also be moved to view the midplane inner wall, while TIR can be moved to see the midplane inner wall and the upper outer wall, mainly to measure synchrotron radiation and heat deposition due to runaway electrons. Recent developments in TCV's IR systems include (i) tile diffusivity and conductivity measurements to assure the precision of heat flux estimates; (ii) the addition of one new VIR heated valley tile and two rooftop TIR tiles, for measurements of fast heat flux transients; (iii) the implementation of long-pass wavelength filter of 4095 nm, to diminish the measurement of plasma parasitic infrared light, mainly from deuterium 5-4 emission at 4051 nm. Despite these developments, the main sources of uncertainty for IR in TCV are still parasitic infrared light and the determination of the surface layer heat transmission factor, both of which mainly affect the VIR system.
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Submitted 1 April, 2026; v1 submitted 12 March, 2026;
originally announced March 2026.
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An upper pressure limit for low-Z benign termination of runaway electron beams in TCV
Authors:
M Hoppe,
J Decker,
U Sheikh,
S Coda,
C Colandrea,
B Duval,
O Ficker,
P Halldestam,
S Jachmich,
M Lehnen,
H Reimerdes,
C Paz-Soldan,
M Pedrini,
C Reux,
L Simons,
B Vincent,
T Wijkamp,
M Zurita,
the TCV team,
the EUROfusion Tokamak Exploitation Team
Abstract:
We present a model for the particle balance in the post-disruption runaway electron plateau phase of a tokamak discharge. The model is constructed with the help of, and applied to, experimental data from TCV discharges investigating the so-called ``low-Z benign termination'' runaway electron mitigation scheme. In the benign termination scheme, the free electron density is first reduced in order fo…
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We present a model for the particle balance in the post-disruption runaway electron plateau phase of a tokamak discharge. The model is constructed with the help of, and applied to, experimental data from TCV discharges investigating the so-called ``low-Z benign termination'' runaway electron mitigation scheme. In the benign termination scheme, the free electron density is first reduced in order for a subsequently induced MHD instability to grow rapidly and spread the runaway electrons widely across the wall. We show that the observed non-monotonic dependence of the free electron density with the measured neutral pressure is due to plasma re-ionization induced by runaway electron impact ionization. At higher neutral pressures, more target particles are present in the plasma for runaway electrons to collide with and ionize. Parameter scans are conducted to clarify the role of the runaway electron density and energy on the free electron density, and it is found that only the runaway electron density has a noticeable impact. While the free electron density is shown to be related to the spread of heat fluxes at termination, the exact cause for the upper neutral pressure limit remains undetermined and an object for further study.
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Submitted 15 June, 2025; v1 submitted 19 December, 2024;
originally announced December 2024.
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Comparison of detachment in Ohmic plasmas with positive and negative triangularity
Authors:
O. Février,
C. K. Tsui,
G. Durr-Legoupil-Nicoud,
C. Theiler,
M. Carpita,
S. Coda,
C. Colandrea,
B. P. Duval,
S. Gorno,
E. Huett,
B. Linehan,
A. Perek,
L. Porte,
H. Reimerdes,
O. Sauter,
E. Tonello,
M. Zurita,
T. Bolzonella,
F. Sciortino,
the TCV Team,
the EUROfusion Tokamak Exploitation Team
Abstract:
In recent years, negative triangularity (NT) has emerged as a potential high-confinement L-mode reactor solution. In this work, detachment is investigated using core density ramps in lower single null Ohmic L-mode plasmas across a wide range of upper, lower, and average triangularity (the mean of upper and lower triangularity: $δ$) in the TCV tokamak. It is universally found that detachment is mor…
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In recent years, negative triangularity (NT) has emerged as a potential high-confinement L-mode reactor solution. In this work, detachment is investigated using core density ramps in lower single null Ohmic L-mode plasmas across a wide range of upper, lower, and average triangularity (the mean of upper and lower triangularity: $δ$) in the TCV tokamak. It is universally found that detachment is more difficult to access for NT shaping. The outer divertor leg of discharges with $δ\approx -0.3$ could not be cooled to below $5~\mathrm{eV}$ through core density ramps alone. The behavior of the upstream plasma and geometrical divertor effects (e.g. a reduced connection length with negative lower triangularity) do not fully explain the challenges in detaching NT plasmas. Langmuir probe measurements of the target heat flux widths ($λ_q$) were constant to within 30% across an upper triangularity scan, while the spreading factor $S$ was lower by up to 50% for NT, indicating a generally lower integral Scrape-Off Layer width, $λ_{int}$. The line-averaged core density was typically higher for NT discharges for a given fuelling rate, possibly linked to higher particle confinement in NT. Conversely, the divertor neutral pressure and integrated particle fluxes to the targets were typically lower for the same line-averaged density, indicating that NT configurations may be closer to the sheath-limited regime than their PT counterparts, which may explain why NT is more challenging to detach.
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Submitted 23 January, 2024; v1 submitted 18 October, 2023;
originally announced October 2023.