J. Plasma Fusion Res. SERIES, Vol.5 (2002) 201-204

High Energy Particle Measurements during Long
Discharge in LHD
OZAKI Tetsuo, GONCHAROV Pavelr, LYON Jim3, MURAKAMI Sadayoshi, SUDO Shigeru,
NAKANISHI Hideya, KOJIMA Mamoru, YAMAUCHI Kenji, SHOJI Mamoru, KUMAZAWA Ryuhei,
MUTOH Takashi, SEKI Tetsuo, WATARI Tetsuo, SAITO Kenji2, TORII Hiroki2, OKA Yoshihide,
OSAKABE Masaki, TAKEIRI Yasuhiko, TSUMORI Katsuyoshi, KANEKO Osamu, OHDACHI Stoshi,SASAO Mamiko, SAKAKIBARA Satoru, INAGAKI S., PETERSON Byron, KUBO Shin,SHIMOZUMA Takashi, IDEI Hiroshi, KAWAHATA Kazuo, NAKAMURA Yukio,
NODA Nobuaki, OHYABU Nobuyoshi, MOTOJIMA Osamu, FUJIWARA Masami
and Gl/G2 Experimental Group
National Institute for Fusion Science, 322-6 Oroshi Toki Gifu, Japan
lThelJniversity for Advanced Studies, Japan^graduate"Nagoya University, Nagoya 464-8603, Japan
3oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA(Received: 11 December 2001 / Accepted: 10 July 2OO2)

Abstract
The spatial resolved energy spectra can be observed during a long discharge of NBI plasma bycontinuously scanning the neutral particle analyzer. In these discharges, the plasmas are initiated by theECH heating, after that NBI#2 (Co-injection) sustains the plasma during 40-60 seconds. The scanned
pitch angle is from 44 degrees to 74 degrees. The injected neutral beam (hydrogen) energy of NBI#2 isonly 130 keV because the original ion source polarity is negative. The shape of spectra is almost similarfrom 44 degrees to 53 degrees. However the spectra from 55 degrees are strongly varied. It reflects theinjection pitch angle of the beam according to the simulation (53 degrees ot R* = 3.75 m in simulation).
The beam keeps the pitch angle at incidence until the beam energy becomes to the energy, which thepitch angle scattering is occurred by the energy loss due to the electron collision. The low flux region canbe observed around 10-15 keV, which is 15 times of the electron temperature. The energy region may beequal to the energy at which the pitch angle scattering is occurred. At the energy, the particle is scatteredby the collision with the plasma ions and some of particles may run away from the plasma because they
have a possibility to enter the loss cone. According to the simulation, the loss cone can be expected at the10 keV with the small angular dependence. The depth of the loss cone is deep at the small pitch angle.
The hollow in the spectrum may be concluded to be the loss cone as the tendency is almost agreed withthe experimental result.

Keywords:
TOF neutral particle analyzer, long discharge, horizontal scan, pitch angle@20O2by The Japan Society of Plasma
Science and Nuclear Fusion ResearchC o rr e sp o ndin g aut ho r' s e - mail : o zaki @ nifs. ac.j p20r

Ozaki T. et al., HighBnergy Particle Measurements during Long Discharge in LHD

1. lntroduction.
The time-of-flight type NPA (neutral particle

The scan control and the angle reading system areshown in Fig.2. The position (=angle) can be measured
from the length of the stainless wire between the stage

analyzer, maximum/minimum observable energy 0.5/

370 keV, typical energy resolution lVo) has thecapability of a high S/N ratio against the radiation
including soft/hard X-rays from plasmas [11. Theand a fixed point. The position data are sent to aWindows computer. At the same time, the timing dataanalyzer and the movable stage are installed at the mid-triggered by the LHD discharge initiation.

