J. Plasma Fusion Res. SERIES, Yol.I (1998) 27-29

Profile Gontrol Studies on Heliotron-E
OBIKI Tokuhiro*, OKADA Hiroyuki, KONDO Katsumir, SANO Fumimichi, ZUSHI Hidekil,
HANATANI Kiyoshi, MIZUUCHI Tohru, BESSHOU Sakael, NAGASAKI Kazunobu,
WAKATANI Masahiror, NAKAMURA Yujil, NAKASUGA Masahikor, UIRI Yoshiyuki,
5ENJU Tohru, YAGUCHI Keiji, KOBAYASHI Sakuji, TOSHI Kiyoshi, SAKAMOTO Kinzo,KURIMOTO Yuji, HAMADA Takateru, SUDO Shigeru2, SATO Motoyasu2, IDA Katsumi2,FUNABA Hisamichi2, KADO Shinichiro2, PETERSON Byron J.2, MURAOKA Katsunori3,
SUGAI Hideoa, TOYODA Hirotakaa, SASAKI Koichia, KOKURA Hikarua, MATSUO Keijis,SERGEEV Madimir Yu.6. KHLOPENKOV KonstAntiN V.6, CHECHKIN ViCtOT V.7
and VOITSENJA Vladimir S.7
Institute of Advanced Energy, Kyoto University, Uii 611-0011, Japan
IGraduate School of Energy Science, Kyoto University, Uii 611-0011, Japan
2National Institutefor Fusion Science, Toki 509-5292, Japan
3Interdisciplinary Graduate School of Engineering Science, Kyushu Univ., Kasuga 816-8580, JapanaFaculty of Engineering, Nagoya University, Nagoya 464-8602, Japan
5Faculty of Engineering, Fukuoka Institute of Technology, Fukuoka 811-0295 Japan
6State Technical University, St. Petersburg 195251, Russia
TKharkov Institute of Physics and Technology, Kharkov 310108, Ukraine(Received: 30 September t997/Accepted: 22 October L997)

Abstract
In Heliotron-E device, the effects of combined heating with ECR and NBI on profile formationand confinement have been studied. The various profiles can be obtained by the control of the heatingpower, the heating method and the density. With the high power NBI, the peaked electron density andion temperature profiles are achieved simultaneously. On the contrary, the peaked electron temperatureand flat density profile is brought by ECH. The profile effects on the global energy confinement in themedium density region are discussed in this paper.
Keywords:
global confinement, profile control, high 4 mode, LHD scaling, local transport, neutral beam injection,
electron cyclotron heating

ing-out'phenomena[2] except for the high density case.
When the ECH pulse is applied on the target NBI
plasma, the electron temperature in the central region
was increased and peaked since the power density ofthe ECH at the center is comparable to that of NBI although total ECH power is low (about 0.4 MW) compared with the total NBI power (1-3 MW). At the1. lntroduction
In order to study the transport in the rare collisional region for the aims of improvement of the confinement and the expansion of the operation range, thecombined heating of the ECH and NBI has been carried out in Heliotron-E under the boronized wall condition[1]. Typical ECH plasma is characterized by thebroad density profile caused by strong particle 'pump' Corresponding@1998 by The Japan Society of Plasma
Science and Nuclear Fusion Researchauthor's e-mail: obiki@ iae.kyoto'u.ac.ip27

Obiki T. etal.. Profile Control Studies on Heliotron-E

same time the density in the central region decreases
because of strong 'pumping-out'. In NBI heating plasmas, high d mode was reported[3] for the example ofthe confinement improvement. In this mode, the central
ion temperature increases as the peakedness of the2.5{2oelectron density increases. We studied on the relation-between the density peakedness and the appearance ofhigh { mode.
In this paper, we discuss the global confinement

1.5Low T, Modetime of the ECH and/or NBI heated plasmas in themedium density range (from 1.0x101e m-3 to 6x101em-3;. The relation between the global confinement, thelocal transport and various plasma profiles is investigated. The electron temperature and density profiles
are measured by Thomson scattering and the ion temperature profile is measured by the charge exchange
recombination spectroscopy. The stored energy is calculated from these data with the assumption that theion density equals to the electron density. The global
confinement time zf is derived by the equation,

r$: W/(P^o"- dw/dt)

1l.s

2

2.5

3

3.5

44.s

ng(0Y<ne>Fig. 1 The ion temperature-peaking parameter versus theelectron density-peaking parameter (open circle:NBl, solid rectangular: ECH overlapped NBI). High (mode region and low f, mode region are separated.

ECH Property

(1)

3.5

where W is the total stored energy, P"o. is the total ab-f3

sorption power by NBI heating and/or ECH. The lastterm of the denominator on the right hand side is estimated from the diamagnetics signals. In most of all dataprocessed, dW/dt is less than 10% of P"0,.

?
F{ ,.t22. Peaking Parameter Range

11.5

2

2.5

3

3.5

4

4.5

ns(0ftn6>

In this section, the peaking parameter range for theelectron density (4), tl" electron temperature (f) andFig.2 The electron temperature-peaking parameter versus the electron density-peaking parameter (opentriangle: ECH, open circle: NBl, solid rectangular:

the ion temperature ( l) is described. The peaking parameter is defined as follows, d:a(O)/ ( a), wherea(0) is the central value of the parameter 'a' and ( a)denotes the averaged value in the poloidal cross section. In this study d is from 1.2 to 4.5. This range is
obtained only by NBI heated plasmas (P*", is from 1 to3.3 MW). The parameter 4 of. ECH overlapped NBI
heating plasmas does not become large because of theparticle 'pumping-out' in the core region by ECH effect. With higher NBI power, larger fi"is obtained.
The parameter 4 of NBI heated plasma is in theECH overlapped NBI). The peaked f, and peaked n"

profiles can not be achieved simultaneously.

