Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 1 Highlights on EGYPTOR Progress By H. Hegazy Plasma Physics Dept., NRC, Atomic Energy Authority Enshass, Egypt

Beijin, China2nd 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 cm The minor radius(a):10 cm Cross sectional view of the vacuum chamber

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 3 Photograph of EGYPTOR Device

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 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 kJ. Toroidal Field System

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 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. OH System

Beijin, China2nd 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 By H. Hegazy Plasma Physics Department, NRC, EAEA, Inshass, Egypt and Yu.V.Gott, M.M.Dremin Russian Research Center “Kurchatov Institute”, Moscow, Russian Federation

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 7 INTRODUCTION The 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 MHD instabilities *. The influence of impurities. So we tried to analyze all this reasons

Beijin, China2nd 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.

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 9 1. Operation of the Ohmic Heating Power Supply System With existing circuitry it critically depends on normal operation of Vacuum Interrupter (VI) in the circuit of so called “slow” battery.

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 10 Operation of the Ohmic Heating Power Supply System Because 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.

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks THE COMPENSATION OF STRAY MAGNETIC FIELDS For 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 compensation The 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 is about 1.2x10 -3 U OH [kV] ; U OH is the OH battery voltage

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 12 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. Pick-up coil  B tor

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 13 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 series 1 – 4 – loops, 5 – vacuum chamber The 1 – 2 coils connections Difference between signals from loops 1 and 2 (or 3 and 4), gives after integration the value of vertical magnetic flux

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 14 The vertical component of the TF measured by coils 1+2 Estimation 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 its duration

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks Investigation of the plasma column equilibrium For 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 formulae where  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.

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 16 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) Tokamak axis

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 17 if we adjust the signals from these two Mirnov probes in accordance with their toroidicity and 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 difference is not more than displacement 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 )

Beijin, China2nd 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.

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks MHD instabilities Are 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  (B t /B  )(a/R) where B t is toroidal magnetic field, B  is the azimuthal field of plasma current B  [Gs] = 2  J p [A]/a[cm] Taking in mind that R = 30 cm for q we obtain formulae q = 1.7  10 3 B t [T]a 2 [cm]/I p [A] For B t = 0.4 T (corresponding to U tor = 1 kV), J p = 5 kA, a = 7 cm q =1.7  10 3  0.4  49 / 5  10 3 = 6.7 This value is large enough because most dangerous MHD modes have q values of 2 and 3. So MHD instabilities most likely couldn’t be responsible for short duration and small amplitude of plasma current.

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks Estimations of plasma electron temperature T e They were based on the dependence of plasma resistivity  on T e expressed by formulas  H = 1.65  ln  /T e 3/2 Ohm  m, T e in keV,  Z = N(Z)  Z  H. Knowing the plasma resistance from plasma current J p and loop voltage U taken in the moment of maximum plasma current U L = L p  J p /  t L p is the inductance of plasma column equals to zero due to  I p /  е = 0 R = U/J p one can estimate the plasma resistivity  = R  S/l where S is the plasma cross section  a 2 a 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).

Beijin, China2nd 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 With these parameters we obtain the formulae  = U[V]a 2 [m]/0.6J p [A] = 1.01  /T e 3/2 [keV] and T e [keV] = 1.54  (J p /Ua 2 ) 2/3 For plasma current J p = 5 kA and loop voltage 25 V and assuming a = 7 cm we obtain T e = 1.54  (5  10 3 /25  49  ) 2/3  20 eV

Beijin, China2nd 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)

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 23 Glow Discharge in EGYPTOR Smooth 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.

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 24 IN CONCLUSION For 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 C 1 = mF, C 2 = 5 mF, C 3 = 2200 mF CASTOR Tokamak CDX-U Spherical Tokamak

Beijin, China2nd 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

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 26 Toroidal Current Organization E*R V 4-5 V fastSlow - stationary

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 27 Plasma column “slow” Lower voltage circuit “ fast” High voltage circuit Previous version Problems with interference Does not work

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 28 Now “fast” Plasma column “slow”  It works.  Due to the increased ratio “M/L “ the efficiency of the induced loop voltage generation also increased substantially.

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 29 “fast ” circuit “slow” circuit chamber Scheme on the Tokamak

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 30 T.F. = 400 V OHF = 4 KV OHS = 400 V

Beijin, China2nd 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.

Beijin, China2nd 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= 5x10 12 cm -3 *. Electron Temp.= eV *. Ion Temp.= 15 eV

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 33 Primary Current and Toroidal Induced Electric Field eqs

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 34 Ion/electron Energy Balance eqs

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 35

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 36 Plots of Primary/Plasma Currents, Central temperatures, Scenario of Battery and Plasma Loop Voltage

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 37 Plots of the temporal behavior of the inductance voltage and toroidal magnetic field

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 38 Radial/Temporal Behavior of the Electric Field

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 39 Electron Temperature

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 40 Ion Temperature

Beijin, China2nd 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), , (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

Beijin, China2nd 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.

Beijin, China2nd RCM - IAEA - CRP On Joint Research Using Small Tokamaks 43