Overview of the Helicity Injected Torus Program

Size: px

Start display at page:

Download "Overview of the Helicity Injected Torus Program"

Ella Reynolds
5 years ago
Views:

1 Overview of the Helicity Injected Torus Program B. A. Nelson, T. R. Jarboe, W. T. Hamp, V. A. Izzo, R. G. O Neill, A. J. Redd, P. E. Sieck, R. J. Smith, J. A. Rogers, G. A. Andexler, and D. E. Lotz University of Washington Seattle American Physical Society Meeting, Division of Plasma Physics Savannah, GA November 24

2 Abstract The Helicity Injected Torus with Steady Inductive Helicity Injection (SIHI) spheromak experiment (HIT-SI) [Jarboe, Fus. Tech., (36)1, p.85, 1999] addresses critical issues for spheromaks, including current drive, operation at high beta, and confinement. HIT-SI features an optimal high-beta plasma shape and current profile, steady-state operation, minimal plasma-wall interaction, and injected power always flowing into the plasma. HIT-SI has a bow-tie shaped 1 cm thick Cu flux conserver with major radius R =.33 m and axial extent of.57 m. A half torus helicity injector at each end of the flux conserver produces conjugate sinusoidal flux (4 MW peak) and loop voltages (2 MW peak) at 5 khz by IGBT-based switching power amplifiers. Injector flux and loop voltages are phase controlled to maintain power flow always inward. Insulating breaks for the oscillating flux and loop voltage are provided by a novel double viton o-ring system. HIT-SI uses the diagnostic suite previously used by the HIT-II experiment, (presented in an accompanying poster.) Results and 3D MHD simulations will be presented.

3 Introduction Critical issues for spheromaks include current drive, operation at high β, and confinement. The Helicity Injected Torus with Steady Inductive Helicity Injection (SIHI) spheromak, HIT SI, addresses all of these issues. SIHI also features an optimal high-β current profile, steady-state operation, minimal plasma-wall interaction, plus injected power and helicity always flow into the plasma. HIT SI is commissioning and optimizing an improved set of power supplies, and incorporating the HIT II diagnostic suite. I inj 12 ka for 5 ms achieved with Poynting flux inward.

4 HIT Personnel Faculty/Staff Support Staff Graduate Students Thomas R. Jarboe Daniel E. Lotz William T. Hamp Brian A. Nelson Matthew B. Fishburn Valerie A. Izzo Roger Raman Dennis Peterson R. Griff O Neill Aaron J. Redd Dzung Tran Paul E. Sieck Roger J. Smith Susan D. Griffith Jonathan Wrobel John A. Rogers Andrew P. Cassidy George L. Sutphin George R. Andexler Undergraduates Rorm Arestun Annamarie Askren Jonathan Setiawan Chris Pihl James Newman Rabih Aboul Hosn Edwin Penniman Ellen Griffin Aaron Siirila

5 Coaxial Helicity Injection (CHI) has n= Symmetry K inj = 2V inj ψ inj λ inj µ I inj ψ inj n= source produces n=1 relaxation to form n= equilibrium

6 n=1 Source Requires only one Relaxation Process n=1 n= λ inj λ transition > λ sph One relaxation process Fernadez et al., Phys. Plasmas, 1989

7 n=1 Source Can be Replaced by Toroidal Pinch V loop Source can be a oscillating toroidal pinch K inj = 2V inj sin (ωt)ψ inj sin (ωt) Two toroidal injectors, phased 9, allow steady inductive helicity [ injection (SIHI) K inj = 2V inj ψ inj sin 2 (ωt) + cos 2 ] (ωt)

8 Details of SIHI: an SIHI Half-Cycle A) Right injector max flux; left injector zero flux B) Right injector reducing flux; left injector building up flux C) Right injector building up flux (reversed from A); left injector reducing flux D) Right injector full reversal; left injector zero flux

9 β 1% in Bow-tie Flux Conserver / Hollow λ (ψ) Poloidal Flux q.5 1 p ψ.3.2 β z w z w All q edge is on geometric axis Bow-tie reduces q edge higher dq/dψ β 1%

