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NSTX-U. Supported by. NSTX-U Status and Plan. Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U Tsukuba U U Tokyo JAEA Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI NFRI KAIST POSTECH Seoul National U

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NSTX-U Status and Plan

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Nstx u status and plan


Supported by

NSTX-U Status and Plan

Culham Sci Ctr

U St. Andrews

York U

Chubu U

Fukui U

Hiroshima U

Hyogo U

Kyoto U

Kyushu U

Kyushu Tokai U


Niigata U

Tsukuba U

U Tokyo


Hebrew U

Ioffe Inst

RRC Kurchatov Inst





Seoul National U


ENEA, Frascati

CEA, Cadarache

IPP, Jülich

IPP, Garching

ASCR, Czech Rep

Columbia U


General Atomics



Johns Hopkins U





Nova Photonics

New York U



Princeton U

Purdue U


Think Tank, Inc.

UC Davis

UC Irvine



U Colorado

U Illinois

U Maryland

U Rochester

U Tennessee

U Washington

U Wisconsin

Masayuki Ono

NSTX-U Project Director

PPPL, Princeton University

In collaboration with the NSTX-U Team

The First A3 Foresight Workshop on Spherical Torus (ST) 

Jan. 14-16, 2013

SNU, Seoul, Korea

Nstx u status and plan

Talk Outline

  • NSTX-U Mission

  • NSTX Experimental Overview

  • NSTX-U Construction Status

  • NSTX-U Experimental Plan

  • Summary

Nstx u status and plan

NSTX-U Mission Elements

Fusion applications of low-A spherical tokamak (ST)

  • Develop plasma-material-interface (PMI) solutions for next-steps

    • Exploit high divertor heat flux from lower-A/smaller major radius

  • Fusion Nuclear Science/Component Test Facility (FNSF/CTF)

    • Exploit high neutron wall loading for material and component development

    • Utilize modular configuration of ST for improved accessibility, maintenance

  • Extend toroidal confinement physics predictive capability

    • Access strong shaping, high b, vfast / vAlfvén, and rotation, to test physics models for ITER and next-steps (see NSTX, MAST, other ST presentations)

  • Long-term: reduced-mass/waste low-A superconducting Demo

Nstx u status and plan

NSTX Upgrade will access next factor of two increase in performance to bridge gaps to next-step STs


Power Plants

ARIES-ST (A=1.6)

JUST (A=1.8)

VECTOR (A=2.3)

  • * Includes 4MW of high-harmonic fast-wave (HHFW) heating power

Key issues to resolve for next-step STs

Confinement scaling (electron transport)

Non-inductive ramp-up and sustainment

Divertor solutions for mitigating high heat flux

Radiation-tolerant magnets (for Cu TF STs)

Nstx u status and plan

NSTX Upgrade will address critical plasma confinement and sustainment questions by exploiting 2 new capabilities











constant q, b, r*

2x higher BT and IP increases T, reduces n* toward ST-FNSF to better understand confinement

Provides 5x longer pulses for profile equilibration, NBI ramp-up

NSTX Upgrade


ITER-like scaling

Normalized e-collisionality ne*  ne /Te2

TF OD = 40cm

TF OD = 20cm

IP=0.95MA, H98y2=1.2, bN=5, bT = 10%

BT = 1T, PNBI = 10MW, PRF = 4MW



2x higher CD efficiency from larger tangency radius RTAN

100% non-inductive CD with q(r) profile controllable by:

tangency radius, density, position

RTAN [cm]


50, 60, 70, 130

60, 70,120,130


New 2nd NBI

Present NBI

J. Menard, et al., Nucl. Fusion 52 (2012) 083015

Nstx u status and plan

A schematic of the new center-stack and the TF joint area

New TF-Flex-Bus Designed and Tested to Full Cycles

TF cooling lines

TF flex-bus

TF Coil

CHI bus

PF Coil 1c

PF Coil 1b

CS Casing

PF Coil 1a

OH Coil

Nstx u status and plan

The NSTX-U Inner TF Bundle Manufacturing Stages

New Zn-Cl-Free Soldering Technique Developed

Nstx u status and plan

NSTX-U Support Structural Upgrades

4x Electromagnetic Forces

Nstx u status and plan

Relocation of the 2nd NBI beam line box from the TFTR test cell into the NSTX-U Test Cell.

