Overview of Experimental Studies on IR-T1 Tokamak

Transcription

1 1 EX/P4-15 Oveview of Expeimental Studies on IR-T1 Tokamak Pejman Khoshid 1), M. Ghoanneviss 2), M. Razavi 1), S. Saboohi 2), M. Mollai 1), A. Hojabi 2), D. Doanian 2), M.K. Salem 2), R. Takeshian 2), R. Avin 2), S. Mohammadi 2), A. Talebitahe 2), A. Nikmohammadi 2), M.R. Yousefi 2), A. Shokouhi 2), A.H. Sai 2) and IR-T1 team 2) 1) Depatment of Physics, Mashhad Campus, Islamic Azad Univesity, Mashhad, Ian 2) Plasma Physics Reseach Cente, Science and Reseach Campus, Islamic Azad Univesity, Tehan, Ian contact of main autho: Abstact. An oveview of expeimental studies on IR-T1 tokamak is pesented. Seveal issues of plasma displacement measuement ae investigated. An analytic solution of the Biot Savat law, which is used to calculate magnetic fields ceated by tooidal plasma cuent, is pesented. Results of calculations ae compaed with the expeimental data obtained in no-plasma shots with a tooidal cuent-caying coil positioned inside the vessel to simulate the plasma movements. The esults show a good linea behavio of plasma position measuements. An aay of Minov coils employed fo measuement of plasma position, too. The esults show that Minov aay can not be used fo this measuement without concening high field side eos. An extenal esonant helical magnetic field (RHF) applied to plasma. The aim of these expeiments was to undestand the effect of RHF on light impuities adiation and hoizontal displacement measuements. Measuements esults of visible line emissions of O II, C III impuities and H α adiation with and without RHF (L=2) show that the addition of a elatively small amount of esonant magnetic helical field (L=2 & L=3) could be effective fo impoving the quality of the dischage by educing of light impuities adiation. The effect of RHF in plasma displacement measuement shown an incease in flux value about %5 fo L=2, L=3 sepaately and about %10 fo L=2&3 when apply togethe. In othe expeiments, Studies of plasma inteaction with titanium coated feitic steel have been pefomed. Depth of impuity penetation and etention, and the suface oughness wee measued using suface analysis methods. The esults show that titanium acts as an effective gette fo oxygen but its fast eosion poses a poblem. A change in oughness with espect to position of samples has been obseved. 1. Intoduction IR-T1 tokamak is an ohmically heated ai coe tokamak with majo adius R=0.45 m and mino adius a=0.125 m defined by two poloidal stainless-steel limites. The vacuum chambe has cicula coss-section with two tooidal beaks and mino adius b=0.15 m. Tooidal magnetic field B t ~ T, plasma cuent I p ~25-30 ka, aveaged electon density m -3 in hydogen, plasma dischage duation t d ~30ms and electon density T e (0)~200 ev. The tokamak also has extenal esonant helical field (RHF) coils. The main goals of IR-T1 tokamak ae studies of Magnetohydodynamic (MHD) activities, tokamak edge physics and developing the plasma physics education. In this contibution the wok developed on IR-T1 tokamak will be pesented as plasma displacement measuements, applying a esonant helical magnetic field on plasma and plasma wall inteaction. 2. Plasma Displacement Measuements In seveal configuations of magnetically confined plasmas, the position of the plasma column is a majo deteminant of plasma behavio fo contolling the plasma equilibium. Seveal methods ae employed fo displacement measuements, such as optical and magnetic methods. Fo the magnetic method, almost it is used sine-coil. The Ampee s theoem and the Biot Savat law ae well known tools used to calculate magnetic fields ceated by cuent distibutions [1-4]. The fome is often used in high-symmety poblems of magnetisms. At