10 HIT SI: High β Spheromak with SIHI HIT SI Cut-away View X-section of high β bow-tie flux conserver and injectors

11 Photos of HIT SI HIT SI X Injector HIT SI Y Injector

12 HIT SI Addresses Critical Spheromak Issues High-β flux conserver shape Optimal high-β current profile Steady-state operation Minimal plasma-wall interaction Injected power and helicity always flow into the plasma

13 HIT SI Parameters Parameter Symbol Value Major Radius R.33 m Minor Radius a.2 m Spheromak Area A sph.212 m 2 Spheromak λ λ sph 11 m 1 Injector Radius R inj.33 m Injector Area A inj.24 m 2 Injector λ λ inj 3 m 1 Flux conserver 1.2 cm thick chromium copper Electrical breaks for flux and loop voltage

14 HIT SI Inherits HIT II Diagnostic Suite Multi-point Thomson scattering FIR interferometry SPRED, VUV, IDS, bolometry, Z eff, H α, SXR CCD imaging camera Internal magnetic and electric probes See Jarboe et al. for more information

controlled V inj (Eventually I inj control) Flux Coil Circuit Mostly

15 HIT SI uses Switching Power Amplifiers (SPAs) for V inj and ψ inj Control Voltage Coil Circuit Mostly resistive Driven 5 khz LC tank Feedback controlled V inj (Eventually I inj control) Flux Coil Circuit Mostly inductive Direct pulse width modulation (2 pulses per cycle) Feedback controlled ψ inj

16 SIHI Uses Two Quadrature Voltage and Flux Circuits Two injectors with 9 phasing SIHI rate: K inj = 2Vinj ( ψ inj sin 2 ω t + cos 2 ω t ) Transformer primary (V inj ) Voltage Circuit Injector flux (I inj ) Flux Circuit

17 HIT SI Power Supply Design Specifications Parameter Voltage Circuit Flux Circuit (2 ea, 9 phasing) (2 ea, 9 phasing) Main Frequency 5 khz 5 khz Load Type Plasma Secondary 4 12-turn Coils (mostly resistive) (mostly inductive) I max 32 ka 96 ka-turns Load Impedance 2 mω 17 µh Power 2 MW 2 4 MW Feedback Method Push-Pull LC tank Direct PWM drive Carrier Frequency 5 khz 5 khz ( MW carrier) (Triangle carrier) Pulse width modulation

18 V inj will lead I inj Have ψ inj lead I inj Injector plasma inductance causes V inj to lead I inj. Constrain ψ inj to lead I inj by phase δ to prevent outgoing power during de-fluxing of injector plasma. δ I inj V inj ψ inj Adjust δ to have I inj and V inj cross zero at the same time Spheromak and other injector circuit will aid de-fluxing of plasma secondary λ inj = µ I inj /ψ inj averages to injector eigenvalue Power flow into spheromak, not insulator

19 Stabilized Pinch During Flux Buildup, RFP During Flux Reduction Keep Poynting Flux Inward Flux Coil V loop V loop + + Injector X section λ < inj During flux buildup λ, stabilized pinch λ > inj During flux reduction λ, RFP Flux circuit adds flux in same direction as edge injector plasma

20 HIT II Switching Power Amplifiers (SPAs) are Modified for HIT SI Each HIT SPA provides up to ±16 A at 1 kv SPAs are operated in parallel using fan-outs of the fiber optic switching signals (excellent current sharing) Power requirements of voltage circuit met by push-pull driven LC tank circuit Flux circuit coil driven by pulse width modulation (PWM) at higher frequency than in HIT II

21 IGBT Switches are Used in an H-Bridge S1 S3 I + V S2 S4 Each HIT SI switching power amplifier (SPA) uses V/4A IGBTs, and can be pulsed to ±16 A at 1 kv.

