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Highlights on EGYPTOR Progress By H. Hegazy Plasma Physics Dept., NRC, Atomic Energy Authority 13759 Enshass, Egypt

Highlights on EGYPTOR Progress By H. Hegazy Plasma Physics Dept., NRC, Atomic Energy Authority 13759 Enshass, Egypt.

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Highlights on EGYPTOR Progress By H. Hegazy Plasma Physics Dept., NRC, Atomic Energy Authority 13759 Enshass, Egypt

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  1. Highlights on EGYPTOR ProgressBy H. HegazyPlasma Physics Dept., NRC, Atomic Energy Authority13759 Enshass, Egypt 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  2. The basic item of EGYPTOR is its Stainless Steel discharge vessel consisting of two toroidal segments insulated from each other and sealed- off by two viton O- ring.The chamber has a rectangular cross section 25cm by 20cm. The major radius(R):30 cmThe minor radius(a):10 cm 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  3. Photograph of EGYPTOR Device 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  4. Toroidal Field System 140 rectangular toroidal field coils (TF) are directly glued onto the insulated chamber by epoxy resin. The inductance of the TF coil is approximately 1.4 mH. The TF is created by discharging a 116mF electrolyte capacitor bank energized up to 270 kJ for a maximum charging voltage 2.16kV, however the nominal charging voltage is 1.7 kV, then the nominal bank energy is 167.6 kJ. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  5. OH System 100 primary Ohmic heating (OH) turns form the cylinder air solenoid for the OH transformer. The design of the OH systems consists of two capacitor banks; the ionization bank and heating bank as shown in fig. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  6. Plasma Investigations and Studying Obstacles Preventing the Prolongation of Plasma Discharge and Plasma Current in EGYPTOR Tokamak ByH. HegazyPlasma Physics Department, NRC, EAEA, 13759Inshass, EgyptandYu.V.Gott, M.M.DreminRussianResearchCenter “Kurchatov Institute”, 123182Moscow, Russian Federation 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  7. INTRODUCTIONThe main target of this experimental work is to clarify the possibility to obtain the plasma discharge and to prolong its duration as much as possible. There could exists several reasons as a possible obstacles preventing obtaining this result:*.improper operation of power supply system, *. the high level of stray magnetic fields, *. the lack of equilibrium, *. the influence of MHDinstabilities *. The influence of impurities. So we tried to analyze all this reasons 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  8. The duration of toroidal field pulse is long enough (30 ms with half battery), so the time interval with relatively small (20%) variation of toroidal field is about 10 ms.That’s why first of all we checked the operation of the Ohmic heating power supply system. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  9. 1. Operation of the Ohmic Heating Power Supply SystemWith existing circuitry it critically depends on normal operation of Vacuum Interrupter (VI) in the circuit of so called “slow” battery. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  10. Operation of the Ohmic Heating Power Supply SystemBecause without VI the “slow” battery couldn’t give the loop voltage necessary to breakdown discharge,we were forced to obtain the discharges with the help of only ”fast” battery which could provide for discharge duration of only1 ms. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  11. 2. THE COMPENSATION OF STRAY MAGNETIC FIELDSFor the measurements of vertical magnetic field from OH coil the pick up coil was used [1]. This coil was placed in the plasma chamber center. without compensation with compensationThe compensation reduces the stray magnetic field about 4.6 times.Taking into account the sensitivity of the pick-up coil, then the value of the stray magnetic field after compensation isabout 1.2x10-3UOH[kV] ; UOH is the OH battery voltage 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  12. Pick-up coil Btor  The measurement of the vertical component of the toroidal magnetic field with help of the same pick-up coil is practically impossible because it is very difficult to place this coil properly Pick-up coil Btor Position of the pick-up coil for stray magnetic field measurement.The plan of pick-up coils must be parallel to the toroidal magnetic field Btor. If it is not so in pick-up coil will be generated signal which is proportional to sin. Practically the value of this signal is much greater than signal from stray magnetic field. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  13. 