Status of the NCSX Project
G. H. Neilson1, J. F. Lyon2, M. Zarnstorff1, J. L. Anderson1, A. Brooks1,T. Brown1, M. Cole2, J. Chrzanowski1, L. Dudek1, H. M. Fan1, P. Fogarty2,K. Freudenberg2, P. Goranson2, P Heitzenroeder1, M. Kalish1, G. Labik1,R. Maingi2, B. Nelson2, S. Raftopoulos1, W. Reiersen1, B. Stratton1,
R. Strykowsky1, M. Viola1, M. Williams1, and D. Williamson2
1 Princeton Plasma Physics Laboratory
2 Oak Ridge National LaboratoryTopics• Mission and Design• Component Status• Assembly Status• Schedule Update• Research Program PlanningNCSX Objectives
Understand the effect of 3-D quasi-axisymmetric shaping• Pressure limits and limiting mechanisms• Disruptions and operating limits• Transport and confinement with low quasi-axisym. ripple• Relationship between NCSX and tokamak transport• Equilibrium islands and tearing-mode stabilization, role ofreversed magnetic shear• Divertor operation with good core performance• Energetic-ion stability and confinement
Determine degree of 3-D quasi-axisymmetric shaping for• High β, good confinement, compatible with steady state,
without disruption risk
• Can the design constraints be simplified, with improved
understanding? ⇒ simpler engineering design?

NCSX Configuration Properties
Configuration was optimized for target physics properties• Low R/〈a〉 (4.4); 3 periods• Quasi-axisymmetric withPlasma Cross Sections
1

low effective ripple
vertical, kink, ballooning,
NTM instabilities

ATF

Z (m)

• Stable at β = 4.1% to0.1

LHD
shifted in0.01

!

CHS

3/2

W 7-ASeffW 7-X

0.001• Reverse shear q profile• 25% of transform fromQPSHSX0.0001

NCSX

bootstrap current• Good magnetic surfaces
at high β• Constrained byengineering feasibility
metrics

R (m)

10- 5
0.2

0.3

0.4

0.5

0.6

("/"0.7)

0.8

0.9

1/2

edge

Understanding of 3-D quasi-axisymmetric shaping
can also lead to tokamak improvements, e.g.,
improved stability, disruption avoidance

1

NCSX Configuration Integrates Low Aspect
Ratio and Quasi-Axisymmetry• 3 periods, R/〈a〉 = 4.4, 〈κ〉 ~ 1.8• Low flow damping, tokamak-likeorbits ⇒ enhanced confinement• Stable for at least 〈β〉 > 6.5% byadjusting coil currents
equilibrium maintained evenwith total loss of β or Iplasma

poloidal angle• Passive disruption stability:
UfinalU⊥

U||toroidal angle

NCSX Machine DesignCoils wound on forms to create a robust
structural shell minimizes deflections• Major radius: 1.4 m; plasma aspect ratio 4.4• Magnetic field (pulse length): 2.0 T (0.2 s); 1.2 T (1.7 s)• Flexible coil sets; LN-cooled• ≤ 12 MW plasma heating: NBI: 6 MW; ECH & ICH: 6 MW

Modular Coil Winding is Proceeding Well

• Flexible copper cable conductor is wound onto winding
surfaces machined to ±0.5 mm accuracy• Winding packs are adjusted to desired dimensions withclamps• 14 coils have been wound and potted. Last coil scheduled
for May 2008

Procedures Were Developed to Achieve
Required Accuracy
C Coils Current Center Shift Relative to Designdx

lateral

0.080
0.060

Offset, inches

0.040
0.020

C1C20.000

C3
C4020

40

60

80

100-0.020

C5-0.040-0.060Clamp#• Current center (from measurements ofwinding pack outside dimensions)follows design trajectory within ±0.5 mm⇒ acceptably small field errors• All coils pass warm terminal resistanceand electrical insulation strength tests• First coil was successfully cooled to LN
temperature and tested at full current

Coil Positioning Tests• Demonstrated fixturesand handling of parts• Demonstrated metrology
and fine adjustment
techniques for positioning
parts within ±0.25 mm

TF Coils Are in Production
4 coils
have beendelivered• Provides variable background field (±0.5 T) for iota flexibility• 18 D-shaped coils (one per modular coil) with steel wedge support• Met ±3 mm accuracy on inner leg• Last coil is scheduled for Sept. 2008

NCSX Vacuum Vessel Was Built in 3 Sectors±5 mm tolerance and µ ≤ 1.02µ0 were achieved; bakeable to 350 C

