Design of a feedback control system for KTX Hong Li, on behalf of KTX team The 17th International RFP Workshop, October , 2015, Hefei 1

Outline Typical parameters of KTX Feedback control system Passive control of MHD and error field Active control for TM/RWM and error field actuators sensors strategy Numerical analysis of TM/RWM with KTX geometry 2

ParametersKTX Major Radius1.4m Minor Radius0.4m Aspect Ratio3.5 Time of Vacuum Vessel2ms Time of Conducting Shell20ms Proximity1.07 Vertical Gaps Number2 Horizontal Gap Number1 Saddle Coils Number24×4 Error Field Control Coils Number16×2 Typical parameters on KTX Feedback control 3

Passive Control: vacuum vessel and conducting shell Stainless steel vacuum vessel  Vacuum vessel and conducting shell are attached closely  Proximity b/a ~ 1.07  Ceramic spraying used for insulating between vacuum vessel and shell  6mm vacuum vessel  Magnetic penetration time 2ms: good for PPCD  Two vertical gaps: for ohmic heating  Stainless steel material: for wall condition research  the maximum diameter of port :15 cm, for error field reduction  Vacuum vessel and conducting shell are attached closely  Proximity b/a ~ 1.07  Ceramic spraying used for insulating between vacuum vessel and shell  6mm vacuum vessel  Magnetic penetration time 2ms: good for PPCD  Two vertical gaps: for ohmic heating  Stainless steel material: for wall condition research  the maximum diameter of port :15 cm, for error field reduction 4

Passive Control: vacuum vessel and conducting shell  Two shells used:  1.5 mm thick copper shell is attached tightly on the vacuum vessel with proximity of 1.07  Magnetic penetration time 20ms  Two vertical gaps and one horizontal gap  Two pieces of second shell are overlapped on the first copper shell at two vertical gaps to reduce radial field caused by eddy current  Two shells used:  1.5 mm thick copper shell is attached tightly on the vacuum vessel with proximity of 1.07  Magnetic penetration time 20ms  Two vertical gaps and one horizontal gap  Two pieces of second shell are overlapped on the first copper shell at two vertical gaps to reduce radial field caused by eddy current += 5

Copper bolts keep electric connection  16 Copper bolts connect auxiliary copper shell over the vertical gap  Current through the copper bolt act to balance the plasma and suppress the error field  16 Copper bolts connect auxiliary copper shell over the vertical gap  Current through the copper bolt act to balance the plasma and suppress the error field 6

 Auxiliary shells suppress error field by conducting equivalent ‘passing through’ current  Auxiliary shells change the magnetic field penetration time near the gap first copper shell Auxiliary shells suppress error field auxiliary copper shell 7

Saddle coils for feedback control  4*24 saddle coils had settled down over the shell surface for MHD feedback control  Each saddle coils can be drived independently to suppress mode amplitude and drive mode rotation according to feedback strategy  4*24 saddle coils had settled down over the shell surface for MHD feedback control  Each saddle coils can be drived independently to suppress mode amplitude and drive mode rotation according to feedback strategy Saddle Coils Number24×4 Turns per Coil40 Maximum Current per Turn 200A Radial location0.417m Radial Pertubation Magnetic field 16 mT Resistance per coil0.55Ω Self Inductance per coil1.5 mH Mutual Inductance (adjacent coil) 0.22 mH Mutual Inductance (diagonal coil) 48 μH 8

3D EM field simulation of feedback control system  A 3D electromagnetic field model has been used to study the field generated by saddle coils with independent current carrying. 9

Error field control coils EF Control Coils Number 16×2 Turns per Coil48 Maximum Current per Turn 150 A Radial location0.46 m Radial Pertubation Magnetic field 15 mT Resistance per coil0.17 Ω Self Inductance per coil0.62 mH Mutual Inductance (adjacent coil) 15.7 μH Mutual Inductance (interval coil) 1.9 μH stability shell auxiliary copper shell Error field control coils Copper bolt connection Saddle coils Saddle coils 10

Construction magnetic field by numerical simulation and experiment in platform  Polodial distribution of radial field by 16 EF coils (m=1) simulation result  Polodial distribution of radial field by 16 EF coils (m=1) simulation result  2D Megnetic radial field distribution (m=0) experiment result 11

Sensors for feedback control TypeMeasurement parameterLocation Channel number EF magnetic probeError field2 vertical gap 3D magnetic probeMagnetic fieldInside of vacuum vessel46×4×3 Saddle sansorradial magnetic flux Between the copper shell and vacuum vessel 24×4 Eddy current arrayEddy current on shell Outside of copper shell, have same (θ,φ) coordinate with 3D magnetic probe 46×4×2 12

Eddy current array 13 Sketch of eddy current probe and its platform experiment. by Li zichao

Eddy current and control coils current (1,4)+(1,5)

KTX Feedback Control Strategy Eddy Current Array J(θ,φ) 3D Magnetic Probes FFT (by FPGA) FFT (by FPGA) Magnetic signal Current signal PID Control B(θ,φ) Active control coils 15 PID Control PID Control Plasma Power Amplifier B e (θ,φ)

Resistance wall mode in KTX 16 by Bai wei, Zhu ping, Luo bing Growth rates Safety factor profile Plasma displacement Perturbed radial magnetic field

Tearing mode in KTX locking thresholds for the main TMs in KTX : 1mT CG Li, P Zanca and W Liu, PPCF 56 (2014) TM(1, 8), Lundquist number S =1e6 Perturbed radial magnetic field & plasma velocity profile presented by NIMROD simulations by Luo bing, Zhu ping

Conclusion and next plan A feedback control system include conducting shell for KTX is designed to control Resistive Wall Modes, Tearing Modes and Error Fields. Control coils and sensor array have settled down on KTX, while power amplifiers and electronics are expected to accomplish on phase II. Attempt to consider the control strategy difference by two kind of inputs: perturbed magnetic field or eddy current. 18

Thanks for your attention 19