INITIAL RESULTS FROM THE MST REVERSED FIELD PINCH

Transcription

1 NTAL RESULTS FROM THE MST REVERSED FELD PNCH (Poster presented at the 30th Annual Meeting of the Division of Plasma Physics of the American Physical Society October 31-November 4, 1988, Hollywood, FL) J.A. Beckstead A.F. Almagri S. Assadi G. Chartas X. Deng D.J. Den Hartog R.N. Dexter S.A. Hokin D.W. Kerst D. Kortbawi T.W. Lovell S.C. Prager T.D. Rempel J.S. Sarff E.E. Scime W. Shen C.W. Spragins J.C. Sprott PLP 1045 December 1988 Plasma Studies University of Wisconsin These PLP Reports are informal and preliminary and as such may contain errors not yet eliminated. They are for private circulation only and are not to be further transmitted without consent of the authors and major professor.

2 Abstract nitial Results from the MST Reversed Field Pinch. * J.A. Beckstead, A.F. Almagri, S. Assadi, G. Chartas, X. Deng, R.N. Dexter, D.J. Den Hartog, S.A. Hokin, D.W. Kerst, D. Kortbawi, T.W. Lovell, S.C. Prager, T.D. Rempel, J.S. Sarff, E.E. Scime, W. Shen, C.W. Spragins, and J.C. Sprott, University of Wisconsin-Madison. The MST ( Madison Symmetric Torus) began operation in June The vacuum vessel has a 5-cm thick aluminum wall, major radius of 1.5 m, and a minor radius of 52 cm. t has an unconventional RFP design in that the vacuum vessel serves as the liner, the conducting shell, and the toroidal equilibruim field coils. The gap protection scheme acts as a limiter, 1 cm from the wall. nital RFP results will be presented, as well as results of non reversed operations. * Work supported by U.S.D.O.E.

3 Outline 1) Design Features of MST 2) Physics Goals 3) Plasma Parameters 4) A Typical Shot 5) An mplied Temperature 6) F - Theta Constant p 7) Sawteeth Like Oscillations 8) Conclusions and Future Work - 2 -

4 Design Features of MST MST was designed to minimize field errors, to allow for easy access to the machine, and to allow for easy disassembly. This was accomplished by incorporating the following design features. 1) The vacuum vessel is made of 5 cm. thick Aluminum. R = 1.5 m. and a = 0.52 m. - The vacuum vessel also acts as the toroidal field winding coil and the stablizing conducting shell. - This results in the toroidal and poloidal gaps being exposed to the plasma. They are protected by ceramic insulators being proven up to at least 400 Volts. 2) Pumping is done through a manifold. - The manifold is connected to the vacuum vessel by /2 " Dia. holes. - This decreases the field error due to larger pumping ports while maintaining a high pumping speed. -3-

5 3) The poloidal field system will consist of three windings. - A DC bias winding is used to obtain the full 2 weber flux swing of the iron core. - A poloidal field winding is positioned in order to closely match the wall currents at the poloidal gap. t is wrapped tightly around the core to allow easy diagnostic access to the vacuum vessel. - Continuity windings and a guard core prevent surface currents from flowing on the outer surface of the shell. - A poloidal flange is used to electrically connect the shell to the continuity windings. This allows for proper matching of the wall currents between the poloidal gap and the four legs of the continuity winding. 4) The vacuum vessel is used as the toriodal field winding. - This reduces the toriodal field ripple due to a finite number of windings. - A toroidal flange is used to connect the vacuum vessel to four poloidal current feeds. -4-

6 East View of MST Poloidal Field Winding located for optimum plasma current (not shown) DC Biasing Winding (not shown) Upper Continuity winding 2 Volt sec ron Core for driving plasma current Guard Core Vacuum Vessel Upper Half ( removable) Box Port for Diagnostic / Pumping Manifold Poloidal Current Feed Leg ( one of four) Small ron Core for generating Bt - 5 -

7 Upper Continuity winding Poloidal Field Winding located for optimum plasma current ( not shown) South View of MST r Volt sec ron Core for driving plasma current Guard Core Vacuum Vessel UpperHal ( removable) DC Biasing Winding (not shown) 0'1 Poloidal Flange Vacuum Vessel Lower Half Pumping Manifold Poloidal Current Feed Leg ( one of four) Small ron Core for generating Bt

8 Poloidal Field Winding MST Poloidal Field System Poloidal Flange Vacuum Vessel mage Currents in the wall -J Bias Windings Continiuity Windings Plasma Current

9 MST Toroidal Field Sytem nner Toroidal Gap ( electrically insula ted ) Vacuum Vessel acts as Toroidal Field Winding Toroidal Flange Arrows show path of Poloidal current! Outer Toroidal Joint Poloidal Current Feed Leg ( one of four) Small ron Core for generating Bt ==

