11 th International Conference on Open Magnetic Systems for Plasma - - PowerPoint PPT Presentation

• M. Yoshikawaa, K. Ohtaa, M. Chikatsua, Y. Shimaa, J. Kohaguraa, R. Minamia,
• Y. Nakashimaa, M. Sakamotoa, M. Ichimuraa, T. Imaia, R. Yasuharab, I. Yamadab,
• H. Funabab, and T. Minamic
• a Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki, JAPAN

b National Institute for Fusion Science, Toki, Gifu, JAPAN c Energy Science Institute, Kyoto University, Uji, Kyoto, JAPAN

11th International Conference on Open Magnetic Systems for Plasma Confinement 8–12 August 2016, Novosibirsk, Russia

• 1. Introduction
• 2. GAMMA 10/PDX and Thomson scattering (TS)

system

• 3. Radial electron temperature and density

measurements

• 4. Multi-pass TS system in GAMMA 10/PDX
• 5. End region TS system
• 6. Summary

• 1. Introduction

— Thomson scattering (TS) is the most reliable diagnostic to measure the

electron temperature and electron density. In the tandem mirror GAMMA 10/PDX, the yttrium-aluminium-garnet (YAG)-TS system was constructed with the large solid angle of TS collection optics. In GAMMA 10/PDX, the plasma density is low compared with other fusion plasma devices, about 2×1018 m-3. We used high speed oscilloscopes for direct acquisition of TS signals, because we have to check the TS signals shot- by-shot.

— For increasing the TS signal intensity, improved optical collection system

and the multi-pass TS system are considered.

— The radial electron temperatures and densities of six radial positions in

GAMMA 10/PDX are successfully obtained.

— We constructed the acquisition program for six oscilloscopes to obtain

the 10-Hz TS signals in a single plasma shot. Then we can obtain the time dependent electron temperatures and densities in a single plasma shot.

— Moreover, we are developing the multi-pass TS system for increasing the

TS signals to improve the measurement accuracy and high time resolved electron temperatures.

1-2. GAMMA 10 TS system

l In GAMMA 10, a ruby-laser TS system had installed to measure the

electron temperature. However, the system experienced problems and removed.

l In fund year (FY) 2008, we started to design YAG-TS system for

measuring electron temperature and density in a single plasma shot. The requirement of TS system in GAMMA 10 is to obtain the electron temperature and density in a single laser shot in a single plasma shot. We designed GAMMA 10 YAG-TS system and installed.

l We started to obtain TS signals in GAMMA 10 from FY 2009. l We are constructing the multi-pass TS system for increasing the TS

signals from FY 2011.

1980220 1983

• 2000
• 2008

2009 2010 2011 2012 2013 2014 2015 2016

GAMMA 10

• GAMMA 10/PDX
• Ruby-laser Thomson

(TS) scattering system

• YAG-Thomson scattering system
• Double-pass TS system
• Multi-pass TS system

• 2. GAMMA 10/PDX tandem mirror

ne = ni ~ 2×1018 m-3 Te ~ 20 ~ 80 eV Ti ~ 5 keV D-module YAG-Thomson

2-2. G10/PDX-TS system side view

1910 1200 873 YAG Laser Beam dump Laser house Focusing lens Plasma OSC

50 CH. AMP

Polychromator OSC Shield box QDC Bundled optical fiber Spherical mirror Fiber setting slot Mirror flipper Reflection mirror Focusing lens Mirror Additional mirror

Mirror : φ600, f = 873, R = 1200 NA = 0.19 M = -0.459 Fiber : input 2 x 7, output φ4.8, NA 0.47 Solid angle: 0.078 str The optical fibers are set to measure the radial positions of X = 0, ±5, ±10, ±15, and ±20 cm. Additional mirror φ 200 mm R = 1200 mm Optical fiber

2-3. GAMMA 10-YAG-TS system

Typical performance of G10-Thomson system

• 1. Temperature range ： 0.02 ~ 2 keV (ΔTe ~ 10 eV)
• 2. Observable range ： ±20 cm (0, ±5, ±10, ±15, ±20 cm, Δd ~1.5 cm)

Now, we have six observing channels in a single laser and plasma shot.

• 3. Time resolution ： ~ 10 Hz ( ~ 10 ns)
• 4. Laser ： Nd:YAG 1064 nm, 2 J/pulse(Powerlite 9010)
• 5. Collection system ： Concave mirror (R ~ 1200 mm, φ = 60 cm

and 20 cm) & 9 channel bundled optical fiber.

• 6. Spectroscopic system ： 5ch. filter polychromator with Si-APD,

TS139 (PerkinElmer, C30950E), TS056, TS149, TS030, TS136 , TS002 (PerkinElmer, C30659-1060-3AH).

• 7. Data collection system ： We use the high speed digital
• scilloscopes (IWATSU DS5524).

3-1. Radial electron temperatures and densities

5 1017 1 1018 1.5 1018 2 1018 2.5 1018 3 1018

• 20
• 15
• 10
• 5

5 10 15 20 t = 60 ms t = 160 ms

Electron density [ m-3 ] X [ cm ]

20 40 60 80 100

• 20
• 15
• 10
• 5

5 10 15 20 t = 60 ms t = 160 ms

Te [ eV ] X [ cm ]

0.2 0.4 0.6 0.8 1 1 2 3 4 5 50 100 150 200 Diamagnetism Line density

Diamagnetism [ x 10-4 Wb ] Line density [ x 1017 m-2 ] Time [ ms ]

t = 60 ms t = 160 ms

• Time dependent electron temperatures and densities of six

radial positions are successfully measured simultaneously by TS system.

