J. Plasma Fusion Res. SERIES, Vol. 3 (2000) 444448

Preliminary Results of the Neutral Particle Measurements
in Large Helical Device
OZAKI Tetsuo*, SUDO Shigeru, SHOJI Mamoru, MURAKAMI Sadayoshi, KADO Shinichiro, IDA Katsumi,
NARIHARA Kazumichi, TANAKA Kenji, KOBUCHI Takashir, NAKANISHI Hideya, KOJIMA Mamoru,
OHDACHI Stoshi, MORITA Shigeru, GOTO Motoshi, SASAO Mamiko, KHRASHILNIKOV Anatori,SAKAKIBARA Satoru, PETERSON Byron, KANEKO Osamu, KUMAZAWA Ryuhei, MUTOH Takashi,WATARI Tetsuo, KUBO Shin, SHIMOZUMA Takashi, IDEI Hiroshi, OKA Yoshihide, OSAKABE Masaki,SATO Kuninori, SEKI Tetsuo, TAKEIRI Yasuhiko, TSUMORI Katsuyoshi, KAWAHATA Kazuo,
NAKAMURA Yukio, NODA Nobuaki, OHYABU Nobuyoshi, MOTOJIMA Osamu,
G1/G2 Experimental Group, XU Y. Yuhong2, ZHONG Guang3, ZANZ,A Vincenzoa,
BRACCO Giovannia, SIBIO Alessandroa and TILIA Benedettoa
National Institute.for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan'The Graduate University for Advanced Studies
2lnstitutefor Plasma Physics, Academia Sinica, 230031, Hefei, Anhui, China'Southwestern Institute of Physics, ChinaaENEA Frascati, Enrico-Fermi, Frascati, Rome, Italy(Received: 18 January 2000 / Accepted: 19 April 2000)

Abstract
The development of high energy neutral particle measurement system for ion temperature
measurements and high energy particle confinement analysis during neutral beam injection and ion
cyclotron resonance frequency heating experiments in the Large Helical Device (LHD) is described. The
control, data acquisition systems and the horizontal movable stage are prepared to investigate pitch angle
distribution and loss cone for a long discharge in LHD. The preliminary results in plasma experiments
including long discharges are described.

Keywords:
TOF neullal particle analyzer, ion temperature, high energy tail, horizontal scan, long discharge

1. lntroduction

from the negative ion sources will be used in Phase I of
the LHD experiment schedule and three or four 360 keV
deuterium beams (15 MW) will be used in Phase II.
NBIs will inject tangentially and the birth pitch angle ofthe ions from NBI is 0-20 degree. In the experimentwith the ICRF heating of 12 MW, the hydrogen and He3will be used as minorities, whose high energy tails ofover 100 keV can be expected.

High energy neutral particle measurement is among
importantthediagnostics for ion temperature and highenergy particle confinemi:nt analysis during electron
cyclotron resonance (ECR) heating (ECH), neutral beam

injection (NBI) heating and ion cyclotron range
frequency (ICRF) heating (ICRH) in the Large HelicalDevice (LHD, major radius = 3.9 m, average minor
radius = 0.6 m) [l]. Concerning NBI heating, two 180
keV hydrogen beams (8 MW, from l0 sec to 30 min)*

It is important to observe the energy dependence of@2000 by The Japan Society of Plasma
Science and Nuclear Fusion ResearchC o rre s p ondin g aut ho r' s e - mail : o zaki @ nifs. ac.j p444

Ozaki T. et al., Preliminary Results of the Neutral Particle Measurements in Large Helical Device

the pitch angle distribution to investigate theconfinementbf high energy partictes. For this purposethe neutral particle analyzer should have a wide
observation energy range for accelerated particles by(ICRH) and the ability to separate the particle above themaximum energy of the NBI (or accelerated species ofhydrogen, deuterium and helium-3/-4. It is importantthat it has the ability to exclude the noises from D-D
neutron and the strong radiation during heating. We
adopt a time-of-flight (TOF) neutral particle analyzer
which had been developed in ENEA Frascati [2].
The first initiation of LHD succeeded on March of1998. Until now a 80-second discharge has beenachieved. It is important that the analyzer should bematched to long pulse discharges in the control and data

TOF Analyzer

7,'i
NBI#I'

acquisition systems. The spatial scanning ofthe analyzer

Fig. 1 The arrangement of NBI#1, #2 and analyzer.

during long discharges is also important forinvestigating the pitch angle and ion temperature

The analyzer can be scanned horizontally 35
degrees. NBI#1 and #2 are the co- and counterinjectors, respectively.

distributions. The detailed neutral particle measurement
system is described in the reference [3,4j.