2 of 3 are sectors complete, last scheduled for Jan. 2008
• Heating and cooling hoses• Heater tapes, thermocouples• Diagnostic flux loops

Ex-Vessel Magnetic Diagnostics Are Designed
for Equilibrium Reconstuction• >200 saddle coils

mounted on vessel• ~2500 free-boundary
equililbria analyzed toidentify critical regions formeasurement• Array distributed across
3 periods + extra coils tosense symmetric andnon-symmetriccomponents
N. Pomphrey, E. Lazarus

Several strategies are being developed for equilibrium reconstuction:• V3FIT – reconstruction code based on VMEC (cannot represent islands)• PIES – 3D equilibrium with islands• 3-D external flux fit (e.g. filament code), to find boundary shape andcharacteristics

NCSX Assembly is Done in Stages

Assemble 3 coils
for half field period
Start in Dec-Jan

Install 3-coil set
over vacuum
vessel sector
Connect 3 field periods

Require coil current center
accurate to ±1.5 mm
Connect 2nd 3-coil Add ports & TF
set over vacuum coils to complete
vessel sectora field period

Requirements on Inter-coil Hardware(Fasteners, Shims) Are Challenging• Handle complex structural loads withoutslippage or excessive deflections• Position coils accurately (±1 mm) within
the array• Provide insulation to break up long-lived
eddy currents (τ < 30 ms)

5 welds/period incentral region

Solutions• Outboard: bolts with enhanced-friction

shims• Inboard, within each field period: welded
shear plates, compression shim
• Inboard, between field periods:
compression shims

Modular Coil Interface Development
Coated testsurfaces

Welded Interface Development Trials• Permeability OK• Dimensional stability controlled by:– design configuration– low-distortion weld procedures(e.g., MIG welding, rapid quench)**Acknowledgement to W 7-X and CERN
colleagues for valuable advice.

Enhanced-Friction Coatings• Alumina coatings tested under load
at cryogenic temperature• Friction coefficient 0.67 exceeds
requirements by ~50%
• Required friction maintained in life
tests (130,000 cycles)Trim Coils Will Be Designed to Reduce
Field Errors• Initial design:
rectangular coils
between modular andTF coils• Monte-Carlo analysis of
the assembly indicatesthese coils can correct
residual low-order (n =1, 2, 3) resonant errors• Only moderate currents(< 20 kA-turns) required⇒

NCSX Schedule
FY-08

FY-09

FY-10

FY-11

Fabrication Project
Phase 1 & 2 Equipment

FY-12
1 2

FY-13

3

FY-14

FY-15

4

1st Plasma
Phase 3 Equipment

1st plasma scheduled for Dec. 2011

Full field, more diags.
Full PFCs & divertor

1. Stellarator acceptance testing and first plasma (ends fabrication project)

2. Magnetic configuration studies: electron-beam mapping studies (2012)
3. Initial heating experiment (2013)– 3-MW NBI; ECH?
– B ≥ 1.2 T– partial PFC coverage– initial diagnostics, magnetics, profiles (ne, Te, Ti, vφ, Prad) and SOL
4. Initial high-beta experiments (2015)– 6-MW heating, NBI & ECH– B = 2T; divertor and full PFC coverage– improved diagnostics

Campaigns in FYs 2013 and 2015 will
Investigate Critical Issues• FY 2013: Study effect of quasi-axisymmetric shaping andeffective ripple on confinement and rotation damping– resilience to disruptions from MHD instabilities, density limits– initial comparisons between observed and calculated MHD
stability thresholds• FY 2015 with 6 MW, 2 T operation will determine– β-limits and limiting mechanisms– safe operating area against disruptions– local transport properties; impurity transport– fast ion transport due to effective ripple. Alfvenic-mode
stability– initial divertor effectiveness; scrape-off layer characteristics

NCSX Program Status• A series of government reviews of NCSX is in progress due
to large cost and schedule increases– Review of cost and schedule estimates (Aug.)– Compact stellarator science: benefits and issues (Sept.)– NCSX design and construction within tolerances (Oct.)• DOE decision on future of NCSX is expected in November• Thanks to our stellarator colleagues who havecontributed to these reviews

Summary• Component production is progressing well
– vacuum vessel manufacture complete; component
installation in progress– modular coils nearly complete– TF coil deliveries have started• NCSX construction to date meets technical requirements• Trim coils and modular coil interfaces are in design• Schedule has been delayed: first plasma Dec. 2011
• Detailed planning of experimental campaigns has started