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

Hughes, Paul L.; Capecchi, W.; Elliott, Drew; Zakharov, L.; Bell, R.E.; Hansen, Chris; Boyle, Dennis; Gorelenkov, Stepan N; Majeski, R.; Kaita, R.

doi:10.1088/1361-6587/ac0b9f

Cited by 3 publications

(2 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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

Self Cite

View full text Add to dashboard Cite

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.

show abstract

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

Self Cite

View full text Add to dashboard Cite

show abstract

“…Additionally the flow shear introduced by NBI could provide stabilization against density gradient driven modes [8]. Initial NBI operation and concurrent modeling, however, suggest near total prompt loss of beam ions [9]. In this work we consider 'prompt' losses to be any ions lost prior to completion of their first drift orbit [10].…”

Section: Introductionmentioning

confidence: 99%

Neutral beam prompt loss in LTX- β

Capecchi¹,

Anderson²,

Boyle³

et al. 2021

Nucl. Fusion

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Estimates of global recycling coefficients for LTX-β discharges

Maan,

Boyle,

Majeski

et al. 2024

Physics of Plasmas

View full text Add to dashboard Cite

We report the first observation of global recycling coefficient R near 0.5 in the Lithium Tokamak eXperiment-β (LTX-β), significantly below the minimum R previously reported in other devices. In a series of experiments with varied Li wall conditioning, estimates of the recycling coefficient have been made using a Lyman-α array and DEGAS2 modeling. A progressive reduction in Lyman-α emission with increased lithium and an increase in edge electron temperature are observed. It is also observed that with increasing Li coating thickness, the effective particle confinement time τp* is reduced and approaches TRANSP calculated energy confinement time (τE), with τp* near τE,TRANSP for the lowest recycling coefficients. Edge temperatures approaching core plasma temperatures, first reported in LTX, can now be directly connected to estimates of the recycling coefficient and qualitatively agree with previous UEDGE simulations. The particle flux to the limiting surfaces appears to be significantly reduced in comparison with fluid scrape-off layer (SOL) models, indicating that a large fraction of the SOL ions are mirror trapped. SOL collisionality drops more than an order of magnitude below the banana regime boundary, indicating the importance of kinetic effects. Full-f 1x2v gyrokinetic simulations of SOL field lines with the GKEYLL code indicate that the fraction of ions trapped along field lines increases as collisionality drops, as a result of increased lithium evaporation.

show abstract

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

Cited by 3 publications

References 28 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

Neutral beam prompt loss in LTX- β

Estimates of global recycling coefficients for LTX-β discharges

Contact Info

Product

Resources

About