Neutral beam prompt loss in LTX-
                  β

Capecchi, W.; Anderson, J. K.; Boyle, Dennis; Hughes, Paul L.; Maan, A.; Majeski, R.; Elliott, Drew; Hansen, Chris

doi:10.1088/1741-4326/ac2bbf

Cited by 2 publications

(1 citation statement)

References 22 publications

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“…Initially, the beam was installed with a tangency radius of R = 19 cm, with the option of re-aiming the beam to larger radius (R = 27 cm) by swiveling the source on its bellows mount. Over this range, operation at a smaller tangency radius produces a larger population of fast ion first orbit losses, according to modeling with a full ion orbit code [40]. When the beam source is oriented at the largest available tangency radius, part of the beam footprint is blocked by the vacuum vessel port.…”

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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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: 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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Estimates of global recycling coefficients for LTX-β discharges

Maan,

Boyle,

Majeski

et al. 2024

Physics of Plasmas

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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.

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Neutral beam prompt loss in LTX- β

Cited by 2 publications

References 22 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

Estimates of global recycling coefficients for LTX-β discharges

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