# Presentation: 275114

## NSTX

*NSTX*

***Supported by   ***

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***TRINITI***
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***ASIPP***
***ENEA, Frascati***
***CEA, Cadarache***
***IPP, J******ü******lich***
***IPP, Garching***
***ASCR, Czech Rep***
***U Quebec***

**Development and characterization of intermediate-****δ**** discharge with lithium coatings**

**Josh Kallman**
*For the LLD Team*

**NSTX Research Forum 2009**
**ASC TSG Meeting**
**December 9**

## In preparation for LLD, the need exists to benchmark a robust discharge that optimizes pumping and performance

**In preparation for LLD, the need exists to benchmark a robust discharge that optimizes pumping and performance**

- LLD will be run with various discharge shapes, providing various degrees of pumping
- High triangularity discharges will be well-characterized in the 2009 run campaign
- strike points on inner divertor, with less pumping from LLD
- Discharges with strike point on bull-nose tile will have lover triangularity and seek to balance pumping and performance
- an intermediate δ (0.55) discharge, such as 115495, will run with the strike point just inboard of the LLD

## In ELM-free discharges, behaviors of plasma density and radiated power over shot duration are still not well understood

**In ELM-free discharges, behaviors of plasma density and radiated power over shot duration are still not well understood**

## LITER investigation of density behavior and radiated power is enhanced by new diagnostics and capabilities

**LITER investigation of density behavior and radiated power is enhanced by new diagnostics and capabilities**

- New diagnostic capabilities will provide more information and insight into mechanism for increased radiated power
- XEUS spectrometer with dedicated operator (J. Clementson, Berkeley grad student) for better time-resolved measurements
- new divertor bolometer channels provide increased spatial coverage
- RMP provides a means for triggering ELMs to study transport, radiated power, and density behavior
- discrete ELM triggering could allow control of density rise and radiated power

## Pre-LLD phase will develop and benchmark LLD-era discharge at intermediate triangularity

- First phase of XP (1 day) will utilize enhanced strike point control to place strike point at R~.63 m
- Establish pre-lithium equilibrium baseline
- determine magnetic configuration and stability
- obtain radiation, impurity, and hydrogenic density evolution profiles with new diagnostics
- Run LITER to suppress ELMs
- adjust fueling as necessary
- comparison to pre-Li baseline in terms of radiation, density, etc
- Introduce ELMs using RMP
- confirm that intermediate δ (0.55) discharge will survive braking introduced by RMP
- can radiation and density rises be mitigated?
- Scan in fueling if time permits

## The LLD and associated diagnostics will provide further capabilities for investigating consequences of lithium-surface divertor

**The LLD and associated diagnostics will provide further capabilities for investigating consequences of lithium-surface divertor**

- The LLD will provide (at least) two significant benefits over LITER only discharges to study reproducibility of lithium effects on density
- persistence: greater volume of Li kept liquid in the LLD will provide longer-lasting pumping ability
- recovery: ability to re-activate passivated surface through HeGDC
- LLD-era diagnostic capabilities will provide more information on plasma conditions that affect density behavior
- high-density divertor Langmuir triple-probe array for edge Te, ne to aid in the modeling of transport, recycling, sputtering yields, etc
- new edge x-ray spectrometer with high spatial resolution to enhance impurity measurement capabilities (LLNL)

## LLD-era component of XP will address results of initial half of XP and will mesh with simulation results

**LLD-era component of XP will address results of initial half of XP and will mesh with simulation results**

- 1 day in FY10 run to compare results under LLD conditions based on suitable strike point control demonstrated in FY09
- strike point could also be swept to take advantage of probe array to determine particle fluxes and SOL parameters
- Presence of high density Langmuir probes and x-ray spectrometer will improve plasma characterization
- will provide more detailed set of data for core and edge transport simulations and improve understanding of plasma-wall interactions

- 0D pumping code (Maingi) shows expected density control from LLD
- goal is highest performance discharge that will permit high LLD pumping (due to strike point proximity to LLD plate)

- Planned LLD position and
- size give ~55% density
- reduction

## Goal is to develop in-depth characterization of intermediate triangularity discharge over lithium PFC development lifecycle

- Emphasis on shot development and documentation to study of evolution of plasma behavior under various lithium PFC configurations
- Once pre-Li baseline equilibrium developed, lithium introduction (LITER) will show worst-case density/impurity/radiation evolution once ELMs are suppressed
- utilize RMP and fueling to control discharge evolution
- In LLD regime, reproducibility will be tested and new physics examined utilizing new control and diagnostics tools
- investigation into late-discharge behavior (acceptable radiation and density levels) with more durable lithium configuration
- study of physics results with new diagnostics improved modeling