can be provided to the computer from a timer, which isplane of LHD on the 10-O port. There are two NBIs
(NBI#I and#2) at neighboring ports to 10-O. (Fig.1) In
particular, the beam path of NBI#I crosses the sight lineof the analyzer. Therefore a large amount of particles
from the plasma center can be expected, which issuitable for the high-energy distribution measurement.
The scanning is performed with the pivot in front of the2. Results in NBI Long Discharge
The spatial resolved energy spectra can be observed
during a long discharge of NBI plasma by continuously
scanning the neutral particle atalyzer [2]. Figure 3(a)shows the time evaluated (-angular distributed) 3
dimensional spectrum obtained by overlapping of three
NBI plasma discharges. The pitch angle means the angle
between the sight line and the central magnetic axis. In
these discharges, the plasmas are initiated by the ECH
heating, after that NBI#2 (Co-injection) sustains thel0-O port by using a motor, which is remotely
controlled from -2 degrees to +31 degrees (0 degrees
indicates the direction perpendicular to the 10-O port
flange surface). The angles are equal to the pitch angle(the angle between the magnetic axis and the sight line)of 100 degrees and 40 degrees, respectively. A CCD

plasma during 40-60 seconds. The scanned pitch angle

camera monitors the angle.

Fig. 3 (a) The spatial-resolved neutral particle energyspectrum in NBI long discharge.

Fig. 1 The spatial-resolved neutral particle energy spectrum in NBI long discharge.

10r8

ffi

r4:
r51

1 017

rot'5lt\51

1-tl::

0de(isqr5i 9de(\5! 9de(rt.7I

vc$t
3de{

1or5t
1014

Energy(keV)
Fig. 3 (b) Energy spectrum of each pitch angle obtained

Fig. 2 The apparatus ofthe neutral particle analyzer andby Fig. 3(a).

LHD.

202

Ozaki T. et al., High Energy Particle Measurements during Long Discharge in LHD

3. Results in ICH PlasmaHigh-energy particles over 250 keV can beobserved from ICH in NBI plasma. The pitch angle

is from 44 degrees to 74 degrees. The electron density
measured by an interferometer is kept to be almostZxl}te cm-3 during the discharge except the plasma
initiation phase. At the initiation phase by ECH plasma,

distribution can be obtained by using the same scanning
method as the scanning in NBI plasma. Figure 5(a)shows the spectra during the ICH phase. The

the high-energy particle flux is enhanced as the density

is too low and the background neutral density is high.
The injected hydrogen neutral beam energy of NBI#2 isonly 130 keV because the original ion source polarity iscomplicated energy spectrum can be obtained when theparticle is integrated along the sight line because thehigh-energy particle has the pitch angle dependence. It
is easy to compare with the predicted simulation result
when the spectra are translated on to the velocity phasenegative. The high-energy beam over the injection beamenergy cannot be observed, as there is no ICRF heating.

Figure 3(b) shows the spectra at some typical pitchangles. The shape of spectra is almost similar from 44space. (Fig. 5(b)). The Vperp and Vpara can be obtained

degrees to 53 degrees. However the spectra from 55
degrees are strongly varied. It reflects the injection pitch
angle of the beam according to the simulation (53from the pitch angle and the energy in Fig. 5(b) [3]. The
equatorial line shows the logarithm of the flux. The

degrees at Rq - 3.75 m in simulation). The beam keeps

which is well known in the theory, can be obtained. Thethe pitch angle at incidence until the beam energy

difference of the sight line length (flux) is not so

becomes to the energy, which the pitch angle scattering

effective against the structure because the equatorial line

is occurred by the energy loss due to the electronis plotted in logarithmic scale. The pitch angle ofparticles accelerated by ICH is oblique rather than"butter-fly" shape structure (peak angle of 63 degree),collision. The low flux region can be observed around
1G-15 keV which is 15 time so the electron temperature.
The energy region may be equal to the engrgy at which
the pitch angle scattering is occurred. At the energy, theparticle is scattered by the collision with the plasma ion
and some of particles may run away from the plasma

ICRH Ho.izontal Scant0 ''1017
48 deg.
1 016

because they have a possibility to enter the loss cone

^ lotu(the ripple diffusion). Figure 4 shows the simulation

E ro'oresult. According to the simulation, the loss cone can be?,0"

expected at the l0 keV with the small angulardependence. The depth of the loss cone is deep at thesmall pitch angle. The hollow in the spectrum may be

1011

i ro',--a- - e7 deg

AI1010concluded to be the loss cone as the tendency is almost
agreed with the experimental result. Changing theplasma magnetic axis can reduce the loss cone.

