ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 The Effect of the Poles Distances on Plasma Characteristic of Discharge Tube N. H.Ali , M. A.Yeser, N. F.Ali Dpartme nt of Physics,College of Science, Unive rsity of Kufa Received in: 21 June 2011 ,Accepted in:18 October 2011 Abstract The effects of p oles distances of a discharge tube (cathode and anode) wer e invest igated. The distances(90,95,100,110,115,120,130,140)mm are considered. The influence of (25mT) p arallel and (2mT) normal magnetic f ields with resp ect to the discharge tube on electron temp erature under a pressure of (6p ascal) and (900volt) was st udied by imp lementing double Lan gmuir e p robe into p lasma. Curves fitt ing were p erformed to find the op timum valu es of electron temp erature for all cases in this work.We found that the electron temp erature as a function of p oles dist ances is exp onential form. Keywords: Glow discharge, Langmuire probes, Plasma diagnoistics. Introduction A glow discharge is a self sust aining dischar ge through gas which occurs at p ressures well below atmosp heric pressure [1,2].The low p ressure glow discharge p lasma is created by applying a p otential differ ence between two electrodes of certain d istance a p art [3]. It has obvious glowing r egions and fills the full cross-section of the tube [2]. Glow discharge used in various app lications such as deposition of thin films, etching and modification of surfaces in semiconductor industry and materials technology [3]. Lan gmuir e p robes are commonly used diagnost ics in low-p ressure p lasma dischar ge <1 torr [4]. Of all the way to measure a p lasma, the Lan gmuir p robe is p robably the simplest , intrusive and not remote technique [5]. The diagnost ics of p lasma are very comp lex and are very difficult, mainly because we want avoid d isturb the plasma , so we use the double p robe because it does not disturb the plasma as much as the single probe with is non-flo ating anode connection [6 ,7,8]. The structure of a double floating electric p robe consist s of t wo Langmuir p robes with the same size and shap e[9], one to draw electron current and one to draw ion current .The two together , however, draw no net current [10 ]. The p robes are located very close together to ensure that the plasma prop erties are app roximately equal [9], and the current from one to t he other is measured as a function of the voltage difference between them, the (Id-Vd ) characterist ic is then sy mmetrical and limited to the region between the Isat , s on each p robe [5]. The temp erature T of the particles in p lasma is often exp ressed as the value of the energy KT in units of electron volts .Thus a temperature of the (1eV) corresp onds t o (11600K). Not that t his energy of the p articles, which would be (3/2) KT [1,11,12]. A glow dischar ge consists of no .of bright and dark regions between the cathode and the anode electrodes across the tube [2,3]. These regions are (Aston dark sp ace, cathode glow region, cathode dark sp ace, the negative glow, Faraday dark sp ace, positive column, anode glow and anode dark sp ace) [13]. M ost of the p otential drop occurs near the cathode over a r egion called the cathode fall where ions are accelerated into the cathode at sufficient energy to cause emission of ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 secondary electrons from the cathode. These electrons are accelerated away from the cathode p roducing further electrons and ions as a result of ionizin g collisions [2]. The positive colu mn is usually st riated into bright and dark a few centimeters a p art. They result from not very lar ge periodic f luctuations electron density and energy initiated in the cathode region [11]. (1-1) The Variati on of The Se paration Distances