# Presentation: 084065

##                                            Supported by   

**H. W. Kugel****, PPPL**
*For the NSTX Research Team*

**NSTX 5 Year Plan Review for 2009-13**
**Conference Room LSB-B318, PPPL**
**July 28-30, 2008**

***College W&M***
***Colorado Sch Mines***
***Columbia U***
***Comp-X***
***General Atomics***
***INEL***
***Johns Hopkins U***
***LANL***
***LLNL***
***Lodestar***
***MIT***
***Nova Photonics***
***New York U***
***Old Dominion U***
***ORNL***
***PPPL***
***PSI***
***Princeton U***
***SNL***
***Think Tank, Inc.***
***UC Davis***
***UC Irvine***
***UCLA***
***UCSD***
***U Colorado***
***U Maryland***
***U Rochester***
***U Washington***
***U Wisconsin***

***Culham Sci Ctr***
***U St. Andrews***
***York U***
***Chubu U***
***Fukui U***
***Hiroshima U***
***Hyogo U***
***Kyoto U***
***Kyushu U***
***Kyushu Tokai U***
***NIFS***
***Niigata U***
***U Tokyo***
***JAEA***
***Hebrew U***
***Ioffe Inst***
***RRC Kurchatov Inst***
***TRINITI***
***KBSI***
***KAIST***
***POSTECH***
***ASIPP***
***ENEA, Frascati***
***CEA, Cadarache***
***IPP, J******ü******lich***
***IPP, Garching***
***ASCR, Czech Rep***
***U Quebec***

**                                           ****Supported by   **

## Motivation for NSTX Lithium Research

- • NSTX research with solid lithium is aimed initially towards using liquid  lithium to control density, edge collisionality, impurity influxes, and  eventually power handling.
*- Solid Li provides short pulse capability but can saturate; liquid Li has much**  higher LiD capacity, and has potential for power handling and self healing.*
- • Over the longer term, NSTX will investigate if liquid lithium can help  integrate 4 important potential benefits for fusion
-        a. Divertor pumping over large surface area compatible with high           flux expansion solutions for power exhaust and low collisionality
- b. Improved confinement (reported in FY08)
- c. ELM reduction and elimination (reported in FY08)
- d. High-heat flux handling (via capillary flowing Li, swirl tubes,      hypervaportrons, evaporative cooling)

## NSTX Has a 3 Phase Lithium Plan

- • The 3 Phase NSTX Lithium Plan for Particle Control and Power Handling is moving aggressively toward the 3rd Phase:
*      **I. Lithium Injection Experiments (2005-2008)**	*
*	*• Li pellet injection: 2-5 mg pellets, on graphite divertor (2005)
- • Li powder tests: 50 m Li powder on graphite divertor (2007-2008)
*     **II. *_*Lit*_*hium *_*E*_*vaporator  [LITER]  (2006-2009)*
*	*• 1 LITER: deposition on graphite divertor (2006-2007)
- 	• 2 LITER: deposition on graphite divertor (2008)
- 	• 2 LITER: deposition on graphite and LLD-1 (2009-2010)
*     **III. Liquid Lithium Divertor [ SNL - NSTX Collaboration] (2009-2013)*
*	**• **LLD-1: Li evaporated on thin porus Mo/SS on Cu baseplate*
* **	**• **LLD-2: Li capillary flow to load a Mo mesh surface over wider area *
*	**• **LLD-3: long pulse (5s) power handling capillary surface with active cooling**                            *(via capillary flowing Li, swirl tubes, hypervaportrons, evaporative		cooling) *for high-power 16 MW (10 MW NBI + 6 MW RF) operations*

## Liquid Lithium Divertor Physics Design Goals

- • Physics Design Goals
-    1) LLD-1: Achieve density control for increased neutral beam current                    drive capability in the range (from recent simulations):
-  ne ~ 5 x1019 m-3 at IP = 750 kA
-  (15-25% ne decrease from present exps)
-  highest non-inductive fraction discharges presently    often evolve toward ne/nGW 1
-    2) LLD-2: Enable ne scan capability in long pulse H-mode (e.g.,~ x2)
-                    by varying lithium thickness
-  Increase filling rate (e.g. capillary flow, powder dropper) to wider    area mesh surface
-  Test ability to operate at significantly lower density
-  NHTX (ne/nGW = 0.5) and ST-CTF (ne/nGW = 0.25)
-    3) LLD-3: Investigate LLD with long-pulse (5s), high heat flux for
- 	      16 MW (10MW (2 NBI) + 6 MW RF) power handling capability

