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Lithium Walls: The Ultimate Technology for Fusion. D.N. Ruzic, M. A. Jaworski 1 , T.K. Gray 1 , V. Surla, W. Xu, S. Jung, P. Raman 1 current address: Princeton Plasma Physics Laboratory. Outline. Introduction Why Lithium is so Good – but you all know that already !

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Lithium walls the ultimate technology for fusion

Lithium Walls: The Ultimate Technology for Fusion

D.N. Ruzic, M. A. Jaworski1, T.K. Gray1, V. Surla,

W. Xu, S. Jung, P. Raman

1current address: Princeton Plasma Physics Laboratory


Outline

Outline

  • Introduction

    • Why Lithium is so Good – but you all know that already !

  • Solid/Liquid Lithium Divertor Experiment (SLiDE)

    • Experimental Facility

    • Results

    • Theory

  • Lithium Molybdenum Infused Trenches (LiMIT)

    • - How this could work for HT-7 and future devices

  • Lithium in Divertor Erosion Vapor Shielding Exp. (DEVeX)

  • Lithium in the Ion-Interaction Experiment (IIAX)

  • Conclusions


No cold hydrogen returns from wall plasma stays hot

What Very-Low Recycling Does for Fusion

No cold hydrogen returns from wall: Plasma stays hot

Standard Case

Lithium Case

Courtesy: PPPL


Consequences of lithium

Consequences of Lithium

  • Increased Confinement Time – seen across the world

  • Higher Temperatures

  • Suppression of ELMS (for tokamaks)

  • Control of Density is possible, even with NBI

  • Lower Z-effective

  • Less Fuel Dilution (seen on NSTX)

    • Negative Consequences?

  • Helium pumping? We have shown this!

    M. Nieto, D.N. Ruzic, W. Olczak, R. Stubbers, “Measurement of Implanted Helium Particle Transport by a Flowing Liquid Lithium Film”, J. Nucl. Mater., 350 (2006) 101-112.

  • Power handling? See the rest of this talk!


Lithium walls the ultimate technology for fusion

First Evidence? TFTR Supershots(1984)

Courtesy: PPPL


What can go wrong with a lithium divertor

What Can Go Wrong with a Lithium Divertor?

  • Lithium melts at 180 C and evaporates very quickly above 400 C

    So, it will have to be used ultimately as a flowing liquid

  • It is a liquid conductive metal and therefore subject to MHD effects. After all, fusion devices have large circulating currents and high magnetic fields.

    So, careful planning is needed. Maybe it’s MHD effects can be utilized?

  • It has an extremely low density (half of water) and high surface tension (4 times water) and therefore difficult to deal with. It is also highly corrosive to some materials, such as copper.

    So, careful engineering is needed and new materials (for fusion) need to be developed


Outline1

Outline

  • Introduction

    • Why Lithium is so Good – but you all know that already !

  • Solid/Liquid Lithium Divertor Experiment (SLiDE)

    • Experimental Facility

    • Results

    • Theory

  • Lithium Molybdenum Infused Trenches (LiMIT)

    • - How this could work for HT-7 and future devices

  • Lithium in Divertor Erosion Vapor Shielding Exp. (DEVeX)

  • Lithium in the Ion-Interaction Experiment (IIAX)

  • Conclusions


Cdx u results the unexpected happened

CDX-U Results - The Unexpected Happened

Surface tension drives flow

Qinput

Centerstack

Lithium in tray

Visible image

R. Majeski et al., “Final results from the CDX-U lithium program,” Presentation at 47th Annual Meeting of the Division of Plasma Physics (APS-DPP), Denver, Colorado, October, 2005.

  • Trying to melt lithium in CDX-U:

    • - 50 MW/m2heat flux redistributed from spot heat

    • - No evaporation despite lithium's tendency to do so (and purpose of e-beam run!)‏

  • Why did the lithium melt the entire tray and not evaporate?

    • - First explanation was thermocapillary phenomena

    • - Temperature dependent surface tension resulted in flow and strong convection away from hot spot

    • - If true, will this work in a divertor without over heating the Li ?


