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

C. NeumeyerNSTX/MAST Engineering Workshop

National Spherical Torus Experiment (NSTX)National Spherical Torus Experiment (NSTX)

NSTX Design OverviewNSTX Design Overview

NSTX/MAST NSTX/MAST

Engineering WorkshopEngineering Workshop

C. NeumeyerC. Neumeyer

http://nstx.pppl.gov/nstx/Engineering/NSTX_Eng_Site/Home/NSTX_Engr_Home.html


OutlineOutline

• Engineering OverviewEngineering Overview

• Magnet Design Issues and Magnet Design Issues and Details for TF & OH CoilDetails for TF & OH Coil


NSTX MissionNSTX Mission• NSTX is an alternate concept NSTX is an alternate concept Proof of Principle Proof of Principle

experiment whose mission is to demonstrate the experiment whose mission is to demonstrate the PhysicsPhysics and and TechnologyTechnology of the of the Spherical TorusSpherical Torus (ST) plasma (ST) plasma

USDOE Fusion Roadmap

Concept Exploration

Proof of Principle

Proof of Performance

Energy Technology

DEMO


• 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 EngineeringNSTX Facility and Engineering

NSTX at 1st Plasma


NSTX Ratings and ParametersNSTX Ratings and ParametersPlasma Major Radius (R0) 85.4 cm

Aspect Ratio (R/a) 1.26Volume 12m3

Elongation 1.6 ≤ κ ≤ 2.2Triangularity 0.2 ≤ δ ≤ 0.5Current 1.0 MA(1.5 )MA

Ramp Time 0.2 - 0.4 sec ( )Flat Top Inductive 0.5 600 sec per sec ( - )Flat Top non Inductive 5.0 300 sec per sec

Toroidal Field Field @ R0 3.0/6.0 kG Ohmic Heating ( )Flux double swing 0.9 -volt sec

Initiation Loop Voltage @ R0 5.0 /volt turn/Heating ( ) High Harmonic Fast Wave HHFW RF6.0 , 30 , 5 MW MHz sec Current Drive ( )Coaxial Helicity Injection CHI 500 50 1kA via kA injection @ kV

( )Neutral Beam Injection Upgrade NBI5.0 , 80 , 5 MW kV sec-Pre Ionization Electron Cyclotron 30 , 18 , 0.1 kW GHz sec

Bakeout Bakeout Temperature 350o , 150C PFCs o C VV


NSTX Machine Cross SectionNSTX Machine Cross SectionUmbrella 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


Center Stack ArrangementCenter 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


Mechanical Support SchemeMechanical 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

= OH Coil

= TF Coil

= Metal Structure

= Insulating Structure

= Sliding Interface

= Spring

= Turnbuckle

= PF Coil


TF Inner Leg AssemblyTF 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 R0

• 11.8 MPa (1.7ksi) insulation shear


OH SolenoidOH Solenoid

• approx. 1000 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


Center Stack AssemblyCenter Stack Assembly

• Compact interlocking CFC tiles on Inner Wall (∆R=14mm, 0.55”)• Center Stack Assembly is completely removable


TF Outer LegsTF Outer Legs

• Demountable bow shaped outer legs with turnbuckle supports


Vacuum VesselVacuum Vessel

• Continuous 304 Stainless Steel VV (thickness = 16mm, 5/8”)• Sliding supports for outer PF coils and internal hardware


Internal Hardware & Plasma Facing ComponentsInternal Hardware & Plasma Facing Components

• CuCrZr passive stabilizer plates with heating/cooling system• approx. 3000 tiles (design provided by ORNL)


Diagnostic SensorsDiagnostic 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


RF SystemsRF Systems

• High Harmonic Fast Wave (HHFW) RF– 6MW @ 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


Neutral Beam Injection (NBI)Neutral Beam Injection (NBI)

• One TFTR Beam Line @ 5MW, 80kV, 5 seconds


Magnet Power SuppliesMagnet 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


Key Engineering FeaturesKey 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


Research PlanResearch 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

Te(r), ne(r)

Inductive

1 MA 1 s ~ 6 MW 5 MW 0.5 MA 25% 40% heating, density

j(r), Ti(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 PlasmaFebruary 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

