1. D-T Fusion Produces Severe
Fast Neutron Damage
* D-T fusion products include 14.1 MeV fast neutron
* Fast neutrons penetrate meters into structure
* Neutron flux causes point defects and dislocations in
lattice, as well as radioactivation
* Damage rate can be orders of magnitude greater
than seen in fission reactors
HBT-EP Geometry
* Nominal plasma minor radius a = 15cm
* Shell minor radius can be set between 16cm and 20cm
* Circular cross-section plasma
* Operates at typical edge q between 2 and 4
> Primary MHD is 3-1 and 4-1 kinks, and 2-1 tearing modes
* Stainless steel vacuum vessel
> 6cm off-center from plasma, 25cm radius
* Plasma edge defined by stainless steel limiters
> 6 positionable limiters: 2 outboard, 2 top, 2 bottom
> 10 flanges between vessel segments also inboard limiters
* Upper and lower sets of stainless steel shells
> Shells 3 and 8 house half of each poloidal high-density array
> Half of each shell houses control coils and magnetic sensors
> Shell coverage is partial, covering most of outboard side
For More about the Ferritic Wall...
* Rotation feedback control with bias probe under development
> May lead to much clearer frequency dependence results
* See P. E. Hughes, J. P. Levesque, N. Rivera, M. E. Mauel,
and G. A. Navratil, Rev. Sci. Inst. 86, 103504 (2015)
* Contact at: peh2109@columbia.edu
Simple Model: Red. MHD FWM
Poloidal Flux Function Derived
* Ferromagnetic, destabilizing response opposes
diamagnetic, stabilizing eddy currents
* Flux compression and finite B field give boundary conditions
* Ferritic material enhances poloidal field in wall region
> Increases radial field near plasma edge (less stable)
> Fast mode rotation tends to shield out ferritic effect
[ 1
μlocal
∂ ψ
∂ r ]∂
=0 [ ψ]∂=0
Ferritic Wall Enhances RMP Response
* The ferritic wall enhances resonant field amplification (RFA)
when resonant magnetic perturbations (RMPs) are applied
* RFA measured as n = 1 amplitude measured on toroidal array
by cosine fit averaged over RMP time
* Disruptivity of plasma for a given RMP strength is also enhanced
when the ferritic wall is inserted
Ferritic Material Near Plasma Enhances MHD Instabilities
Adding ferritic material to odd-numbered shell pairs and retracting even-numbered shell pairs is expected to
produce MHD comparable to retracting all shells: faster growth rates, greater RMP response, earlier disruptions
Ferritic Wall Increases Natural Growth Rates
Ferritic Shells RetractedFerritic Shells Inserted
Ongoing Ferritic Wall Mode studies on HBT-EP
Paul Hughes, M.E. Mauel, J.P. Levesque, G.A. Navratil
(Columbia University)
HBT-EP research supported by
U.S. DOE Grant DE-FG02-
86ER53222
Ferritic Wall Assembly on the Bench and In-Vessel
* Destabilizing effect can be measured
by comparing scrit
for a configuration
against scrit
for an ideal wall at 16cm
* The ferritic wall increases growth
rates of the m/n = 3/1 external kink
* Mode amplitude measured by
cosine fit at each time point
* Fit exponential to growing amplitude
Wall Configuration  [s-1
] rms
[s-1
]
Ferritic (9 shots) 4300 650
Stainless (12 shots) 2000 300
sc=
scrit
F /R wall
scrit
ideal wall
RMP
89153 89199
“Phase-Flip” RMP