Transport and re-deposition of limiter-released metal impurities

Claaßen, H.A.; Repp, H.

doi:10.1088/0029-5515/23/5/003

Cited by 10 publications

(12 citation statements)

References 11 publications

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“…In one class of models [7,8], M(y) and E(y) are highly non-linear, rising rapidly just near the limiter. In another class of models M(y) and E(y) are linear [9][10][11] or quasi-linear [12]. Since it is not known, at this time, which class of model is more realistic, both have been tried in the analysis.…”

Section: Outline Of Approachmentioning

confidence: 99%

“…(2) SOL 2 is an ad hoc linear model [9][10][11], which approximates to a (different) collisionless model [12]:…”

Section: Outline Of Approachmentioning

confidence: 99%

“…impurity 'cloud' sizes and ^(0)/$° values. A number of other impurity transport codes and models have (3) been developed [9][10][11][14][15][16][17] to describe behaviour near divertor plates and limiters but the Monte Carlo approach seems best suited to incorporating impurity heating and parallel diffusion.…”

Section: Details Of the Lim 1 Codementioning

confidence: 99%

“…(3) The ions heat up according to T,(t) = T B -(T B -T o ) exp(-t/T T ) (10) where v 0 = (8kT 0 /m,7r) m and T T is the Spitzer value.…”

Section: Details Of the Lim 1 Codementioning

confidence: 99%

“…OL = T( to within ± 2 0 % . (10) connection length (separation of limiters along B = 2L C ) a plasma minor radius a w limiter-wall distance At time step x 0 , y 0 launch point of Z x = 1 ions ov iz (T) ionization rates…”

Section: T T*\mentioning

confidence: 99%

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Monte Carlo modelling of impurity ion transport for a limiter source/sink

Stangeby¹,

Farrell

Hoskins

et al. 1988

Nucl. Fusion

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In relating the impurity influx , 0 [atoms per second] into a plasma from the edge to the central impurity ion density n,(0) [ions-m~3], it is necessary to know the value of T, SOL , the average dwell time of impurity ions in the scrape-off layer. It is usually assumed that T, SOL = L c /c s , the hydrogenic dwell time, where L c is the limiter connection length and c s is the hydrogenic ion acoustic speed. Monte Carlo ion transport results are reported here which show that, for a wall (uniform) influx, T, SOL is longer than L c /c s , while for a limiter influx it is shorter. Thus for a limiter influx n,(0) is predicted to be smaller than the reference value. Impurities released from the limiter form ever large 'clouds' of successively higher ionization stages. These are reproduced by the Monte Carlo code as are the cloud shapes for a localized impurity injection far from the limiter.

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Section: Outline Of Approachmentioning

confidence: 99%

“…(2) SOL 2 is an ad hoc linear model [9][10][11], which approximates to a (different) collisionless model [12]:…”

Section: Outline Of Approachmentioning

confidence: 99%

Section: Details Of the Lim 1 Codementioning

confidence: 99%

“…(3) The ions heat up according to T,(t) = T B -(T B -T o ) exp(-t/T T ) (10) where v 0 = (8kT 0 /m,7r) m and T T is the Spitzer value.…”

Section: Details Of the Lim 1 Codementioning

confidence: 99%

Section: T T*\mentioning

confidence: 99%

See 3 more Smart Citations

Monte Carlo modelling of impurity ion transport for a limiter source/sink

Stangeby¹,

Farrell

Hoskins

et al. 1988

Nucl. Fusion

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Dynamics of Impurities in the Scrape‐Off Layer

Stangeby

1988

Contrib. Plasma Phys.

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U n i v e r s i t y o f Toronto I n s t i t u t e f o r Aerospace Studies 4925 D u f f e r i n S t r e e t , Downsview, Ontario, Canada, M3H 5T6 and JET J o i n t Undertaking, Abingdon, Oxon OX143EAA b s t r a c t I m p u r i t y m o d e l l i n g o f t h e Scrape-Off Layer, SOL, i s reviewed. Simple a n a l y t i c models a r e sometimes adequate f o r r e l a t i n g c e n t r a l i m p u r i t y l e v e l s t o edge plasma c o n d i t i o n s and f o r e x p l a i n i n g t h e p a t t e r n s o f n e t e r o s i o n / d e p o s i t i o n found on l i a i t e r s .More s o p h i s t i c a t e d approaches, which a r e a l s o necessary, are categorized and reviewed.A p l e a i s made f o r t h e a c q u i s i t i o n o f a more comprehensive data base o f edge plasma p r o p e r t i e s s i n c e r e l i a b l e i m p u r i t y m o d e l l i n g appears t o be dependent on more e x t e n s i v e use o f experimental i n p u t . I n t r o d u c t i o n reasons, each one o f which could be considered s u f f i c i e n t t o warrant a major e f f o r t on t h e problem:A. I n o r d e r t o p r e d i c t / e x p l a i n/ reduce t h e c e n t r a l p l asma iinpuri t y d e n s i t y i t i s necessary t o understand t h e i m p u r i t y source and s i n k -both o f which a r e a t t h eedge.l a r g e l y governed by edge plasma conditions. ( b ) Generally t h e r e i s an upper l i m i t t o t h e t o t a l plasma pressure ( f l -l i m i t ) and thus ImpWhy study t h e behaviour o f i m p u r i t i e s i n t h e edge plasma? There a r e several &. Even t h e i m p u r i t y t r a n s p o r t , t h a t i s , t h e l i n k between source and s i n k , i s o f t e nThe presence o f i m p u r i t i e s i n t h e main imply high l e v e l s o f c e n t r a l r a d i a t i o n , Prad, which lowers A c e n t r a l i o n temperatures, Ti, thus t h e f u s i o n power, PF. t o ntotal; t h e r e f o r e an increase i n s. i m p l i e s a decrease i n GDT ( f u e l d i l u t i o n )and hence a r e d u c t i o n i n PF. It i s b e l i e v e d t h a t h i g h r a d i a t i v e l e v e l s i n t h e o u t e r r e g i o n o f t h e main plasma, o r perhaps even within t h e SOL i t s e l f , induce Parfes, D e t a c h 4 Plamas, t h e d e n s i t y 1 i m i t d i s r u p t i o n s , etc; t h e r e f o r e i n t h e high-iie approach t o f u s i o n i m p u r i t i e s again reduce PF.Net erosion.(c) B.A separate problem i s t h a t t h e edge s t r u c t u r e i s g r a d u a l l y destroyed by plasma c o n t a c t , compromising t h e p h y s i c a l i n t e g r i t y o f t h e device. F o r t u n a t e l y most o f t h e removed m a t e r i a l re-deposits elsewhere i n t h e vessel, only a f r a c t i o n being permanently removed by t h e vacuun pumps. Whether t h e r e -d e p o s i t i o n w i l l occur where i t i s needed and whether t h e plasma-resistance p r o p e r t i e s o f t h e re-deposited m a t e r i a l are as good as t h e o r g i n a l remains t o be demonstrated. C.Ash Removal. Even i f a l l plasma-wall i n t...