Nstx u status and plan

2nd NBI alignment performed and confirmed

Nstx u status and plan

Beam-line Component Refurbishment

Ion Dump

Calorimeter upgrade

Bending Magnet

  • 11

Nstx u status and plan

JK cap tack welded to the vacuum vessel after completing alignments, and full welding is now underway (Jan. 3, 2013)

Nstx u status and plan

NBI Duct and Torus Vacuum Pumping System (TVPS) components being procured and fabricated

Rectangular bellows

Exit spool piece

40” Torus Isolation (Gate) Valve received

Spool section & supports

TVPS valves, hardware, TMPs, and shields

Circular bellows

Nstx u status and plan

NSTX In-Vessel View and CHI Gap Protection Enhancement

Expect x 10 Higher Heat Load Into the CHI Gap


Center Stack

Secondary Passive Plates



NBI Armor




Primary Passive Plates






Nstx u status and plan

Non-inductive ramp-up from ~0.4MA to ~1MA projected to be possible with new centerstack (CS) + more tangential 2nd NBI

  • New CS provides higher TF (improves stability), 3-5s needed for J(r) equilibration

  • More tangential injection provides 3-4x higher CD at low IP:

    • 2x higher absorption (4080%) at low IP = 0.4MA

    • 1.5-2x higher current drive efficiency

TSC simulation of non-inductive ramp-up from IP = 0.1MA, Te=0.5keV target at BT=1T

More tangential 2nd NBI

Present NBI

Nstx u status and plan

NSTX-U CHI Start-up Configurations

X 2 Higher CHI Driven Currents Expected

Nstx u status and plan

NSTX-U ECH/EBW System for Non-Inductive Start-Up and Sustainment

28 GHz – 1MW Gyrotron by

U. of Tsukuba

A schematic of the NSTX-U ECH/EBW launcher

Nstx u status and plan

Stability control improvements significantly reduce unstable RWMs at low li and high bN; improved stability at high bN/li

Unstable RWM

Stable / controlled RWM

Resonant Field Amplification (RFA) vs. bN/li

  • Disruption probability reduced by a factor of 3 on controlled experiments

    • Reached 2 times computed n = 1 no-wall limit of bN/li = 6.7

  • Lower probability of unstable RWMs at high bN/li



  • Mode stability directly measured in experiments using MHD spectroscopy

    • Stability decreases up to bN/li = 10

    • Stability increasesat higher bN/li

    • Presently analysis indicates consistency with kinetic resonance stabilization

S.A. Sabbagh

J. Berkery IAEA

Nstx u status and plan

Disruptivity studies and warning analysis of NSTX database are being conducted for disruption avoidance in NSTX-U


Warning Algorithms




All discharges since 2006

  • Physics results

    • Low disruptivity at relatively high bN ~ 6; bN / bNno-wall(n=1) ~ 1.3-1.5

      • Consistent with specific disruption control experiments, RFA analysis

    • Strong disruptivity increase for q* < 2.5

    • Strong disruptivity increase for very low rotation

  • Results

    • ~ 98% disruptions flagged with at least 10ms warning, ~ 6% false positives

    • False positive count dominated by near-disruptive events

S. Gerhardt IAEA

  • Disruption warning algorithm shows high probability of success

    • Based on combinations of single threshold based tests

Nstx u status and plan

NSTX “Snowflake” Divertor Configuration resulted in significant divertor heat flux reduction and impurity screening

Higher flux expansion (increased div wetted area)

Higher divertor volume (increased div. losses)

  • Maintained stable “snowflake” configuration for 100-600 ms with three PF coils

  • Maintained H-mode confinement with core carbon reduction by 50 %

  • NSTX-U control coils will enable improved and up-down symmetric snowflake configurations

V. Soukhanovskii, NF 2009

Nstx u status and plan

Lithium Improved H-mode Performance in NSTX

Te Broadens, tE Increases, PH Reduces, ELMs Stabilize

Te broadening with lithium

No lithium (129239);260mg lithium (129245)

With Lithium

Without Lithium

H. W. Kugel, PoP 2008

tE improves with lower collisionality

tE improves with lithium

Pre-discharge lithium evaporation (mg)

S. Kaye, IAEA (2012)

R. Maingi, PRL (2011)

Nstx u status and plan

Li core concentration stays well below 0.1% for LLD temperature range of 90°C to 290°C

R=135-140 cm, t=500-600 ms

  • Li core concentration remained very low ≤ 0.05%. C remains dominant impurity even after massive (hundreds of milligrams) Li evaporation

  • No apparent increase in Li nor C core concentration even at higher LLD surface temperature.

