RADIO-FREQUENCY WALL CONDITIONING FOR STEADY-STATE STELLARATORS

Transcription

1 RAIO-FREQUENCY WALL CONIIONING FOR SEAY-SAE SELLARAORS Yu. S. Kulyk, V.E.Moisko,. Wauts, A.I.Lyssoiva Istitut of Plasma Physics, Natioal Scic Ct Khakiv Istitut of Physics ad chology, 68 Khakiv, Ukai Laboatoy fo Plasma Physics - ERM/KMS, Associatio EURAOM - BELGIAN SAE, Avu d la Raissac 3, Bussls Blgium

2 MOIVAION Poblm of Wall Coditioig i Psc of Stady Magtic Fild Wall coditioig i magtic fusio dvics is usd aft opig th vacuum chamb to ai o, what is lss hamful, aft usag of vacuum locks. uig such opatios, som substacs a bought to vacuum chamb ad adsobd by its wall. h goal of th dischag wall coditioig is to mov adsobd spcis so that thy may th b pumpd out of th vacuum chamb. A advatag of a RF dischag that is dscibd h is that it could b aagd i stady magtic fild. his is impotat fo th dvics with supcoductig magts at which switchig o/off th magtic fild is much mo complicatd tha i dvics usig copp magts. o b fficit i gatig th utal atoms ad to povid uifom claig th RF dischag should b volumtic ad its plasma should hav low tmpatu.

3 RF ISCHARGES HA USE SLOW WAVE A dischag sustaid by xcitatio of slow wavs at fqucis blow th io cycloto is usd fo wall coditioig. asf of gy fom th wav to th lctos is du to biay collisios. I th dischag plasma is gatd with a dsity substatially lss tha th dsity of utal hydog gas. By th itactio of th plasma ios ad utal hydog atoms with th wall sufacs volatil substacs a fomd. h latt ca b pumpd out fom th vacuum chamb. I such a dischag it is impotat that th plasma dsity is ot high i od to dcas th pobability of ioizatio of dsobd impuitis. Bfo, a simila dischag, but at fqucis high tha io cycloto, has b aalysd ad xpimtally tstd [V.E. Moisko, t al. Nucl. Fusio 54 (4) 339].

4 ELECROMAGNEIC WAVES IN LOW ENSIY PLASMA wo wavs xists i cold plasma: Fast magtosoic wav (dos ot popagat bcaus of low plasma dsity); Slow wav dispsio quatio is It ca popagat if Slow wav k k is dampd fficitly owig to th lcto-utal collisios ca b shot-wavlgth. k k k.

5 EXCIAION OF SLOW WAVES h slow wav ca b xcitd by a ata havig cuts paalll to th stady magtic fild. h fam ata is th simplst ata havig this ability. h ata ca b small-sizd. h sigl fam ata was usd bfo i th calculatios ad xpimts. Pvious umical calculatios idicatd that th fam ata is ot optimum fo such a dischag sic it xcits low k wavs. Fo succssful stat-up of th dischag, it is cssay to povid ovlappig of th slow wav global soacs. his is difficult to povid fo low k soacs. o xcit th slow wav, a doubl fam ata was usd istad of th sigl fam ata. his suppsss xcitatio of logwav mods (low k ).

6 GLOBAL RESONANCE OVERLAPPING h ladig cotibutio to th collisioal dampig of th wav is mad by th imagiay pat of Im R( ), wh is th lcto-utal collisio fqucy. I th plasma colum, th slow wav foms global soacs. Each of thm is chaactizd by 3 umbs: l - adial, m - azimuthal ad - tooidal mod umb. If th wav is dampd th soac is boadd. h boadig is od of th, s Im, s imagiay pat of th igvalu R, s dampig h distac btw ighboig soacs could b stimatd usig th dispsio quatio, s, s - coditio of ovlappig fo azimuthal mods, s l, cost, s dampig h lowst distac is btw ighboig azimuthal global soacs, ad thy ovlap, s, s, s m, fist. Aft comig to th dg of azimuthal, s l cost s,, m, cost, s l, mcost spctum, couplig of ighboig adial o tooidal mod is possibl, s