## LLD-1 Plate Design With Thin Lithium Film on High-Z  Bonded to Copper is Highest Confidence Approach

- • Each toroidal section electrically grounded to vessel at one mid-segment location  to control eddy currents
- • Each toroidal section fastened at 4 corners to divertor copper baseplate with   fasteners providing structural support, electrical isolation, and accommodating   thermal expansion (design adopted from JET PPPL collaboration)
- • Narrow graphite tile  transition regions between sections contain thermocouples,   an array of Langmuir probes, and magnetic & current sensors

- • _Location_  - lower outer divertor in four 90°sections.
- • _Width_ 	  - 20 cm starting 5 cm outboard of CHI gap.
- • _Shape  __	_  - replaces present graphite tiles.
- • _Structure_  - 0.01cm Mo flame-sprayed on 0.02 cm SS    	     brazed to 1.9 cm Cu. Resistive heaters 	     and cooling lines maintain 200-400°C.
- • _Li Loading_ - 2 lithium evaporators.

## Particle Balance and Recycling Model Used to Estimate 0-D LLD-1 Pumping Projections and Sensitivities

- R.Maingi, ORNL

- (V. Soukhanovskii, LLNL)

- Li surface particle sticking probability - 0.85

- (LLD)

- * Red items estimated from CCD camera data

- _Iterative Procedure_
- • Convert measured D luminosity to particle flux using 20 ionizations per photon
- • Estimate LLD-1 flux intercept fraction from candidate discharge data for  a given time slice
- • Vary RLLD in steps of 1 cm
- • Repeat for different WLLD, RP CORE  and other input parameters

## NSTX Data Used to Enable Analysis of Expected Performance of LLD-1 for Low δ Plasmas

**R. Maingi ORNL**

**Low ******** : reduce n****e**** by 50%**

**CHI gap**

**LLD**

- Density
- Reduction

**10cm**
**15cm**
**20cm**

- Shown for different LLD-1 widths

**R=0.65**

**R=0.84**

## Pumping by LLD-1 20 cm Wide on Outer Divertor Will Provide Density Control for Inner Divertor Broad SOL Dα Profile High δ Plasmas

**High ******** : reduce n****e**** by 25%**

- • Density reduction will depend on proximity of outer strike point to LLD-1

**20cm**

**15cm**

**10cm**

**R. Maingi, ORNL**

- Soukhanovskii LLNL

- Shown for different LLD-1 widths

- Density
- Reduction

## LLD-1 Design Derives from Extensive International Liquid Lithium R&D 

- • Lithium surface tension forces in capillary media (metal wire meshes, metal felts, sintered metals, flame-sprayed porous metals) have been shown to form, control, confine, and redistribute liquid Li uniformly over plasma-wetted surface in presence of JxB forces, gravity, and thermal gradients.
- No thermal induced cracking in lithium filled medium
- No fatigue
- No radiation swelling
- Exiting flows can remove codeposition
- Continuous flow provides replenishment during erosion
*Provides recycling control*
*Provides impurity control*
*Provides low collisionality edge conditions *
*Maximum allowable incident heat fluxes >100MW/m**2*
- Examples: Mo wire meshes [T-11, FTU], flame-sprayed porous Mo [LTX]
- LLD-1 design and plans are following an integrated R&D approach

## Integrated Approach: LTX R&D Aiding in Performance Projections and Design of NSTX LLD-1

- • LTX is preparing to begin lithium operations
- Recycling on liquid Li at more relevant edge parameters than CDX-U
- Test plasma fueling w/ gas puffing, jets when recycling particle source is small
- Examine Li sputtering w/ hotter edge
- • LLD-1 relevant lithium wall implementations
-   developed for LTX
- NSTX & LTX have been working closely with Sandia to determine LLD-1 design for operations in FY09
- Flame-sprayed porous Mo adoptedfor NSTX LLD-1 capillary surface

- Candidate LLD-1 porous molybdenum surface -
- Originally developed for 2nd LTX shell (Phase II SBIR w/ Plasma Processes, Inc.)