A typical fusion heat flux

A Typical Fusion Heat Flux

J.N. Brooks, et al. J. Nucl. Matl.337-339 (2005) 1053-1057.

  • Magnetic configuration concentrates power in “diverted” plasma

    • -Peak heat flux, steady-state typically 5-20 MW/m2

    • -Radiant heat flux at solar surface is ~63 MW/m2

    • -Transients can push the peak higher

  • Thermally driven phenomena depend on heat flux gradients, not just peak values


Slide at illinois overview

SLiDE at Illinois - Overview

E-beam source

10cm

25cm

Current density profile

10cm

10cm

Tray

  • Solid/Liquid Lithium Divertor Experiment (SLiDE)‏

    • - Produces temperature gradients with an electron beam

    • - Creates magnetic field with external magnet system (these tests at normal incidence)‏

    • - Measures temperature distribution in tray containing lithium

    • - Active cooling for steady-state operation

    • Camera system monitors surface velocity

  • Designed, constructed and operated for this work


Machine layout

Machine Layout

  • A sheet electron beam hits an instrumented tray filled with lithium in a magnetic field.

  • Future versions will allow the tray to tilt so the angle between the heat flux and the field will be like in a tokamak – almost parallel.


Electron beam drawings and simulations

Electron Beam Drawings and Simulations

There are four filaments, each 10cm long, parallel to eachother

7 keV, 2 A, 16 G

20 keV, 0.75 A, 1 kG


Electron beam

Electron Beam

  • Designed to mimic divertor heat flux

    • - Actual run parameters shown in table

    • - Operated at 300W in this set of experiments – capable of 15kW, which is 35 MW/m2 !

    • - Typical q0 in NSTX is ~10MW/m2

    • - Typical dq/dx in NSTX is ~100 MW/m2-m . We matched this number.

  • Line source with gaussian profile


Tray system overview

Tray System Overview

  • Coolant supplied from building sources

    • - Water at 35 psi

    • - Compressed air at 80 psi

    • - Steady-state cooling with liquid lithium temperatures and input power range of 50W – 1500W (with stainless steel tray)‏

  • 28 thermocouples within tray

    • - 14 positions for heat flux modeling

    • - 4 external TCs for coolant calorimetry


Data acquisition and control

Data Acquisition and Control

  • Thermocouple data acquired via computer system

    • - LABJACK USB data modules and amplifiers digitize analog signals. LabVIEW VI monitors temperatures in real time

    • - Control of magnets and eBeam voltage via computer system (filaments on manual)‏

  • Post-run analysis handled semi-autonomously

    • - Analysis program written to reference and analyze data sets

    • - Output summarizes and formats for easy plotting and further analysis


Camera system

Camera System

  • Mirror used to view lithium surface

    • - Electron beam occludes direct view

    • - Mirror requires periodic cleaning from lithium evaporation

  • Two cameras used

    • - Low quality webcam for simple monitoring

    • - High quality, high-definition camera used for velocity measurement movies

    • - Both utilize mirror illumination provided by electron beam filaments


Thermocapillary flow basics

Thermocapillary Flow, Basics

Thermocapillary

- “Thermo” meaning temperature

- “Capillary” meaning related to surface tension

- Temperature gradient on surface of a liquid creates surface tension gradients

- Surface tension gradients result in flow generation

Long history of study from mid-19th century

Surface tension drives flow

Qinput

  • Other surface tension driven flows

    • - “Tears” or “legs” in wine glass (concentration gradients from alcohol evaporation)‏

    • - Soap boats with detergent droplet (concentration gradient)‏


Thermoelectric mhd basics

Thermoelectric MHD, Basics

  • Thermoelectric effect

    • - Causes thermocouple junction voltages

    • - Thermoelectric power present in most materials

    • - Electromotive force generated by temperature gradients

    • - Requires different material (or TE power) to provide current return path and generate current

