PLASMA PHYSICB LABORATORY

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MEASUREMENT OF ALPHA PARTICLES ON PLT

By

T.J. Htirphy and J.O. Strachan

DECEMBER 1984

PLASMA

PHYSICB

LABORATORY

PRINCETOH UNI¥1ES3ETY

PRINCETON, N E W J13ES1T

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DE85 005339

MEASUREMENT OF ALPHA PARTICLES OS PLT

T.J. Murphy and J«D* Strachan

Plasma Physics Laboratory Princeton University

Princeton, NJ 08544

ABSTRACT

The radial evasion profit of the d<3fe.P>« * » ! « reaction was mea.ur.ii

on PLT by pitch angle resolution of the escaping 3.7-HeV alphas. The d-^He

reactions vere produced by 3m minority ICRF and the erosion was strongly

peaked at the ICRF resonance layer.

DISCLAIMER

This report was prepared as an account or work sponsored by an agency of the United States Government. Neither the United Slates Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi­ bility for the accuracy, completeness, or usefulness &f any inftrmation, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer­ ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom­ mendation, or favoring by the United States Government o* any agency thereoT. The views and opinions of authors expressed herein do not necessarily slate or reflect Ihoie of the United States Government or any agency thereof.

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1. INTRODUCTION

Although ion cyclotron resonance heating has raised the central ion and

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electron temperatures on tokamaks, ' tl:e influence oC ICHF heating on the energy confineitent remain:; uncertain. One difficulty in deducing the energy confinement is the fact that the BP eneroy deposition profile is not an experimentally measured quantity. Theoretical calculations are difficult since they require simultaneous three-dimensional modelling of R? wave propagation and damping, particle acceleration and trajectories, as well as possible particle minor radial transport which may be different inside and outside of the RF resonance layer.

In this paper, we report measurement of the radial emission profile of the d(3He,p)a fusion reaction by use of the escaping 3.7-MeV alphas. These

d-3H e reactions are created by the most energetic of the 3H e minority tail,

which can reach energies of 200 kev in P L T .4"6 The principal result is that

the d- He reaction rate i3 peaked strongly at the RF resonance layer as if the reactions are caused primarily by banana trapped He ions with banana tips in the resonance layer. Although we have aeasured the radial profile of the most energetic of the RF heated minority, it is still difficult to specify thd radial RF power profile to the plasma since most of the power is coupled to the thermal ions by lower energy 3He ions which do not cause the d-3He fusion

reactions.

The d- He fusion reaction is usually monitored on PLT by measurement of the 15-Mev p r o t o n .2 , 4'6 However, this proton has so much energy that its

gyrodiaraeter is roughly the minor radius of P L T4 and spatial resolution is

difficult. The measurements reported here are the first measurement of energetic alphas from a toXamak plaama. The eventual use of tritium in tokaoaks will make measurements of the 3,5-MeV alpha from the d(t,n)a fusion

reaction important, since the confinement of that alpha 13 required for

ignition to occur.

II. EXPERIMENT

The PLT plasma (B^ - 32.5 XG, I$ =- 575 to, R =- 132 cm, a » 40 cm,

ng = 3 -x 1 01 3e m ~3, T_ a 2-3 kev, TL a 2-3 keV) was heated by 2 HW of 30-HHz

ICRF i n the 3He minority mode where the 3He d e n s i t y vas about 5-15* of the

e l e c t r o n d e n s i t y . The d ( d , n )3H e f u s i o n r e a c t i o n r a t e was 2 . 8 - 4 . 3 x 1 01 1 per

discharge as monitored by the 2.5-MeV neutron e m i s s i o n .

The escaping 3.7-Hev alphas were monitored by a CR-39 p l a s t i c nuclear track d e t e c t o r .7 - 9 The p l a s t i c was placed behind a pinhole (0.18-mm diameter)

and a s l i t ( 0 . 2 2 mm width) (Fig. 1) and exposed to f i v e PLT plasmas, each having 0.2 s e c duration ICRF. The pinhole was placed d i r e c t l y below the plasma (In the d i r e c t i o n of ion d r i f t s ) and was a l i g n e d p a r a l l e l to the edge of the plasma ( F i g . 1 ) . The p l a s t i c was then etched for 6 hours i n a 6.25N NaOH s o l u t i o n a t 70 C t o reveal the t r a c k s .