2 2 EX/P4-15 fist section of this wok, an analytic solution of the Biot Savat law, which is used to calculate magnetic fields ceated by tooidal cuent-caying coil positioned inside the vessel to simulate the plasma movements, is pesented. In the second section a sine-coil, which is a Rogowski coil with a vaiable wiing density is designed and fabicated fo measuement of no-plasma shot expeiments with cicle coil of adius R=0.45 m. The last section contains measuing the poloidal magnetic field components with discete pick up coils placing diametically on the oute suface of tous Biot-Savat Analytical Magnetic Field Measument Now we ty to use the Biot-Savat law to calculate the field in the tooidal coodinate of the cicula wie coil of adius = 0.45 cm. Accoding to Maxwell equation the magnetic field, B, is given by B = µ 0 J, since the. B = 0 and using expession of.( F ) = 0, we can v wite B = A, whee J is cuent density and A is vecto potential so that the above expession yields, ' µ 0 J ( ) A( ) = dv' ' (1) 4π and by defining J ( ) dv = Idl, B() leads to, µ 0 I dl ( 2 1) B( ) = c 3 4 (2) π 2 1 This equation has been solved using a numeical method, and the topology of the whole magnetic fields calculated. The esult has been investigated fo measuement of cuent caying coil position with espect to sine-coil position. In this calculation, we fixed the sinecoil position and moved the cuent coil in hoizontal diection. The esults of flux calculation by Biot-Savat law has been compaed with expeimental data as shown in FIG.1. The eo is less than 2.5% and it has been compaed with othe methods of measuements of the plasma position [5]. Relative H-Displacement Biot-Savat Calculation Expeimental Measuement FIG. 1. Compaison of calculations with actual plasma position. The ectangle and the tiangle symbols show the Biot-Savat law calculation and the measuements with the sine-coil, espectively.

3 3 EX/P Plasma Displacement Measuements via Discete Method This is one of the simple possible techniques, which measues the local values of poloidal magnetic field at some points aound the plasma by placing magnetic pobes diametically opposite fo magnetic field measuement. Combination of the signals poduced by these pobes is popotional to the displacement of the plasma column. In this method, twelve Minov coils has been used. The esults shown that high field side effect needs coection fo hoizontal displacement measuement. 3. Resonant Helical Field Expeiments The RHF in IR-T1 tokamak is an extenal magnetic field which can impove the plasma confinement. This field is poduced by two winding with optimized geomety conductos wound extenally aound the tokamak tous with a given helicity. The mino adius of these helical windings ae 22cm (L=2, n=1) and 23cm (L=3, n=1). In the expeiments pesented hee, the cuent though the helical windings was between A, which is vey low compaed with the plasma cuent itself (25-30kA) Effect of RHF on Light Impuities Radiation The aim of these expeiments was to undestand the effect of RHF on light impuities adiation and suppessing majo disuptions. The length and the magnitude of the pulse feeding the helical windings could be pogammed. Measuements esults of visible line emissions of O II (4416A ), C III (4644A ) impuities and H α (6563A ) adiation with and without RHF (l=2) show that the addition of a elatively small amount of esonant magnetic helical field could be effective fo impoving the quality of the dischage by educing of light impuities adiation and possible suppessing majo disuptions. FIG. 2 shows the measuement esults of visible line emissions of O II (a, b), C III (c, d) impuities and H α adiation (e, f) with and without RHF (L=2) [6]. (a) (b) With RHF L=2 (c) (d) With RHF L=2 H α (e) H α (f) With RHF L=2 FIG. 2. The measuement esults of visible line emissions of O II (a, b), C III (c, d) impuities and H α adiation (e, f) with and without RHF (L=2).