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2D Transport Calculations for Carbon Ions in the Plasma Edge

Claaßen¹,

Gerhauser²,

Reiter³

1990

Contrib. Plasma Phys.

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i t e r ') I. I n t r o d u c t i o nFor p r e s e n t day tokamaks t h e i m p u r i t y t r a n s p o r t t h e o r y is m a r g i n a l l y a p p l i c a b l e in the low c o n c e n t r a t i o n l i m i t , s i n c e t h e i n e q u a l i t y h o l d s ( -, + , z denote r e s p e c t i v e l y e l e c t r o n s , hydrogen ions and z-fold i o n i z e d i m p u r i t i e s ) .The t r a c e i m p u r i t y t r a n s p o r t problem is u s u a l l y t r e a t e d f o r given hydrogen plasma par a m e t e r s (from experimental o b s e r v a t i o n s o r simple t h e o r e t i c a l c o n s i d e r a t i o n s ) , a lthough t h e u l t i m a t e g o a l is t o combine t h e impurity.transport c a l c u l a t i o n s with t h o s e f o r t h e hydrogen background i n t r o d u c i n g s coupling v i a t h e r a d i a t i o n l o s s e s and t h e e l e c t r o n temperature dependence of both Langmuir s h e a t h p o t e n t i a l and p h y s i c a l s p u tt e r i n g y i e l d of t h e l i m i t e r ( o r d i v e r t o r t a r g e t ).There a r e b a s i c a l l y t h r e e methods t o t r e a t t h e t r a c e impurity t r a n s p o r t problem: a s t a t i s t i c a l Monte-Carlo method / l / , a d i r e c t k i n e t i c method a t t e m p t i n g t o o b t a i n an exact a n a l y t i c a l s o l u t i o n / 2 / or a numerical e v a l u a t i o n of t h e k i n e t i c e q u a t i o n satisf y i n g microscopic boundary c o n d i t i o n s , and t h e moment method. The l a t t e r s o l v e s t h e k i n e t i c e q u a t i o n and t h e corresponding boundary c o n d i t i o n s only approximately by int r o d u c i n g a t r u n c a t i o n when expanding t h e d i s t r i b u t i o n f u n c t i o n i n t o b a s i s f u n c t i o n s with expansion c o e f f i c i e n t s s u b j e c t t o moment ( t r a n s p o r t ) e q u a t i o n s . Whereas a l l t h r e e methods can i n p r i n c i p l e handle t h e whole c o l l i s i o n a l i t y regime of t h e p a r t i c l e spec i e s under c o n s i d e r a t i o n (concerning t h e s e r i e s expansion s e e , f o r i n s t a n c e , / 3 / ) , t h e moment method h a s i t s s p e c i a l merits in d e a l i n g w i t h c o l l i s i o n dominated t r a n s p o r t phenomena ( f l u i d model, see / 4 / ) , s i n c e t h e convergence of t h e s e r i e s expansion im-proves with i n c r e a s i n g c o l l i s i o n a l i t y when u s i n g a p p r o p r i a t e b a s i s f u n c t i o n s . * In t h e following ue use t h e moment method t o d e s c r i b e t h e c l a s s i c a l ( " 8 ) andanomalous (xB) i m p u r i t y i o n t r a n s p o r t in a high density-low temperature edge plasma in c o n t a c t w i t h a l i m i t e r (assumed t o have a plane s u r f a c e IS). In t h i s c a s e t h e b a s i s f u n c t i o n s f o r t h e moment E t h o d should i n z e r o o r d e r approximation reduce t o a s h i f t e dMaxwellian accounting f o r t h e p o s s i b i l i t y of l a r g e p a r a l l e l ("B) i o n flow v e l o c i t i e s i n f r...

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Transport and re-deposition of limiter-released metal impurities

Cited by 10 publications

References 11 publications

Monte Carlo modelling of impurity ion transport for a limiter source/sink

Monte Carlo modelling of impurity ion transport for a limiter source/sink

Dynamics of Impurities in the Scrape‐Off Layer

2D Transport Calculations for Carbon Ions in the Plasma Edge

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