Spectrometric Diagnosis Groupin Plasma Chemistry and Physics

박영동 1, 오수기 2

1Department of Chemistry, 2Department of Physics,

Ajou University, Suwon 443-749, Korea

Vision/MissionHigh Resolution Spectroscopy/Optical Diagnosis Group

ChemistryLaser SpectroscopyMolecular Beam SpectroscopyPhotoionization Spectroscopy

PhysicsInterferometry OpticsFabry-PerotAtomic and Plasma Physics

Stength/CapacityChemistry

Molecular SpectroscopyTheoretical Spectroscopy

PhysicsOptics – Fourier optics, interferome-

tryPlasma Physics

Tokamak PlasmaThe magnetic field lines inside the toka-

mak chamber are divided into two groups:

the “scrape-off” re-gion

cold and diluted

the magnetic separatrix sur-

face

the “core” regionhot and dense

One forming nested closed surfaces in the main chamber without touching the material wall

the other leading to the divertor chamber

The heating effect of the electric current, joule-heating, is less than 50 million degrees. The need for additional heating has led to neutral beam heating. CXS is an appropriate tool to measure the effect of neutral beam heat-ing.

The Charge Exchange Recombination Spec-troscopy (CXRS)

ion tempera-ture

poloidal and toroidal

rotation speed

impurity den-sity

Doppler broad-ening

Doppler shift

total intensity

charge exchange between neutrals in the neutral beams and ions in the plasma

H0 + C6+ → H+ + [C5+]*

CXRS system in JT-60U

Doppler Broadened Data

Mirrors

Fabry-Perot interferometer

Piezo actuator

Photon counter

Design of a spectrograph system for temperature measure-ment in Fusion Reactor using Doppler Broadening

Fabry-Perot interferometer systemAdvantages

can achieve very high spectroscopic reso-lution

Disadvantages1. Need very sharp filter to separate pho-

tones outside of free spectral range2. input beam should be stable during

scan period.3. hard to employ large aperture system

McPherson Model 2062 2-meter focal length f/14.1 Monochroma-tor, $200,000

GratingGroove Density (g/mm)

1200

Resolution** (nm) 0.005Dispersion (nm/mm)

0.4

McPn CXRS

2-meter

531.95 532.00 532.05

0

10000

20000

30000

40000

50000

Inte

nsity

(a.u

.)

Wavelength(nm)

0.07 A FWHM fitted experimental data

CCD

LightSource

Entrance Slit

Collimating Mirror

Focusing Mirror

Grating 21800 gr/

mm1st order

Grating 11200 gr/

mm-1st order

GratingGroove Density (g/mm)

1200+1800

Resolution** (nm) 0.007Dispersion (nm/mm) 0.7

AJOU CXRS 50 cm

AJOU CXRS

AJOU CXRS

FIG. 4. The measured Ne I spectrum lines by the two-grating spectrometer equipped with the PhotonMax 512B CCD camera.

AJOU CXRS

Ne I =529.8189 nmNe I =530.4758 nm

Ne I =528.0085 nm

FIG. 5. The spectrum signals are obtained with the two-grating spectrometer (triangle) and conventional spectrometer (square) for the KSTAR plasma. It is shown that the S/N ratio of the two-grating spectrometer is much larger than that of the conventional spectrometer.

528.5 529.0 529.5 530.00

50

100

150

200

Wavelength (nm)

Inte

nsity

(a. u

.) Conventional (80 ms, 1760 mm) Two-grating (96 ms, 1720 mm)McPherson spectrometer(80 ms)Ajou two-grating spectrometer(46 ms)

AJOU CXRSMcPn CXRS

The Ajou system is ~10 times better in S/N for a fraction

of the cost for ‘old’ system.

1.7 1.8 1.9 2.0 2.1 2.2 2.30.0

0.4

0.8

1.2

1.6

1.7 1.8 1.9 2.0 2.1 2.2 2.30

35

70

105

140

Conventional (1.70 s)

Ti (k

eV)

Two-grating (1.75)

Conventional (1.70 s)

Vt (

km/s

)

Major radius (m)

(b)

Two-grating (1.75 s)

(a)

FIG. 6.(a) The ion temperature profiles and (b) toroidal rotation velocity measured with both spectrometers for the KSTAR plasma shot number of 4364are compared.

Ajou

McPher-son

exposure(ms)

46 80

intervals(ms)

50 100

The Charge Exchange Recombination Spectroscopy (CXRS) system in an upper port plug for ITER.

Figure from http://www.rijnhuizen.nl/annual_report/2007/02_the_research_at_rijnhuizen/2_2.html

diagnostic neutral beam

the viewing lines

optical fiber bundle

spectrometers

ITER CXRS

Number of channels toroidal : 23 poloidal : 36Spatial resolution toroidal : 5 cm poloidal : 0.8/1.5 cmTime resolution 16.7 ms

JT-60U

What’s Next?

K-STARtarget

Number of channels The more, the better 128 channelsTime resolution 16.7 ms 20 ms

1. Increase S/N by a factor of 3 or greater.2. Needs a CCD detector at Ajou.3. Design multilayer spectrometer systems.4. A few researchers.(Grads, Post doc.)

올해도 복스러운 해가 되기를 기원합니다

[Spectroscopic principle for CXRS]Neutral atom (H0) and impurity ion (Aq+) undergo a charge transfer that leaves the product ion in an excited state.

H0 + Aq+ → H+ + [A(q-1)+]*

Aq+ = C6+. carbon is one of intrinsic impurities and they are fully stripped throughout the plasma volume. Emissions are excited at wavelengths long enough for making accurate Doppler broadening and shift measurements.

[Diagnostic Method]One of heating beams NB #14 is used for this measurement (see figures). Due to the above reaction, carbon ions near the neutral beam emit green light (529.2 nm at n=8-7 transition).

Doppler broadening (→ temperature), Doppler shift (→ rotation velocity) and its area (→ impurity density). According to the ionization balance, there are C5+ ions in the edge region, which can emit at the same transition due to direct excitation by electrons (not by neutral beams). Therefore it is important to separate the spectrum by beam excitation from that by electron excitation. In order for this, CXRS system in JT-60U has an exclusive optics for the background spectrum.

From Y. Koide, A. Sakasai, Y. Sakamoto, H. Kubo and T. Sugie, Rev. Sci. Instrum. 72, 119 (2001)