200kACHI

TOPICS


NSTX 2001NSTX 2001

ParametersBaseline 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


Best Performance (non-simultaneous)Plasma Current Ip ≤ 1.4 MAIp Flat Top @ 1MA ≤ 300 msdIp/dt ~ 5.5 MA/sEjima Coefficient = ∫Vresdt/µ0R0Ip ~ 0.35Stored Energy W ~ 180 kJConfinement time E ~ 120 mS

= T 2µ0< >/p B 02 ~ 25%

Te ~ 3.7keVT i ~ 2keV

ne 1 ~ 6 10x -19 m-3

ne/n greenwald ≤ 1.4Pnbi ≤ 5 MWPhhfw ≤ 6 MWIp CHI ≤ 360kAZeff 1.5 ~ 3


DesignAssumption

Plate Support

Center Stack

Plasma DisruptionsPlasma Disruptions

• Disruption / halo current j x B forces were a major design concern

• Vertical Displacement Events (VDEs) result in fast disruptionsdIp/dt ≈ 166 MA/sec as predicted

• Observed halo-currents are modest, ≤ 5 % of Ip (10% was design

requirement)


Magnet Design IssuesMagnet 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


1. Electromagnetic (field, flux, stray field, eddy currents, etc.)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|≤ 1.3Vloop/( r2) = 3 gauss @ 4.5 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 radialoffset and tilt specs to +/- 5mm for outer PF coils)


• 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


2. Mechanical/structural (forces, load paths, stresses)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


Finite Element Modeling


Br due to OHBr due to OH


TF Torsional Constraints


Torsional Moment on TF Inner Legs


TF Stress Summary(Itf=72kA, Ioh=24kA, Ipf1a=2kA)

TF insulation zero compression shear allowable is 2.9ksi

Copper Insulation (maximums at various locations) von Mises shear xy shear zy Max Resultant shear zx

ksi MPA ksi MPA ksi MPA ksi MPA ksi MPAEOFT Min. -0.9 -6.4 -1.9 -12.9 2.1 14.7 -0.3 -2.1

Max. 10.1 69.8 1.0 7.0 1.1 7.2 1.35EOP Min. -0.8 -5.7 -0.4 -2.5 0.9 6.2 -0.14 -1.0

Max. 10.9 75.4 0.8 5.7 0.4 2.5 1.51


OH Stress Summary(Ioh=24kA, Ipf1a=15kA, Ipf1b=20kA)

Copper InsulationCase Load von Mises Sy Sy Sz Syx Szx

ksi MPA ksi MPA ksi MPA ksi MPA ksi MPA ksi MPA1 Preload 0.15 1.0 0.03 0.2 -0.042 -0.3 -0.119 -0.8 0.002 0.0 0.01 0.12 EM 22.88 157.8 19.8 136.5 0.732 5.0 -6.436 -44.4 0.198 1.4 0.175 1.23 Maximum Temp. 2.27 15.7 -2.46 -17.0 1.499 10.3 -1.196 -8.2 0.106 0.7 0.327 2.34 Temp. at 15.5 sec. 8.23 56.7 8.01 55.2 2.134 14.7 -5.366 -37.0 0.096 0.7 0.959 6.65 Case 2 + 3 23.2 160.0 19.91 137.3 1.978 13.6 -7.248 -50.0 0.29 2.0 0.416 2.9


OH Fatigue Consideration

• OH hoop stress ~ 20ksi• Copper cycles to failure @ 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


3. Thermal/Hydraulic

• Assumed adiabatic conditions during pulsing

• Used “G” function for copper to determine heating

• Designed for temperatures < 95oC

• Protective device settings made with consideration of prospective L/R decay from peak current


G-Function for Thermal Calculationse = electrical resistivityeT0e = electrical resistivity at temperature t0e

T = temperaturee = et0e (1+(T-T0e))Cp = specific heatCpt0c = specific heat at temperature T0c

Cp = Cpt0c +(T-T0c)J = current densityd = densityt = time

eJ2dt = dCpdTJ2dt = dCpdT/e,

J2t = ∫dCpdT/e

G(t) [(A/m2

)2

-sec]

Piecewise integration yields”G” and “G-1

” functions over range 0-120C:

