Summary: EXS, EXW, ICC Abhijit Sen

25th IAEA Fusion Energy Conference

St. Petersburg, 13-18 October, 2014

Thanks to all authors and overview speakers who sent slides Special thanks to C. Greenﬁeld, P. Kaw, H. Yamada

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 1 13-18 Oct., 2014 Outline

Topic Number of Papers Magnec Confinement Expts: Stability (EXS) 56 Magnec Confinement Expts: Waves (EXW) 54 Innovave Confinement Concepts (ICC) 15

Subtopics for EXS & EXW (guided by ITER priority needs)

• Disrupons/Runaways (control, migaon, predicon) • ELMS (control, migaon) & 3D physics • Waves and Energec Parcles • MHD instabilies (nonlinear interacons, control) • Current Drive & RF Heang

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 2 13-18 Oct., 2014 Disrupons / Runaways – a major concern for ITER operaon EX/P3-18, Campbell Main Issues

• Uncertaines associated with disrupon loads that can impact the structural integrity of the machine

• How to limit the number of disrupons to protect machine life • Disrupon avoidance /control • Disrupon predicon

• Need for a reliable disrupon migaon system (thermal, current and runaway migaon) – input required before ﬁnal design review 2017

• Many gaps in physics basis and a lack of fundamental understanding

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 3 13-18 Oct., 2014 Disrupon Research has Increased and Become More Focused since the 2012 FEC

• Predicon and avoidance ü Both empirical and theory-based • Halo currents – measurements and modeling ü Exploraon of various techniques for disrupon avoidance • Characterizaon ü Enlarged experimental database + modeling has led to improved understanding ü Asymmetric events – causes and consequences • Migaon and control ü Thermal/current quench migaon experiments ü Runaway generaon and control

ITPA has played a major role in coordinang and contribung towards joint experimental + modeling acvies

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 4 13-18 Oct., 2014 Disrupon Avoidance / Control

EX/P2-42, Okabayashi Avoidance of tearing mode locking and disrupon with electro-magnec torque introduced by feedback-based mode rotaon control in DIII-D and RFX-mod

RFX

DIII-D Sen, EXS+EXW+ICC Summary 25th IAEA FEC 5 13-18 Oct., 2014 EX/ P8-4, Jayhyun Kim Plasma is less susceptible to minor disruption of n=1 locked mode under stronger n=2 even field.

Early No #8889 (no n=2) > #9367 (n=2, 1 kA/t) > #9368 (n=2, 2 kA/t) disruption disruption

KSTAR

Slide- away

Sen, EXS+EXW+ICC Summary 25th IAEA FEC Relative change 13-18 Oct., 2014 Disrupon Avoidance / Control EX/P4-18, Maurer Strong 3D equilibrium shaping, applied to tokamak like discharges on the Compact Toroidal Hybrid (CTH) expand its disrupon free operang regime

EX/5-3, Tanna; EX/P7-16, Kulkarni; EX/P7-17, Dhyani

• Disrupon control using biased electrodes in ADITYA tokamak to control MHD modes • Similar eﬀects also observed with the use of ICRF at the edge

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 7 13-18 Oct., 2014 Asymmetrical Disrupons in JET and COMPASS P5-33, Gerasimov • Highlights the frequent occurrence of asymmetric disrupons in JET and the magnitude of their consequent sideways forces • Resonance rotaon with the natural vessel frequencies • 3D JET model calculaons for vessel poloidal currents • Comparison with COMPASS data – consistency in terms of amplitude of asymmetry and rotaon behaviour

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 8 13-18 Oct., 2014 Thermal and Current Quench Migaon EX/P2-22, Eidies

• Measurement of Radiated Power Asymmetry During Disrupon Migaon on the DIII-D Tokamak • radiaon asymmetry during the thermal quench (TQ) and current quench (CQ) is largely insensive to the number or locaon of injecon sites

• applicaon of an n=1 error ﬁeld can modify the magnitude of the asymmetry during the TQ, supporng recent modeling results that indicate n=1 MHD during the TQ may be a cause of the radiaon Asymmetry

