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 !
D.N. Ruzic, M. A. Jaworski1, T.K. Gray1, V. Surla,
W. Xu, S. Jung, P. Raman
1current address: Princeton Plasma Physics Laboratory
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.
First Evidence? TFTR Supershots(1984)
So, it will have to be used ultimately as a flowing liquid
So, careful planning is needed. Maybe it’s MHD effects can be utilized?
So, careful engineering is needed and new materials (for fusion) need to be developed
Surface tension drives flow
Lithium in tray
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.
J.N. Brooks, et al. J. Nucl. Matl.337-339 (2005) 1053-1057.
Current density profile
There are four filaments, each 10cm long, parallel to eachother
7 keV, 2 A, 16 G
20 keV, 0.75 A, 1 kG
- “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
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.
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
Movie of spin-down test
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.
Distance from wall
Jaworski Number was always greater than 1 !
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)
How Powerful is the ThermoElectric Effect?
Apparatus for Seebeck Coefficient
Apparatus for Seebeck Coefficient Measurement
T + DT
There is a large difference in S between Li and most other metals and it increases with temperature.
where σ is the conductivity, and ΔS is the difference in Seebeck coefficients.
Seebeck Coefficient of Li
Black: our measurementsLithium
Theoretical vs experimental velocities :
 M.A. Jaworski, et al. Phys. Rev. Lett. 104, 094503 (2010)
Plasma primary heat-flux location
Passive Li replenishment
The top surface of the Li is hotter than the surface that is deeper. Therefore there is a VERTICAL temperature gradient
Heat flux: divertor strike point width, 1cm
This represents the divertor heat flux maximum value for the calculations here, but the concept should work for even higher values..
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
6MW/m2 heat flux
Back flow of Li
E-beam line source
Heat Stripe for SLiDE’s Electron Beam
A. Hassanein and I. Konkashbaev. J. Nuc. Mat., 313–316 (2003) 664-669.
Needed More Edep!
Needed a bigger θ-pinch!
Construction began Fall 2006
(with some grounding issues)
Operational Winter 2008
Cu Flux Conserver
Triple probe density data is consistent with Stark broadening
Target holder with a UHV heater
: Sputtering Yield [atoms/ion]
: sticking coefficient
: fraction reaching to QCM
: mass of target material
: average current
: Mass change on QCM crystal
Evaporation flux of Li
Vapor pressure of Li