  • Replace one material with a liquid in magnetic field

    • - TE current and B-field generate Lorentz foce


Theory tcmhd and temhd

Theory: TCMHD and TEMHD

Thermocapillary and TEMHD produce different flow patterns

TC forces act parallel to surface gradients in surface tension – force vectors radiate away from heat stripe (induce poloidal flow)

TEMHD forces are produced in the bulk lithium due to gradients at the lithium-steel interface

TE current the same process as produces voltages in thermocouple junctions

Cross-product of JTEMHD and B results in azimuthal flow

Beam generated forces (JxB) also result in an azimuthal flow (current converges into impact point) – sense of rotation is opposite of TEMHD

Increased field damps both flows

TCMHD is damped byB-2

TEMHD is damped as B-1 at high fields (due to thermoelectric propulsive force)

Thermocapillary force vectors.

TEMHD current diagram.


Is it really temhd qualitative tests

Is it really TEMHD? Qualitative Tests

  • Magnetic field reversal

    • - Flow direction reverses upon reversal of field

    • - Flow is consistent and steady in swirl

  • Flow direction consistent with TEMHD source

    • - Mirror system reverses apparent sense of rotation

    • - Magnets measured to determine direction

    • - E-beam and TE have opposite rotation senses

  • Addition of insulator halts any swirling flow

    • - Quartz slides added between tray and lithium

    • - No flow observed at all in these cases


Another test spin down

Another test: “Spin Down”

Test based on the time required for the lithium to come to a stop

Viscous damping brings fluid to a rest without additional forces to maintain flow (seconds)

Magnetic fields enhance the destruction of kinetic energy and spin down faster (confirmed with a mercury test)

If thermoelectric currents exist, these will decay at the thermal time constant of the lithium-tray system (minutes)

Maintaining the magnetic field will sustain the flow, as opposed to damping it

Turning magnetic field back on after a viscous spin-down should induce motion once more

Test procedure:

  • Obtain steady thermal conditions and lithium flow

  • Shut off beam and magnetic field and measure spin-down time

  • Return system to steady thermal conditions and lithium flow

  • Shut off beam but maintain magnetic field – measure spin-down time

  • Repeat step 2, but turn magnetic field back on after flow comes to rest and look for spin startup

Movie of spin-down test

“spinDown.mov”


Quantitative analysis velocity

Quantitative Analysis: Velocity

  • Purpose: Bring together thermal and velocity measurements

  • Velocity measurements based on video analysis

    • - Particles measured on a frame-by-frame basis

    • - Multiple measurements made over course of particle visibility

    • - Radial distance also measured

  • Velocity and radius used to determine most likely velocity at r = 1cm

    • - u(r) ~ r0.5 based on Davidson swirling flow theory

    • - Consistent with SLiDE data


Heat flux calculation

Heat Flux Calculation

  • Time series data reduced

    • - Mean taken

    • - Standard error calculated by standard formulas

  • Fourier model applied to calculate heat flux

    • - Scaling factor applied to account for tray warping

    • - Radially symmetric pattern observed

    • - Most obvious in “off-center” sensor sets

    • - Radially symmetric pattern observed in all cases run

    • - Some TC pairs eliminated due to tray damage directly underneath beam strike


Quantitative prediction temhd

Quantitative Prediction: TEMHD

Moderate Hartmann number regime – TEMHD and MHD braking in equilibrium

Dependent on thermoelectric power of the metal pair, P

Temperature gradient along the interface determines flow velocity (for Ha > 1)

Mean current density due to TE currents depends on geometry and conductivities (C variable)

Velocity prediction can be converted to Reynolds number using depth as the characteristic length scale

1D current driven flow in a semi-infinite domain.