The probe assembly shown i n Fig.1 i s 3uch that the v e r t i c a l displacement of tracks corresponds t o r e s o l u t i o n of the gyroradius of the e s c a p i n g p a r t i c l e s . In p r i n c i p l e , one could o b t a i n some energy r e s o l u t i o n of the e s c a p i n g p a r t i c l e s , and for the probe assembly shown i n F i g , 1 the alpha energy r e s o l u t i o n i s about 3 Mev/mm. v e r t i c a l r e s o l u t i o n a l s o i n c l u d e s s e p a r a t i o n of the 15-MeV protons from the 3 . 7 Hev a l p h a s . One-KeV t r i t o n s and 3-HeV protons created by the d ( d , p ) t f u s i o n r e a c t i o n have o r b i t s s o s i m i l a r to the 3.7-HeV alpha t h a t they w i l l not be separated; however, the d e n s i t y of tracks on the p l a s t i c was about seventy times as high as would be expected from 3-MeV proton or 1-Mev t r i t o n tracks as estimated from the 2.5-Mev neutron e m i s s i o n . For pla3ma3 where measurement of the 1S-MeV proton emission was

a l s o a v a i l a b l e , the number of tracks was 70% of the expected number of alpha tracks as estimated from the 15-MeV proton emission ( i . e . , within the experimental u n c e r t a i n t y ) and about ten times the d ( d , p ) t rate as measured by the 2.5-MeV neutrons. Horizontal displacement of tracks on the p l a s t i c corresponds t o r e s o l u t i o n of the p i t c h angle ()<> of the escaping p a r t i c l e s ( F i g . 1 ) . p i t c h angle r e s o l u t i o n of these p a r t i c l e s corresponds to s p a t i a l r e s o l u t i o n from the plasma ( F i g . 2 ) . E s s e n t i a l l y , the escaping 3.7-MeV alphas which can s t r i k e the pinhole a t a p a r t i c u l a r p i t c h angle must have cone down through the plasma on a p a r t i c u l a r t r a j e c t o r y . Thi3 occurs because each alpha t r a j e c t o r y i s a 3 e c t i o n of a very large banana o r b i t or c i r c u l a t i n g o r b i t which i n t e r s e c t s the v e s s e l w a l l , the p a r t i c u l a r o r b i t being determined by the magnetic moment and p a r a l l e l v e l o c i t y of the p a r t i c l e . The t r a j e c t o r i e s in F i g . 2 i n d i c a t e the p o s s i b l e b i r t h l o c a t i o n s of alpha p a r t i c l e s which can contribute to the alpha t r a c k s . Each p i t c h a n g l e corresponds to p a r t i c l e s with a unique midplane c r o s s i n g l o c a t i o n of i t s guiding center (Fig. 3b).

The etched p l a s t i c was analyzed by counting the number of tracks i n 222 micron wide v e r t i c a l s t r i p s corresponding t o s i n g l e p i t c h a n g l e s , and then c o r r e c t i n g for the geometry of the d e t e c t o r . Corrections included f a c t o r s for the projected area of the pinhole and s l i t as seen from various p i t c h and gyroangles, and for the spreading of the tracks due t o the i n c l i n a t i o n of p a r t i c l e t r a j e c t o r i e s t o the p l a s t i c . The number of tracks was divided by the length of the alpha t r a j e c t o r y within 10 cm of the midplane to account for the d i f f e r e n c e i n v e l o c i t y space sampling by d i f f e r e n t o r b i t s ,1 1 then by the

product of the s o l i d angle of acceptance of the h o l e - a n d - s l i t combination and the area of the pinhole to give the d i f f e r e n t i a l fluence of p a r t i c l e s a t the p i n h o l e .