• The electron temperatures and densities at t = 60 ms and t =

160 ms at plasma center are about 35 eV, 60 eV, 1×1018 m-3, and 1.4×1018 m-3, respectively. Electron temperature Electron density

50 100 150 50 100 150 200

Electron temperature [ eV ] Time [ ms ]

5 1017 1 1018 1.5 1018 2 1018 2.5 1018 3 1018 50 100 150 200 ne by Thomson ne by MIF

Electron density [ m-3 ] Time [ ms ]

3-2. Time dependent electron temperature and density

• Time dependent electron temperature and density are successfully observed.
• Electron densities by TS system are comparable to those by using the microwave

interferometer (MIF) system. Electron temperature Electron density

4-1. Multi-pass TS ｓystem in GAMMA 10/PDX

Lens 2 Pass 1 Pass Iris YAG laser He-Ne laser Short pass mirror Faraday rotator Beam dump Pockels cell λ/2 plate Iris Mirror Mirror Mirror Mirror Mirror Mirror 3 pass Polarizer Polarizer Lens f = 2000 f = 2000

Mirror Iris Beam dump YAG laser He-Ne laser Short pass mirror Faraday rotator Polarizer λ/2 plate Lens Lens Reflection Mirror Mirror Mirror Polarizer 1 Pass 2 Pass Mirror Plasma to Polychromator Optical fiber 90°collection optics

Double-pass system Multi-pass system 2 passed beam is dumped by beam dump. We can make more than 4 passing through the plasma. We have constructed the polarization controlled multi-pass system with image relaying system in the GAMMA 10 YAG-TS system. This system is easily constructed with adding a lens, reflection mirrors, and Pockels cell. Single-pass

Beam dump

4-2. Multi-pass TS system

Pockels cell Mirrors Faraday rotators YAG laser Beam dump Polarizers

We are developing the multi-pass TS system with a polarization based system and image relay system based on the GAMMA 10-YAG-TS. Photo diode

4-3. Radial profile of electron temperature

0.01 0.02 0.03 0.04 0.05 100 200 300 400 500 Single-pass Multi-pass

Intensity [V] Time [ns]

1 2 3 4 5 6 7 8 10 20 30 40 50

• 20
• 15
• 10
• 5

5 10 15 20 Single-pass Multi-pass

Electron temperature [eV] X [cm]

We are developing the multi-pass TS system of a polarization based system based on the GAMMA10 YAG-TS. The integrated TS signal of multi-pass system is about 5 times larger than that of 1st pass signal intensity. The radial profile of electron temperature was successfully obtained by using the MPTS system. The errors of electron temperatures in the multi-pass configuration are much smaller than those in the single-pass configuration.

4-4. Time dependent electron temperature and density

Time dependent TS signals show the fast time dependent electron temperatures and densities in 20 and 50 ns periods. By using the signal fitting method, calculated Multi- pass TS intensities are clearly obtained. TS signals Calculated TS intensity

0.02 0.04 0.06 0.08 0.1 100 200 300 400 500 single-pass double-pass multi-pass

Intensity [V] Time [ns]

0.1 0.2 0.3 0.4 0.5 100 200 300 400 500

Intensity [Arb. units] Time [ns]

1 2 3 4 5 6 7 8 9 10

4-5. Time dependent electron temperature

— By calculating each passing TS

signal, we can obtain the time dependent electron temperature. The calculated electron temperatures from 7th-pass to 10th-pass have large error because of low signal to noise ratio.

— In GAMMA 10/PDX plasma, the

electron collision time is about 700

• ns. Then the electron temperature

is almost constant of 22±2 eV during 400 ns from 1st-pass to 10th-pass.

— We successfully constructed the

high time resolved electron temperature measurement system by MPTS in the order of MHz sampling.

10 20 30 40 50 100 200 300 400 500

Te [eV] Time [ns]

• 5. End region TS system

—

70 °back scattered TS signal measurement system.

—

Laser: YAG laser of central cell TS system, 1064 nm, and 2J/pulse.

—

Time resolution: 100 ms (10 Hz).

—

Solid angle of optical collection system: 71 mstr.

—

Electron temperature Te: 0.5 ~ 50 eV, ΔTe < 40 %.

—

Electron density ne: > 0.2 x 1017 m-3.

—

Observation position Y: 0 cm, ΔY ~ 3 cm.

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 1020 1030 1040 1050 1060 1070

Sensitivity TS194 Intensity [ Arb. units ] Wavelength [ nm ]

Polychromator sensitivity

Z = 1070 cm GAMMA 10/PDX

Central TS system End region TS system

• 6. Summary

— We have constructed the GAMMA 10/PDX-TS system by NIFS

research collaboration program.

— We added the second collection mirror to obtain the larger TS

signal intensity in the edge region. The TS signal intensities in the lower plasma region are increased by the additional mirror.

— We can successfully measure the time dependent six

positions electron temperatures and densities in GAMMA 10/PDX plasma with a single laser shot at the single plasma shot.

— We could successfully obtain the multi-pass Thomson

scattering signals and get the 5 times larger Thomson scattering signal than that in the single-pass configuration. Moreover, the fast time dependent electron temperatures are successfully obtained.

Acknowledgements The authors thank the members of the GAMMA 10 group of the University of Tsukuba for their

• collaboration. This study was conducted with the support and under the auspices of the NIFS

Collaborative Research Program, NIFS-KUGM056 and NIFS-KOAH025.