4 4 EX/P Effect of RHF on Plasma Displacement The plasma displacement measued duing Resonant Helical Field application in L=2, L=3 and L=2&3. The esults shown an incease in flux value about %5 fo L=2, L=3 and about %10 fo L=2&3. FIG.3 shows typical Schematic of L=2/1 and L=3/1 RHF winding coil aound the chambe and effect of RHF with diffeent mode on plasma hoizontal displacement. It shows the Magnetic field calculation fom RHF via Bio-Sawat law in best position 0, 45, 145 fo installing Sine-Coil and a sample magnetic field calculated in the 120 as a high nonlinea effective position. 90 Flux [a.u.] (a) D0 D45 D145 (c) Flux [a.u.] Relative HD (b) (d) With L=2 RHF With L=3 RHF With L=2&3 RHF D120 FIG. 3. a) A typical Schematic of L=2/1 and L=3/1 RHF winding coil aound the chambe, b) Effect of RHF with diffeent mode on plasma hoizontal displacement, c) Magnetic field calculation fom RHF via Bio-Sawat law in best position 0, 45, 145 fo installing Sine-Coil, d) A sample magnetic field calculated in the 120 as a high nonlinea effective position. 4. Study of Plasma Wall Inteaction Studies of plasma inteaction with titanium coated feitic steel have been pefomed on IR- T1 tokamak. The main aim of this expeiment is to undestanding effects of glow dischage and plasma on the edge sufaces positioned in the wall and limite aea of IR-T1 Tokamak fo futue studies. We use RF sputteing method with powe 400 W and deposit titanium laye on feetic steel substate, as a potect coating. Some of steel substates baked in 460ºC tempeatue and fo 3 hous befoe analyzing them. Also, we installed some samples on flange at diffeent depth fom plasma coe (=0) in IR-T1 Tokamak in 1 =12.5 cm, 2 =13.2, 3 =13.5, 4 =13.8, 5 =14.2 cm, espectively. The samples positioned in paallel aay. The expeiments caied out with 15 minute glow dischage cleaning and 55 plasma shots.

5 5 EX/P4-15 Suface oughness of samples obtained by AFM (Atomic Foce Micoscopy). We can see an obvious decease at suface oughness of samples at diffeent depth fom plasma coe due to enegetic sputteed paticle impact effect on the neaest sample fom plasma coe. Enegetic paticles have deceased when they impact to the fa sample, and damaging the sufaces deceased. FIG. 4 shows changes in oughness in samples befoe and afte 55 plasma dischages and FIG. 5 shows pofile of compaing oughness of samples befoe and afte dischages [7]. FIG. 4. Changes in oughness at two diffeent positions of the sample with espect to plasma coe. Below one is close to plasma coe. Left figues ae befoe dischages and ight figues ae afte dischage. 60 Befoe Dischage Afte Dischage Roughness FIG.5. Pofile of compaing oughness of samples befoe dischage and afte dischages, whee, (nomalized) is the position of samples with espect to plasma coe. Ruthefod Backscatteing Spectomety (RBS) specta method has been used to measue the content of Oxygen and Titanium, befoe and afte dischages. Simulation was done by SIMNRA softwae as a outine tool to simulate RBS specta [8-11]. RBS specta of Ti laye on Steel obtained by 2000 kev incident on enegy at α=0 degee, β=15 degee and θ=165 degee. We set up samples with diffeent condition but eplaced them in the same distance fom plasma coe in IR-T1 Tokamak. RBS specta show lowe oxygen content in suvivo sample afte plasma-suface inteaction in titaniumized sample (FIG. 6). It may be due to oxygen

