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

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan Outline  RFX design  Main machine limits  What has been done up to now  What can be done?  Open issues  Conclusions

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan RFX design Major radius R 2 m Minor radius a0.46 m Flux swing (from I m 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) Target Plasma current 2 MA Flat top V

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan Winding performances and limits WindingMax current [kA] Max I 2 t per shot [MA 2 s] Note Magnetizing s Toroidal Magnetizing15 Vs with 50 kA Splitted into 4 sections Equilibrium5.2 kA (average) with 2 MA plasma current Splitted into 8 sections Toroidal0.7 T with 18.3 kA Splitted into 12 sectors

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan T ini = 20°C Limit in the max overtemperature is related to the maximum stress in the probes between tiles and vessel T max = 200 °C Machine limits: first wall

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan MA # Machine limits: first wall

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan Present performances Vacuum shot with 50 kA magnetizing current 15 Vs

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan Present performances Toroidal circuit tested up to 12 kA (0.46 T). Commissioning to 16 kA in the next future. Very fast current inversion.

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan Flux consumption & rise time (#23800-#25672) Rt =  Rt =  Rt =  Rt =  Plasma current & volt seconds

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan (theta_w = 1.4, constant) “Plasma” flux consumption

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan Plasma current & volt seconds Very simple plasma with truncated Bessel function model aplasma minor radius r w 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 r w = m theta_w = 1.4 Plasma side

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan “Plasma” flux consumption

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan Fluxes in the machine BB IMIM IpIp IFIF L eq L stay  ST  L +  R BB BB KRKR

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan Simplified circuit Before the converter start: I F = 10.4 I p / 2 [kA] (I p in MA) I MF = I F + I R = 10.4 I p / 2 + V R /R T at the plasma current peak significant magnetizing current and transformer residual flux IMIM IFIF IRIR I conv

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan Varying the transfer resistor Fixed magnetizing current: 40.4 kA 12.1 Vs  ST = 15 (I Mo – I Mres )/50 -  rw (currents in kA)  L +  R =  rw ShotRTRT t max IpIp I Mres  rw  ST LL RR ohmmsMAkAWb L stray =  ST /I p ~ 1.4  H From experiments: Stray inductance * In case of no amper-turn compensation L stray ~ 4  H

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan Varying the magnetizing current - Fixed transfer resistor: 0.42 ohm K R ~ R T = 0.42  From experiments:  R scale about with I p and depends on R T  R ~ K R I p If I p in MA: “Resistive” flux consumption ShotI M0 t max IpIp I Mres  rw  ST LL RR kAmsMAkAWb K R ~ R T = 0.58 

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan What can be done?  =  M0 -  MF =  ST +  L +  R  = 6 I p (I p in R T = 0.58  = 6.5 I p (I p in R T = 0.42 IMIM IFIF IRIR I conv I F = 10.4 I p /2 [kA] (I p in MA) RTRT I R = 50 V p-p / R T (V p-p is the plasma loop voltage during the flat top) I MF = I F + I R - I convF

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan What we have done Case 1 – Rise with R T and flat-top with converters R T = 0.42  V p-p = 20 V V R = 50 V p-p = 1000 V I conv = 15 kA Ip = 1.77 MA Flat-top:20 V & 220 ms 30 V & 150 ms

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan What can be done? Case 2 – Rise with R T and flat-top with converters R T = 0.58  V p-p = 20 V V R = 50 V p-p = 1000 V I conv = 15 kA Ip = 1.92 MA Flat-top:20 V & 220 ms 30 V & 150 ms

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan What can be done? Case 3 – Flat top converters with series configuration (8 kA & 60 V voltage loop) used to rise plasma current (  R probably underestimated) R T = 0.58  V p-p = 60 V V R = 50 V p-p = 3000 V I conv = 8 kA Ip = 2.1 MA Flat-top: 20 V & 50 ms

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan Open issues Can the plasma current further increased with the present machine? Decreasing the resistive flux consumption  R ~ MA With different setting-up from the constant  (matched mode)  L = ~ 6 2 MA and  w =1.4 1 V s  I p = 0.17 MA

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan 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

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan 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 (  R probably underestimated) This case requires power supply improvements and other verifications on peak power from HV grid R T = 0.58  V p-p = 60 V V R = 50 V p-p = 3000 V I conv = 15 kA Ip = 2.38 MA Flat-top: 20 V & 50 ms

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan RUN 1401

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan Shots with higher currents

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan RFX - 1 MA campaign

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan RFX - 1 MA campaign

R. Piovan “RFX-mod: what does...”RFX 2009 Programme Workshop Padova, Jan RFX initial scientific objectives 1.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 2.To study the temperature, beta and confinement time scale with minor radius and current over an extended range 3.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 4.To study the sustainment phase and investigate the density/curren behavior