G(T) = 6.2949e13 + 2.0934e14*T - 2.8709e11*T2

T(G) = 0.13608 + 4.5496e-15*G + 5.3309e-32*G2


OH Cooldown

0

20

40

60

80

100

0 100 200 300 400 500 600

Start

Middle

End

Temperature (deg C)

Time (sec)

OH Coil Temperature at Start, Middle, and End of WindingDuring and After Fifth Pulse, 600 Second Repetition

Period


Water CoolingCoil Flow/

CircuitVelocity No. of Circuits Flow ∆P

(GPM) (ft/s) (GPM) (PSI)OH1X 0.64 7.5 1 0.6 207.3OH1Y 0.64 7.5 1 0.6 207.8OH2X 0.71 8.2 1 0.7 266.3OH2Y 0.71 8.2 1 0.7 266.3OH3X 0.76 8.9 1 0.8 329.7OH3Y 0.76 8.9 1 0.8 331.8OH4X 0.82 9.5 1 0.8 400.0OH4Y 0.82 9.5 1 0.8 400.0PF1a 6.15 9.8 2 12.3 100.0PF1b 3.10 10.2 1 3.1 100.0PF2a 5.38 8.5 2 10.8 100.0PF2b 5.38 8.5 2 10.8 100.0PF3a 3.62 5.9 2 7.2 100.0PF3b 3.62 5.9 2 7.2 100.0PF4b 4.66 7.5 2 9.3 100.0PF4c 4.34 6.9 2 8.7 100.0PF5a 3.59 5.6 2 7.18 100.0PF5b 3.59 5.6 2 7.18 100.0TF 3.20 3.3 36 115.2 94.8

Totals 61.0 202.7

Mode OH ESW PF ESW TF ESW PulsedLoss

RepPeriod

Avg. Loss

(sec) (sec) (sec) (MJ) (sec) (kW)Inductive 0.525 1.0 1.5 75.1 600.0 125.2PartialInductive

0.238 5.0 6.0 104.5 300.0 348.2

Non-Inductive

0.000 5.0 6.0 96.3 300.0 321.1


4. Electrical

Type I Type II

Type III Type IV

Circuit Volts

(+/-kV)

Peak

Amps

(kA)

Equiv. Square Wave

(ESW) @

Peak Amps (sec)

TF 1 35.6(71.2)

5.3(1.3)

OH 6 +/-24 0.525PF1a U 2 15 5PF1a L 2 15 5PF1b 2 20 1PF2 U 2 20 5PF2 L 2 20 5PF3 U 2 20 5PF3 L 2 20 5PF4 U&L in Series 3 20 5PF5 U&L in Series 3 20 5


Coil Current Waveforms(simulated via PSCAD)

0

10

20

30

40

50

60

70

80

0 1 2 3 4 5 6

TF Current (kA)

Time (sec)

-30

-20

-10

0

10

20

30

0 0.5 1

OH Current (kA)

Time (sec)


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

• ∫i2(t) protection - ∫i2(t) simulator with single constant exponential decay

• Digital Coil Protection under development


5. Insulation SystemsInsulation Design Details

TF Inner Leg OHTurn InsulationEpoxy-glass IMI 2258XS IMI 2258XSThickness (10% compression) 0.0054” 0.0054”Number of Layers 3 half lapped 1 half lappedEpoxy-glass/Kapton n.a. IMI 2259XSThickness (10% compression) n.a. 0.008”Number of Layers n.a. 1 half lappedTotal Build 0.032” (0.064” turn-turn) 0.026 (0.0525” turn-turn)Vo ltage Stress 15.6 volts/mil @ 1kV 85.7 volts/min @ 4.5kVGround Insulation (Outer)Epoxy-glass 3M Scotchply #1003 3M Scotchply #1003Number of Layers 2 half-lapped 3 half-lappedThickness (10% compression) 0.009” 0.009”Total Build 0.036” 0.054”Ground Insulation (Inner) n.a.Teflon n.a. 0.002”Number of Layers n.a. 2 half-lappedEpoxy-glass n.a. IMI 2258XSThickness (10% compression) n.a. 0.0054”Number of Layers n.a. 3 half-lapped

Total Build n.a. 0.036”


