1. 1 21 Sep 2004M. Vervier Tests and matching analysis of a load resilient ICRH antenna on TEXTOR M. Vervier, P. Dumortier, S. Grine, A. Messiaen, G. Van Wassenhove Trilateral Euregio Cluster Laboratoire de Physique des Plasmas / Laboratorium voor Plasmafysica, EURATOM Association, B-1000 Brussels, Belgium

2. 2 21 Sep 2004M. Vervier Side view of the tuneable antenna pair DIMENSIONS l AC = 0.517 m l AB = 0.21 m l CD = 0.35 m Zc CD = 30 Ohm/m C p from 15 to 200pF In the insert the top view shows on the R side the upper part and on the L side the lower part V Cp I Cp IAIA VAVA

3. 3 21 Sep 2004M. Vervier Equivalent circuit of the tuneable strap C represent the vacuum adjustable capacitor R the ohmic losses L the inductance of the antenna strap and the coaxial line B is the tap point

4. 4 21 Sep 2004M. Vervier Antenna on its support for calibration

5. 5 21 Sep 2004M. Vervier Antenna inside TEXTOR

6. 6 21 Sep 2004M. Vervier Schematic diagram of the antenna system 2 tuneable vacuum capacitors 2 line stretchers  4 parameters instead of the usual 2 parameters for the matching of the antenna

7. 7 21 Sep 2004M. Vervier CALIBRATION AND LOW POWER MEASUREMENTS Y G =Y T11 +Y T22 +2Y T12

8. 8 21 Sep 2004M. Vervier PROBES AND IMPEDANCE MEASUREMENTS V C limit the power at the generator I C limit the pulse length V A, I A, DC X, V X used to compute the antenna impedance

9. 9 21 Sep 2004M. Vervier Smith Chart at 32.5 MHz at tap point Big dots: actual values of the impedance for detuning of -10, -5, 0, +5 and +10 pF. Curves: calculated impedance at the tap point (using the best fit parameters), for different antenna coupling resistance (from 0.5 to 60 Ohm/m) and detuning of capacitor (from -10 to +10 pF).

10. 10 21 Sep 2004M. Vervier From vacuum measurements From the S parameters measured at resonance a) calculated absolute value of reflection coefficient at generator in fct(LS L,LS R ) Ratio of power b) transmitted to the Right strap; c) radiated by the Right strap; d) exchanged between the straps, to the total power. 2 solutions of matching with  Cp=0 at 32.5 MHz: (LS) L =0.95+24 m, (LS) R =1.83+28.5 m ; rpR=65%; rprR=52.5%; rpexch=12.5% (LS) L =1.71+24 m, (LS) R =1.07+28.5 m ; rpR=38.5%; rprR=51.5%; rpexch=-13%

11. 11 21 Sep 2004M. Vervier Study of load resilience in presence of mutual coupling As first approximation: plasma loading only change resistive part of Z CL-CR matrix 10 < mf (multiplication factor) < 65 corresponds roughly to 3<Ra<20  /m  fit to obtain best 4 parameters! (  |K G | 2 minimum ) Cp L =78 pF, Cp R =56.6 pF, (LS) L =25.45 m, (LS) R =30.06 m

12. 12 21 Sep 2004M. Vervier results using best parameters Smith chart of admitance at T Red curve: admitance at the Right side of the T Green curve: admitance at the Left side of the T Dots correspond to Ra=3,6,9,...,30  /m Red circles: conductance of (VSWR=1.4) -1 /2 and VSWR/2 Green circle: conductance of 0.5 Blue circle: K G =0.16 corresponding to a VSWR of 1.4 for 3<Ra<20

13. 13 21 Sep 2004M. Vervier Results A good load resilience is achieved in a broad loading range BUT  varies continually Radiated power unbalanced between the straps !

14. 14 21 Sep 2004M. Vervier PRACTICAL WAY Find matching on vacuum with  C P =0 (well function) For operation with plasma: detune capacitors respectively of -7.5 and +7.5 pF dCp L =-7.5 pF dCp R =+7.5 pF

15. 15 21 Sep 2004M. Vervier Or... Z = mf * real(Z V )+ imag(Z V ) dCpL dCpR dCp L =-11.4pF dCp R =6.8pF rpR rpRr rpLr rpL rpexch for 3<Ra<20 rpL=y TL /(y TL +y TR ) rpLr=R[(R(za(1,1))*i L +R(za(1,2))*i R )*conj(i L )]

16. 16 21 Sep 2004M. Vervier But different if plasma loading affects also imaginary part of Z CL-CR Z = mf * real(Z V )+ (1-mf/500) * imag(Z V ) dCp L dCp R dCp L =-7.5 pF dCp R =+7.5 pF

17. 17 21 Sep 2004M. Vervier CONCLUSIONS Good resilience can be achieved, even with a small variation of the imaginary part of Z CL-CR  always varying with plasma load but its sign can be chosen (depending of the positions of LS) Unbalanced power between the straps (2 times more power in one strap in some cases !)  Computation of Antenna Impedance during plasma will help to choose the right values for Cp and LS.