球型トカマク炉実現への

QUESTが担える役割及び期待
Roles and Opportunities of the QUEST Program forthe Spherical Tokamak Reactor Development

Masayuki Ono
PPPL, Princeton University
QUEST 10th Anniversary Research Meeting
July 20, 2018
QUEST １０周年記念研究会–July 20, 2018 (M. Ono)1

Outline• Motivation for Spherical Tokamak (ST)• ST Development Paths• QUEST in the world ST program• QUEST/NSTX-U Collaboration• Summary

QUEST １０周年記念研究会–July 20, 2018 (M. Ono)2

STs have higher natural elongation
Elongation k = b / ab = vertical ½ heighta = minor radiusba

Higher elongation improves stability, confinement
QUEST １０周年記念研究会–July 20, 2018 (M. Ono)

3

ITER will be first device to access “burning plasma”•Burning plasma: majority of plasma heating power
comes from fusion alpha particles from DT reactions
•••DT reaction energy split: 1/5 in alphas, 4/5 in neutrons

ITER goal Q = Pfusion / Pexternal heating = 10
Q = 10  Palpha / Pexternal = 2Palpha / Palpha + external = 2 / 3 > 50%
A=3.1, R=6.2m, B =5.3T, I =15MATPITER under construction in Cadarache, France

QUEST １０周年記念研究会–July 20, 2018 (M. Ono)

4

ITER magnets will be largest ever built• 18 toroidal field magnets• 12 Tesla at coil
• Weight: 6500 tons

• 80,000 km of Nb3Sn
superconducting strand
in total length

Plasma current: Toroidal field current
165 million amps
15 million amps
QUEST １０周年記念研究会–July 20, 2018 (M. Ono)

Theseare largenumbers
5

Favorable average curvature improves stability
STTokamak

Plasmaspendsless timein unstable
curvatureregionA ~ 2.5-4
k = 1.5-2
bT = 3-10%

A ~ 1.3-2
k = 2-3
bT = 10-40%

Aspect Ratio A = R /a Elongation k = b/a Toroidal beta bT = p / (BT02/2m0)
QUEST １０周年記念研究会–July 20, 2018 (M. Ono)

6Higher bT enables higher fusion power and compact
FNSF for required neutron wall loading
Pfusion ∝ p 2 x Vol

Product

BT04 x Vol

Physics
Knob$Investment

bN = 640
Toroidal b (%)

Pfusion ∝ bT2

Data base from START, MAST,PEGASUS and NSTX

54ST-FNSF
320Tokamak2ITER

High neutron wall loading Wnpossible in a compact ST00Wn ∝ Pfusion / Area

4Ip/aBT0 (MA/mT)

8Wn ∝ bT2 BT04 a (not strongly size dependent)
Wn ~ 1 MW/m2 with R ~ 1 m FNSF feasible!
QUEST １０周年記念研究会–July 20, 2018 (M. Ono)7

ST Development Paths
Fusion Power Can Be Generated in Diverse Range of STs
ST-FNSFs

A=2, R0 = 3m HTS-TF
FNSF / Pilot Plant

ORNL
R=1.0m: TBR < 1 (≈ 0.9)

ARIES-ST Cu Power Plant

R0 ~ 3.2 m
JUST SC ST Power Plant

PPPL
Cryostat volume and
ITF ~ 1/3 of ITER

PPPL
R=1.7m: TBR ≥ 1Pfusion = 520 MW
Qeng = 1.35
Pnet = 73 MW

VECTOR, Slim CS
QUEST １０周年記念研究会–July 20, 2018 (M. Ono)

R0 ~ 4.5m
8Spherical Tokamaks have the potential attractivenessfor fusion development paths
Attractiveness of Spherical Tokamaks for Fusion Energy Development:• Projected to access high neutron wall loading for fusion material andengineering development at moderate R0, Pfusion
Wn ~ 1-2 MW/m2 , Pfus ~ 50-200MW, R0 ~ 0.8-1.8m• Modular, simplified maintenance• Tritium breeding ratio (TBR) near 1 in a compact size (R ~ 1.7m)
Requires sufficiently large R0, careful design• Net electricity possible for an ST with R = 3m

R&D Needs for Fusion Energy Development:• Non-inductive start-up, ramp-up, sustainment
Low-A  minimal inboard shield  no/small transformer• Divertor solutions for high heat flux
• Confinement scaling (especially electrons)• Stability and steady-state control• Radiation-tolerant magnets, design
QUEST １０周年記念研究会–July 20, 2018 (M. Ono)

9

Operating ST Research Facilities Since 2000
NSTX and MAST: MA-class STs, other STs addressing topical issues
NSTX, USAPEGASUS, USAHIST,Japan