Temhd solution 1 semi infinite domain

TEMHD Solution 1: Semi-Infinite Domain

  • Solution for free surface

    • Identical to Shercliff, 1979 channel flow

    • Lithium-Iron example: P = 20e-6[V/K], h=5[mm], dT/dy = 1000[K/m]

    • Pre-factor = 8.4[m/s]

  • Solution depends on several factors

    • Hartmann again present

    • “C” is ratio of liquid/wall impedances

    • “Pre-factor” and velocity function {...}


B dewadt hartmann flow

Bödewadt-Hartmann Flow

  • Bödewadt flow

    • - Rotating fluid over stationary disk

    • - Variation of Karman flow (rotating disk)‏

    • - Use Karman similarity variables to analyze

  • Bödewadt-Hartmann flow

    • - Rotating flow with a magnetic field

    • - Non-dimensionalized system of equations results

  • Elsässer No. - Balance of MHD to Coriolis force


Approximate solutions for velocity profile

Approximate Solutions for Velocity Profile

  • Make use of Davidson, 2002 approximate solutions

    • Linearized equations about core flow solution

    • Compares well with direct numerical integration

    • Aids further analysis

Distance from wall


Quantitative assessment consistent with data

Quantitative Assessment --- Consistent with Data

  • Theory of TEMHD driven swirling flow predicts radial velocities -- agrees with data ! No free parameters

  • Range of Hartmann number covers peaking area of swirling flow theory

  • Range of Elsässer number covers MHD and Coriolis dominated flows

  • Torque balance method works ! TEMHD fits observables.


Spin down time constant also consistent

Spin Down Time Constant – Also Consistent

  • Spin down time requires thermal gradients to sustain currents

  • Thermal time constant of the system can be estimated

    • - Simple thermal resistance model applied

    • - Measurements from the system used to make calculation

    • - 78 seconds is theoretical thermal time constant

  • Observed spin down time is equivalent to 2-3 thermal time constants – and that is what is observed.


Quantitative prediction thermocapillary mhd

Quantitative Prediction: Thermocapillary MHD

  • Consider a semi-infinite domain

    • - Free-surface at y=h

    • - Magnetic field B

    • - Surface subject to constant temperature gradient b

  • Two cases

    • - No return flow (dP/dx = 0)‏

    • - Return flow (dP/dx related to height of the fluid)‏

  • Surface tension boundary condition

    • - Surface tension gradient results in viscous shear at surface


Which one does theory say is dominant ratio of semi infinite solutions

Which one does theory say is dominant?Ratio of Semi-Infinite Solutions

  • Ratio of TEMHD to TCMHD velocity:

    • - Ratio = 1 indicates equal effectiveness

    • - Ratio > 1 indicates TEMHD dominance

    • - Ratio depends on material parameters capture by dimensionless number, ς, the “Jaworski” number.

    • - Also depends on container geometry captured in F(Ha) function

  • In Lithium-steel system, TEMHD dominates for Ha > 1


Ratio of temhd to tc in slide

Ratio of TEMHD to TC in SLiDE

  • All quantitative data cases show evidence of swirling flow.

    • - TEMHD indirectly shown for Ha>1.4 by temperature

    • - TEMHD directly shown for Ha>17

  • However, TC was capable of being seen in an oscillatory flow behavior.

    • TEMHD flow distributes heat and smooths out the gradient along the Li – steel interface

    • With no gradient there, only the surface temperature gradient exists, therefore TCMHD until interface gradient builds up again

Jaworski Number was always greater than 1 !


Can you see tcmhd in the lulls

Can you see TCMHD in the lulls?

  • If conditions are right, when the TEMHD flow stops, TCMHD “Maragoni-effect” flow can be seen (motion on surface away from heated stripe due to surface temperature gradient causing a surface tension gradient)

If conditions are right, when the TEMHD flow stops, TCMHD “Maragoni-effect” flow can be seen (motion on surface away from heated stripe due to surface temperature gradient causing a surface tension gradient)

TCflowExample.mov


Outline2

Outline

  • Introduction

    • Why Lithium is so Good – but you all know that already !

