Compact Torus Injection for Fuelling* C. Xiao, A. Hirose, STOR-M team (chijin.xiao@usask.ca) Plasma Physics Laboratory University of Saskatchewan 1 \
STOR-M Experiments Improved confinement induced by Electrode/limiter biasing (early 1990s) Turbulent heating Compact torus injection AC operation (O. Mitarai) Compact Torus Injector (mid 1990 now) Resonant Magnetic perturbations (last few years) Plasma aided material processing 2
Compact Torus (CT) research at Univ. of Saskatchewan 1990: CTF (CFFTP contract, R. Raman) Demonstrated disruption free CT injection into TdeV 1992: Construction of USCTI (low mass CT for STOR-M) CT induced improved confinement 2003: Vertical CT injection (D. Liu-Ph.D.) 2008: Repetitive CT operation 0.3 Hz (A. Pant-M.Sc.) 1-10 Hz (M. Dreval and T. Onchi-PDF) Goal: 100 Hz More recently: Momentum injection (A. Rohollahi-Ph.D.) 3
Outline Compact torus (CT) injection fuelling CT formation principle and experimental setup Main results CTI induced improved confinement Vertical CT injection Repetitive CT operation Moment injection into the STOR-M discharge 4
5 Motivations Fuelling o Current fuelling technology (pellet, SMBI etc. ) is unable to directly fuel the reactor core o Fuel recycling is complicated, involving radioactive tritium Compact Torus (CT) Injection o Only candidate for deep fueling o Able to optimized pressure profile increase bootstrap current o Momentum injection by tangential CT injection Control flows (increase tolerance to error field)
What is a Compact Torus (CT)? Magnetically confined robust and stable plasmoid in Taylor minimum energy state High in density, small in size Large acceleration, high velocity CT can be formed and accelerated in a coaxial gun 6
USCTI Layout 7
CT Device Features High voltage, high power, fast pulse discharges 25 kv, 20 μf banks Low inductance High current 150-220 ka 2.5 μs quarter cycle rising time. 8
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Formation of a CT is like blowing a bubble, only one at a time Repetitive operation is needed for a reactor 11
CT penetration and fuelling High density, small CT to fuel the tokamak core 12
Penetration requirement CT directional kinetic energy density must exceed the tokamak magnetic field energy density n ct : CT ion density m i : CT ion mass v ct : CT velocity B tok : tokamak toroidal magnetic field 13
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Tangential CT injection is a unique feature of USCTI/STOR-M experiments 15
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20-30 ka 17
18 Key question? What is the optimum CT injection direction? Tangential and vertical CT injection How CT interact with tokamak plasma Induces improved confinement Momentum injection Quasi-steady state fuelling repetitive CT operation
Results CT Induced Improved Confinement 19
Density H α decrease MHD Fluctuations Floating potential fluctuations Energy confinement time 20
Vertical CT Injection 21
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Results Repetitive CT Operation (Simple approach: high current power supplies 0.3 Hz) 25
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Results Repetitive CT Operation (Burst Mode 10 Hz) 27
Power Supply Block Diagram 28
Bank Voltages (long time scale) 1.7 Hz rep-rate 29
Discharge Waveforms (short time scale) V FS =-15 kv 30
Results CT induced modification of toroidal plasma flow 31
Ion Doppler Spectroscopy Normal view: Wavelength calibration PMT array: Time resolved flow measurement Bt Ip Tangential view: Doppler shift Choices of impurities spatial resolution: CIII: r=7cm OV: r= 4cm CVI: r=0cm 32
Flow modification by CT injection (normal tokamak current direction) v t Changes of the flow velocity are along CT injection direction (CT momentum is approximately 10 times the plasma rotation) 33
Flow modification by CT injection (reversed tokamak current direction) v t Reversed plasma flow direction Changes in flow velocity are still along CT injection direction 34
Conclusions Compact torus injection improves confinement Tangential CT injection transfers momentum to toroidal rotation Vertical CT injection by deflecting CT direction reduces CT velocity High bay hall for vertical CT setup Repetitive CT injection up to 10 Hz have been achieved Bottlenecks for 100 Hz will be identified CT injection experiment must be tested in larger tokamak! 35
Thank you! 36
Extra Slides 37
CT formation principle (cont.) 38
39 Effect of CTI on Toroidal Flow
Storage Bank IGBT Stacks Single Gate Fast Bank Sample Circuit Diagram 40