NSTX/MAST Engineering Workshop C. Neumeyer National Spherical Torus Experiment (NSTX) NSTX Design Overview NSTX/MAST Engineering Workshop C. Neumeyer

NSTX/MAST Engineering Workshop C. Neumeyer Outline Engineering OverviewEngineering Overview Magnet Design Issues and Details for TF & OH CoilMagnet Design Issues and Details for TF & OH Coil

NSTX/MAST Engineering Workshop C. Neumeyer NSTX Mission NSTX is an alternate concept Proof of Principle experiment whose mission is to demonstrate the Physics and Technology of the Spherical Torus (ST) plasmaNSTX is an alternate concept Proof of Principle experiment whose mission is to demonstrate the Physics and Technology of the Spherical Torus (ST) plasma USDOE Fusion Roadmap Concept Exploration Proof of Principle Proof of Performance Energy Technology DEMO

NSTX/MAST Engineering Workshop C. Neumeyer Located in the Hot Cell adjacent to the TFTR Test Cell, making extensive use of existing facilities: - AC power - Magnet power supplies - RF systems - NBI systems - Water systems - Buildings and HVAC systems - Many components from TFTR 1st Plasma in February 1999 Total Project Cost $23.6M Site Credits ≈ $77M NSTX Facility and Engineering NSTX Facility and Engineering NSTX at 1st Plasma

NSTX/MAST Engineering Workshop C. Neumeyer NSTX Ratings and Parameters

NSTX/MAST Engineering Workshop C. Neumeyer NSTX Machine Cross Section Umbrella structure Center stack (TF inner legs & OH coil) Outer legs of TF coil Vacuum Vessel Inner PF coils Passive stabilizer plates Outer PF coils Ceramic Insulator Vacuum Vessel Support Legs Center Stack Pedestal

NSTX/MAST Engineering Workshop C. Neumeyer Center Stack Arrangement Compact nested TF Inner Legs –efficient use of space –ease of manufacture OH Tension cylinder –launching load reaction –ease of manufacture Four layer, 2-in-hand OH –high performance solenoid –rapid cool down time OH-CS Casing gap –∆R ≈ 10mm, 0.4” for thermal insulation, diagnostics & installation clearance –Microtherm insulation ∆T ≈ 500C

NSTX/MAST Engineering Workshop C. Neumeyer Mechanical Support Scheme Center Stack rests on pedestal on floor TF Inner Leg assembly thermal growth - slides inside OH tension tube - connects to outer legs via flex joint - connection to top umbrella via sliding spline joint TF Inner Leg assembly torsion - collar/hub ass’ys transfer load via umbrella to outer VV TF Outer Leg dead weight and overturning moment - reacted to outer VV via turnbuckles OH Thermal Growth - slides over tension tube and inside CS casing - compresses washer stack at top Center Stack Thermal Growth absorbed by bellows VV Thermal Growth - sliding joints to legs, umbrellas, PF coils, and spline

NSTX/MAST Engineering Workshop C. Neumeyer TF Inner Leg Assembly 12 inner + 24 outer = 36 turns Each turn water cooled Radial flags secured by wedged hub assembly 72kA/turn, 1kV produces 6kG at R MPa (1.7ksi) insulation shear

NSTX/MAST Engineering Workshop C. Neumeyer OH Solenoid approx turns in 4 layers wound 2-in-hand 8 parallel cooling paths, 600 second cool down +/- 24kA/turn, 6kV produces 0.9 volt-sec flux swing Central B approx. 8T, 138 MPa (20ksi) Cu stress

NSTX/MAST Engineering Workshop C. Neumeyer Center Stack Assembly Compact interlocking CFC tiles on Inner Wall (∆R=14mm, 0.55”) Center Stack Assembly is completely removable

NSTX/MAST Engineering Workshop C. Neumeyer TF Outer Legs Demountable bow shaped outer legs with turnbuckle supports

NSTX/MAST Engineering Workshop C. Neumeyer Vacuum Vessel Continuous 304 Stainless Steel VV (thickness = 16mm, 5/8”) Sliding supports for outer PF coils and internal hardware

NSTX/MAST Engineering Workshop C. Neumeyer Internal Hardware & Plasma Facing Components CuCrZr passive stabilizer plates with heating/cooling system approx tiles (design provided by ORNL)

NSTX/MAST Engineering Workshop C. Neumeyer Diagnostic Sensors Compact Ip Rogowski’s in center stack (∆R=3.5mm, 0.135”) High temp (up to 600C) in-vessel sensors 17 Rogowskis, 105 flux loops, 135 Mirnovs, 24 Langmuirs, 128 TCs

