1/19

On energetic particle diagnostics based on gamma-ray measurement

M. Nakamura (for Y. Nakao)

Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka, 812-8581, Japan

E-mail: nakamura@nucl.kyushu-u.ac.jp

Contents1. Introduction ― what process is

employed ?2. Estimations ― what can be diagnosed ?3. Concluding Remarks

11th ITPA Topical Group Meeting on Diagnostics,Sep. 4, 2006, Tohoku Univ., Sendai, Japan

2/19

1. Introduction ― what process is employed ?

2. Estimations ― what can be diagnosed ?

3. Concluding Remarks

3/19

1.1 Introduction: gamma-ray measurement

Resonant reactions Threshold reactions

Gamma-ray measurement

Vigorously used for energetic particle diagnostics

What kinds of reactions are especially important ?

especially at JET experiments

6Li (t, p)8Li* proposed by our group Voronchev, Kukulin, JPG (2000);

Voronchev, Kukulin, Nakao, PRE (2001);Nakamura, Voronchev, Nakao et al., JPSJ (2006)

D(,γ)6Li* proposed by Ochiai et al.

4/19

1.2 Introduction: properties of the 6Li(t,p)8Li* reaction

γLi

p9810LitLi

8fs12

86

.st.gr

.

i. The reaction threshold is 181 keV in the centre-of-mass system

ii. The excited state has a short lifetime of 12 fs.

The rate of the 0.981-MeV gamma-ray emission is sensitive to the population of energetic

tritons.

102 10310-9

10-7

10-5

10-3

10-1

101

6Li(t,p)8Li*

Cro

ss s

ection (b)

Centre-of-mass energy (keV)

D(t,n)

181 keV

Voronchev, Kukulin JPG (2000);Voronchev, Kukulin, Nakao PRE (2001)

5/19

1.3 Introduction: the preliminary estimation

ttttt dEEEEfY

tt EP

The reaction probability function Pt (Et )

0 1000 2000 3000 40000.1

1

Pt(E

t) (A.U

.)E

t (keV)

In order to briefly estimate the 6Li(t,p)8Li* reaction rate, we introduce the function Pt(Et).

Occurrence of the 6Li(t,p)8Li* reaction is sensitive to the presence of energetic tritons

above the energy of 1 MeV.

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1.4 Introduction: the objective of the present work

Speculation

One could obtain information on the energy distributions of energetic tritons and alpha-particles by comparing the 0.981-MeV gamma-ray measurement with kinetic model prediction incorporating the alpha knock-on effect.

The present objective

To develop such an early qualitative discussion

We analyze diagnostic information carried by the 0.981-MeV gamma-rays.

Nakamura, Voronchev, Nakao et al., JPSJ (2006)

7/19

1. Introduction ― what process is employed ?

2. Estimations ― what can be diagnosed ?

3. Concluding Remarks

8/19

2.1 Energetic tritons and the gamma-rays

The source of the gamma-rays

Energetic tritons Alpha knock-on tritons

D-beam knock-on tritons

DD (burn-up) tritons

These populations can be evaluated by solving the Fokker-Planck equation for energetic ions.

102 10310-9

10-7

10-5

10-3

10-1

101

6Li(t,p)8Li*

Cro

ss s

ection (b)

Centre-of-mass energy (keV)

D(t,n)

181 keV

t

9/19

Ignoring the DT fusion reaction induced by knock-on deuterons and tritons. Considering that Energetic ions slow down only through Coulomb scattering. Ignoring losses of energetic ions during slowing-down (that is, their confinement is good).

2.2 The energetic triton population

(6Li’s are assumed to be at rest.)

Assumption

The gamma-ray emission from the 6Li(t,p)8Li* reaction would be determined by the alpha-knock-on tritons.

Conditions T = 20 keV,

nd = nt = ne/2 = 0.5×1020 m-3,ENBI = 1 MeV,PNBI = 73 MW,Vplasma = 730 m-3

102 1031010

1012

1014

1016

1018

10-11

10-9

10-7

10-5

10-3

10-1cross section

D-beam knock-on

burn-up

knock-on

f t(E

t) (1/m

3 /ke

V)

Et (keV)

bulk

6 Li(t,p) (ba

rn)

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2.3 The gamma-ray yield and energy spectrum

10 20 30 40 50107

109

1011

1013

1017

1018

1019

Y (m

-3s-1

)

Ion temperature (keV)

Yn

bulk

burn-up

D-beam knock-on

Yn (m

-3s-1

)

knock-on

The energy spectrumThe yield

The yield and energy spectrum of 0.981-MeV gamma-rays are solely governed by the energetic triton population,

900 950 1000 1050105

107

109

1011

bulk

D-beamknock-on

burn-up

knock-on

dY/

dE (m

-3ke

V-1s-1

)E (keV)

nd = nt = ne/2 = 0.5×1020 m-3

ENBI = 1 MeV

T = 20 keV,nd = nt = ne/2 = 0.5×1020 m-3

ENBI = 1 MeV

especially the alpha knock-on tritons.