2. The Experimental Setup
The analyzer and the movable stage are installed at

the middle plane of LHD on l0-O port. Manydiagnostics for observing the mid-plane plasma are on
the central stage (in our case, Al stage) because themid-plane is located 6 m above the LHD floor. We put

the analyzerlstage at a fan-shape base on Al stage
because the weight of the analyzerlstage is 2 tons andAl stage above is not strong enough. There are twoNBIs (NBI#I and #2) at neighboring ports to10-O.
Especially the beam path of NBI#I is crossed to thesight line of the analyzer. Therefore a large amount ofparticle from the plasma center can be expected, whichis suitable for the high energy distribution measurement(Fig. 1 and Fig.2). The analyzer is set at 5 m from theplasma center in order that the confinement magnetic
field is not disturbed by the analyzer box (magnetizedFig. 2 Photograph of the analyzer stage in LHD.

The analyzer is settled on the movable stage. To
prevent the strong magnetic field of LHD, theturbo pumps are set vertically.

material). The analyzer can be scanned from -2 degrees

to +33 degrees (0 degrees indicates the direction

magnetic axis of the standard configuration plasma,
which can cover the loss cone region according toparticle transport calculations. The rail and screw for thehorizontal scan are made from stainless steel 304(SS304) because the installation of magnetized material
to LHD is restricted. SS304 is too soft to move the stagesmoothly due to bending when the stage with the weightof 2 tons is put on it. Therefore we prepare the fanshaped stainless base under the rail. A stepping motorwith water cooling whiih has enough torque is used todrive the stage. The maximum scanning speed is 20

perpendicular to the 10-O port flange surface).

The merit of LHD is the production of a longsteady plasma. Therefore the spatial ion energy
spectrum/temperature and pitch angle distribution can beobtained by scanning the analyzer during long shots. We

have prepared the movable stage with the scanningradius of 4 m, the horizontal angle of 35 degrees and thevertical angle of 27 degrees (vertical scan is nowimproving). During horizontal scanning, the scanning
angle ranges from 23 to 93 degrees against the central
445

Ozaki T. et al., Preliminary Results of the Neutral Particle Measurements in Large Helical Device

seconds per degree in horizontal scan due to lower
motor torque, therefore l2 minutes is required for full

five times the central temperature.
The ion temperature obtained from the neutral
particle measurement is compared with one from thecharge exchange recombination spectroscopy (CXRS).
The central ion temperature by CXRS is assumed thatthe shape of the ion temperature profile is equal to oneof the electron temperature because CXRS did not viewthe central ion temperature profile in the experiments.
The both results agree within the accuracy of llvo asshown in Fig. 4.
The neutral flux and ion temperature increase
extremely during ICRH phase. An ion temperature
increase of 300 eV is observed although the storedenergy increases only 70 kJ in this shot. The
temperature of 2.5 keV is observed. The power
dependence between the absorbed ICH power and theion temperature increase is shown in figure 5. The ion
temperature and the stored energy are increased by theICH power. The fact indicates that the ion cyclotron
heating performs efficiently to the ion energy deposit.

scanning.

Due to the super-conducting coil of LHD, the LHD
vacuum vessel is covered by a bell-jar. Therefore theviewing port is too narrow to obtain the large viewing

angle. To obtain the viewing angle of 35 degree, thepivot of the movable stage which is supported by l0-O
port is inside the main port surface of l0-O. The
analyzer system is electrically insulated by a ceramic

break at the pivot and by the glass-epoxy at the fanshaped base. The bending by scanning at the pivot isabsorbed by the bellows. The stress at the pivot due tothe fluctuation of the stage in forward-backward
direction is absorbed bv another one-dimensional
bellows at the duct.

The slit for limitation of particle is exposed tostrong magnetic fields (0.1 T) because it is set near theLHD port. Therefore it is driven by super-sonic motors

with encoders. The controllers/drivers of both thestepping motor and the super-sonic motors are settled on

the movable stage. They are remotely controlled by
RS232C with optical fibers and the Windows NT

Calc. vs EIp. at 3 kev

44machine in the control room.

..}

3. The Preliminary Results

pOto,
xiid+oIn the third experimental cycle, not only ECH butalso NBI and/or ICRH plasma experiments wereLog neduced Flux(€b.)- IN

ios neatit, rluxlexp.lo938

performed. The analyzer is set at the standard position ato5su 'the center of the horizontal fan (= 17 degrees). Thestress for the bellow and the cutoff of the viewing are
the smallest there. The angle between the viewing andthe central magnetic axis is 68 degrees at this position.
Figure 3 shows the typical energy spectrum of thehydrogen plasma heated by NBI. In this shot, ECH
plasma is heated by NBI (NBI#z, 160 kev, lMW,
counter injection). The spectrum has a MaxwellianJ34

Ti=3i05

10152025

Energy (keV)

Fig. 3 Typical Energy spectrum at the NBI plasma.
The straight line indicates the calculation results.