  • Solid/Liquid Lithium Divertor Experiment (SLiDE)

    • Experimental Facility

    • Results

    • Theory

  • Lithium Molybdenum Infused Trenches (LiMIT)

    • - How this could work for HT-7 and future devices

  • Lithium in Divertor Erosion Vapor Shielding Exp. (DEVeX)

  • Lithium in the Ion-Interaction Experiment (IIAX)

  • Conclusions


Lithium walls the ultimate technology for fusion

39

How Powerful is the ThermoElectric Effect?

Apparatus for Seebeck Coefficient

Apparatus for Seebeck Coefficient Measurement

DV

T + DT

T

Lithium Extrusion

HEATER


Big use it with what holds the lithium

Big! Use it with what holds the Lithium

There is a large difference in S between Li and most other metals and it increases with temperature.[3]

  • Like a thermocouple, a voltage is created at a junction of two metals dependent on the temperature.[1]

  • A current will flow based on that voltage difference:

    where σ is the conductivity, and ΔS is the difference in Seebeck coefficients.[2]

Seebeck Coefficient of Li

Black: our measurementsLithium

Lithium

j

Molybdenum

j


Does it work yes slide results

Does it work? Yes! SLiDE Results

  • As I showed previously, TEMHD is real and moves Lithium at significant velocities.

Theoretical vs experimental velocities :

[4] M.A. Jaworski, et al. Phys. Rev. Lett. 104, 094503 (2010)


The idea limit design

The Idea: “LiMIT” Design

HT-7 Cross-section:

  • Left is a cross-section of HT-7 showing the toroidal limiter.

  • Right is the LiMIT concept: molybdenum tiles with radial trenches containing lithium. The trenches run in the radial (polodial) direction such that they lie primarily perpendicular to the torroidal magnetic field.

Plasma primary heat-flux location


Lithium flow in the trenches is self pumping

Lithium Flow in the Trenches is Self-Pumping

Heat flux

Hot

Li flow

Cooling channels

Outlet

Inlet

Passive Li replenishment

The top surface of the Li is hotter than the surface that is deeper. Therefore there is a VERTICAL temperature gradient

  • Concept for heat removal using TEMHD. The Li flows in the slots of the Mo plate powered by the vertical temperature gradient. This vertical temperature gradient generates vertical current, which when “crossed” by the torroidal magnetic field, will create a radial force on the Li driving it along the slot. This flow will transfer the heat from the strike point to other portions of the torroidal limiter. The bulk of the Mo plate could be actively cooled for a long-pulsed device or passively cooled for something like NSTX. Under the plate the Li flows back naturally.

J

F

B


Thermoelectric driven flow calculation

Thermoelectric Driven Flow Calculation

Heat flux: divertor strike point width, 1cm

Z direction

t

w

Flow

h

Grad T

TE current

B

L

  • Look just at one channel. All channels are equivalent

  • The width of Li (w) is 1mm and the width of the Mo (t) trench is 1mm. The depth of Li (h) is 5mm. The length of the Li (L) is 100mm. The magnetic field is 2T. The heat flux on top surface isThe unit for heat flux is MW/m2 and the unit for x is m. (based on the formal HT-7 heat flux data)

This represents the divertor heat flux maximum value for the calculations here, but the concept should work for even higher values..


Heat flux on the limiter along radius direction

Heat flux on the limiter (along radius direction)

The heat flux figure is from F. Gao et al. Fusion Engineering and Design 83 (2008) 1–5

6 MW/m2 on our geometrical segment is 960 W


Heat load on limit what velocity is needed

Heat load on LiMIT: What Velocity is Needed?

  • The assumed heat flux means the 1mm Li slot needs to handle 960W heat load.

  • To put this in the proper perspective, the temperature rise over the 5 second shot of an uncooled one-half inch thick (1.2cm) Mo plate the same size as our imagined Li/Mo trench/finger can be calculated using as follows: E = 960W*5s = 4800 J. V = (0.2cm)(1.2cm)(10cm) = 2.4 cm3Cv=2.57 J cm-3 K-1 for Mo. Therefore the temperature rise for a passive plate is 778K.