- R. Majeski, R.Kaita

***Solid Li melting***

***Liquid Li flowing ******over porous Mo***

## NSTX-SNL Collaboration Has Considered Two Candidate Surfaces for LLD-1

- • Two candidate Li surfaces have been under investigation
-       1) Thin flame sprayed porous Mo, on thin SS on thick Cu baseplate is            highest confidence initial approach
-          	- LTX style plate (tested offline)           	   (prepared by Plasma Processes Inc.)
-  Experiments and simulations of LLD-1 behavior  (porousity, gravity, thermal, JxB forces) in progress (N. Morley, UCLA)
-        2) Chemical vapor deposited Mo on vitreous carbon mesh
- 	- under investigation at SNL (not tested; testing planned) 	   (prepared by Ultramet Inc.)

- • Key properties for an acceptable LLD-1 lithium surface
-        - ability of liquid Li to flow across a metal surface (wetting capability)
-        - minimize temperature rate of rise of Li  rapid heat transfer         					           from Li to baseplate

## Plasma Facing Views of the Basic LLD-1 Copper Plate Substrate

- GRAPHITE DIAGNOSTIC TILES

- 4 Toroidal 90° segments separated by graphite Diagnostic Tiles

## LLD-1 Operation Requires Additional Diagnostics for NSTX Control and Characterization for Step Devices

*• **Each  LLD-1 90° segment has control and monitoring sensors:*
-  12 thermocouples embedded in the heaters for monitoring heater limits
-  12 thermocouples embedded in copper baseplate for monitoring heat transfer
-  2 strips of 4 thermocouples each for torodial and radial temperature variations
-  1 center post halo current Rogowski for monitoring JxB effects
*• **Each set of inter-segment graphite tiles has diagnostic sensors:*
-  Bay H: existing 2D magnetic sensor array and 2 thermocouples
-  Bay B: 120 LP array with some UIUC signal conditioners for triple probes
-  Bay E and Bay K: 2 biased electrodes, 5 LP, 1 thermocouples
*• **External Diagnostics:*
-  Bay H: Slow IR camera,  Bay E: Fast IR camera
-  Bay G: Lyman- Diode Array for recycling measurements at the LLD-1              highly reflective liquid lithium surface

## LLD-1 Li Surface Will Be Supplied Using the 2 LITER Units

**• ****LITER central aiming axis to graphite divertor and gaussian angle at 1/e (dashed)**

**• ****Photo of LITER on probe & loaded    with Li under argon**

**LLD-1 Li Surface Will Be Supplied Using the 2 LITER Units**

**LLD-1**

## Dual LITER System Used Routinely as a New Operational Capability for Establishing Lithium Wall Conditions 

- In recent experiments, the dual LIThium EvaporatoR (LITER) evaporated 120g of Li into NSTX (+60 g on LITER shutters)
- The LITERs deposited lithium on the lower divertor target for 10 min, at combined rates of 10-70 mg/min
- Prior to each discharge, the LITERs were withdrawn behind shutters
- If HeGDC was applied, the shutters remained closed
- The shutters were then reopened as soon as the diagnostic window shutters closed, and the deposition cycle repeated
- Became routine operational tool used to establish lithium wall conditions 	• used for many FY08 experiments; the next slides       show some of the initial results.

## Stored Energy (WMHD) Increases After Li Deposition Mostly Through Increase in Electron Stored Energy (We)

**M. G. Bell**

## Solid Lithium Surface Coatings Increase Confinement, Stored Energy, and Pulse Length

- •	Comparison for pre-Li and post-Li reference shots with constant NBI, constant external gas, etc.
- •	Lithium (188 mg) reduced density in initial period up to 0.6s
- pre-Li discharge was ELMy
- ELMs were absent on Li shot
- •	In time, the lack of ELMs causes the density in the discharge with Li to overtake the shot without Li.