22 Switching Signals Determine Load Voltage S1 and S4 on: V> (for I>) S2 and S3 on (or all off): V< (for I>) S2 and S4 on: V= (for I>) S1 S3 I + S1 S3 I + S1 S3 I + V V V S2 S4 S2 S4 S2 S4 S1 and S4 on (or all off): V> (for I<) S2 and S3 on: V< (for I<) S1 and S3 on: V= (for I<) S1 S3 I + S1 S3 I + S1 S3 I + V V V S2 S4 S2 S4 S2 S4 Switching signals S1 S4 are digital fiber optic. Successive timing of S1 S4 determines V time history.

23 PWM Determines Flux Circuit Switching Signals Error = Demand Feedback Triangle Comparator Waveform Error S1 S2 S3 S4 +V V

24 HIT SPAs are in Modular Rack-mounted Boxes SPA boxes IGBTs, driver boards, and caps

25 5 khz Flux Waveform w/feedback by 5 khz PWM.5.25 X Injector Flux HIT-SI Pulse 126 ψ inj X (mwb) I flux coil X (ka) X Flux Coil Current Time (ms) Feedback maintains flux waveform in presence of injector current

26 V inj Driven by 2-Parallel-SPA Tank Circuit I volt X 1-2 (ka) 2 1 X Volt Coil Currents 1-2 HIT-SI Pulse 126 I volt coil X (ka) V inj X (V) X Volt Coil Current Total X Injector Loop Voltage Time (ms)

27 Initial Voltage Circuit is a Driven LC Tank Circuit Square Wave Driver Trigger Tank Circuit Cont troller Switching Signal F/Os Fault F/O H Bridge C L Coil Z Injector Plasma Series LC tank circuit driven by 5 khz square wave Parallel SPAs receive fanned out switching signals Voltage coil primary can be 1, 2, 3, or 6 turns

28 V inj Driven by Push-Pull LC Tank Circuits Feedback Signal In Integrated Output to Digitizer Demand Input "MW" Comparator Waveform In Trigger Tank PWM Cont troller Switching Signal F/Os Fault F/O H Bridge C L Coil Z "MW" Comparator Waveform Error = Feedback Demand Injector Plasma Feedback Rogowski LC Tank Driving Voltage

29 ψ inj leads I inj by Approximately 4 HIT-SI Pulse X Primary Current I volt coil X (ka) X Secondary Loop Voltage 2 V inj X (V) X Injector (Secondary) Plasma Current 5 I inj X (ka) X Injector Flux.25 ψ inj X (mwb) Time (ms) ψ inj leads through zero, aiding I inj reversal at V inj reversal

30 Plasma Impedance Used to Produce Phase Lag H Bridge C L Coil R Primary current I pri sin ωt Secondary plasma current Injector Plasma I inj sin ωt x cos ωt x2 1 + x 2 H Bridge C L L_mag Equivalent Circuit R where x = R/ (ωl mag ) Flux circuit is feedback controlled to ψ inj cos ωt Plasma impedance is 2 35 mω with ωl mag 8 mω x 3 ψ inj leads I inj without active δ feedback control

31 Voltage Circuit Maintains Inward Poynting Flux I inj X,Y (ka) V inj X,Y (V) P inj X,Y (MW) 15 1 X Injector Current Y Injector Current X Loop Voltage Y Loop Voltage X Injector Power Y Injector Power HIT-SI Pulse Time (ms)

32 Total Power of Flux and Voltage Circuits is Inward P tot X,Y (MW) P tot (MW) W tot (kj) Total X Power Total Y Power -2 8 Total Power Total Input Energy 15 1 HIT-SI Pulse Time (ms)

33 Increased Plasma Lifetime with Injector Puffing Without Injector Puffing V inj [V] ψ inj [mwb] I inj [ka] dk/dt [Wb 2 /s] P inj [MW] n e [x1 19 /m 3 ] Injectors - Shot Loop Voltage Injector Flux Injector Plasma Current Helicity Injection Rate Power into Plasma Electron Density Time [ms] With Injector Puffing V inj [V] ψ inj [mwb] I inj [ka] dk/dt [Wb 2 /s] P inj [MW] n e [x1 19 /m 3 ] Injectors - Shot Loop Voltage Injector Flux Injector Plasma Current Helicity Injection Rate Power into Plasma Electron Density Time [ms] See Sieck et al. for more information