Insulation Stress LevelsInsulation R&D Results

TF Inner Leg OHBi-axial shear @ 600lbscompression (avg. psifailure)

6062 psi @ 60oC, 8samples

3710 psi @ 100oC, 10samples

Fatigue test @ 600lbscompression (test w/ofailure, 1e6 cycles)

2400 psi @ 60 oC, 6samples

1000 psi @ 100 oC, 6samples

DC Hipot (avg. kV failure) 16kV (420 volt/mil), 16samples

Not tested

• Hipot Testing- 1 minute DC tests at V = 2E+1000- OH @ 13kV (210 V/mil) factory, 9kV (145 V/mil) field- TF @ 3kV (44 V/mil) factory, 2kV (30V/mil) field

Extrapolated zero compression TF insulation shear strength at 60C is 5883 psi


OH Ground Plane

OH Coil

Existing Lo

Resistance

Tecknit Paint

Existing

Hi Resistance

Ranbar Paint

Flexible Braid, plated

copper, approx. 3/4"

wide x 1/16" thick

Adhesive Kapton

Tape 1" width

G-10

1/16" x 1"

G-10

1/8" x 1"

SS Worm

Gear Clamp

Tack

Weld

90

o

270

o

180

o

0/360

o

270

o

Ranbar

Teknit

Ranbar @ 2000-5500 ohms/square Technit @ 1 Ω/square


Dielectric Breaks on Machine25

24

22

23

21

20

19

16

17

15

14

13

10

11

2

3

4

5

6

7

8

9

1

18

26

12

Gap ID#'s Vmax(kV )

Hipot(kV )

Comments

CS Casing/Outer VV 18/17 2 5 Ceramic insulatorsCS Casing/OH GroundPlane

18/26 2 5 Microtherm in CS gap

CS Casing/PF1a GroundPlane

18/2, 18/4 2 5 Microtherm in CS gap

CS Casing/PF1b GroundPlane

18/12 2 5 G-10/Kapton spacers

CS Casing/HubAssembly

18/1, 18/5 2 5 G-10/Kapton spacers

OH Tension Tube/TFInner Leg

3/24 3 3 TF Inner Leg GroundInsulation

Hub Assembly/Umbrella 1/25,5/7 2 5 G-10 spline on top, turnbuckleson bottom

Lower HubAssembly/Pedestal

5/6 2 5 G-10 spacer

Lower VV Leg/UpperVV Leg

9/13 2 5 G-10 spacer

Umbrella/TF Coil 7/24, 25/24 3 7 TF ground insulation plusgrouting under clamp attachedto leg

TF Leg Supports/TF Coil 14/24,21/24

3 7 TF ground insulation plusgrouting under clamp attachedto leg

PF2/Outer VV 11/17,23/17

6 13 PF coil ground insulation

PF3/Outer VV 10/17,22/17


PF4/Outer VV 15/17,20/17


PF5/Outer VV 15/17,20/17

4 9 PF co il ground i nsulation plusG-10/Kapton spacers


6. High Current Joints

Feature DescriptionSize & Number of Bolts (4) 5/16" boltsBolt Material A286Bolt Length 11 in.Nominal Joint Pressure 2000 psiAllowable Contact Resistance 2µΩ/in2

Cross Sectional Area 5.0 in2

Average Current Density @ 71.6kA 14.3kA/in2

Load per Bolt 2500 lbAxial Stress in Bolts 43000 psiShear Stress in Bolts 2300 psiPullout Yield Load for Insert 5000 lb Factor of Safety for Pullout 2


SummarySummary• • Operations have been highly successfulOperations have been highly successful

- - (≤ 25%) and confinement (≤ 1.6(≤ 25%) and confinement (≤ 1.6EEELMyELMy) very good) very good

- Challenging current sustainment phase comes next- Challenging current sustainment phase comes next

• • Engineering systems taken to ≥ ratings, Engineering systems taken to ≥ ratings, - except pulse length and 350- except pulse length and 350ooC bakeoutC bakeout

• • Some problems, but were able to recoverSome problems, but were able to recover- TF water leaks- TF water leaks - TF torque collar- TF torque collar- OH ground fault- OH ground fault - CHI bus- CHI bus- OH hipot difficulties- OH hipot difficulties

Documents

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