7-th International Workshop, Asti09/23-25, 2006

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Edge plasma effects in ITER-typeTOKAMAK caused by an enhancement of

DD/DT reaction in metals at high current-low energy deuteron bombardment

Andrei G. LipsonInstitute of Physical Chemistry and

Electrochemistry, Russian Academy ofSciences, Moscow, 119991, Russia

7-th International Workshop, Asti09/23-25, 2006

Introduction I- Expected Sources ofRadiation Corrosion of First Wall

First wall/divertor of TOKAMAK isbombarded by intensive beams of keVcharged particles (d+, t+, He4++,He3++) resulting in sputtering/erosion.

ITER materials are bombarded by highintensity 14 MeV neutrons from DTreaction caused bulk radiation damage.

7-th International Workshop, Asti09/23-25, 2006

Introduction II- Possible LENRcontribution to First Wall damage

LENR effects could also affect the processes at thefirst wall and divertor of TOKAMAK. Now LENR arenot taken into account as a possible source ofradiation damage in thermonuclear reactors .

What kind of LENR effects may potentially to destroythe first wall ?

DD/DT reaction enhancement producing excessiveenergetic He-4 and He-3 (blistering).

Low energy He4 from DD reaction (if any in W or St.steel) diffusing into the bulk.

Soft X-ray deposition at the metal surface –sputtering increase

7-th International Workshop, Asti09/23-25, 2006

Enhancement of DD-reaction in metaltargets at low deuteron energy (1.0<Ed<10

keV)

Most metals show enhancement of DD-reaction yieldat Ed << 10 keV compared to the standard yieldobtained by extrapolation of the DD-reaction cross-section to these Ed (see accelerator experiments: F.Raiola et al., Nuclear Physics, A719, 61C (2003), J.Kasagi et al., J. Phys. Soc. Jpn., 71(12), 2881(2002)).

Recently, high-current glow discharge measurementshowed strong enhancement of DD-yield – about 9orders of magnitude at Ed =1 keV in Ti target (A.Lipson et al., JETP, 100, 1175 (2005).

7-th International Workshop, Asti09/23-25, 2006

Comparison of High Current- Low Energy

D+ Accelerator and Pulsed GD parameters

±10.0%

200-10002.0-10.0,D2

200.02.5- 0.40100-600mA

**Pulsed GlowDischarge

± 1.0%100-350510-7,vacuum

2.0100.0- 2.510-400μA

*High CurrentAccelerator

E(D+)spread

T,K,target

P, mm HgWmax,[W]

Ed(lab),keV,range

I, rangeParameter

7-th International Workshop, Asti09/23-25, 2006

Comparative parameters of the edgeplasma flux (ITER) and high-current

glow discharge

ITER/DEMO: power deposition at the first wall W ~ 1kW/cm2; at ion temperate Ti ~ 0.5-1.0 keV, the fluxof bombarding ions with the energy Ei ~ 1.0-2.0 keVwould be Ji ~ 0.5-1.0 A/cm2, T 800 K

High current pulsed glow discharge (PGD) in D2 at p~ 0.5-9.0 mm Hg: pulses 0.2-1.0 ms duration (risingtime < 1.0 s), Ed ~ 0.5-2.5 keV, J ~ 0.2-2.0 A/cm2.

The disadvantage of a larger energy spread in thePGD case, is outweighed by the higher current andlower voltage capability.

This GD might well simulate the edge-plasma effectsat the first wall of ITER.