10 The radial field errors due to the toroidal field system are: Br ( n = 4, m = 0) = 0.2 % of the toroidal field on axis in vacuum. ( see Almagri, et.al. poster 7V9 ) -9-

11 600 Plasma Current Shot CT k 400 A m 300 p s 200 f, dt 9147 Amp. sec o o " 100, Loop Voltage,,. 80 v o 60 t 40 s 20 o L o time ( msec )

12 Physics Goals Study the effect of the boundary conditions on RFP physics as related to stability, turbulence and transport. nitially this will be done by varing the vacuum region with a toroidal rail limiter. q scaling studies from the RFP regime to that of low q Tokamaks. Support for the next generation RFP's, ZT - H and RFX, by extending the current RFP scaling laws to larger machines. -11-

13 Plasma Parameters Predicted Plasma Current Loop Voltage Ohmic Heating Aver. Tor. Field Tor. wall Core Flux Energy confinement Pulse Duration Pessimistic 400 kamps 75 Volts 30 MWatts 1 kgauss -300 kgauss 1.8 Volt sec 0.4 msec 10 msec Optimistic 1 MAmp 4 Volts 4 MWatts 2.5 kgauss -150 kgauss 1.6 Volt sec 10 msec 40 msec Achieved to date ( Oct ) Typical Shot Best to date * Plasma Current 400 kamps Loop Voltage 30 Volts Pulse Duration 30 msec Reversal Du ration 10 msec Reversal Parameter, F Pinch Parameter, Theta 1.6 Electron Density 1 X 1013 fcm3 0.5 MAmps 20 Volts 35 msec 20 msec X 1013 fcm3 * Different shots

14 400 Toroidal Field at the Wall Shot CT G 200 a 100 u s 0 s w 1400 Ave rage T oro id a Fiel d 1200 G 1000 a 800 u s 600 s a time ( msec )

15 1 Reversal Parameter, F Shot OCT in i j 0.5 o > -== \OON'\....l:> L- -L 2 i Pinch Parameter, Theta o! o time ( msec )

16 ex] CXJ m U o 0 -+-' Q)..r: - (j) > LL,,.,,,,, ".,,, J LO o LL ;,,, - \ ". (jj e 0 <- +-' U e :::: LL ill 1l 1l ill m, - ' LO H ro +> H Q)..c. LO. LO O. o l-

17 MST is able to operate at a range of F, e values at fixed plasma current 1 Reversal Parameter, F i. i>, i ii ] ) i i 0.5 o l i it Pinch Po rameter, f) 300 Plasma Current " -'-. - "-- 1,,\\ m 1_1 '\....., 1 \ 1 k 200 A p s 100 o o Time ( msec ) o. o Time ( msec ) l

18 Oxygen lines are burned through early in the discharge 1 implying a multi-hundred ev temperature Oxygen V (1 038) i i 1 Oxygen V (789) i i i i A 0.8 r l b 0.6 U n 0.4. t 0.2 s A 0.8 r b 0.6 U n 0.4. t 0.2 s o f' TV ' 1 Oxygen V (630) i i i i i o J.. nytv...tw"' dt!d.w",, o ff 1 -v)tnu W'"'11!1!"M,.., Oxygen (703), -..,...-=-.-!...:. --r o " \ 1'eJJ... L..., 1. 7 P 350 a 300 s m a c 150 u 100 r r 50 e.,. J "rtjt.4l lo t o time ( msec ) Time ( msec ) n

19 When MST is operated in reversed discharges, sawteeth like oscillations occur in Btwall and < Bt >. 500 Plasma Current 400 k A 300 Dotted ines corresponds to the expanded F - Theta graph below m P 200 s Toroidal Field at the Wall 1400 : Average Toroidal Field : G 200 a 100 u s 0 s Time ( msec ) G 1000 a 800 u s 600 s o " o time ( msec )

20 1 These sawteeth result in increased wall interactions. Aluminum line 3092 A 0. 8 r b 0.6 U n Dotted ines corresponds to the expanded F - Theta graph below t 0.2 s Soft Xray 1 Visible A 0. 8 r b 0.6 U n t o.2 s time ( msec ) o! o time ( msec )

21 These sawteeth result in F - () oscillations F vs. () Shot CT Boxes are drawn every 0.5 msec starting at 7.00 msec. start F Thet.a

22 Conclusions and Future Work Conclusions The design goals of MST have been met. Plasmas have been obtained with Plasma Currents of 0.5 MAmps, pulse lengths of 35 msec., and Loop Voltages of 20 Volts. Field errors due to the toroidal field system are Br ( n = 4, m = 0) = 0.2 % ( see Almagri, et.at, this session 7V9 ) Future Machine Modifications Further wall cleaning is expected with continued operation. Complete installation of Poloidal Field winding resulting in further reduction of the field errors. nstall a toroidal rail limiter