11 th International Conference on Open Magnetic Systems for Plasma Confinement 8–12 August 2016, Novosibirsk, Russia M. Yoshikawa a , K. Ohta a , M. Chikatsu a , Y. Shima a , J. Kohagura a , R. Minami a , � Y. Nakashima a , M. Sakamoto a , M. Ichimura a , T. Imai a , R. Yasuhara b , I. Yamada b , H. Funaba b , and T. Minami c � � 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 �
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 × 10 18 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 � 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 � � � � � � � � � � � 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. �
2. GAMMA 10/PDX tandem mirror � YAG-Thomson � D-module � n e = n i ~ 2×10 18 m -3 T e ~ 20 ~ 80 eV T i ~ 5 keV �
2-2. G10/PDX-TS system side view � Mirror : φ 600, f = 873, R = 1200 NA = 0.19 M = -0.459 Fiber : input 2 x 7, output φ 4.8, NA 0.47 Reflection mirror Solid angle: 0.078 str Additional mirror Focusing lens φ 200 mm Beam dump R = 1200 mm � Mirror flipper Bundled optical fiber Plasma Fiber setting slot 1910 Additional mirror QDC 1200 Spherical mirror 873 OSC Optical fiber � OSC Laser house 50 CH. AMP YAG Laser Polychromator Shield box The optical fibers are set to measure Focusing lens the radial positions of X = 0, ±5, ±10, ±15, and ±20 cm. � Mirror
2-3. GAMMA 10-YAG-TS system Typical performance of G10-Thomson system 1. Temperature range ： 0.02 ~ 2 keV (ΔT e ~ 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 oscilloscopes (IWATSU DS5524).
3-1. Radial electron temperatures and densities � Electron temperature � Electron density � 100 3 10 18 t = 60 ms t = 60 ms t = 160 ms t = 160 ms 2.5 10 18 80 Electron density [ m -3 ] 2 10 18 60 Te [ eV ] 1.5 10 18 40 1 10 18 20 5 10 17 0 0 -20 -15 -10 -5 0 5 10 15 20 -20 -15 -10 -5 0 5 10 15 20 X [ cm ] X [ cm ] t = 160 ms t = 60 ms 1 5 • Time dependent electron temperatures and densities of six Diamagnetism [ x 10 -4 Wb ] 0.8 4 Line density [ x 10 17 m -2 ] radial positions are successfully measured simultaneously by 0.6 3 TS system. • The electron temperatures and densities at t = 60 ms and t = 0.4 2 160 ms at plasma center are about 35 eV, 60 eV, 1 × 10 18 m -3 , 0.2 1 Diamagnetism and 1.4 × 10 18 m -3 , respectively. � Line density 0 0 50 100 150 200 Time [ ms ]
3-2. Time dependent electron temperature and density � Electron temperature � Electron density � 3 10 18 150 2.5 10 18 Electron temperature [ eV ] Electron density [ m -3 ] 2 10 18 100 1.5 10 18 1 10 18 50 5 10 17 n e by Thomson n e by MIF 0 0 50 100 150 200 50 100 150 200 Time [ ms ] Time [ ms ] • 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. �
4-1. Multi-pass TS ｓ ystem in GAMMA 10/PDX Double-pass system � Multi-pass system � to Polychromator Optical fiber Lens Lens Mirror 90 ° collection optics Mirror Lens Lens Reflection Mirror f = 2000 Single-pass � f = 2000 Mirror 2 Pass 1 Pass Plasma Polarizer Iris Faraday rotator Beam dump � Short pass mirror Polarizer λ /2 plate 2 Pass 1 Pass Polarizer Iris Iris Short pass mirror Faraday rotator Polarizer Mirror λ /2 plate Mirror Mirror Beam Mirror 3 pass dump Mirror Beam dump Pockels cell Mirror Mirror 2 passed beam is We can make more YAG laser YAG laser dumped by than 4 passing He-Ne laser beam dump. � through the plasma. � He-Ne laser 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. �
4-2. Multi-pass TS system � Beam dump � Polarizers � Faraday rotators � YAG laser � Pockels cell � Photo diode � Mirrors � We are developing the multi-pass TS system with a polarization based system and image relay system based on the GAMMA 10-YAG-TS. �
4-3. Radial profile of electron temperature � 50 0.05 Single-pass Single-pass 1 Multi-pass Multi-pass Electron temperature [eV] 40 2 0.04 3 Intensity [V] 30 4 0.03 6 5 0.02 20 7 8 0.01 10 0 0 0 100 200 300 400 500 -20 -15 -10 -5 0 5 10 15 20 Time [ns] 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 1 st 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 � TS signals � Calculated TS intensity � 0.1 0.5 1 single-pass double-pass multi-pass 0.08 0.4 3 4 Intensity [Arb. units] 2 Intensity [V] 0.3 0.06 5 6 0.2 0.04 8 7 0.1 10 0.02 9 0 0 0 100 200 300 400 500 0 100 200 300 400 500 Time [ns] Time [ns] 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. �
4-5. Time dependent electron temperature � By calculating each passing TS signal, we can obtain the time 50 dependent electron temperature. The calculated electron temperatures from 7th-pass to 40 10th-pass have large error because of low signal to noise ratio. 30 T e [eV] In GAMMA 10/PDX plasma, the electron collision time is about 700 20 ns. Then the electron temperature is almost constant of 22±2 eV during 400 ns from 1st-pass to 10 10th-pass. We successfully constructed the high time resolved electron 0 temperature measurement system 0 100 200 300 400 500 by MPTS in the order of MHz Time [ns] sampling.
5. End region TS system � Z = 1070 cm � GAMMA 10/PDX � Central TS system � End region TS system � Polychromator sensitivity � Sensitivity TS194 0.4 70 °back scattered TS signal measurement system. 0.35 Intensity [ Arb. units ] 0.3 Laser: YAG laser of central cell TS system, 1064 nm, and 2J/pulse. 0.25 Time resolution: 100 ms (10 Hz). 0.2 Solid angle of optical collection system: 71 mstr. 0.15 Electron temperature T e : 0.5 ~ 50 eV, Δ T e < 40 %. 0.1 Electron density n e : > 0.2 x 10 17 m -3 . 0.05 0 Observation position Y: 0 cm, Δ Y ~ 3 cm. 1020 1030 1040 1050 1060 1070 Wavelength [ nm ]
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