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

[ 1μlocal

∂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 InstabilitiesAdding 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-EPPaul 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 s

crit 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 650Stainless (12 shots) 2000 300

sc=scritF /Rwall

scritideal wall

RMP89153 89199

“Phase-Flip” RMP