NSTX/MAST Engineering Workshop C. Neumeyer RF Systems High Harmonic Fast Wave (HHFW) RF 30MHz, absorbtion mainly by electrons –Six PPPL sources, TFTR xmission lines, new 12 strap antenna –Tuning and matching network designed by ORNL Electron Cyclotron (EC) Pre-ionization system provided by ORNL

NSTX/MAST Engineering Workshop C. Neumeyer Neutral Beam Injection (NBI) One TFTR Beam 5MW, 80kV, 5 seconds

NSTX/MAST Engineering Workshop C. Neumeyer Magnet Power Supplies Extensive use of existing facilities One MG set to buffer load from grid –Smax ≈ 200MVA, Wmax ≈ 170MJ Modular TFTR rectifier design –74 six-pulse bridges available –Direct digital control from central computer Advanced 3-wire, antiparallel configuration –4-quadrant operation –separate control of upper and lower PF coil pairs

NSTX/MAST Engineering Workshop C. Neumeyer Key Engineering Features Compact, removable Center StackCompact, removable Center Stack –Nested two-tier TF inner leg conductors –Four layer, two-in-hand high performance OH solenoid –Tight tolerances and precise assembly –Compact inner wall PFC tile design –Miniature diagnostic sensors –Microtherm insulation Unique support schemes and mechanical load pathsUnique support schemes and mechanical load paths Extensive use of TFTR facility and componentsExtensive use of TFTR facility and components

NSTX/MAST Engineering Workshop C. Neumeyer Research Plan  Noninductive  Integration >>  E Plasma Current Pulse HHFW Power NBI Power CHI Startup Toroidal Beta Bootstrap Control Measure   0.5 MA   0.5 s   4 MW   0.2 MA  current, R, shape  T e (r), n e (r) Inductive   1 MA   1 s  ~ 6 MW   5 MW   0.5 MA   25%   40%  heating, density  j(r), T i (r), flow, edge Non-Inductive Assisted  ~ 1 MA   5 s  ~ 6 MW  ~ 5 MW  ~ 0.5 MA   40%   90%  profiles, modes  turbulence Full Non-Inductive 1st Plasma February 99 1 MA (FY99)(FY00) (FY01-FY03) (FY04-FY06) (14 weeks) (40weeks) (40weeks) Capabilities  Ohmic studies  Initial CHI  Initial HHFW  Transport  Full HHFW  Macro-stability  Full CHI  Plasma-wall   -  E integration  Turbulence  Active Stabil.  Edge control NBI, 4MW HHFW 200kA CHI TOPICS 

NSTX/MAST Engineering Workshop C. Neumeyer NSTX 2001 Parameters Baseline and (Achieved) Elongation ≤ 2.2 (2.5) Triangularity ≤ 0.6 (0.5) Plasma Current 1 MA (1.07 MA) Toroidal Field 0.3 to 0.6 T (≤0.45 T) Heating and CD 5 MW NBI (3.2 MW) 6 MW HHFW (4.2 MW) 0.5 MA CHI (0.26 MA) Pulse Length ≤ 5 sec (0.5 sec) NSTX/MAST Engineering Workshop

C. Neumeyer Best Performance (non-simultaneous)

NSTX/MAST Engineering Workshop C. Neumeyer Design Assumption Plate Support Center Stack Plasma Disruptions Disruption / halo current j x B forces were a major design concern Vertical Displacement Events (VDEs) result in fast disruptions dI p /dt ≈ 166 MA/sec as predicted Observed halo-currents are modest, ≤ 5 % of I p (10% was design requirement)

NSTX/MAST Engineering Workshop C. Neumeyer Magnet Design Issues 1. Electromagnetic -field, flux, stray field, eddy currents, disruption, etc. 2. Mechanical/structural - forces, load paths, stresses 3. Thermal/hydraulic - adiabatic temperature rise, cooldown 4. Electrical - power supply matching, response, faults, transients, etc. 5. Dielectric - insulation systems 6. High current joints

NSTX/MAST Engineering Workshop C. Neumeyer 1. Electromagnetic (field, flux, stray field, eddy currents, etc.) Basic EM design of machine developed early on by Physics - outer PF coil designs and positions set by S-1 constraints - coil currents determined for range of plasma shapes - OH flux requirements determined via TSC Stray fields - required |B|≤ 1.3V loop /(  r 2 ) = volt/turn - required the m=2, n=1 component of the vacuum error field (at the q=2 surface) ≤  gauss to avoid locked modes (set radial offset and tilt specs to +/- 5mm for outer PF coils)

NSTX/MAST Engineering Workshop C. Neumeyer Eddy currents - LRSIM used to assess coil and power supply performance and axisymmetric eddy current effects for plasma initiation field null- found eddy currents in TF inner legs to be benign (  ~ 1mS) Disruptions - disruption assumption based on Physics analysis (TSC) prediction of 1MA/6mS maximum decay rate - LRSIM used to assess axisymmetric eddy currents in structures - also used SPARK for disruption to benchmark LRSIM - halo currents assumed 10% of Ip with toroidal peaking factor of 2:1