  • To see if a flowing surface can remove that much power with a lower temperature rise, we can use the following equation [5] :

  • Here the first term is the heat conduction term and the second is the heat convection which transfers the heat along the trench. ΔT+ is the temperature difference across the depth of Li and ΔTll is the temperature difference between the inlet and outlet of the Li trench. When using the HT-7 heat flux data, and both temperature differences are assumed to be 200K, the velocity needed is u=35.2cm/s.With this flow the temperature rise would only be 200K.


What velocity is generated by temhd

What Velocity is Generated by TEMHD ?

  • The Seebeck coefficient for Mo is about 13μV/K (at 400C). The value for Li reported in the literature and measured ourselves is 43μV/K (at 400Cfor a difference of 30μV/K

  • The current and velocity can be calculated with these two equations

    [1]

    [1]

  • Here P is the difference of Seebeck coefficient (thermoelectric power) between two material. Ha is the Hartmann number . C is a parameter coming from the conservation of current:

  • The velocity with a higher thermoelectric power is 59.6 cm/s. This is large enough to carry away the heat and prevent the Li from getting more than 200C hotter than when it came in.


Further analysis 3d fluent calculation

Further Analysis: 3D – FLUENT Calculation

Mo plate

Li channel

6MW/m2 heat flux

Back flow of Li

  • What will really happen to the temperature of the Li when the strike point heat flux hits LiMIT? Is the 200K gradient assumption reasonable? A simple 3D heat transfer model is run with FLUENT.

  • FLUENT has convection flow and 3D heat transfer included.

  • Boundary Conditions: The Li flows through the slot between two Mo plate and flow back below the Li slot. The inlet velocity is set to be 60 cm/s. The initial temperature is 470K. The top heat flux is that on HT-7. The bottom temperature is set to be 470K as a constant. Will we remain under 670K as the one-D calculation indicated?


Answer yes

Answer: Yes !!!!

  • Left figure is the temperature distribution of the top surface of Li slot and right figure is the temperature change along the center line of the top surface.

  • The temperature difference between the inlet and the outlet is about 200K– great! The highest temperature is 691K (418C). There will be evaporation there – which gives additional cooling not included in the model. Some evaporation (radiative cooling) is acceptable and even desired.


Does the radial temp gradient cause ejection

Does the Radial Temp. Gradient Cause Ejection?

Lorentz Force

Heat flux

B

Li

Grad T

TE current

Mo

  • One concern about using free surface Li is the ejection problem. The temperature gradient along the Li flowing direction will generate a thermoelectric current along the same direction and the Lorentz force may could eject the Li into the plasma. Fortunately the primary gradient pushes the Li downward.

  • On the inboard side, the force is upward. Similar to the capillary porous system (CPS) [6] which effectively has very narrow channels, LiMIT’s trench design has very narrow slots (1 mm) to utilize the capillary force to hold the Li in place.

J

J

F

F


Does it work capillary force balance

Does it Work? Capillary Force Balance

  • The thermoelectric current parallel to the Li flowing direction is [1]. Here the temperature difference is also assumed to be 200K and the temperature gradient dT/dy=2000K/m. Under these conditions jTEMHD=1.78*105A/m2. So total current along the Li trench is 0.89A. But only about 2cm Li will provide a upward force and the force from the TEMHD is 0.035N.

  • The capillary force is 2ΣL and Σ=0.3N/m [7] at 600K. So the capillary force is about 0.06N.

  • Aren’t there radial fields and eddy currents that could make things bad? Sure, but there are also a number of mitigating factors:

    • The capillary force is not effected by the thermoelectic power, P. It P is actually smaller, the forces will balance. Also, if the trenches were narrower instead of 1mm wide, the force would be higher. A coarse mesh could even be used which would have even higher restorative forces.

    • The leading edges of the Mo fingers could be Mo-sprayed, greatly increasing the surface area and therefore the capillary force. This would easily hold the Li in too.

    • Also, the part of the Li with the highest ejection force is also the hottest Li and has likely already evaporated anyway!