7-th International Workshop, Asti09/23-25, 2006

Pulsed Glow discharge set up

7-th International Workshop, Asti09/23-25, 2006

Thick target yield and enhancement ofDD-reaction

Thick target yield: All deuterons are stopped inthe target: R(Ed) < h(Target)

Yt(Ed) = ND(x)(Elab)(dE/dx)-1dEND(x)- D concentration in target,(Elab) - cross section at Elab,dE/dx – stopping power in target

Enhancement factor:f(E) = Yp(E)/Yb(E)=exp[(E)Ue/E]Yp(E) – experimental yield at E=Ed, Yb(E) – bare yield, 2(E) =

31.29 Z2(/E)1/2, Ue- screening potential of deuterons in target.

7-th International Workshop, Asti09/23-25, 2006

Yields of 3.0 MeV protons before and afternormalization to deuterium concentration in

PGD with Ti cathodeYields of 3.0 MeV protons from Ti-cathode vs

deuteron energy

R2 = 0.8649

R2 = 0.905

0.00E+00

1.00E+00

2.00E+00

3.00E+00

4.00E+00

5.00E+00

6.00E+00

7.00E+00

8.00E+00

0.5 1 1.5 2 2.5 3Deuteron Energy, [keV]

D(d

,p)T

-rea

ctio

nYi

eld,

[p/C

]

BeforeNormalization

AfterNormalization

Expon. (BeforeNormalization)

Expon. (AfterNormalization)

7-th International Workshop, Asti09/23-25, 2006

Normalization of PGD 3.0 MeV proton yields tothat of 2.45 keV

7-th International Workshop, Asti09/23-25, 2006

DD-reaction enhancement factor (f(E) =Yp(E)/Yb(E)=exp[(E)Us/E] for Ti-target: (1)-

accelerator; (2)-PGD

7-th International Workshop, Asti09/23-25, 2006

Thick target yields for accelerator (Ti and Au)and PGD (Ti) normalized to that at Ed = 10

keV compared to bare yield (solid line)

7-th International Workshop, Asti09/23-25, 2006

DD-reaction enhancement in Ti targetdepending on deuteron current and targettemperature.

609.2610±150> 7003100.8-2.45Ti -GD,Lipson-Karabut

75.265±152000.132.5-10.0Ti -accelerator,Kasagi

20.7302900.0545.0-30.0Ti,accelerator,Raiola

Fit:Ue= 68.23lnId+219.9 [eV]

Ue, [eV]T, [K]<Id>, [mA]D+- energyEd(lab),

[keV]

Target/Ref

7-th International Workshop, Asti09/23-25, 2006

Screening potential in Ti target is a logarithmic functionof the bombarding deuteron flux F: F = J ~ y=Me/D

Screening Potential vs. DeuteronCurrent on Ti-target

y = 68,231Ln(x) + 219,88R2 = 0,9991

0100200300400500600700800

0,010,11101001000

Deuteron Current, I [mA]

Scr

een

ing

po

ten

tial

,[e

V]

7-th International Workshop, Asti09/23-25, 2006

Data are taken from F. Raiola et al, Europhys. J.A19, 283 (2004) atT0=290K, J0=0.03mA/cm2, Ed5keV.Points are consistent with increase in y = Me/D: Hf, Y, Lu, Sc, Gd, Tm, Ti,Ce, Yb, Sm, Zr, Er, Pr, Eu, Ho, La, Ge, C, W, Sr, Ir, Ba, Ru, Au, Ag, Re, Ni,Nb, Ta, Zn, Bi, Mo, Mn, Mg, Cu, Rh, Fe, Pt, V, Pb, Pd, In, Tl.

Screening potentia l v s. free deuteron concentration,deduced from the data by F.Raiola et al, [6]

y = 145,28Ln(x) + 71,293

0

100

200

300

400

500

600

700

800

0 30 60 90 120

Fre e de ute ron conce ntration, y= [M e /D]

Scr

een

ing

po

ten

tial

,[eV

]

7-th International Workshop, Asti09/23-25, 2006

Ue = (T/T0)-1/2[a ln(y) +b]- semi empirical equation forscreening potential vs. free deuteron concentration y (a

and b are numerical constants)

y = ky0(J/J0), where y0 = Me/D at T0=290K andJ0=0.03 mA/cm2, k = exp(dT/kBTT0), d-activationenergy of D+ escape from the surface, T = T-T0and kB- Boltzman constant.