NSTX/MAST Engineering Workshop C. Neumeyer 2. Mechanical/structural (forces, load paths, stresses) Major issues are…. TF - torsion from J x B forces including OH and PF1a coils - combined shear and compression forces on inner leg turn insulation - axial thermal expansion of inner legs - interface between inner and outer legs OH - hoop stresses in conductor - axial thermal expansion

NSTX/MAST Engineering Workshop C. Neumeyer Finite Element Modeling

NSTX/MAST Engineering Workshop C. Neumeyer Br due to OH

NSTX/MAST Engineering Workshop C. Neumeyer TF Torsional Constraints

NSTX/MAST Engineering Workshop C. Neumeyer Torsional Moment on TF Inner Legs

NSTX/MAST Engineering Workshop C. Neumeyer TF Stress Summary (Itf=72kA, Ioh=24kA, Ipf1a=2kA) TF insulation zero compression shear allowable is 2.9ksi

NSTX/MAST Engineering Workshop C. Neumeyer OH Stress Summary (Ioh=24kA, Ipf1a=15kA, Ipf1b=20kA)

NSTX/MAST Engineering Workshop C. Neumeyer OH Fatigue Consideration OH hoop stress ~ 20ksi Copper cycles to 20ksi ~ 400,000 cycles Fatigue guideline…..  ≤ 1/2 stress to failure at design cycle life  ≤ stress to fail at 20x design cycle life - second criteria is limiting: 400,000 cycles/20/2 per pulse = 10,000 pulses 1/2 of stress to failure at 10,000 pulses = 20,000 cycles would be 26ksi

NSTX/MAST Engineering Workshop C. Neumeyer 3. Thermal/Hydraulic Assumed adiabatic conditions during pulsing Used “G” function for copper to determine heating Designed for temperatures < 95 o C Protective device settings made with consideration of prospective L/R decay from peak current

NSTX/MAST Engineering Workshop C. Neumeyer G-Function for Thermal Calculations  e = electrical resistivity  eT0e = electrical resistivity at temperature t 0e T= temperature  e =  et0e (1+  (T-T 0e )) C p = specific heat C pt0c = specific heat at temperature T 0c C p= C pt0c +  (T-T 0c ) J = current density  d = density t= time  e J 2 dt =  d C p dT J 2 dt =  d C p dT/  e, J 2 t = ∫  d C p dT/  e  G(t) [(A/m 2 ) 2 -sec] Piecewise integration yields”G” and “G -1 ” functions over range 0-120C: G(T) = e e14*T e11*T 2 T(G)= e-15*G e-32*G 2

NSTX/MAST Engineering Workshop C. Neumeyer OH Cooldown

NSTX/MAST Engineering Workshop C. Neumeyer Water Cooling

NSTX/MAST Engineering Workshop C. Neumeyer 4. Electrical

NSTX/MAST Engineering Workshop C. Neumeyer Coil Current Waveforms (simulated via PSCAD)

NSTX/MAST Engineering Workshop C. Neumeyer Coil Protection Grounding and ground fault protection - resistive grounding (10kΩ) w/virtual null - ground fault detector (electromechanical I/t and fast electronic) Analog Coil Protection - pulse duration - repetition period - peak current ∫i 2 (t) protection - ∫i 2 (t) simulator with single  constant exponential decay Digital Coil Protection under development

NSTX/MAST Engineering Workshop C. Neumeyer 5. Insulation Systems

NSTX/MAST Engineering Workshop C. Neumeyer Insulation Stress Levels Hipot Testing - 1 minute DC tests at V = 2E kV (210 V/mil) factory, 9kV (145 V/mil) field - 3kV (44 V/mil) factory, 2kV (30V/mil) field Extrapolated zero compression TF insulation shear strength at 60C is 5883 psi

NSTX/MAST Engineering Workshop C. Neumeyer OH Ground Plane ohms/square 1 Ω/square

NSTX/MAST Engineering Workshop C. Neumeyer Dielectric Breaks on Machine

NSTX/MAST Engineering Workshop C. Neumeyer 6. High Current Joints

NSTX/MAST Engineering Workshop C. Neumeyer Summary Operations have been highly successful Operations have been highly successful -   (≤ 25%) and confinement (≤ 1.6  E ELMy ) very good - Challenging current sustainment phase comes next Engineering systems taken to ≥ ratings, Engineering systems taken to ≥ ratings, - except pulse length and 350 o C bakeout Some problems, but were able to recover Some problems, but were able to recover - TF water leaks- TF torque collar - OH ground fault- CHI bus - OH hipot difficulties