34 RFP F Θ Swept out Each Half-Cycle θ F λ inj [/m] I TF X [ka] ψ inj [mwb] I inj X [ka] 2 X Injector - Shot Injector Plasma Current -2 1 Injector Flux -1 2 Injector Flux Circuit Current -2 1 Injector Lambda Reversal Parameter Pinch Parameter Time [ms]

35 Injectors Transition from Stabilized Pinches to RFPs 1.5 X Injector: Shot 12167, ms 1..5 F θ

36 Summary HIT SI produces up to I inj 12 ka for 6 ms Power is always inward during high I inj Next Steps: Finalize injector operation with improved control V inj : Parallel LC tank push-pull (I inj control) ψ inj : Use I inj for part of the demand (λ and δ control) Study spheromak production

37 Next Experiments to Improve Feedback Control Implement push-pull feedback control of I pri, and charge tank circuits to higher voltage Optimize δ phase lead of ψ inj over I inj Complete fielding of HIT II diagnostics Study spheromak formation

38 Flux Circuit will Feedback to Voltage Tank Circuit Demand current for one injector phasing: I DEM inj = I (t) sin (ω t) Ideal injector flux demand (with phase lead δ ) is: Which can be approximated as: ψ DEM ψ DEM inj = ψ (t) sin (ω t + δ ) inj µ cos δ λ I Actual inj + ψ (t) sin δ cos ω t ψ inj feedback to Iinj Actual corrects voltage circuit phase errors to first order. Flux modifications for startup can also be added.

39 Schematic of HIT SI Feedback Scenario Feedback Rogowski Voltage Circuit Func Gen Trig Trig Flux Circ Func Gen Out/Phase Trig Flux Circ Func Gen In/Phase U(t) I(t) Master Trigger 6 Hz Zero Cross Detect µ cos(δ) / λ In Out Reset Voltage Control Circuit Synch Flux Control Circuit U(t) cosω t U(t) sinω t On PWMs: F = Feedback In D = Demand In CWI = Comparator Waveform In O = Integrated Ouput (of F) I(t) sinω t "MW" Phase Trg Sync Aux. Control Circuit X Σ X Σ I(t) cosω t Trig To Digitizer "MW" Phase 9 To Digitizer 17 OCT 23 BAN/DEL/TRJ F O D CWI Trig F O D CWI Trig Tank PWM To Digitizer Tank PWM To Digitizer To/from Fault box Feedback Fluxloop F O D Trig To/from Fault box F O D Trig 5 khz PWM Feedback Rogowski To/from Fault box Feedback Fluxloop 5 khz PWM H Bridge H Bridge To/from Fault box H Bridge H Bridge Volt coil Phase Volt coil Phase 9 Flux coil Phase Flux coil Phase 9 Z Injector Plasma Z Injector Plasma

40 Future Work Improve SPA controllers More flexible and programmable FPAAs and digital circuitry for flexibility Add equilibrium coils for long pulses Add stability coils for n=1 tilt and shift modes (if needed) Rotating n=1 drive may mitigate these modes

41 Other HIT Presentations Monday CO3.6, R. Raman, Solenoid-free Startup in HIT II and NSTX Wednesday (this session) HP1.44, T. R. Jarboe, HIT SI Diagnostics HP1.45, P. E. Sieck, HIT SI Results Thursday PI1A.1, T. R. Jarboe, Spheromak Tutorial PI1B.4, V. A. Izzo, NIMROD Simulations of HIT SI PP1.22, A. J. Redd, HIT II Results PP1.23, R. J. Smith, Internal Probing of HIT II PP1.24, R. G. O Neill, FIR and IDS on HIT PP1.25, D. Mueller, CHI Edge Drive in HIT II

A modular Cap bank for SSPX 1

A modular Cap bank for SSPX 1 Bick Hooper, H. S. McLean, R. D. Wood, B. I. Cohen, D. N. Hill Lawrence Livermore National Laboratory, Livermore, CA 94551 A new, modular capacitor bank being constructed