1 2 5 3 4 2 1 For the measurements of the stray vertical field from toroidal field coils the four (1-4) additional loops were used. These loops were placed on the bottom and top sides of vacuum chamber. The coil 1 was connected with the coil 2 in series1 – 4 – loops, 5 – vacuum chamber The 1 – 2 coils connectionsDifference between signals from loops 1 and 2 (or 3 and 4), gives after integration the value of vertical magnetic flux 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  14. The vertical component of the TF measured by coils 1+2Estimation of the value of stray vertical fields from toroidal coil and Ohmic heating coil gives no more than 5 Gs is deduced.So we can conclude that the measured values of stray magnetic fields can’t prevent the discharge breakdown and limit itsduration 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  15. 3. Investigation of the plasma column equilibriumFor these estimations we use the pair of Mirnov probes (outer and inner) installed in vacuum chamber. The precise evaluation of plasma position in the chamber envisage the calibrated measurements of poloidal magnetic field and average vertical magnetic field in accordance with formulaewhere is horizontal displacement of plasma column, a is minor plasma radius, R is major plasma radius,b is minor radius on which the Mirnov probes are placed, J is the plasma current, B+ and B - are the aziumuthal magnetic field measured by outer and inner Mirnov probes accordingly, B - averaged transverse magnetic field measured by loops 1-2 or 3-4. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  16. 3 Tokamak axis 1 2 4 Mirnov’s probes locations. Because Mirnov probes and these loops were not calibrated.If the center of plasma current coincides with the center of chamber i.e. at equal distances from both probes) these signals must be equal (in cylindrical approximation). In torus these signals will differ due the toroidicity in ratio (R + b)/(R – b) 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  17. if we adjust the signals from these two Mirnov probes in accordance with their toroidicityand subtract these signals we will obtain the signal proportional to displacement of plasma current.one can see from these signals that their shapes are similar and repeat practically the shape of plasma current signal. The relative differenceis not more than 0.125displacement 0,06b, The signals from Mirnov’s coils;i.e.  0.5 cm. coil1 (Ch. 3) , coil2 (Ch. 4), plasma current (Ch.1), and loop voltage (Ch. 2 ) 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  18. So we can conclude that the plasma equilibrium in these discharges is good enough and in any case couldn’t be the reason for their short duration or small plasma current value. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  19. 4. MHD instabilitiesAre MHD instabilities responsible for short duration and small amplitude of plasma current ?Conditions for this development are characterized by the q parameter which is determined as q  (Bt/B)(a/R) where Bt is toroidal magnetic field, B is the azimuthal field of plasma currentB[Gs] = 210-5Jp[A]/a[cm]Taking in mind that R = 30 cm for q we obtain formulae q = 1.7103Bt[T]a2[cm]/Ip[A]For Bt = 0.4 T (corresponding to Utor = 1 kV), Jp = 5 kA , a = 7 cm q =1.71030.4  49 / 5103 = 6.7 This value is large enough because most dangerous MHD modes have q values of 2 and 3. SoMHD instabilities most likely couldn’t be responsible for short duration and small amplitude of plasma current. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  20. 5. Estimations of plasma electron temperature Te They were based on the dependence of plasma resistivity  on Te expressed by formulasH = 1.6510-9ln/Te3/2 Ohmm, Te in keV,Z = N(Z)ZH.Knowing the plasma resistance from plasma current Jp and loop voltage U taken in the moment of maximum plasma currentUL = LpJp/tLp is the inductance of plasma column equals to zero due to Ip/е = 0 R = U/Jpone can estimate the plasma resistivity = RS/lwhere S is the plasma cross section a2a is the plasma minor radius which usually can be taken as limiter radius, l = 2R is the length of plasma axis ( R =0.3 m is the plasma major radius). 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  21. The value of Coulomb logarithm ln is weakly dependent on plasma density and can be taken as 17. Parameter N is weakly dependent on effective charge of plasma ions Z and in assumption that the main impurity is carbon (Z  5) can be taken as 0.72.With these parameters we obtain the formulae  = U[V]a2[m]/0.6Jp[A] = 1.0110-7/Te3/2[keV] andTe[keV] = 1.5410-5 (Jp/Ua2)2/3For plasma current Jp = 5 kA and loop voltage 25 V and assuming a = 7 cm we obtain Te = 1.5410-5(5103/254910-4)2/3 20 eV 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  22. This value is very close to so called “radiation limit” which was observed in first Tokamaks and is associated with high level of impurities. So as an obvious way to improve the plasma performance in EGYPTOR tokamak we consider the decreasing of the level of plasma impurities using cleaning discharge system ( Dc Glow discharge, as the first step &50 Hz Taylor discharge as the second step if it is still necessary) 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  23. Glow Discharge in EGYPTORSmooth operation of 600V, 0.6 A DC Glow Discharge is in operation and special study of the impurity contents using Emission Spectroscopy will be part of the aim of the next year. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  24. IN CONCLUSIONFor simultaneously operation of both batteries in EGYPTOR, the tokamak power supply system must be modified. For instance, the system used in many other Tokamaks such as in CASTOR OR CDX-U Tokamak C1= 412.5 mF, C2= 5 mF, C3= 2200 mF CASTOR Tokamak CDX-U Spherical Tokamak 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  25. Modification of the Toroidal Current Generation Scheme in EGYPTOR Tokamak By H. Hegazy Plasma Physics Dept., NRC, Cairo, EGYPT And K. Dyabilin Institute for High Temperatures Moscow, Russia 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  26. Toroidal Current Organization E*R 20-30 V 4-5 V fast Slow - stationary 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  27. Previous version “slow” Lower voltage circuit “ fast” High voltage circuit Plasma column • Problems with interference • Does not work 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  28. Plasma column Now “slow” “fast” • It works. • Due to the increased ratio “M/L “ the efficiency of the induced loop voltage generation also increased substantially. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  29. Scheme on the Tokamak “fast ”circuit chamber “slow” circuit 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  30. T.F. = 400 V OHF = 4 KV OHS = 400 V 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  31. Features of the new scheme • Positive • Very cheap, no needs for expansive vacuum interrupters, powerful diodes, … • Very effective. • At the stationary phase amplitude of the loop voltage can be up to 10 V. • Negative • Separation of both circuits is not absolute (mutual flux influence),but orders of magnitude lower than in previous version. • One need to induce an additional compensation coil in the same way as it was done previously. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  32. Numerical Estimations and Expectations Part of the activity was devoted few numerical estimations and expectations of the possible Tokamak plasma parameters. This is obtained by creating a one dimensional and time dependent code. The primary current , radial profile of the electric field, ion and electron temperatures were yielded by solving set of coupled nonlinear equations. It was shown that expected parameters are: *. plasma current= 4-10 kA *. Time duration 5-7 ms *. Plasma density= 5x1012 cm-3 *. Electron Temp.= 100-200 eV *. Ion Temp.= 15 eV 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  33. Primary Current and Toroidal Induced Electric Field eqs 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  34. Ion/electron Energy Balance eqs 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  35. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  36. Plots of Primary/Plasma Currents, Central temperatures, Scenario of Battery and Plasma Loop Voltage 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  37. Plots of the temporal behavior of the inductance voltage and toroidal magnetic field 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  38. Radial/Temporal Behavior of the Electric Field 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  39. Electron Temperature 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  40. Ion Temperature 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  41. Output Publications 1-H. Hegazy, and F. Zacek “Calibration of Power Systems and Measurements of Discharge Currents Generated for Different Coils in The EGYPTOR Tokamak”, J. of Fusion Energy V. 25 (1-2),73-86, (2006) 2-H. Hegazy, and F. Zacek “Absolute Measurements of the Magnetic Field Generated by different Coils in the Center of EGYPTOR Tokamak”, J. of Fusion Energy V. 25 (1-2),115-120, (2006) 3- H. Hegazy, Yu. V. Gott, and M. M. Dremin “Plasma Investigations and Studying Obstacles Preventing the Prolongation of Plasma Discharge and Plasma Current in EGYPTOR Tokamak, in Press 4- H . Hegazy, and K. Dyabilin “ Modification of the Toroidal Current Generation Scheme in EGYPTOR Tokamak”, in press 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  42. Expected activities for the Next year Experimental Activities: *.Improvement of Plasma discharge and Current Ramp up *.Wall Conditioning of EGYPTOR vessel. *. Study of impurities emitted during the cleaning discharge By Emission Spectroscopy. *.Measurements of Electron Temperature in EGYPTOR Tokamak using Langmuir probe. *.Development of Control System for EGYPTOR based on Data Acquisition Theoretical Activities: *.Study the effect of External Electric Field on Drift of the Plasma Across the Magnetic Field in Tokamak *. Study of Surface waves propagation along a Toroidal Plasma Column. 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

  43. THANK YOU 2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks

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