7 NUMERICAL MOEL h Systm of th Balac Equatios of Paticls ad Egy P RF k B V V C a 3 H is th plasma dsity, is th dsity of molcul hydog, is th lcto tmpatu, is th pow dsity of RF lcto hatig, is th Boltzma s costat, (R.K. Jav t al. Elmtay Pocsss i Hydog-Hlium Plasmas. Coss Sctios ad Ractio Rat Cofficits, Spig Sis o Atomic, Optical, ad Plasma Physics. 987) is th paticl cofimt tim, is th vacuum chamb volum, / 3.5 is th atio of th ambipola pottial gy to th lcto thmal gy a k B P k v v v t RF B k (C ) d d kb q E d iv H dt dv H V i i cost d i is th dissociatio at, is th xcitatio at, is th ioizatio at, d V, i 5.6V,. 5V V H a B i

8 NEOCLASSICAL PARICLE AN ENERGY FLUXES H, K dk K, m K,, B E is th moo-gtic diffusio cofficit, wh m E is th lcto mass, is th collisio at, is th lcto vlocity, is th adial compot of th lctic fild k E q B 3 3 k E B 3

9 MAXWELL S EQUAIONS is th lctic fild, is th xtal RF cuts, //, ig ig t is th dilctic tso (it is fuctio of plasma dsity ad lcto tmpatu), wh, // i P,, g, i c c p i c c p xt i c j E E ˆ E j xt

10 OUBLE FRAME ANENNA LAYOU Ata is simulatd by xtal RF cuts, which satisfy to coditio j xt. h xplicit xpssios fo ata cuts a substitutd ito th Maxwll s quatios. j xt

11 h Maxwll s quatios solutio allows o to dtmi th valu of local RF hatig pow of lcto plasma compot, which iflucs o th ioizatio at ad, i this way, o th volutio of plasma dsity. h RF pow dsity i cylidical systm of coodiats ads P HE RF POWER EPOSIION RF * Im( E E E // E E Im ) g z NUMERICAL CALCULAIONS h Cak-Nicholso mthod is usd fo th solvig of systm of th balac quatios. im volutio paamts of plasma ad utal gas a calculatd usig th Rug-Kutta mthod. h Maxwll s quatios a solvd at ach tim momt fo cut plasma dsity ad tmpatu distibutios. h Maxwll s quatios a solvd i usig th Foui sis i th azimuthal ad th logitudial coodiats. Fo th disctizatio i adial coodiat, th uifom fiit lmts mthod is mployd that uss a spcial st of wight (tst) ad basis (shap) fuctios.

12 HE PARAMEERS OF CALCULAION R 3.5 4cm a 6cm B 3 a a a 45cm cm majo adius of quivalt tous plasma colum adius adius of mtallic wall magtic fild adial positio of ata agl width of ata azimutal siz of ata

13 , cm -3 3E+9 E+9 E+9 E+ 8E-4 4 6, cm NUMERICAL RESULS EXAMPLE OF CALCULAION Pofil of plasma dsity i tim momt t, V s p RF, W/cm 3 6E-4 4E-4 E-4 E+ 4 6, cm Pow dpositio pofil i tim momt t -3 s 4 6, cm Pofil of lcto tmpatu i tim momt t -3 s

14 EXAMPLE OF CALCULAION () < >, cm -3 3E+9 E+9 E+9 E+9 5E+8 E+ E+ 8E-4 E-3 t, s < >, V im volutio of avag plasma dsity 3E+ E+ E+ E+ 8E-4 E-3 t, s im volutio of dissociatio at, /s im volutio of avag lcto tmpatu E+ 8E-4 E-3 t, s dissociatio at

15 CONCLUSIONS A advatag of a RF dischag that is dscibd h is that it could b iitiatd i magtic fild. o xcit th slow wav, a doubl fam ata was usd istad of th sigl fam ata. his suppsss xcitatio of log-wav mods. h ata ca b small-sizd. his scaio is good bcaus it uss a stadad fqucy gato. h iitial stag of dischag is pstd i calculatios. Futh dischag laxatio is xpctd i diffusio tims. h simulatio idicatd that th dischag ca b statd ad sustaid by hatig th RF pow of kw i a mdium-siz stllaato. h at of gatio of utal atomic hydog is high tha atoms p scod.