between Cathode and Anode The cathode fall region is essential for the existence of the discharge .The p ositive column p rovides a conducting connection to the anode. Thus if the sep aration distance between the electrodes is varied (k eep ing pressure and current constant) T he cathode fall will remain un chan ged and the len gth of p ositive column will vary [1]. (1-2) The Influence of Magnetic Field [14,15]: )1()(  BvqF  The above equation represents the magnetic force effect on a charges (+,-) when E=0.The cy clotron frequency can be defined as follows: )2( m Bq c    We defin ed the Larmor radius t o be: If now we allow an electric field (E)to be p resent, t he motion will be found to be the su m of two motions: the usual circular Lar mor gy ration p lus a drift of the guidin g center. The equation of motion is now: )4()(  BvEqF  So the p article drifts in crossed electric and magnetic f ields will be as shown in fig.(1). Where the electrons are more effected by magnetic field than ions. )5(..  ei LL rrei  This behavior can be att ributed to the smallness of electron mass. In this study the magnetic field is used to control the electron distribution in the discharge tube in two way s [16]: 1-collimation: In this case the magn etic field is p arallel to t he electric field, so t he magnetic field p revents an excessive fraction of the electron bein g went to the walls of the discharge tube and constrains t he discharge in the tube to a narrow column. Electrons att empting to travel across )3(  Bq mvv r c L    ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 the lines of for ce are for ced into a sp iral path. T he electrons scattered by collisions within the p lasma are still trapp ed in the column by the magnetic field. 2-Path lengthenin g: Here the electric field and the magnetic field at ri ght angles and the p rimary fun ction of the magn etic is to p revent the electrons travelling d irectly to the anode in a direction determined by the electric field. The result is a greatly increased p ath length for the electron and therefore a reduction in the gas p ressure is necessary to give a sufficient ionization p robability to maintain the discharge. Experime nted Setup Fig.(2a,b) shows a p hotograph p icture and schematic diagram of the exp erimental setup resp ectively. A cy lindrical d ischar ge cell made of Py rex glass tube of (30cm) len gth and(3cm) diameter. Two p arallel movable circular electrodes of (2.5 cm) d iameter were enclosed in the dischar ge tube. The dischar ge tube was evacuated usin g rotary p ump (type SM C) to abase p ressure of (1×10 -3 p ascal). The tube was filled with the working gas (helium) at p ressure (6 p ascal), the applied voltage between the cathode and anode was (900V). The glow discharge region of current between (3-6.65)mA with different distances between cathode and anode (90- 140)mm. A double Lan gmuir e probe was immersed at the center of the tube to investigate the p lasma (electron temp erature ) of positive column of the helium glow discharge. The double p robe is identical in diameter whi ch every one has (1 mm). They (the two tip s) oriented perpendicular to t he electric field in p arallel plate sy stem. A p ermanent magnetic field is located at a distance 1.3cm from the discharge tube near the anode electrode. In this p resent work, we st udied the influence of variation of the sep aration distance between cathode and anode and the effect of the p arallel and nor mal magnetic fields with resp ect to the electric field b etween cathode and anode on the electron temp erature. The intensity of the p arallel magnetic (B║) field was (25mT) and (2mT) for the normal on e (B  ). Experime ntal Re sult and Discussion 1-The Id-Vd Characteristic Curves of the Discharge: The Id-Vd characteristic curves at different separation dist ances between cathode and anode for three cases (B=0 , B  ,B║) which were taken by using double Lan gmuire probe are illustrated in figures(3,4,5). ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 As shown from all these three figures that when the sep aration distance (d) increases t he p robe current (Id) decreases. The reason for this behav ior was as the sp ace between cathode and anode incr eases, the p lasma density decreases, (i.e. it distributed on a lar ger volume) so the charges whi ch collected by the double probe will decrease for recording the current. The figur es (3,4 and5) can b e drown in other method as se en in figur es(6,7,8,9,10,11,12,13). By comp arably the figures (6,7,8,9,10,11,12,13) with each other we can see that (Id) at (B=0) has the highest value for all sep aration distances (i.e. for all of them).Because there is no magnetic field constraining the plasma which leads t o reduce the no. of charges collecting by the probe for recording the current. Also we can see that, in sp ite of the low value of normal magnetic field in comparison with the value of p arallel magn etic field,(Id) at t he first one(Id) will be smaller than the value of the second one at (d=90mm) as seen in f ig (6) , more increasing in (d) makes the two currents approaches from one to another, until they would be nearly comp atible at dist ances (130mm).As shown in figs.(7,8,9,10,11,12). Furt her increasing of the separation dist ance (d), i.e.at (d=140mm), causes (Id) of the normal magnetic field will be lar ger than (Id) of the parallel on e, see fig. (13). The reasons for t his can be exp lained as follows: The p lasma distributed on a small vo lume at small sep aration distances, so the p arallel magnetic f ield will confin e the p lasma at rather narrow column, as the sep aration distances increase the p lasma wi ll be d istributed on a lar ger volume, then the p arallel magnetic field will confin e the char ges at a more n arrow column, by anther sp eech a lar ge amount of ch arges will be constrained by magnetic f ield which reduces much more char ges collecting by the p robe to record the current. 2-Measurements of Electron Te mperature: The electron t emp erature (Te) was measured from the Id- Vd characteristics curves by the application of the followin g equation: [17,18] )6( 4 )( 0 21    dv d d e dI dVII T Where I1 and I2 is the ion saturation current for p robe 1 and p robe 2 resp ectively It can be seen from f ig.(14) that as (d) increases, the electron temp erature increases because of the increase in (d) means increase in sp ace, so t he mean free p ath will increase so the electrons will have more chance for acquisition of an acceleration through the electric field i. e they acquire kinetic ener gy . Also it can be seen from fig.(14) that t he electron temp erature has the largest value when B=0 ,because there is no magnetic field mak e the electrons to have more collisions which leads to lost their energy then decrease in their temp erature, this result is agreement with p ublished work [13]. We can see also from fig.(14) the influence o f normal magnetic field (p ath lengthin g effect ) in decreasing the electron t emperat ure is much more t han the influence of parallel magnet ic field (co llimat ing effect) in spit e of the smaller value of t he first one (2mT)than t he value of the second on e (2 5mT ). Curv e fitt ing was performed fo r the three cases (B=0, B║ an d B  ) to find the opt imum value of t he elect ron t emperat ure as a funct ion to the distance bet ween t he t wo poles. ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 (Te) as a funct ion of (d) is given by t he formula: )7()exp ( 10  daaTe When B=0: a0=5.57015 a1=0.00247635 B║: a0=4.57372 a1=0.00370314 B  : a0=3.07331 a1=0.00595367 Conclusion Id-Vd characterist ic curves of the glow dischar ge were st udied at different sep aration distances, whenever the distance between the two p oles increase, the p robe current (Id) decrease and so this make exp onential incr ease in electron t emp erature . ( Id ) of applied p arallel magnetic field will b e lar ger than (Id ) of normal one at small distance. Further increase in (d) causes (Id) of nor mal magnetic field will be lar ger than (Id) of p arallel one. Also (T e) was determined in different three cases : (B=0, B║ and B  ) (Te) will has the largest values when B=0,and its value at B║ larger than at B  ). Re ferences 1.Lieber man,M .A.and Lchtenberg, A.J. (1994), Princip les of Plasma Discharges and M aterials Processing, Wiley and Sons,New y ork. 2. Howatson, A.M . (1965), An Introduction to Gas Discharges, Pergaman Press, Oxford. 3.Hassouba, M .A. and M enanna,E.A.,(2009), Electrical Characteristics of (N2-H2) Gas M ixture DC glow Discharge, International Journa l of Phy sics Sciences, 4(11) :713-721. 4.Cohen,Ira M . (1963), A sy mptotic Theory of Sp herical Electrostatic Probes in a Sligh ly Ionized, Collision –Dominn ated Gas'', The Physics of Fluids, 6: 1492-1500. 5.Chen,F.F.(2003), Langmuire Probe Diagnost ics",M ini-Course on Plasma Diagnost ics,IEEE- ICOPS meetin g,Jeju,Korea. 6.Wan g,A.Y. (1984), Introduction to Exp erimental Pl asma Phy sics,UCLA. 7.Leal-Quiros,E. (1989), Novel Probes and Analyzers for Controlled Fusion Research, U of M issouri-Columbia. 8.Clements,R.M . (1978), Plasm Diagnost ics with Electric Probes,J.Vac.Sa.Technol., 15(2) : 193-198. 9.Zheng,P. (1990),Lansmuir p robe for electron-cyclotron-resonace p lasmas,M SC.Thesis,Graducte Faculty of Texas University . 10.M icgregor,D.R. (2002), Growth Optimization and Characterization of reactively sp uttered zirconium Nitride thin films for III-VBuffer Lay er App lications'',M SC.Thesis,Nort h Carolina st ate University . 11.Heald,M .A.and Wharton,C.B. (1965), Plasma Diagnosri cs with M icrowaves , Wiley ,Newy ork. 12.Thornton,A.J. (1978), M asnetron Sp uttering:basic Phy sics and application to cylindrical magnetrons,J.Vac.Sa.Technol, 15(2) : 171-177. ي .13 ي) 1990(،فتحي محمد جاسم البدران تاثیر المجال المغناطیسي المحوري في متغیرات بالزما التفریغ التوھج ر . ، رسالة ماجستیر، كلیة التربیة، جامعة الموصل “ في غاز النتروجین عند الضغوط المعتدلة المستم ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 14. M iy amoto,K. (2005), Plasma Phy sics and Controlled Nuclear Fusion”,Sp ringer, Ber lin. 15.Chen ,F.F. (1984), Introduction in Plasma Phy sics and Controlled Fusion,Plenu m Press,New York. 16.Ry ssel,H.and Glowisching,H.,(1982), Ion Imp lantation Teehniques,Springer- Verla g,Newy ork. 17. Grill,A. (1994), Cold Plasma in M terials Fabricntion,IEEE Prees,Newy ork. لاللكترونات في تصمیم وتشغیل منظومة الكترونیة لتحدید ودراسة دالة التوزیع السرعي)1999(،علي خلف حسین الجبوري.18 ، .البالزما، رسالة ماجستیر ، كلیة العلوم، جامعة الموصل Fi g.(1) :Parti cle drifts in crosse d electri c an d m agne ti c fiel ds ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 Fig. (2a): A photogra ph picture of the experimental set up 1. High volt age anode: connect with the anode o f t he discharge t ube. 2. P ump-line: to get vacuum environment in t he discharge t ube. 3. P robe: used for measurem ent of plasma parameters. 4. Anode: anode of t he discharge t ube. 5. Cat hode: cat hode of t he discharge t ube. 6. Discharge t ube: plasma generat e in it . 7. Gas supp ly port : used for charging gas into discharge t ube. 8. High volt age catho de: connect with the cat hode of t he discharge t ube. 9. The permanent magnetic field. Fig.