LTX/CDX-U, USALATE, JapanGLOBUS-M, Russia

TST-2, Japan

MAST, UK

UTST, Japan

R0 ~ 0.75 m
QUEST/CPD, Japan
VEST,Korea

R0 ~ 0.85 m
HIT-II,USAGLOBUS-M
HIT-IISUNIST, China

ETE, Brazil

PEGASUSMAST
ST25(HTS)NSTX/LTX

z

z KTM

QUEST
HIST
VEST
SUNIST
LATE
TST-2
TS3/4
UTST

TS3/4, Japan

ST25, UKETEz

STs operated since 2000

QUEST １０周年記念研究会–July 20, 2018 (M. Ono)

10

QUEST is the only ST which can operate long-pulse
QUEST is also unique in hot-wall, high power ECH, and CHI
Record ECH Start-UpTarget

Hot wall
Long-Pulse Plasmas

Coaxial Helicity Injection

QUEST １０周年記念研究会–July 20, 2018 (M. Ono)

11

NSTX Upgrade Device and Test Cell – Aerial View

QUEST １０周年記念研究会–July 20, 2018 (M. Ono)

12

NSTX Upgrade will access new physics
with 2 major new tools:
1. New Central Magnet

Higher T, low n* from low to high b
BT = 1 T for 5 sec,
Ip = 2 MA

2. Tangential 2nd Neutral Beam

Full non-inductive current drive
PNBI = 10 MW
PHHFW = 5 MW

QUEST １０周年記念研究会–July 20, 2018 (M. Ono)13

Solenoid-free Start-up and Ramp-up are Critical Issues
for Compact ST and Tokamak-based Reactors• ST has been addressing criticalissue of solenoid-free start-up–

A compact ST has little space fora central solenoid–

Solenoid-free start-up is also
attractive for tokamak designs

IP [MA]

Current ramp-upphase

NSTX-U

Solenoid-freeStart-up phase

NBI•

Maximizing solenoid-free start-up
currents reduces reliance on lessdeveloped non inductive current
ramp-up scenarios

HHFW

ECH/EBW, CHI, LHI

0 MA•

Few MA start-up current is projected
for reactors

0.4 MW

1 MATimeECH / EBW – Utilize 1 – 2 MW, 28 GHZ gyrotron
CHI, LHI – Coaxial Helicity Injection and local helicity
injection up to ~ 400 kA– Higher currents may be feasible
NSTX-U will not conduct solenoid-free start- HHFW ~ 4 MW 30 MHZ High Harmonic Fast Wave
up / ramp-up experiments near term
NBI ~ 10 MW NBIQUEST １０周年記念研究会–July 20, 2018 (M. Ono)

14

NSTX-U and QUEST are complementary
Short-pulse vs. Long-pulse
QUEST

NSTX-UHigh field – high power for a few sec Long-pulse non-inductive operations
All carbon wall without hot wall,no ECH and CHI in near term

CHI and high power ECH,
all metal hot wall, steady-state

NSTX-U would like to collaborate with QUEST to pursue ECH, CHI, long-pulse, all metal hot wall
QUEST １０周年記念研究会–July 20, 2018 (M. Ono)

15

QUEST Has an Active World-Class Program on ECH Start-Up
NSTX-U Plans to Contribute via. Theory and Diagnostic Support• QUEST and its high power ECH system has an impressive physics capability:-Focusing and steering capability to control the ECH deposition profiles.

-Capable of scanning in NII and polarization for wave physics.

-BT scanning to explore the resonance layer position dependence.

Develop comprehensive picture of QUEST ECCD:• Provide fast electron generation with GENRAY and CQL-3D for
ECH fast electron generations. (N. Bertelli, R. Harvey)• Measure time and spatially resolved soft x-ray profiles using
NSTX-U multi-energy soft x-ray Pilatus camera together withother x-ray detectors on QUQEST. (L. Delgado-Aparicio, M. Ono)

• Developing a new synthetic diagnostic tool for multi-energy soft
x-ray camera with UT/TST-2 to obtain fast electron evolutions.
(L. Delgado-Aparicio with H. Yamazaki)• Aim to develop a comprehensive predictive modeling including
the ECH generated fast electron transport and confinement. (M.
Ono, N. Bertelli, G.J. Kramer)
QUEST １０周年記念研究会–July 20, 2018 (M. Ono)16

A Tokamak Start-up Modeling being Developed
Initially Multi-pass Non-Phased Electron Cyclotron Heating

2ΩeLayer

Strong ECH
focusing forsingle passabsorption

QUEST １０周年記念研究会–July 20, 2018 (M. Ono)17

Grad-B and Processional Currents can lead to closed flux configuration
ECH without directionality – low absorption – multi-pass expected
J B

