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Lithium Effects on Edge Neutral Density

This study examines the impact of lithium deposition on plasma edge neutral density and its effects on edge electron temperatures and densities. The results show that the effects of lithium are short-lived and the plasma returns to its previous state after a few shots. However, the edge electron densities decrease by nearly 50% inside the separatrix. Additionally, TRANPS calculations suggest that decreased edge density may increase beam power deposited into the plasma.

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Lithium Effects on Edge Neutral Density

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  1. Lithium Effects on Edge Neutral Density Patrick Ross

  2. Edge Neutral Density Diagnostic (ENDD) measures light emitted by the plasma edge Inboard Outboard The ENDD uses a 2-D ccd camera to measure Dβ emissions. The emission profile is then Abel-inverted to provide a radial profile.

  3. XP 719, Day 1 Edge Neutral DβEmissions Day 1, most of the shots had a fairly long current flattop (250-750 ms). Arbitrary Units Radius Edge Neutral emissions by radius. Shot 12474 is the reference shot, after which the lithium deposition began. Lithium in excess of 200 mg had a measurable effect on the plasma.

  4. XP 719, Day 1 Edge Neutral DβEmissions Day two deposited over 9 grams of lithium. Later shots were not used because they did not run as long. Radius Day 2 consisted of increased deposition between shots. After depositions > 300 mg, the shots were short, with <100ms flattop. The edge neutral emissions decreased with increasing lithium.

  5. Day 2- High Lithium Deposition shortened shots Radius During day 2 of XP 719, much more lithium was deposited. After periods where >300 mg of lithium was deposited, the shots were either fizzles or significantly shortened. In general, they exhibited the same behavior as shots with less lithium.

  6. Lithium Edge Neutral Effects only last for a few shots The reference shots from day 1 to day 2 are very similar, even though more than 1.8 grams of Lithium was deposited into NSTX during Day 1 operation. The lithium effects are seen in the final shot of Day 1 (shot 123489), but have completely disappeared by the reference shot of Day 2 (123505). Radius

  7. Edge Temperatures are not significantly different with Lithium while densities vary somewhat Although the central electron temperature is significantly higher after lithium deposition (~1.5x), the edge electron temperature does not appear to change significantly before and after lithium deposition. The edge electron density is slightly higher near the seperatrix before lithium deposition. Beyond 150 cm, the electron densities are the same.

  8. Edge Neutral Density Affects Charge Exchange Losses TRANSP Calcluations of Beam Power Losses due to Edge Neutral Density of shot 120442. Density is cm-3 and lost power is in kW. BPCXX – External Charge Exchange Loss (Beam particles charge exchange outside Last Closed Flux Surface) BPCXI – Internal Charge Exchange Loss (Beam particles C-X inside LCFS) BPLIM – Fast Ions born on bad orbits, lost immediately to the wall

  9. Conclusions • The lithium affects the edge neutral emissions, but the effects are short lived. Within a few shots after the lithium deposition, the effects are gone and the plasma returns to the previous state • Edge electron temperatures are not sigificantly affected by lithium • Edge electron densities are decreased due to lithium by nearly 50% inside the seperatrix, but outside, the electron density is unchanged. • TRANPS calculations show that decreased edge density may increase beam power deposited into the plasma.

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