SPIKY DENSITY FLUCTUATION AND RELAXATION OSCILLATION IN AN ANOMALOUSLY RESISTIVE PHASE

(1)

HAL Id: jpa-00219266

https://hal.archives-ouvertes.fr/jpa-00219266

Submitted on 1 Jan 1979

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

SPIKY DENSITY FLUCTUATION AND RELAXATION OSCILLATION IN AN ANOMALOUSLY RESISTIVE PHASE

Y. Takeda, M. Yokota

To cite this version:

Y. Takeda, M. Yokota. SPIKY DENSITY FLUCTUATION AND RELAXATION OSCILLATION IN

AN ANOMALOUSLY RESISTIVE PHASE. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-

577-C7-578. �10.1051/jphyscol:19797279�. �jpa-00219266�

(2)

JOURiVAL DE PHYSIQUE CoZZoque C7, suppZ6ment atr n07, Tome

40,

JuiZZet

1979,

page C7- 577

SPIKY DENSITY FLUCTUATION AND RELAXATION OSCILLATION IN AN ANOMALOUSLY RESISTIVE PHASE

Y. Takeda and

M.

Yokota.

Department of Physics, College of Science and Technology, Nihon University, Tokyo, Japan.

1. Introduct*

Over t h e p a s t decade c o n s i d e r a b l e e f t h e dominant p h y s i c a l mechanisms i n v o l v e d phenomena and b e h a v i o r s o f a plasma r e l a t wide r a n g e depending on t h e n o n l i n e a r mech son o f t h e o r y and e x p e r i m e n t s have n o t bee n o n l i n e a r i t y of t h e phenomena.

I n t h i s p a p e r we p r e s e n t t h e f i r s t ex r e s i s t i v i t y which a c c o r d w i t h b e h a v i o r s p r m s n t q

n f

s t r n n r T,an~muir tu r b u l e n c e . 1 ) 72) means of microwave s c a t t e r i n g t e c h n i q u e co e t a 1 . 3 ) which p r e d i c t e d t h e e x i s t e n c e of l o c a l i z e d d e n s i t y c a v i t y i n t h e s t r o n g Lan

f o r t h a s been d i r e c t e d toward i d e n t i f y i n g i n anomalous r e s i t i v i t y of plasmas. The e d w i t h anomalous r e s i s t i v i t y v a r y o v e r a , anism t o be r e s p o n s i b l e . D e t a i l e d compari- n p o s s i b l e due t o t h e complexity and s t r o n g

p e r i m e n t a l o b s e r v a t i o n s o f t h e anomalous e d i c t e d by t h e r e c e n t t h e o r e t i c a l d e v e l o p - Our o b s e r v a t i o n of d e n s i t y f l u c t u a t i o n s by n f i r m e d t h e n u m e r i c a l s i m u l a t i o n by Decroot l a r p e n o t e n t i a l jumps ( d o u b l e L a y e r s ) and gmuir t u r b u l e n c e g e n e r a t e d i n an anomalous- l y r e s i s t i v e p h a s e .

2 . E x p e r i m e n t a l Arrangements

We have c a r r i e d o u t h e a t i n g d i s c h a r g e s i n a magnetic m i r r o r w i t h m i r r o r r a t i o Rhl

=

1 . 2 5 . An i n i t i a l plasma was produced by a hydrogen o r deuterium-immersed t i t a n i u m washer gun. The power of h e a t i n g d i s -

c h a r g e i s s u p p l i e d from a c a p a c i t o r o f 2 . 2

DIRECTIONAL COUPLER

p F w i t h a c h a r g i n g v o l t a g e up t o 30kV.

Main d i a g n o s t i c s u s e d i n t h e p r e s e n t experiment a r e as f o l l o w s . I n o r d e r t o c l a r i f y t h e r e l a t i o n between t h e anomalous r e s i s t i v i t y and t u r b u l e n c e , e l e c t r o s t a t i c

f l u c t u a t i o n s a r e p i c k e d up by a c a p a c i t i v e -

_{TO PUMP}

l y - c o u p l e d probe i n s e r t e d r a d i a l l y i n t o

t h e d i s c h a r g e v e s s e l a t t h e c e n t e r of t h e a p p a r a t u s . A p i c k e d - u p s i g n a l i s p a s s e d

PREAMP.

t h r o u g h a h i g h - p a s s f i l t e r i n o r d e r t o

e l i m i n a t e low f r e q u e n c y (1-2 MHz) and l a r ge a n p l i t u d e components and rough s p e c t r a l

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797279

(3)

analysis of fluctuations using several ban The 4mm microwave scattering system a in Fig. 1. A 400 mW microwave of frequen ularly to the plasma column with the wave of the magnetic field (ordinary mode). I angle Bs is fixed at 9 0 ' .

3. Behaviors of the turbulence in the ph In Fig. 2, typical time traces are s plasma I (b) the HF electrostatic fluct

P'

and detected through a high-pass filter w video out put of the 4mm microwave scatter filters having the center frequency of 70 the lower trace, respectively. It must be dips. one in the early phase, t = 0.4-1.8-

U S , and the other slightly on the flat

tops, t = 3 . 0 - 4 . 3 ~ s ~ henceforth called the phase I and phase I1 respectively.

The resistivity is 3 x 1 0 - ~ ohm-meter in the phase I, nearly twice larger than the Buneman's resistivity. Hence the early stage of the phase I is characterized by the strong two-stream instability.

As seen in Fig. 2 ( b ) , electrostatic fluctuations picked up by the C-coupled probe exhibit fast relaxation oscilla- tions in the saturated state of the phase I, presumably demonstrating the collapse of the plasma waves into spatially localized region.') ")

The filtered video outputs of the 70 GHZ microwave scattering system at eS=9o0 in the midplane show notably spiky fluctu- ation and a feature of relaxation oscilla- tions. These behaviors coincide with the external measurement of turbulent waves with the C-coupled probe.

d-pass filters has been performed.

nd the experimental apparatus are shown cy wi/27r

=

70 GHZ is launched perpendic- electric field polarized in the direction n the present experiment, the scattering

ase of anomalously high resistivity.

hown for (a) heating current through the uations picked up by the C-coupled probe ith pass band 18 !WZ - 145 MHz, (c) the ed signals detected through band-pass MHz for the upper trace and 350 MHz for noted that the time trace of I D shows two

t b )

18-145 MHz

200 n y d i v

65-85 M H z

330-370 MHz 500 n y d i v

Fig.2 References

(1) G. J. Ebrales and Y. C. Lee, Phys.

of Fluids 19, 690 (1976)

(2) K. Elsasser and H. Schamel, Plasma Phys. 19, 1055 (1977)

(3) J. S. DeGroot, C. Barnes, A. E.

lalstead, and 0. Buneman, Phys. Rev.

Lett. 38, 1283 (1977)