Accordingly the equation for Ue, in ITER case atJ=1.0 A/cm2 and T = 773 K;

For tungsten: y0(W) = 3.45, d(W) = 0.05 eV;Ue(W)= 1200 eV. Enhancement: fDT(2 keV) ~1.2x104;

For iron: y0(Fe) = 16.7, d(Fe) = 0.06 eV,Ue(Fe) = 1350 eV. Enhancement: fDT(2 keV) ~ 4x104.

7-th International Workshop, Asti09/23-25, 2006

Rough estimate of DT-reaction intensity at thesurface of W and Fe in ITER’s First Wall:

IDT = JdNeff(T) Here Jd – deuteron current density; Neff(T) – effective

concentration of bounded D/T in metal attemperature T, captured at depth x: (Neff(T) =N0exp(-dT/kBTT0), where N0 – D/T concentration atT0 = 290 K; f(E) – enhancement factor; DT – is thebare DT- cross-section; dE/dx – is the stoppingpower in target calculated with Monte-Carlo codeSRIM (J.F. Ziegler and J.P. Biersack, code SRIM2003)

dEdEdxEEfdE

DT )/)(()(0

7-th International Workshop, Asti09/23-25, 2006

Numerical integration results

Taking into account hypothetical First Wallbombardment parameters: Jd=1.0 A/cm2, <Ed> =2.0 keV, T 773K and screening potentials Ue(W) =1200 and Ue(Fe) = 1350 eV, rough d(t, n)-reactionrate at the reactor’s edge would be: IDT (1-2) 104

s-1-cm-2. During one year of operation: DT-reaction alpha

fluence ~ 7x1011/cm2 or up to N4He 1015 cm-3

atoms over depth ~ 6 μm for 3.6 MeV alphas fromdt-reaction.

7-th International Workshop, Asti09/23-25, 2006

X-ray yield per deuteron increases exponentiallywith the applied deuteron current at Ed ~ 1.5-

2.0 keV

X-rayyieldper deuteronvs. effectivepower at p=4.2mm

y=5E-05e0.0355x

R2 =0.977

0.00E+00

5.00E-051.00E-04

1.50E-04

2.00E-04

2.50E-04

3.00E-04

3.50E-04

4.00E-04

0 20 40 60 80Power P*, [W]

X-r

ayy

ield

7-th International Workshop, Asti09/23-25, 2006

Possible Consequences of DD/DT- ReactionEnhancement and X-ray Generation at High

Current Low Energy Deuteron Bombardment I

Vacancy generation over near-surface layerof reactor’s edge by MeV alphas.

The He-atom precipitation along dislocationsor capturing by dislocation atmosphere.

Additional stress and blistering, plasticityreduction even at low level (~ 1015 cm-3) 4Heaccumulation.

Sputtering rate may also increase due tovacancy generation and soft X-ray absorptionat the First Wall surface

7-th International Workshop, Asti09/23-25, 2006

Consequences II

Reduction in plasticity (e.g. in W) due to theHe-4 capture would cause a micro-crackgeneration over intermediate area betweensurface and the bulk (1-10 μm depth).Enhancement of First wall fracture andshortening of ITER/DEMO operation time.

Intense soft X-ray emission at the surface mayalso enhance erosion of first wall caused by X-ray energy deposition in the near-the-surfacelayer during charged particle bombardment.

7-th International Workshop, Asti09/23-25, 2006

Conclusions

The edge plasma effects at the first wall,including corrosion, would be partiallyunderestimated because the enhancement ofDD/DT reaction and accompanying radiationprocesses at very low deuteron energy areneglected.

The high current pulsed GD with appropriatecathode materials (W, St. steel) could be asuitable instrument to simulate edge plasmaeffects at ITER’s first wall.