6 6 EX/P4-15 getteing of titanium popeties. Coated steel captue amount of oxygen by titanium laye, then titanium laye with content of impuity (oxygen) eoded fom suface because of suface defects. So, we can see lowe content of oxygen in this sample. This esult isn't good conclusion because of plasma puity, but it geneally emphasis to lowe oxygen penetation o pemeability in steel and titanium impuity absoption. The esult is shown in Table I Counts Ni Fe 400 C Ti N O Channel FIG. 6. The analyses of RBS measuements with SIMNRA Code. 5. Conclusion TABLE I: OXYGEN GETTERING EFFECT OF T i LAYER. Samples Thickness ( A) Ti (%) O 2 (%) With out Baking ( Ti) Afte Baking ( Ti) Afte Baking (3191-4Ti) Compaing the esults of the model expeiment we conclude that the sine-coil can be exploited fo measuement of plasma displacement in the IR-T1 tokamak. The eo is less than 2.5% and it has been compaed with othe methods of measuements of the plasma position. In addition, this method will be used in the feedback position contol system and tests of feedback contolle paametes. Duing Resonant Helical Field application the expeimental esults suggest that the addition of a elatively small amount of esonant magnetic helical field (L=2 & L=3) to the basic tous configuation could be effective fo impoving the quality of the dischage by educing of light impuities adiation and suppessing majo disuption. Also, the stuctue of magnetic field lines in tokamak with RHF has been investigated by means of analytically calculation of the Biot Savat law. The behaviou of plasma displacement is diffeent when the L is diffeent. It is found that in both cases, RHF influences on displacement measued by sine-coils. The esults shown an incease in flux value about %5 fo L=2, L=3 sepaately and about %10 fo L=2&3 when apply togethe. Theefoe RHF can influence in Plasma displacements and then on the plasma feedback contol, so it needs some consideation in the esults. Plasma inteaction with Titanium coated feetic steel has been pefomed on IR-T1 Tokamak. AFM analyses befoe and afte dischage in = cm caied out. The esults shown that, we should use methods that decease titanium eosion.

7 7 EX/P4-15 Titanium-substate adhesion and coating technique should be modified, thickness of laye may be help us in this way, and we must use feetic steel with diffeent composition such as type of feetic steel with no content of nickel o less chomium content. Depth of impuity penetation and etention, and the suface oughness wee measued by using Ruthefod Backscatteing Spectomety (RBS) specta method has been used to measue the content of nitogen, oxygen and titanium, befoe and afte dischages. The esult has been shown a change in oughness with espect to position of samples. Also, the esults shown that the concentation of oxygen deceases afte titanisation. Refeences [1] CHEN L., ZHAO Q., ZHU Y., FANG Z., FAN H., Measuement of plasma position on HT-7 tokamak Jounal of Fusion Engineeing and Design, 34-35, 721 (1996). [2] CHOUDHURY M.H., Electomagnetism John Wiley and Sons, New Yok (1989). [3] CHARITAT T. and GRANER F., About the magnetic field of a finite wie, Eu. J. Phys. 24, 267 (2003). [4] CAVALLERIY G., SPAVIERIZ G. and SPINELLI G., The Ampee and Biot Savat foce laws Eu. J. Phys. 17, 205 (1996). [5] KHORSHID P., et al., Designing a Sine-Coil fo Measuement of Plasma Displacements in IR-T1 Tokamak AIP Conf. Poc. Volume 996, pp. 224 (2008). [6] HOJABRI A. et al Effect of otating magnetic helical field on the impuity adiation and the magnetic island in IR-T1 Tokamak 32 nd EPS, Taagona, Spain, ECA 29C, P4.064 (2005). [7] GHORANNEVISS M. et al., Study of Plasma Inteaction with Titanium Coated Feitic Steel in IR-T1 Tokamak, AIP Confeence Poceedings, Volume 996, pp. 172 (2008). [8] ZINKLE S.J., et al., Effect of initial oxygen content on the void swelling behavio of fast neuton iadiated coppe, J. Nucl. Mate , 919 (2004). [9] APICELLA M.L., et.al, Effects of wall titanium coating on FTU plasma opeations, ECA, VOL.24B, 1573 (2000). [10] TSUZUKI K., et al., High pefomance tokamak expeiments with a feitic steel wall on JFT-2M, Nucl. Fusion 43, 1288 (2003). [11] MAYER M., SIMNRA, A Simulation Pogam fo the Analysis of NRA, RBS, Ameican Institute of Physics Confeence Poceedings, 475, 581 (1999).