Can also work with porous material

Can Also Work with Porous Material

  • Utilize porous material infused with liquid metal

    • - Porous material structure creates TE loops with liquid metal

    • - Small pores create strong capillary forces at free-surface (similar to CPS)‏

    • - Pore size can be engineered to optimize TEMHD effect

  • Primary temperature gradient is due to incident heat flux

    • - Pumps liquid metal radially

    • - Passive replenishment system for a liquid surface !


We will test this future work at illinois

We will test this: Future Work at Illinois

E-beam line source

Magnet coil

Li Tray

Heat Stripe for SLiDE’s Electron Beam

B

  • The SLiDE experiment at Illinois is being reconfigured to test this concept. We expect to be able to show radial flows of Li along radial trenches in a Mo plate and measure the flow velocity compared to calculations. An electron beam is used to provide the heat flux while the magnet can generate about 800 Gauss magnetic field parallel to the tray surface. The temperature rise of the Li will also be monitored and compared to theory.

  • Return channels (lithium hydraulic engineering) will also be tested to find a design compatible with tokamak operation. I have ideas on this for HT-7.


Conclusions for limit

Conclusions for LiMIT

  • A Mo trench structure with flowing Li is proposed as a potential method to absorb the high heat flux on the torroidal limiter. The thermoelectric effect is utilized to drive the Li flowing along the radius trench direction.

  • The heat transfer ability is estimated based on the 1-D heat transfer model and simulated in the 3-D domain. Both give positive results showing the ability of flowing Li to mitigate the peak heat flux and to transfer the heat without an unacceptable temperature increase.

  • The ejection problem is analyzed and should be able to be suppressed by the capillary force.

  • A simple trench structure system is under construction at UIUC to validate this design. Use on NSTX is being contemplated. It works for divertor tokamaks too.


Reference

Reference

  • [1] M.A. Jaworski, Ph. D. thesis, University of Illinois, Urbana, IL (2009)

  • [2] J.A. Shercliff, Thermoelectric magnetohydrodynamics, J. Fluid Mech. 91, 231 (1979)

  • [3] P. Ioannides, et al. Journal of Physics E 8, 315 (1975)

  • [4] M.A. Jaworski, et al. Phys. Rev. Lett. 104, 094503 (2010)

  • [5] M.A. Jaworski, et al. Journal of Nuclear Materials 390–391, 1055–1058(2009)

  • [6] V. A. Evtikhin, et al., Fusion Engineering and Design 49–50 (2000) 195–199.

  • [7] M. A. Abdou,et al. On the exploration of innovative concepts for fusion chamber technology: APEX interim report.282 Technical Report UCLA-ENG-99-206, University of California, Los Angeles, November 1999.


Outline3

Outline

  • Introduction

    • Why Lithium is so Good – but you all know that already !

  • Solid/Liquid Lithium Divertor Experiment (SLiDE)

    • Experimental Facility

    • Results

    • Theory

  • Lithium Molybdenum Infused Trenches (LiMIT)

    • - How this could work for HT-7 and future devices

  • Lithium in Divertor Erosion Vapor Shielding Exp. (DEVeX)

  • Lithium in the Ion-Interaction Experiment (IIAX)

  • Conclusions


What is vapor shielding

What is Vapor Shielding?

  • What is Vapor Shielding?

    • -- High density of eroded material at PFM surface

    • -- Vapor absorbs a significant fraction of incident plasma energy

    • -- Reradiates absorbed energy

  • Should:

    • -- Reduce PFM surface temperature

    • -- Therefore reduce amount of material eroded

  • Effect had not been directly verified experimentally, so we built an experiment at Illinois to investigate the phenomenon

A. Hassanein and I. Konkashbaev. J. Nuc. Mat., 313–316 (2003) 664-669.


Divertor edge vapor shielding exp devex

Divertor Edge Vapor Shielding Exp. (DEVeX)

ESP-gun (2004-2006)

  • 500 J Capacitor Bank

  • 1017 ≤ ne ≤ 5(10)18 m-3

  • Te ~ 50 eV

  • Edep ~ few Joules

Needed More Edep!