ECH, the range of i is t o- I.3 to 2.4.It is greatly extended by ECH up to 4.1. The on-axis 106GHz ECH
realizes the highest Q. The electron temperature andthe density cannot be peaked simultaneously because
the density 'pumping-out' mechanism can not be overcome when [(0) is high or ECH power in the central
region is not sufficient when n"(0) is large. With highrange from t.4 to 2.7. \and a have positive correlation for high 4 mode plasmas, as shown in Fig. 1. Thistendency agrees with the discussion of high { mode.
There is no high I plasma in the low d" region. But
there is another branch in the large d" region, i.e. thelow 7] mode plasma exists in this region, too. The key
issue of the bifurcation is still under investigation. ECH
plasmas can not extend the range of f" and d. How-

power NBI, the ECH effect on 7" and f" disappears
due to the insufficient ECH power and cutoff according
to the high density of that parameter region.

3. The Profile Effects on the GlobalConfinement Time
When the characteristics of the global confinement
time is considered, the empirical scaling is usually used

ever, ECH has great effect on Z: Glg. 2). Without

28

Obiki T. eral.. Profile Control Studies on Heliotron-E

to discuss the improvement, the parameter dependence,and so on. We use the LHD scaling[4] as the standardof the global confinement because it is deduced fromthe data set of Heliotron-E experiment. The parameter3r

dependence is as follows,P 0.9

1.21.1rlno : 0.17 dR0.7s P-0r8ue0.6e80.84 (2)*%ECH on NBIo'to.7

where a is the minor radius (m), R, the major radius(m), P"o, total absorption power (MW), n", the line
averaged density (1020 6-:; and B, the magnetic field

1.5

2

2.5

3

3.5

4Te(O/<Ts>

strength (T) at the axis.
The global confinement time for low d mode normalized by LHD scaling decreases with f" as shown inFig. 3. The flat density profile is preferable from thispoint of view. The LHD scaling is deduced from thedata with low i". This plot covers more wide area of n".
High { mode plasma appears at around 2.5 or higherof 1". The slope for high { mode plasma is very small
compared with that for low { mode. Therefore, the degradation of the global confinement in the peaked density seems to be compensated by high 4 mode. Thisfactor of improvement is not so large compared withthat of the ion local heat conduction coefficient in theplasma central region which decreases by factor 10.
The effect of Q on the global confinement is different from that of A €ig. 4). The plots for the global
confinement of the combined heating plasma are lo-Fig.4 The relation between the global confinement andthe electron temperature-peaking parameter (opencircle: NBl. solid rectangular: ECH overlapped NBl,
open rectangular: ECH overlapped NBI in the lowdensity region). The plots of global confinement of
the combined heating plasmas in the low density
region are located in the different region from theNBI data.

4. Summary
With ECH and NBI heating, temperature and density profiles have been controlled in the wide range.
The peaking parameter range is as follows, 4: t.2-4.5,Tr:, I.4-2.7, T": t.3-4.L. But all parameters cannot becontrolled independently. There are several restrictedconditions, for example, the peaked electron temperature and the peaked density profile cannot be achieved
simultaneously. Peaked ion temperature profiles appear
only with the peaked density profiles. The fwo peaking
parameters have linear correlation. The global confinement time for low d mode normalized by LHD scaling
decreases as the density becomes peaked. But the slopeof the global confinement of high f, mode against d" isvery small compared with that of low { mode. This improvement of the global confinement property is considered to be due to high { mode effect.

cated in the different region from those of NBI plasmas. The peaking parameter for the NBI plasma is nar-row, therefore, there is no dependence of the global
confinement time on Q for NBI plasmas. The dependence of the global confinement on the pressure
peakedness is similar to that of f".
1.3
1.2
1.1

Acknowledgment

elU

This work was partly supported by the Collaboration Program of the Laboratory for Complex Energy
Processes, IAE, Kyoto University.

: o.e.,% 0.,o.7

References
1.5[1] T. Obiki et al., Plasma Physics and Controlled Nuclear Fusion Research,1994 (Proc. 15th Int. Conf.,Seville, 1994), Vol.1, IAEA, Vienna, p.757 (1995).
I2l K.Uo et al., Plasma Physics and Contolled Nuclear
Fusion Research, 1982 (Proc. 9th Int. Conf.,Baltimore, 1.982), Vol.2, IAEA, Vienna, p.209 (1983).
[3] K. lda et al., Phys. Rev. Lett.76, L268 (L996).
[4] S. Sudo etal., Nucl. Fusion 30, 11 (1990).

22.533.544.5s
nc(oY<ne>Fig. 3 The relation of the global confinement and the den-sity-peaking parameter (open circle: NBl, solid rectangular: ECH overlapped NBl, solid circle: high {mode NBI). For low I mode plasmas, the global
confinement decreases as the density-peaking parameter increases. The tendency for the high {mode plasma is different.
29