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RFX – mod: what does the present device allow to do? R. Piovan

RFX – mod: what does the present device allow to do? R. Piovan. Outline. RFX design Main machine limits What has been done up to now What can be done? Open issues Conclusions. RFX design. Major radius R 2 m Minor radius a 0.46 m Flux swing (from I m to 0) 15 V s

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RFX – mod: what does the present device allow to do? R. Piovan

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  1. RFX – mod: what does the present device allow to do? R. Piovan RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  2. Outline • RFX design • Main machine limits • What has been done up to now • What can be done? • Open issues • Conclusions RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  3. RFX design Major radius R 2 m Minor radius a 0.46 m Flux swing (from Im to 0) 15 V s Toroidal field 0.6 T (old 0.7) Loop voltage 700 V First wall graphite tiles Shell time constant 70 ms (old 450 ms) Plasma current 2 MA Flat top 250 ms @ 18 V Target RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  4. Winding performances and limits Magnetizing 15 Vs with 50 kA Splitted into 4 sections Equilibrium 5.2 kA (average) with 2 MA plasma current Splitted into 8 sections Toroidal 0.7 T with 18.3 kA Splitted into 12 sectors RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  5. Machine limits: first wall T ini = 20°C Tmax = 200 °C Limit in the max overtemperature is related to the maximum stress in the probes between tiles and vessel RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  6. Machine limits: first wall 1.6 MA # 24533 RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  7. Present performances Vacuum shot with 50 kA magnetizing current 15 Vs RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  8. Present performances • Toroidal circuit tested up to 12 kA (0.46 T). • Commissioning to 16 kA in the next future. • Very fast current inversion. RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  9. Flux consumption & rise time (#23800-#25672) Plasma current & volt seconds Rt = 0.584 Rt = 0.420  Rt = 0.467  Rt = 1.011  RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  10. “Plasma” flux consumption (theta_w = 1.4, constant) RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  11. Plasma current & volt seconds Plasma side Very simple plasma with truncated Bessel function model a plasma minor radius rw internal vessel minor radius Further hypothesis: plasma current rise with reversed toroidal field (RFP) and constant theta Values assumed in the model: a = 0.42 m rw = 0.459 m theta_w = 1.4 RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  12. “Plasma” flux consumption RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  13. Fluxes in the machine IF IM Ip Bq Bq Bq YST YL+ YR KR Leq Lstay RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  14. Iconv IF IM IR Simplified circuit Before the converter start: IF = 10.4 Ip / 2 [kA] (Ip in MA) IMF = IF + IR = 10.4 Ip / 2 + VR/RT at the plasma current peak significant magnetizing current and transformer residual flux RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  15. Stray inductance Varying the transfer resistor Fixed magnetizing current: 40.4 kA 12.1 Vs YST = 15 (IMo – IMres)/50 - Yrw (currents in kA) YL + YR = Yrw From experiments: Lstray = YST/Ip ~ 1.4 mH * In case of no amper-turn compensation Lstray ~ 4 mH RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  16. “Resistive” flux consumption Varying the magnetizing current - Fixed transfer resistor: 0.42 ohm From experiments: YR scale about with Ipand depends on RT YR ~ KR Ip If Ip in MA: KR ~ 2.1 @ RT = 0.42 W KR ~ 1.6 @ RT = 0.58 W RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  17. What can be done? DY = YM0 - YMF = YST + YL + YR DY = 6 Ip (Ip in MA) @ RT = 0.58 DY = 6.5 Ip (Ip in MA) @ RT = 0.42 IF = 10.4 Ip/2 [kA] (Ip in MA) IR = 50 Vp-p / RT (Vp-p is the plasma loop voltage during the flat top) RT Iconv IF IM IMF = IF + IR - IconvF IR RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  18. What we have done Case 1 – Rise with RT and flat-top with converters RT = 0.42W Vp-p = 20 V VR = 50 Vp-p = 1000 V Iconv = 15 kA Ip = 1.77 MA Flat-top: 20 V & 220 ms 30 V & 150 ms RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  19. What can be done? Case 2 – Rise with RT and flat-top with converters RT = 0.58 W Vp-p = 20 V VR = 50 Vp-p = 1000 V Iconv = 15 kA Ip = 1.92 MA Flat-top: 20 V & 220 ms 30 V & 150 ms RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  20. What can be done? Case 3 – Flat top converters with series configuration (8 kA & 60 V voltage loop) used to rise plasma current (YR probably underestimated) RT = 0.58 W Vp-p = 60 V VR = 50 Vp-p = 3000 V Iconv = 8 kA Ip = 2.1 MA Flat-top: 20 V & 50 ms RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  21. Open issues Can the plasma current further increased with the present machine? Decreasing the resistive flux consumption YR ~ 3.2 Vs @ 2 MA With different setting-up from the constant q (matched mode) YL = ~ 6 Vs @ 2 MA and qw=1.4 1 V s DIp = 0.17 MA RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  22. Conclusions • RFX performances agree completely with design assumptions done almost 30 years ago • 2 MA plasma current, according to the initial specification, can be reached • Volt-second needed for plasma current rise and sustainment experimentally derived from experimental data • Further current increasing saving volt-second with the optimization of plasma setting-up RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  23. What can be done? Case 4 – Doubling the flat top converters with series configuration (15 kA & 60 V voltage loop) used to rise plasma current (YR probably underestimated) This case requires power supply improvements and other verifications on peak power from HV grid RT = 0.58 W Vp-p = 60 V VR = 50 Vp-p = 3000 V Iconv = 15 kA Ip = 2.38 MA Flat-top: 20 V & 50 ms RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  24. RUN 1401 RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  25. Shots with higher currents RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  26. RFX - 1 MA campaign RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  27. RFX - 1 MA campaign RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

  28. RFX initial scientific objectives • Extent the investigations to higher currents to study the confinement properties of RFP type so that comparison with properties of large stellarators and tokamaks can be made • To study the temperature, beta and confinement time scale with minor radius and current over an extended range • To study the setting-up of stable RFP configurations to minimize energy losses and optimize the configuration. This includes studying the effects of density control using gas injection, the first wall condition and impurities including the use of limiters, the importance of field error, the role of wall stabilization and, at a later stage, of operating without a shell • To study the sustainment phase and investigate the density/curren behavior RFX 2009 Programme Workshop Padova, 20-22 Jan 2009

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