Ip = 0 A
Bv = 10 G

J procIp = 556A

Ip = 700A

Ip = 767A

Ip = 834A

Ip = 855A

Ip = 895A
Small closedflux surface
formedQUEST １０周年記念研究会–July 20, 2018 (M. Ono)18

Bootstrap Currents Can Enhance Closed Flux Surfaces
Bootstrap current can rapidly increase the plasma current
PECH = 100 kW
Bv = 10 G
ne = 1012cm-3

Ip = 835A

PECH = 3.35 kW

Ip = 1706 A

Ip = 3769 A

PECH = 30 kW

PECH = 61 kW• ECH generated bootstrap currents were investigated in CDX-U and DIII-D.*• Scaling using ITER 89P confinement scaling was developed which scaling was used here.
• Boostrap current increases cofinement which in term generate more currents.
• More current increases the closed flux surface volume increasing the PECH within the closed
flux surface volume.
• Eventuall reaches saturation since the increasing current increases poloidal fields whichtends to reduce poloidal beta.
*Y.S. Hwang, et al., PRL 1996, C.B. Forest, et al., PoP 1994
QUEST １０周年記念研究会–July 20, 2018 (M. Ono)19

Formation of Flux Surface Formation With Pressure-Driven Currents
Ip (A)
4500

4000

3500

3000

2500

Closed flux
surfaces
formed2000

1500

I-boostrap

1000

I-procession
500

I-grad-B002

4681012# of steps
QUEST １０周年記念研究会–July 20, 2018 (M. Ono)20

Transient CHI: It is advantageous to achieve ~ few MAand reduce demand on non-inductive current ramp-up
NSTX• NSTX Transient CHI injects poloidal magnetic
flux from divertor area into vessel on a 1-3mstime scale– Injector flux shaping and injector current ramp-downcauses open flux to form closed flux surfaces (like in asoap bubble)• Obtained ~ 200 kA close flux discharge andaiming to achieve ~ 500 kA in NSTX-U• Significantly ramped up computationalmodeling work to understand CHI scaling• Theory and NSTX-U/HIT-II Experimental work
has resulted in simple scaling relation fortransient CHI to project to reactor scale
devices (Ip Injected flux)• QUEST is testing reactor-relevant CHI
capability – localized electrodes.
R. Raman, F. Ebrahimi, PPPLQUEST １０周年記念研究会–July 20, 2018 (M. Ono)21

Biased Electrode Concept to protect CHI insulator
from Neutron damage for life of Reactor
Toroidal electrode on top of blanket structure, analogous to CHI ring electrode

Upper portionof blanket

Injector flux
connects upper
portion of vesselto the electrodeplate on theupper portion ofthe blanket
assembly

R. Raman, T. Brown, L.A. El-Guebaly, et al.,Fusion Science & Technology (2015)*Insulator dose:~6x109 Gy @ 6FPY < 1011 Gy limit

QUEST １０周年記念研究会–July 20, 2018 (M. Ono)

* L. El-Guebaly, et al., MCNP Neutronics
22

QUEST (in Japan) is Developing Reactor-Relevant CHI
Configuration & Will Test ECH Heating of a Transient CHI PlasmaInjectorFlux•

In reactor concept insulator
can be shielded from neutrons•Insulator not part of vacuum
boundary as on NSTX–•Plasma
growthInitial injector
current direction

Needs experimental test /verification
CHI system on QUEST issimilar in concept to the oneplanned for NSTX-U

CHI Insulator
Current injection

University of Washington, PPPLQUEST １０周年記念研究会–July 20, 2018 (M. Ono)23

Transient CHI Discharges Successfully Established in QUESTPPPL fast camera used to capture CHI discharges

K. Kuroda, et al., sumitted to PP&CF
QUEST １０周年記念研究会–July 20, 2018 (M. Ono)

24

NSTX-U and QUEST Are Complementary
Looking forward for the long-term collaboration!
•QUEST is unique among the ST worldwide which can operate
long-pulse.

•QUEST is very complementary to NSTX-U and MAST-U. It isaddressing a long term ST reactor problems such as start-up,
long-pulse, high temperature all metal wall not being
addressed by NSTX-U and MAST-U in the near term. Thismotivates our strong collaborations with QUEST.

•NSTX-U wishes to collaborate with QUEST to address physics
areas not covered by NSTX-U in the near term:•Support ECH / EBW start-up studies through modeling and diagnostics.

•Support CHI work through physics support, modeling and diagnostics.

•Support Long-pulse operations through physics support.
QUEST １０周年記念研究会–July 20, 2018 (M. Ono)25