+-89deg

LeA,

EE e\-_\j \.\tl$\:----10"

100

150

- 200

Energy(keV)

Fig. 5 {a) The energy spectrum of each scanning angle.
The vertical error bars are smaler than simbols.

GNET Simulation in LHD
dogl5roo-37*9i4c<jegoo150204060'\ \80100 120Fig. 5 (b) Flux plotting on the velocity phase space. TheEnergy (keV)

maximum flux is observed at the pitch angle ofFig. 4 GNET Simulation in NBI plasma.

63-70 degree.
203

Ozaki T. et al., High Energy Particle Measurements during Long Discharge in LHD

is scanned from 75 to 90 degrees during three-60

perpendicular against the magnetic axis. The fact showsobserved particles are mainly the helically trapped

seconds discharges (Fig. 6). The experimental condition

particles. The helically trapped particles draw theis as follows; the magnetic axis, the magnetic field, thestored energy and the density are 3.6 m,2.75 T, 100 kJ
and lx10-1e m-3, respectively. ICH of the power of 1.0
MW is applied from two antennas at 3.5U and 3.5L. It
makes the resonance region around al2 at the lower
magnetic field side. Unfortunately we cannot succeed tobanana orbit. The particle is perpendicularly accelerated
against the magnetic line by the ion cyclotron heating at
the tip of the banana orbit. However the banana tip is at

the lower magnetic side than the ion cyclotronresonance. Therefore the velocity of the particle on thesee the scanning region, which the structure of thebutter-fly can be expected. However another peak ofthe
flux can be observed near 85 degree lower than 6 keV.
Now we are considering the reason. We can show thepossibility to make clear some generation mechanism ofhigh-energy particle structure by the continuous

cyclotron resonance has the parallel component against
the magnetic line. The peak angle of the butter-fly
shaped depends on the resonance position. The peakangle is about 70 degree on the 4th cycle experimentwhen the resonance is off axis.

scanning on LHD long discharge.

4. Results in ICH Long Discharge
5. Summary

The energy spectra are measured when the analyzer
is continuously scanned in the long discharge. 120
seconds on ICH plasma can be succeeded in the 4th
campaign of LHD. The merit in the diagnostics of thelong discharge is the capability of the accumulation ofThe time-of-flight type neutral particle analyzer
system can be provided the pitch angle distribution inNBI and ICRF heating plasmas. The hollow in theenergy spectrum of NBI plasma may be the loss cone
according to lhe comparison with the simulation. The

data and the spatial scanning under the almost same
experimental condition. In the experiment, the analyzer

spatial distribution of high-energy particles in ICH
plasma can be also obtained. The butter-fly structure ofthe distribution function based on the helically trapped
particle can be observed in NBI plasma.

Referencestll

T. Ozaki, Y.Zanza, G. Bracco, A. Moleti, B. Tilia,A. Sibio, S. Sudo, H. Nakanishi, M. Kojima, M.
Shoji and Gllcz experimental group, Rev. Sci.

Instrum. 7 l(7 ), 2698 (2000).
I2l T. Ozaki. S. Sudo et al.. J. Plasma and Fusion Res.

*-'-*i7i

SERTES 3,444 (2000).

t3l K. Saito, R. Kumazawa, T. Mutoh, T. Seki, T.
Watari, T. Yamamoto, Y. Torii, N. Takeuchi, Y.
Zhoa, A. Fukuyama, F. Shimpo, G. Nomura, M.
Yokota, K. Kato, M. Sasao, M. Isobe, T. Ozaki etal., to be published in Plasma Phys. Control. Fu-Fig. 6 The spatial-resolved neutral particle energy spectrum in ICH long discharge.

sion.

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