  • Liquid


    M. Podesta, IAEA (2012)

    Reason for low lithium core dilution?:

    • Li is readily ionized ~ 6 eV

    • Li is low recycling – sticks to wall

    • Li has high neoclassical diffusivity

    F. Scotti, APS (2012)

    Nstx u status and plan

    Clear reduction in NSTX divertor surface temperature and heat flux with increased lithium evaporation

    • a)

    • b)

    • Lithiated graphite

    • c)

    • d)

    T. Gray. IAEA 2012

    • 2 identical shots (No ELMs)

      • Ip = 0.8 MA, Pnbi ~ 4 MW

      • high δ, fexp ~ 20

    • 2, pre-discharge lithium depositions

      • 150 mg: 141255

      • 300 mg: 138240

    • Tsurf at the outer strike point stays below 400° C for 300 mg of Li

      • Peaks around 800° C for 150 mg

    • Results in a heat flux that never peaks above 3 MW/m2 with heavy lithium evaporation

    Nstx u status and plan

    Radiative Liquid Lithium Divertor Proposed

    Based largely on the NSTX Liquid Lithium Divertor Research

    Divertor Heat and Particles Flux

    Edge Plasma



    Liquid Lithium (LL)

    ~ 1 l/sec


    Core Reacting


    First Wall / Blanket

    At 500°C – 700°C

    Particle pumping by Li coated wall

    Flowing LL Particle Pumping Surfaces

    Li Radiative Mantle

    Li wall coating /


    Scrape Off Layer


    Li path


    Closed RLLD

    Li Evap. /


    Reduced Divertor Heat and Particle Flux

    Flowing LLD Tray

    200 – 450 °C


    Heat Exchanger

    LL In

    LL In

    LL Out

    Divertor Strike Point


    LL Purification System to remove tritium, impurities, and dust

    M. Ono. IAEA 2012

    Nstx u status and plan

    Design studies focusing on thin, capillary-restrained liquid metal layers

    Combined flow-reservoir system in “soaker hose” concept

    Building from high-heat flux cooling schemes developed for solid PFCs

    Optimizing for size and coolant type (Helium vs. supercritical-CO2)

    Laboratory work establishing basic technical needs for PFC R&D

    Construction ongoing of LL loop at PPPL

    Tests of LI flow in PFC concepts in the next year

    Coolant loop for integrated testing proposed

    PPPL Liquid Metal R&D for Future PFCs

    For NSTX-U and Future Fusion Facilities

    Divertor Heat and Particle Flux

    Lithium Radiative Mantle

    Liquid Lithium Divertor Tray


    200°C – 400°C


    EM Pumps


    M. Jaworski et al., PPPL

    Nstx u status and plan

    Draft NSTX-U Research Plan

    Being Formulated

    Nstx u status and plan

    Draft NSTX-U Research Facility Plan

    Being Formulated

    Upgrade Outage

    1.5  2 MA, 1s  5s

    Advanced PFCs, 5s  10-20s

    0.3-0.5 MA CHI

    0.5-1 MA CHI

    Start-up and ramp-up



    Extend NBI duration or implement 2-4 MW off-axis EBW H&CD

    0.2-0.4 MA plasma gun

    up to 1 MA plasma gun



    2 MW

    Boundary physics

    Diagnostics for high-Z wall studies

    Divertor cryo-pump

    Divertor Thomson

    U.S. FNSF conceptual design including aspect ratio and divertor optimization

    Materials and PFCs

    All High-Z PFCs

    Hot High-Z FW PFCs

    U or L

    Mo divertor

    U + L

    Mo divertor

    Li granule injector

    Flowing Li divertor or limiter module

    Full toroidal flowing Li divertor




    MGI disruption mitigation tests

    Enhanced RFA/RWM sensors

    NCC coils

    NCC SPA upgrade


    Transport & turbulence

    DBS, PCI or other intermediate-k

    High kq



    Waves and Energetic Particles

    HHFW straps for EHO, *AE

    Dedicated EHO or *AE antenna

    HHFW feedthru & limiter upgrade

    2nd NBI

    Scenarios and control



    Rotation control

    qmin control

    Control integration

    Nstx u status and plan


    • NSTX-U Aims to Develop Physics Understanding Needed for Designing Fusion Energy Development Facilities (ST-FNSF, ITER, DEMO, etc.)

    • Develop key toroidal plasma physics understanding to be tested in unexplored, hotter ST plasmas

    • Upgrade Project has made good progress in overcoming key design challenges

      • Project on schedule and budget, ~45-50% complete

      • Aiming for project completion in summer 2014

    • Detailed NSTX-U Research Plan is being developed

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