Expressing the corrected number of tracks seen at each pitch angle as a function of the guiding center location Indicates a peak in the emission which is outshifted from the plasma center and is located at the 3H e cyclotron

resonance layer. The width of the emission is approximately equal to the 3.7 MeV alpha gyrodiameter, which determines our spatial resolution for flat emission profiles. The vertical error bars in Fig. 3 are the counting statistics, while the horizontal error bar3 are the uncertainty in the orbit positions caused by lack of knowledge of the plasma current profile. The current profile is assumed to be

r 2 n

j - n -

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i

where n is taken as 3, 4, or 5. The uncertainty in n results in an uncertainty in the guiding center midplane crossing which is largest near the center of the vessel, but is always less than 2 cm, which ia unimportant compared to the gyrodiameter of the alphas.

III. DISCUSSION

p i t c h angle r e s o l u t i o n of the escaping 3.7-MeV alphas has been used t o i d e n t i f y the l o c a t i o n of the d( He,p)a fusion r e a c t i o n s during ICRF resonant h e a t i n g on PLT. This r e s u l t i s r e l a t e d to t h a t of Chrien e t a l . who found that the d-3He rate was maximised when the ICRF resonance l a y e r was near the

plasma c e n t e r . That work was accomplished by monitoring the 15-Mev proton emission l e v e l and s h o t - b y - s h o t changing of the t o r o i d a l magnetic f i e l d to scan the He minority resonance layer through the plasma. The work of Chrien

of the He t a i l while the p r e s e n t work d e s c r i b e s the s p a t i a l l o c a t i o n of the most e n e r g e t i c of the 3He i o n s .

The 15-HeV proton s p e c t r o s c o p i c work of Heldbrink5 i n d i c a t e s that the

e n e r g e t i c He tons causing the d - He f u s i o n r e a c t i o n s have high perpendicular and low p a r a l l e l v e l o c i t i e s . Coupling t h a t information to the p r e s e n t information on the s p a t i a l l o c a t i o n of the d-3He r a t e i m p l i e s t h a t the

e n e r g e t i c He ions probably have 0 . 1 - 0 . 2 HeV of energy and are on banana o r b i t s which have banana t i p s near the Iff resonance l a y e r ( F i g . 4 ) . apparently ( P i g . 3 a ) , some of the He ion3 (~ 10*) are on c i r c u l a t i n g o r b i t s . A3 i n d i c a t e d r e c e n t l y by Hsu e t a l . , t h i s l o c a l i z a t i o n of the d i r e c t l y ICRF heated p a r t i c l e s leads to p o l o i d a l asymmetries i n q u a n t i t i e s such 33 the plasma d e n s i t y and a l s o in the He t a i l h e a t i n g of the background plasma ( e s p e c i a l l y the e l e c t r o n s ) . Furthermore, t h i s l o c a l i z a t i o n of the most e n e r g e t i c He ions t o the region of the resonance l a y e r i n d i c a t e s that t h e s e p a r t i c l e s have not undergone much transport during the time of t h e i r a c c e l e r a t i o n (~ 50 msec) as was a l s o i n d i c a t e d by the time e v o l u t i o n of the d-3He r a t e .6

ACKNOWLEDGMENTS

The authors thank J. HoSea and the PLT group, and D. Hwang, P. Coleatock, R. Wilson, and the ICRF group for their support. They thank W. Heidbrink for helpful discussion and for the orbit code. Valuable discussions with 6. Hammett are also acknowledged. The authors are grateful to G. Estepp for technical assistance. The microscope was provided by S. Cohen, and the oil bath by D. Hcclure.

This work was supported by U.S. Department of mergy Contract No.

REFERENCES

1 J. Hosea eft al., Plasma physics and Controlled Nuclear Fusion Research

(IAEA, Vienna, 1981) p. 95.

2 D. Hwang et al., Plasma Physios r.nd Controlled Nuclear Fusion Research

(IAEA, Vienna, 1983) Vol. 2, p. 3.

3 P.L. Colestock et al. "Heating in Toroidal Plasmas," 2 joint.

Grenoble-Varenna Int. Symposium, Belgium, 1, 471 (1980).

4 s.E. Ovrien et al., Phy3. Rev. Lett. _46_, 535 (1981).