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2.5 Comparison with the 4.44-MeV gamma-ray yield

1-3-10 sm107169810 ..Y

The 4.44-MeV gamma-rays

Emitted in the 9Be(α,n)12C* reaction

The sizable cross section Vigorously used for alpha-particle

diagnostics at JET experiments

Comparison between the 0.981- and 4.44-MeV gamma-yields

Kiptily et al., NF (2002)

Under the plasma conditions typical of ITER:T = 20 keV, nd = nt = ne/2 = 0.5×1020 m-3, nLi/nd = nBe/nd = 0.01,

1-3-10 sm1053444 .~.Y

Comparable!

12/19

2.6 The diagnostic information on the alpha-knock-on tritons

0 1000 2000 3000 40000.0

1.0x109

2.0x109

3.0x109

4.0x109

5.0x109

6.0x109

Yt',g (m

-3 s-

1)

Et' (keV)

0.981 < E < 0.990 MeV

0.990 < E < 1 MeV

1 MeV < E

g,tY

g

E

Ettt

g

g,t

g,t

g,t

dEEyYY1

The physical meaning of : the gamma-ray yield due

to knock-on tritons with energy

The emission of the 0.981-MeV gamma-rays reflects the presence of alpha-knock-on tritons with energy of 0.6-1.6 MeV.

1 g,ttg,t EEE

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2.7 The diagnostic information on the alpha-particles

g

E

Eg

g,

g,

g,

dEEyYY1

The physical meaning of Yα,

g : the gamma-ray yield due to alpha-particles with energy Eα, g< Eα<Eα, g-1

0 1000 2000 3000 4000 50000.0

1.0x109

2.0x109

3.0x109

4.0x109

Y,

g (m

-3 s-1

)

E (keV)

0.981 < E < 0.990 MeV

0.990 < E < 1 MeV

1 MeV < E

The emission of the 0.981-MeV gamma-rays reflects the presence of alpha-particles with energy of 2.0-3.5 MeV.

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2.8 Information on the confinement property

The emission of the 0.981-MeV gamma-rays reflects the presence of alpha-knock-on tritons with energy of 0.6-1.6 MeV, and alpha-particles with energy of 2.0-3.5 MeV.

When the confinement of energetic particles is affected by specific loss mechanisms …..Detection of the gamma-

raysKinetic model prediction

Diagnosing the confinement property of alpha-knock-on tritons and alpha-particles

The present study ….. Assumed that the confinement of energetic particles is

good.

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1. Introduction ― what process is employed ?

2. Estimations ― what can be diagnosed ?

3. Concluding Remarks

16/19

3 Concluding Remarks

The 6Li(t,p)8Li* reaction may have an important applicability to energetic ion diagnostics in DT fusion plasmas.

The yield and energy spectrum of 0.981-MeV gamma-rays is solely governed by the energetic (especially alpha-knock-on) triton population.

The emission of the 0.981-MeV gamma-rays reflects the presence of

If the 0.981-MeV gamma-rays are detected, one can diagnose not only the presence of alpha-knock-on tritons and alpha-particles,but also the confinement properties of these ions.

alpha-knock-on tritons with energy of 0.6-1.6 MeV, and

alpha-particles with energy of 2.0-3.5 MeV.The confinement property of these ions could be diagnosed by comparison of the 0.981-MeV gamma-ray detection with kinetic model predictions.

17/19

On energetic particle diagnostics based on gamma-ray measurement

K. Ochiai

Directorates of Fusion Energy Research, Japan Atomic Energy Agency

18/19

Measurement of 2.186MeV gamma-ray from D(,)6LiFor diagnostics of high energetic a-particle, JAEA-FNS and Kobe University has carried out measurements emitted 2.186 MeV gamma ray from D(,)6Li reaction.

Target C2D2

Kobe university Tandem Van de Graaff accelerator, Pelletron 5SDH-2, +15 line

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Gamma spectra and emission rateFrom our results, the emission rate of the 2.186-MeV gamma from the D(,)6Li reaction in typical burning plasma can estimate 104 /cm3/sec So, in case of ITER, the emission rate is about 1012-13 sec-1 and it is thought that the intensity is sufficient for the measurement for alpha particle diagnostics.

2186

2234~2254 keV 2.186-MeV gamma ray from D(,)6Li Tl-208(2615

)

Carbon C2D4

TiDx

Figure 3 Measured gamma spectra from used C2D4, carbon and TiDx samples

under 3.5-MeV He++ irradiation.

2100 2200 2300 2400 2500 26000

200

400

600

800

1000

1200

1400

Det

ecte

d ga

mm

a ra

y yi

eld

coun

ts/k

eV/m

C

Energy keV

Measured gamma spectra from used C2D4, carbon and TiDx samples under 3.5-MeV He++ irradiation.

2000 2500 3000 3500 400010-2

10-1

100

101

102

103

104Mohr94 + Robertson81

Yie

lds

/mC

E keV

Present data

Dependency of yields of measured photo peak in 2234 < E < 2254 keV on 2.0, 2.25, 3.0 and 4.0 MeV He ion beam ,E, implantation (Open circle: present data and Closed circle: past experimental data).

Emission rate 104 /cm3/sec on typical plasma 1012-13 sec-1 in case of ITER