distribution at the low energy range. The ion
temperature can be obtained from the slope of theT|(NPA) vs Ti(CXBS)/Te(Thomson)

3spectrum. The electron temperature and the electron

2.5q)

density profiles are measured by the Thomson scatteringand the millimeter wave/the fir infrared interferometer.
respectively.
Assuming the background neutral profile and thecentral ion temperature, we can calculate the neutral fluxand compare the spectrum with the experimental one.

ratl

2z.! 1.5

F-1

The straight line in Fig. 3 indicates the calculated
spectrum under the experimental condition. Both spectra
are agreed well at Ti = 3 keV. The results shows that the1

1.5

2

2.5

3

Ti-NPA(r=O)/expected (kev)Fig. 4 The comparison of NPA with CXRS.
Two straight lines shows the 10olo errors.

energy range whose slopes are agreed is from twice to446

Ozaki T. et al., Pteliminary Results of the Neutral Particle Measurements in Large Helical Device

I:;380400

70350

60300

NPA Horizontal Scan in NBI Plasma
101

850

250

40200 :o+80-{.NE ro'u

-376lottc)

rso 5

20100

1050

go0! ro'u

200

400(kw)600

800

degi:-orr53 deg,
+57dcgi,-.1,-r5O degi

30

01o'3- '.- -1OO dtg,dcg,PrcH

1orFig. 5 The preliminary results of ICH heating.

4020

40 60 80 100'120 140Energy (keV)

The stored energy and ion temperature increaseby the lCH.

Fig. 7 Horizontal Scan in NBI plasma.
The values are normalized at the lowest energy.

e150oE 2.5o)

62100

€
.lt

x;1.5-.(t,x15 o.s^:+n.

Tl (k€V)(x t0^19 m-3):

509
t...rwp (kJ)tr00510152025

tto
30

Time (s)Fig. 8 Long Discharge.

Typical ICH long discharge is shown.
Fig. 6 High Energy Tail in ICH plasma.
The high energy tail can be observed during lCH.

with each other up to the energy of several times theelectron temperature.

In the ion resonance mode on ICH plasma, the highenergy tail above 200 keV is observed (Fig. 6). Thisbehavior is remarkable at the low density plasma, andthe high energy tail decreases by the density increase.
The same result can be obtained by the diamonddetector. The angular distribution of the high energy tailis not so large than we expected according to the4. Long Discharge Experiments
In the third cycle, we could succeed a S0-second
discharge by NBI or ICH. Figure 8 shows a typical
waveform and ion temperature. The helium plasma(hydrogen minority) is produced by the initiation by
ECH and additional heating of ICH from 0.5 second to
68.8 second. The radiation slightly increases during
discharge. The breathing was not observed in spite ofhorizontal scan.

We try the horizontal scanning of the neutral
particle measurement in the NBI plasma in order tothe high density (l x l0-ts m-3) because the divertor wascovered with graphite tiles. The ion temperature waskept 1.4 keV. We had measured the ratio of helium tohydrogen by accumulating many signals. The ratio offluxes around l0 keV was equal to the ratio of the gasabundance. We have to keep in mind that this ratio isnear the plasma edge because the helium neutral particle

investigate the high energy particle confinement and theloss cone analysis as shown in Fig. 7 (beam energy of135 keV). Now we are studying and comparing thesimulation results. The spectrum variations above 40
keV come from the amounts of particles with different
pitch angles at the NBI deposition. The significant loss
cone can not be found because each spectrum agrees

is mainly generated there. The long discharge enables us447

Ozaki T. et al., Preliminary Results of the Neutral Particle Measurements in Large Helical Device

to obtain the ratio in one shot. Sometimes bv thesuccessful operation of the analyzer system in theincrease in the ICH power the density decreased.

plasma experiment.

In NBI plasma, a 80-second discharge could besucceeded. The ion temperature was about I keV during

Acknowledgements

the discharge. The plasma was very stable and quiet
similar to the ICH plasma.

for the encouragement. This research is supported byThe authors thank Director General Prof. Fujiwara
Gakujutu Kenkyu of Monbusho.

5. Summary
We have developed the high energy neutral particle
measurement system for LHD. It enables us to observe

References

tll O. Motojima et al., Physics of Plasmas 6, 1843
(l999).

the ion temperature and to investigate the high energy

particle confinement during ECH, NBI and ICRH

t2l G. Bracco et al., Rev. Sci. Instrum. 63, 5685

plasmas including long duration plasmas. The horizontal(1992\.

scan of the analyzer to measure the pitch angle[3] T. Ozaki et al., Fusion Engineering and Design, 34-distribution, especially in the long pulse discharge on

3s, s35 (1997).

LHD has been succeeded. We can confirm the[4] T. Ozaki et al.,RLev. Sci.Instrum.7l,2698 (2000).

448