**R. Maingi, ORNL**

**Li**

**No Li**

## ELM Suppression by 5th Discharge With LiNo ELMs   Immediate Increase in Stored Energy

*** D. Mansfield, PSI08, O-28**** **

- As Li increases
-  ELMs decrease
-  Stored energy increases
-  Pulse lengthens
- • At higher Li evaporation rates and higher PFC accumulations, complete ELM suppression occurs   higher confinement*

## Lithium Edge Conditions Require Large Fueling Increases to Maintain Density

**M. G. Bell**

## LITER Technical Success Demonstrated by Initial Results of Evaporated Lithium Surface Coatings

- The effects of the active lithium surface coatings on standard discharge scenarios include:
- Reduced plasma density in the early phase of the discharge
- Suppression of ELMs
- Improved energy confinement
- Reduced flux consumption and increased pulse length for standard, high-triangularity discharges
- Reduced HeGDC time between discharges to maintain the H-mode
- Increased pedestal electron and ion temperature
- Reduced SOL plasma density and edge neutral density
- Discharges after lithium also benefited from n=1 and n=3 mode control by the external non-axisymmetric coils to reduce deleterious MHD activity.

## LLD-1 Will Be Loaded With Lithium Using LITER

**• **_**LITER Deposition Capability**_
**- for LLD-1 to pump NSTX  plasma from  7x10****13**** cm****-3**** --> 5 x10****13**** cm****-3  ****will require the absorption of 2.4 x 10****20**** D particles, every particle confinement time (~ 50 ms), for 1000 ms, for a total of 4.8 x 10****21**** D particles absorbed. **
**- for a  1:1 D/Li ratio requires at least 5.5x10****-2**** g of lithium (2 ********m). **
**- present LITER deposition efficiency on to LLD ~ 7% of it total output, then the total lithium need is 0.79 g.**
**- using two evaporators at 30 mg /min (FY07 typ) will require about 13 min to coat the LLD-1. **
**- if lower concentration ratio 0.1D/Li is required, then need 7.9 g of lithium (20 ********m), or 4 g per LITER, operating at 100 mg/min for 40 min**.

## New Li Powder Injection Capability Will Be Tested Offline for Potential for Reloading LLD-1 Prior to Discharges

***    *****VELOCITY AT SOL = 4.5 m/s**

- Li powder injected during breakdown and early in discharge reaches lower divertor
- Recent initial results indicate Li powder (50 m) injected early in discharge yielded higher, and broader temperature profiles earlierin the  discharge

**D. Mansfield DPP, APS, 2008 **

- Laboratory experiments are planned to test if this new capability for present discharges can be used to reload the LLD-1 _prior to a series of discharges_

## NSTX Will Test the Potential Benefits of Liquid Lithium Divertor for Integrating High Plasma and PSI Performance

- • LLD-1
-              *• **The Outer Divertor is the initial lowest technical and programmatic risk    **                location for LLD-1 to the high performance, high **** ST research program *
-             • LLD-1, 20 cm wide pumping on Outer Divertor provides reduction in 	 density for increased neutral beam current drive capability
- • LLD-2
-             • Enable ne scan capability in long pulse H-mode
- 	   - Increase filling rate ( powder, capillary) to wider area Mo mesh surface
- 	   - Test ability to operate at significantly lower density (NHTX, CTF)
- • LLD-3
-              • Investigate power handling for long-pulse with high heat-flux
**	****   ***- long pulse (5s) power handling surface with active cooling **                   (capillary flows,swirl tubes, hypervaportrons, evaporative cooling) for **	**	**     16 MW (2NBI + RF) operation*
- 	   - Higher lithium fill rates (capillary flow replenishment planned for FTU)

- • LLD-1 Status
- Final Design Review successful. Final drawings submitted by SNL for procurement.
- Successful CDR for LLD-1 Diagnostics.  LLD Controls FDR scheduled for Sept.
- Planning to complete installation in 2008 for FY09 operation.

## Backup

## Bottom View of LLD-1 Copper Substrate Plate Showing Controls and Sensors

**• ****12 heaters (240v) each with embedded TC for monitoring heater limits**
**• ****12 TC embedded in copper baseplate for monitoring heat transfer **
**• ****2 strips of 4 TC each for monitoring torodial and radial temperature variations**
**• ****1 Center post halo current Rogowski coil for monitoring JxB effects**

**GAS COOLING LINE**

**SINGLE POINT GROUNDING WITH ROGOWSKI HALO CURRENT SENSOR**

**THERMOCOUPLE  NEAR EMBEDDED HEATER FOR CONTROL**

**ELECTRICALLY ISOLATED SUPPORTS ACCOMMODATE THERMAL EXPANSION**

**4 THERMOCOUPLE ARRAY,  2 TORIDAL LOCATIONS**