NSTX APS-DPP: SD/SMKNov Abstract The transport properties of NSTX plasmas obtained during the 2008 experimental campaign have been studied and are reported here. Transport trends and dependences have been isolated, and it is found that both electron and ion energy transport coefficients have strong dependences on local values of n  T, which in turn is strongly dependent on local current density profile. Without identifying this dependence, it is difficult to identify others, such as the dependence of transport coefficients on poloidal magnetic field (or q), plasma current and heating power. In addition, a comparison between discharges with and without Lithium wall conditioning has been made. While the trends in the two sets of data are similar, the thermal transport loss, especially in the electron channel, is found to strongly depend on the amount of Lithium deposited, decreasing by up to 50% of its no-Lithium value.

NSTX APS-DPP: SD/SMKNov Lithium Evaporation Has Been Used as the Main Wall Conditioning Tool in NSTX Lithium evaporation produced H-mode plasmas with long ELM-free durations in 2008 and 2009Lithium evaporation produced H-mode plasmas with long ELM-free durations in 2008 and 2009 –200 mg of Lithium evaporated between shots –P NB from 2 to 6 MW (H-mode accessible with P loss ~ 0.6 MW with Lithium)

NSTX APS-DPP: SD/SMKNov Lithium Evaporation Led to a Significant Reduction in L-H Power Threshold P LH ~ 2.7 MW NBI without Li evaporation (P heat /n e ~0.9 MW/10 19 m 3 ) ~ 1.4 MW NBI with Li evaporation (0.6 MW/10 19 m 3 ) P LH  n e from HHFW expts Normalize P LH by n e due to density differences between plasmas with and without Li evaporation

NSTX APS-DPP: SD/SMKNov Dual LITERs Replenish Lithium Layer on Lower Divertor Between Tokamak Discharges 4 LITER Canisters Modeled deposition pattern ROTATABLE SHUTTER Electrically-heated stainless-steel canisters with re-entrant exit ducts Mounted 150° apart on probes behind gaps between upper divertor plates Each evaporates 1 – 30 mg/min with lithium reservoir at 520 – 630°C Plumes of lithium vapor are roughly Gaussian in angular distribution Rotatable shutters interrupt lithium deposition during discharges & HeGDC Withdrawn behind airlocks for reloading and initial melting of lithium charge LITERs H. Kugel, L. Zakharov

NSTX APS-DPP: SD/SMKNov Thermal Energy Confinement Increases With Increasing Lithium Evaporation Most pronounced increase of confinement in thermal electrons (broader T e profiles) Over factor of 2 increase in  E,  E,e over full range of Li deposition Strong increase in core metals, P rad losses for Li  250 mg D. Ding, S. Kaye et al., accepted for publicaiton in PPCF, 2009 (Deposition between shots)

NSTX APS-DPP: SD/SMKNov Thermal Conduction Loss Is Dominant for Electron Channel “x” denotes local radial position in terms of (  a ) 1/2 ~ r/a >Electrons >Ions

NSTX APS-DPP: SD/SMKNov Understanding Local Parametric Dependences is Important for Assessing Effect of Li on Local Transport  e exhibits explicit dependence on n  T For constrained n  T range,  e (r/a=0.65) increases with local B pol Discharges with no Lithium wall conditioning I p =900 kA B T =0.48 T P heat =5.6 MW

NSTX APS-DPP: SD/SMKNov Electron Thermal Diffusivity Decreases With Increasing q No Lithium evaporation With Lithium evaporation I p =900 kA B T =0.48 T P heat =5.6 MW Constant, I p, B T

NSTX APS-DPP: SD/SMKNov The Current Profile Plays an Important Role in Determining Profiles and Transport From radial force balance,  p=jxB, can relate n  T ~ j  B p ~j  I px, where j  is local plasma current density and I px is total plasma current contained with the radial position, x

NSTX APS-DPP: SD/SMKNov The Thermal Conduction Loss Does Not Depend on Total Plasma Current For given q, P cond,e the same at different I p Smaller conduction loss for larger -n  T Larger -n  T corresponds to larger j   Smaller conduction loss for larger j  B T =0.48 T P heat =5 – 6.25 MW

NSTX APS-DPP: SD/SMKNov Individual Profiles Indicate The Same Relation Between Transport and Current Profile Lower  e for larger j  I p =0.9 MA B T =0.48 T P heat =6 MW I p =1.1 MA B T =0.48 T P heat = 5-6 MW

NSTX APS-DPP: SD/SMKNov Electron Thermal Diffusivity is Well Fit by j  and I px j  is local current density, I px is plasma current contained within radial position, x  e ~ j  -1.1 I px -0.4

NSTX APS-DPP: SD/SMKNov Strong Decrease in  e With Increased Li Deposition At fixed n  T e (removes variation due to explicit dependence of  e on this parameter) Decrease in  e also coincides with increase in P rad /P tot –P rad /P tot > 15% only for Li deposition > 250 mg (Deposited between shots)

NSTX APS-DPP: SD/SMKNov Higher percentage of  i closer to neoclassical with than without Li Improvement Also Seen in Thermal Ion Transport

NSTX APS-DPP: SD/SMKNov Summary Significant increase of confinement with increasing Lithium evaporation –Mostly in the electron channel Understanding the effect of Lithium on local transport properties involves more understanding of the effect of “hidden variables” –Strong explicit dependence of  e on n  T, which itself depends on local current density, j  –Need to constrain data to understand other trends Strong dependence of  e on B pol, q Significant reduction in electron transport with increasing Lithium evaporation –Parametric trends similar between Li and non-Li plasmas Slight decrease in ion thermal losses with Li evaporation

NSTX APS-DPP: SD/SMKNov Plans for 2010 Installation of Liquid Lithium Divertor (LLD) –Should allow for operation at lower collisionality –Test strong collisionality scaling (B  E ~   1 ) Implementation of BES diagnostic –In addition to high-k scattering, will cover wide range of k-space for turbulence measurements