5 W. Heidbrink, Hucl. Fusion 24, 636 (1984).

5 R.E. Chrien and J.D. Strachan, Phys. F l u i d s 26, 1953 ( 1 9 8 3 ) .

E. Muhling, "Eatperimente mit Kernspurdetektoren aur Diagnostik von Protonen und Alpha-Teilchen aua Fusionsplasmen," Max-Planck-Institut fur Plasraaphyaik Report No. IPP 1/210 ( 1 9 8 2 ) .

8 B.G. Cartwright, e t a l . , Nucl. Instrum. Meth. 153, 457 ( 1 9 7 8 ) .

Q "

3 E. Huh ling eft al., to be published.

0 W, Heidbrink, PhD Thesis, Princeton Univ. (1984),

1 W. Heidbrink and J.D. Strachan, "Tokamak Ion Temperature and Poloidal

Field Diagnostics Using 3 MeV Protons," Princeton plasma Physics Laboratory Report No. PPPL-2136 (1984).

FIGURE CAPTIONS

F i g . 1. Schematic of the d e t e c t o r showing the r e l a t i v e placement of t h e p i n h o l e , s l i t , and CR-39 p l a s t i c , and how the parameters of the p a r t i c l e o r b i t a f f e o t the placement of the t r a c k .

F i g . 2. Extreme alpha orbita measured with t h i s d e t e c t o r corresponding t o p i t c h a n g l e s of +0.50 radians ( i n s i d e ) and - 0 . 4 7 radians ( o u t s i d e ) a t the d e t e c t o r (B, = 32.5 kG, 1. « 575 kA).

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Fig. 3. (a) Number of alpha particles reaching the detector per ysr

acceptance angle per cm2 pinhole area per cm alpha path length less

than 10 cm from the mi dp lane. The location of the resonance layer and the diameter of a 3.7-MeV alpha orbit are shown.

(b) Pitch angle at the detector as a function of the major radius of the guiding center midplane crossing for the plasraa parameters mentioned in the text indicating the spatial resolution possible.

Drifting

Alpha Orbit

Pinhole Slit Plastic

Pitcti Angle

X=-0.5 X=0.5

1.75 cm 1.59 cm

MAJOR RADIUS (cm)

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Resonance Layer

Alpha Gyrar.

J.

100 120 140

GC MID-PLANE CROSSING (cm)

160

100 120 140

CC MID-PLANE CROSSING (cm)

160

1 I 1

_{1 1 1 1}

(b)

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MAJOR RADIUS (cm)

D r . Frank J . Paolonl. Unlv ot Wol lonoong, AUSTRALIA

fret. I.R. Jonas, Fllndars Univ., AUSTRALIA

F r o f . K.H, Srennen, Unlv Sydney, AUSTRALIA P r o * , f . Cap, Inst Theo PKys, AUSTRIA

P r o * , frank Verheest, Inst theoretIsene, BELGIUM Dr. 0 . Palumbc, Dg XII Fusion Prog, BELGIUM Ecu I * Royele hi l l t e l r e . Lab dt Phys Plasmas, BELGIUM Dr. P.H. Sakanake, Univ EstadueI, BRAZIL

Or. C.R. Janes, Unlv of Alberta, CANADA P r o f . J . Taieiuwirn, Unlv of Montreal, CANADA Dr. H.H. Skarsgard. Unlv ot Saskateneaan, CANADA P r o f . S.R. Sreanlvason, UnlvarslTy ot Calgary, CANADA P r o f . Tudor K, Johnston, INRS-Enargla, CANADA D r . Hannas Barnard, (Jnlv B r i t i s h Columbia, CANADA Dr. K.P. Bnchynskl, MP6 Technologies, I n c . , CANADA Zhangnu L i , SW Inst Physics, CHINA

L i b r a r y , Tslng Huo University, CHINA L i b r a r i a n , I n s t i t u t e of Physics, CHINA I n s t Plasma Phys, Academla Sin lea, CHINA D r . Petsr Lukae, Komanskaho Unlv, CZECHOSLOVAKIA Tne L i b r a r i a n , Culham Laboratory, ENGLAND P r o f . SehuTziwn, Observatoire ae Nice, FRANCE J . Raaet, CEN-BFS, FRANCE