(2b): A sche matic diagram of the experimental setup 9 9 ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 -150 -100 -50 0 5 0 100 150 90mm 95mm 100mm 110mm 115mm 120mm 130mm 140mm Id(µA) V d(v) B =0 Fig.(3): The Id-Vd characteristi c curves at B=0 -50 -40 -30 -20 -10 0 10 20 30 40 -1 50 -100 -5 0 0 50 10 0 1 50 9 0mm 9 5mm 1 00mm 1 10mm 1 15mm 1 20mm 1 30mm 1 40mm B║ Vd(v) Id(µA) Fig.(4) :The Id-Vd characteristi c curves with application parallel magne tic field (B║) equal s (25mT) ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 -40 -30 -20 -10 0 10 20 30 40 -150 -10 0 -50 0 50 1 00 150 90 mm 95 mm 10 0m m 11 0m m 11 5m m 12 0m m 13 0m m 14 0m m B┴ Vd(v) Id(µA ) Fig.(5) :The Id-Vd characteristi c curves with application normal magne tic field (B  ) equal s (2mT) 90mm -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 -15 0 -100 -50 0 50 100 150 Id(µA) V d (v ) B=0 B║ B┴ Fig.(6) The Id-Vd characteristi c curves for the three cases of magnetic field at d=90mm ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 95mm -50 -40 -30 -20 -10 0 10 20 30 40 -150 - 100 -50 0 50 100 150 Id(µA) V d (v ) B= 0 B║ B┴ Fig(7) The Id-Vd characteristi c curves for the three cases of magnetic field at d=95 mm -40 -30 -20 -10 0 10 20 30 40 -150 -100 -50 0 50 100 150 Id(µA) V d (v ) B=0 B ║ B┴ 100mm Fig.(8): The Id-Vd characteristi c curves for the three cases of magnetic field at d=100 mm ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 110mm -40 -30 -20 -10 0 1 0 2 0 3 0 4 0 - 150 -100 -50 0 5 0 100 1 50 Id(µA) V d (v ) B =0 B║ B ┴ Fig.(9): The Id-Vd characteristi c curves for the three cases of magnetic field at d=110 mm 115mm -40 -30 -20 -10 0 10 20 30 - 150 -10 0 -50 0 5 0 1 00 1 50 Id(µA) V d (v ) B=0 B║ B┴ Fig.(10): The Id-Vd characteristi c curves for the three cases of magnetic field at d=115mm ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 120mm -30 -20 -10 0 10 20 30 -15 0 -10 0 -50 0 50 100 150 Id(µA) V d (v ) B=0 B║ B┴ Fig.(11) :The Id-Vd characteristi c curves for the three cases of magnetic field at d=120 mm 130mm -25 -20 -15 -10 - 5 0 5 10 15 20 25 -150 - 100 -50 0 50 100 150 Id(µA) V d (v ) B=0 B║ B┴ Fig.(12): The Id-Vd characteristi c curves for the three cases of magnetic field at d=130 mm ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 140mm -20 -15 -10 -5 0 5 10 15 20 -1 50 -1 00 -5 0 0 50 100 150 Id(µA) V d (v ) B=0 B║ B┴ Fig.(13): The Id-Vd characteristi c curves for the three cases of magnetic field at d=140mm 80.00 100.00 120.00 140.00 Sepration Distance (mm) 3.00 4.00 5.00 6.00 7.00 8.00 T e m p e ra tu re r (e V ) B No rmal (2 mT ) B Pa ra llel (2 5mT) B=0 Fig.(14): The ele ctron temperature as a function of the separation distance for three cases( B=0 , B║ and B  ) ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 تأثیربعد األقطاب في خواص البالزما في منظومة التفریغ الكھربائي نعیمة ھادي علي ، مھدیة أحمد یسر ، نبراس فاضل علي ھ، قسم الفیزیاء كلیة العلوم ،جامعة الكوف 2011 تشرین االول 18: قبل البحث في، 2011 حزیران21: استلم البحث في الخالصھ أثیر بعد أقطاب إنبوبة التفریغ 9) اتللمساف) الكاثود واألنود(تم في ھذا البحث دراسة ت 0, 9 5, 10 0, 11 0, 115, 120 ,130 ,1 40 )mm الوتاثیرالمج 2mT (و ) 25mT(والعم�ودي ذو ال�شدتین المغناطیسي الم�وازي ـ عل�ى الترتی�ب ف�ي درج�ة ) 900(وفولتیة ) pascal 6( حرارة غاز االلكترونات في منظومة بالزما تعمل بضغط V ( استخدام مجس النكمور المزدوج وذلك ب اد أفضل دالھ. اب إلیج وقد وجد .وقد أجري توفیق منحنى لقیم درجة حرارة غاز األلكترونات التي حصلنا علیھا بالنسبھ الى بعد األقط .أن درجة حرارة غاز األلكترونات بصفتھا دالھ لبعد األقطاب تسلك سلوك دالھ أسیھ مفتاحی لمات ال ات النكمور، تشخیص البالزماا:ةالك .لتفریغ التوھجي، مجس D e b ye L e n g th ( m m ) D e b ye L e n g th ( m m ) ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Haitham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 D e b ye L e n g th ( m m ) D e b ye L e n g th ( m m )