Initial Results From the Newly Upgraded LTX-<i>β</i>

Elliott, Drew; Anderson, J. K.; Bell, R. E.; Biewer, T. M.; Boyle, Dennis; Donovan, David; Hansen, Chris; Hughes, Paul L.; Kaita, R.; Koel, Bruce E.; Kubota, S.; Lunsford, R.; Maan, A.; Majeski, R.; Scotti, F.; Soukhanovskii, V.; Zakharov, L.

doi:10.1109/tps.2020.2983854

Cited by 9 publications

(9 citation statements)

References 24 publications

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“…The LTX-β is a low aspect ratio tokamak with major radius R 0 ∼ 0.4 m, minor radius a < 0.26 m, and elongation κ ∼ 1.5 [20,21]. Typical parameters are toroidal field B T ∼ 3 kG, plasma current I P < 140 kA (100-120 kA in the discharges considered here), and a discharge duration ∼50 ms. LTXβ has retained the 1 cm thick copper shell used in LTX [22,23], which approximately conforms to a flux surface for a full-volume plasma.…”

Section: Configurationmentioning

confidence: 99%

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Extending the low-recycling, flat temperature profile regime in the lithium tokamak experiment-β (LTX-β) with ohmic and neutral beam heating

et al. 2023

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Recent experiments in the Lithium Tokamak Experiment-β (LTX-β) have extended the duration, performance, operating conditions, and diagnosis of the flat-temperature profile, low-recycling regime first observed in LTX. As expected, Li retains hydrogen and suppresses edge neutral cooling, allowing increased edge electron temperature, roughly equal to the core Te. Flat temperature profiles had been obtained transiently in LTX, as the plasma density decayed following the cessation of edge gas puffing. Careful control over the fueling in LTX-β has now been shown to sustain the flat Te profile and hot edge unique to the low-recycling regime for multiple confinement times in high performance discharges with decaying or steady density. With low density, the flat Te profile is also seen to extend into the scrape-off layer. Neutral beam heating is observed in target discharges with relatively flat electron temperature profiles (Tedge ~ Tcore/2), though beam heating is stronger in discharges with higher fueling, higher density, and depressed edge Te. Beam heating produces additional peaking of the Te profile, without degradation of the energy confinement time. Neutral beam heating of target discharges with relatively flat electron temperature profiles similarly results in broad beam heated temperature profiles. Energy confinement in LTX-β generally compares favorably to ohmic and H-mode scalings, frequently exceeding them by factors of 2-4. New and improved diagnostics in LTX-β enable better characterization of this unique regime, including measurements of ion temperature and high field side Thomson scattering profiles. As an initial step toward characterizing turbulence with no Te gradient and roughly equal density and pressure gradient, spectra have been measured in peaked Te discharges using far-forward scattering and fluctuation reflectometry.

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Section: Configurationmentioning

confidence: 99%

“…The upgrade of LTX to LTX-β included the installation of a short-pulse neutral beam (10-20 keV, up to 35 A injected H neutrals) [20,38,39]. The available port geometry on the vacuum vessel (see figure 2) limited the range of tangency radius for neutral beam injection (NBI).…”

Section: Neutral Beam Heated Dischargesmentioning

confidence: 99%

Extending the low-recycling, flat temperature profile regime in the lithium tokamak experiment-β (LTX-β) with ohmic and neutral beam heating

et al. 2023

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“…Cold edge fueling being incompatible with low recycling, LTX exhibited a transient state in which electron density n e decayed as the flat T e regime developed. This need for hot core fueling has been addressed with the addition of a neutral beam [7,8], the application of which to spherical tokamaks has been well studied in various machines [9,10]. The introduction of well-coupled neutral beam injection (NBI) would also permit studies of low recycling discharges with strong auxiliary heating.…”

Section: Introductionmentioning

confidence: 99%

“…The introduction of well-coupled neutral beam injection (NBI) would also permit studies of low recycling discharges with strong auxiliary heating. Maintaining high n e improves the precision of profile measurements from Thomson scattering, and the addition of the neutral beam provides access to impurity ion temperature T Li i profiles through CHERS [8].…”

Section: Introductionmentioning

confidence: 99%

Toroidal plasma acceleration due to NBI fast ion losses in LTX-β

Hughes¹,

Capecchi²,

Elliott³

et al. 2021

Plasma Phys. Control. Fusion

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The recent Lithium Tokamak Experiment-Beta (LTX-β) upgrade includes the addition of neutral beam injection (NBI) in the same direction as the plasma current (co-I P ) and a new toroidal Mirnov array for MHD characterization. In initial NBI experiments, a spontaneously rotating n = 1 MHD mode is seen to accelerate during NBI in the counter-beam direction, accompanied by a rise in electron density consistent with the beam-injected inventory but without a clear increase in plasma pressure. Together with analytic and numerical modeling of beam optics and fast ion confinement, these observations indicate the prompt loss of all or nearly all beam ions. However, the same modeling also suggests that planned upgrades to the Ohmic heating system should provide the fast ion confinement necessary for beam heating and core fueling. A simple analytic model relates the momentum confinement time τ ϕ to the observed evolution of mode rotation due to the combination of NBI momentum coupling, fast ion loss ⃗ J × ⃗ B, and anomalous viscous torques, yielding τ ϕ values consistent with past measurements of electron energy confinement time τ E,e .

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“…A 700 kW neutral beam injection (NBI) system (on loan from TAE technologies) now installed on LTX-β is an integral part of the recent upgrade. Good coupling of the beam to the plasma is particularly important; as edge fueling is incompatible with the low-recycling condition, sustainment through core fueling of NBI is essential in LTX-β [6]. Beyond fueling, the heating and momentum injection effects of NBI are important for several reasons.…”

Section: Introductionmentioning

confidence: 99%

Neutral beam prompt loss in LTX- β

Capecchi¹,

Anderson²,

Boyle³

et al. 2021

Nucl. Fusion

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Prompt loss of beam injected fast ions approaches 100% in lithium tokamak experiment-beta (LTX-β) discharges, though significantly improved confinement is expected for the higher current plasmas made available by a recent upgrade to the Ohmic heating power supply. Modeling of fast ions using TRANSP/NUBEAM finds a maximum coupled beam fraction of 76% at the near-term limits of the LTX-β operating space. The full ion orbit code POET is employed to validate NUBEAM results against possible non-adiabatic effects on fast ion orbits, but corrections to the prompt loss fraction due to collisionless transport are found to be small. The graphical method code CONBEAM is used to investigate the topology of fast ion phase space as it relates to neutral beam deposition, and counter-injected NBI is considered as a way to access a region of high field side beam deposition. A metric is developed within the CONBEAM using a beam filament model to estimate the prompt loss fraction and shown to agree well with both POET and NUBEAM, enabling near real-time analysis and potential feedback to operators between plasma discharges.

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Initial Results From the Newly Upgraded LTX-β

Cited by 9 publications

References 24 publications

Extending the low-recycling, flat temperature profile regime in the lithium tokamak experiment-β (LTX-β) with ohmic and neutral beam heating

Extending the low-recycling, flat temperature profile regime in the lithium tokamak experiment-β (LTX-β) with ohmic and neutral beam heating

Toroidal plasma acceleration due to NBI fast ion losses in LTX-β

Neutral beam prompt loss in LTX- β

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