Needed a bigger θ-pinch!

Construction began Fall 2006

Plasma!

(with some grounding issues)

Operational Winter 2008


Details of devex

Details of DEVeX

Li Magnetron

  • Transmission plates

  • 1” thick Al plates

  • 15 Coaxial Transmission lines

  • Target Chamber

  • 10-7 mTorr base pressure

  • Capacitor Bank

  • -fired by spark gap incurring lots of loss

  • 60kV capacitors, but used at less than 30kV. Ultimate stored energy is 250kJ. We only used up to 20kJ.

Cu Flux Conserver

Segmented θ-coil


Lithium magnetron

Lithium Magnetron

  • Used to deposit thin layers of lithium onto stainless steel (SS) target

    • < 100 nm thick

    • 30 min deposition @ 400 mA

  • Allows the removal of surface contamination from lithium before deposition

    • 30 min -- 2 hours

    • @ 100 -- 200 mA

  • Comparison between bare SS and lithium coated target


Time averaged density of incident plasma

Time Averaged Density of Incident Plasma

  • Stark broadened Hβ line

    • Gaussian fit

    • Hβ line less sensitive to Te

    • Machine broadening ~ 0.036 nm

  • Measured widths range from:

  • Corresponds to

    • For 20 - 25 kV discharges


Target region t e

Target Region - Te

  • Triple probe gives a Te of ~70 eV. This is suspect due to certain aspects of the probe.

  • Triple probe Te data was an over-estimate and not backed up by target temperature rise.

  • We estimate more in the range of 10’s of eV for the Te and Ti in our plasma burst.


Target region n e

Target Region - ne

  • 20 kV → 3 X 1021 m-3

  • 450 μs pulse duration

  • Noise spikes, at beginning, from θ-coil ringing

Triple probe density data is consistent with Stark broadening


Thermal response of target plate

Thermal response of target plate

Top View

TC bead


Target surface temperature

Target Surface Temperature


Outline4

Outline

  • Introduction

    • Why Lithium is so Good – but you all know that already !

  • Solid/Liquid Lithium Divertor Experiment (SLiDE)

    • Experimental Facility

    • Results

    • Theory

  • Lithium Molybdenum Infused Trenches (LiMIT)

    • - How this could work for HT-7 and future devices

  • Lithium in Divertor Erosion Vapor Shielding Exp. (DEVeX)

  • Lithium in the Ion-Interaction Experiment (IIAX)

  • Conclusions


Ion interaction experiment iiax

Ion Interaction experiment (IIAX)

  • Colutron Ion Source ( >1014 ions/cm2-sec) for both Gaseous and Metal Species (H+, D+, He+ and Li+)

Target holder with a UHV heater

Plasma cup

Li evaporator

Gas IN

ExB filter

LiCl holder

QCM

Faraday cup


Quartz crystal microbalance

Quartz Crystal Microbalance

  • Evaporated/Sputtered particles are detected by QCM.

: Sputtering Yield [atoms/ion]

: sticking coefficient

: fraction reaching to QCM

: mass of target material

: average current

: Mass change on QCM crystal


Results li on c has suppressed evaporation

Results: Li on C has suppressed evaporation

Evaporation flux of Li

Vapor pressure of Li

  • Evaporation fluxes from intercalated Li are suppressed.

  • D-saturation also suppresses evaporation fluxes.


Conclusions impact on the fusion community

Conclusions: Impact on the Fusion Community

  • A flowing lithium divertor could be pumped by the very heat flux it is supposed to remove.

  • Temperature of Li could be kept below the point where it significantly evaporates

  • Vapor shielding suggests thin lithium films absorbs large fraction of energy deposited during an ELM or disruption

    • -- Could “save” the PFCs from large temperatures that would otherwise be encountered possibly damaging the underlaying structure behind the lithium PFC.

  • Sputtering of Li is suppressed by impurities and by absorbed D.

  • The future of Lithium is Bright!


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