AH Oupas L i b r a r y , AM Dupas Library, FRANCE Dr. Tan Hue I , Aeuesmy Bibliographic, HONGKONG Preprint L l n r a r y . Cant Res Inst Phys, HUNGARY Dr. S.K. Trehan, Panjab University, INDIA D--. Indre, Hohs,. Lai Das, Banaras Hindu Unlv, INDIA Dr. L.K. Chaves, South Gujarat Unlv, INDIA Dr, R.K. Chhajlani, Var Ruchl Harg, INDIA P. Ka>, Physical Research Lab, INDIA D r . P h i l l i p Roseneu, Israel InsT Tech, ISRAEL P r o f . S. Cupernan, Tel Aviv University, ISRAEL P r o f . G. R o s t a j n l , Unlv Dl Padove, ITALY L i b r a r i a n , I n t ' i Ctr Tt,»o Phys, ITALY Miss C l e l l a Dt PBJO, Assoc ElKATQw-CNEN. ITALY e i b l i o t a c a , del CNR EURATW, ITALY

Dr. H. Yamsto, Toshiba Ses I Dev, JAPAN P r o f . H. Yoshlkava, JAERl, Tokei Res Est, JAPAN P r o f . T. Ut-hloa, UnlverslTY of Tokyo, JAPAN

Research Info Center, Nagoya University* JAPAN P r o f , kyojl NlshlkOKB, Unlv of Hiroshima, JAPAN P r c f . Slgcru f o r i , JAERl, JAPAN

L i b r a r y , Kyoto University, JAPAN P r o f . Ichiro KavekamI, NlhonUnlv, JAPAN P r o f . Setoshl IToh, Kyushu University, JAPAN Tech Info D i v i s i o n , Korea Atomic Energy, KOREA D r . R. England, Ovdad Un I vers I t e r I a, MEXICO BlbMotneek, Fow-lnst voor Plasma, NETHERLANDS P r o f . 6 . S . L l l e y , University of Helkato, NE» ZEALAND Dr. Surasn C. Sharma, Unlv of Calabar, NIGERIA

Dr. Octavlati Petrus, ALI CLE A University, ROXANIA P r o f . M.A. Hellberg, University of N a t a l , SO AFRICA Dr, Jenen ae V I I H e r s , Atomic Energy Bd, SD AFRICA Fusion D l v . l i b r a r y , JEN, SPAIN

P r o f . Hint N l l h a l m o n , Chalmers Unlv Tech, SHE DEN Dr, Lennert S t e n f l o , University of UMEA, SWEDEN Library, Royal Inst Tech, SWEDEN

Or, Erik T. Hanson, Uppsala Untversltet, 5VE0EN Centre de Reeherchesen, Ecole Polytecn f e d , SWITZERLAND Or. w.L. M I S * , t u t ' I Bur Stand, USA

Dr. W,M, Stacey, Georg Inst Tech, USA Dr. S,T, Wu, Unlv Alabama, USA

P r o f . Norman L. Olason, Unlv S F l o r i d a , USA Dr. Benjamin Ha. loaa State Unlv, USA P r o f , Magna K r l s t l a n s a n . Texas Teen unlv, i£A Dr. Raymond Askew, Auburn Unlv, USA

D r . V . T . Tolok, Kharkov Phys Tech Ins, USSR Dr. D.D. Ryutov, Siberian Acad S c l , USSR D r . G.A. E l l s e e v , Kurehatov I n s t i t u t e , USSR Dr, V.A. Glukhlkh, Inst Electro-Physical, USSR I n s t i t u t e Gen. Physics, USSR

P r o f . T . J . Boyd, Unlv College N Kales, WALES Dr. K. Scnlndlar, Ruhr U n l v e r s l t a t , w, GERMANr Nuclear Ras Estab, Jul I eh Ltd, N, GERMANY L i b r a r i a n , Max-Planck I h s t l t u t , K. GERMANY Or. H . J . Keepcler, University Sturrgar-r, W. GERMANr B l b l l o t h e k , Inst Plasmatorscnung, w. GERMANT