• results provide a ﬁrmer understanding of the 3D physics aﬀecng the ITER DMS design

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 9 13-18 Oct., 2014 Sen, EXS+EXW+ICC Summary 25th IAEA FEC 10 13-18 Oct., 2014 EX/5-2, Reux Runaway electron beams stopped only by low-Z gas injected before current quench

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 11 13-18 Oct., 2014 EX/5-2, Reux Runaway Generaon / Control

EX/5-1, Granetz

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 12 13-18 Oct., 2014 DIII-D Expt on RE Migaon using SPI

Step #1 Step #2 Ne SPI impacts at RE edge • Injecon of Ne Shaered Pellets Neon SPI Hot into early CQ is eﬀecve in RE pre-TQ Seed suppressing runaway growthPlasma Cold CQ • RE current dissipaon explained Plasma RE seed in core by RE-ion pitch angle scaering Radiating Impurity 4 – Higher Z more eﬀecve 10 3 at RE dissipaon 10 Minimal or No RE suppression 2 10 EX/PD/1-1, Eidies SSuppresseduppressed RREE 1 10 Integrated HXR (au)

0 10 −1 0 1 2 3 t −t (ms) SPI CQ Spike ELMS – Characterizaon / Migaon / Suppression

Progress since 2012 FEC

• RMP ELM migaon and suppression of Type I ELMs ü Expanded operang space ü Shown to be robust to loss of coils (reassuring for ITER)

• Alternate external suppression methods appear promising • Pellet pacing, SMBI, gas injecon, LHW,…

• Improved understanding of ELM dynamics from beer diagnosc measurements and modeling studies – also some challenges

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 14 13-18 Oct., 2014

Expanded Operating Space EX/1-2, Kirk on ELMsMAST on MAST andAUG AUGEEE Sustained ELM migaon/type I ELM suppression has been achieved on MAST and AUG with magnec perturbaons with a range of toroidal mode numbers

ELM size and target heat loads are reduced but at a price of a reducon in conﬁnement

Dashed curves expanded operating space for the type I ELM suppression/mitigation from MAST and ASDEX Upgrade

Results show that regimes with tolerable ELMs can be established over a wide operating space in a range of devices Sen, EXS+EXW+ICC Summary 25th IAEA FEC 15 13-18 Oct., 2014 Advances in Basic Understanding of ELM Suppression

• ELM suppression achieved • New data reveals bifurcation with as few as 5 internal coils indicative of resonant field penetration at ELM suppression 5 coils

7 coils

11 coils

DIII-D results Highlights importance of plasma EX/1-1, Wade; EX/P2-21, Orlov response to RMP fields EX/1-5, Jeon

KSTAR

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 17 13-18 Oct., 2014 Simultaneous Measurement of ELMs at both High and Low Field Sides in KSTAR

• Comparable mode strength at HFS and LFS • Asymmetries in toroidal/poloidal rotaon velocies • Mode structure at HFS not consistent with Ballooning Mode model • Mode numbers diﬀerent on the two sides

EX/8-1, Park

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 18 13-18 Oct., 2014 ELM migaon by Lower Hybrid Waves in EAST

EX/P3-8, Liang • ELM migaon with LHW obtained

over a wide range of q95

• Aributed to formaon of helical current ﬁlaments in SOL

• ELM freq. increases from 150 Hz to about 1 KHz

Strong modiﬁcaon of plasma edge Sen, EXS+EXW+ICC Summary 25th IAEA FEC 19 13-18 Oct., 2014 Other MHD and 3D physics studies

• Improved understanding of Neoclassical Toroidal Viscosity (NTV) in tokamaks • Feedback control of RWM allows tokamak

operaon at q95≤2 • Helical modes observed in KSTAR • Basic studies of MHD instabilies

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 20 13-18 Oct., 2014 Neoclassical Toroidal Viscosity for Rotaon Control and the Evaluaon of Plasma Response EX/1-4, Sabbagh Highlights Perturbaon experiments measure NTV torque proﬁle and compare to theory q Experimental NTV characteriscs q NTV experiments on NSTX and KSTAR

q NTV torque TNTV from applied 3D ﬁeld is a radially extended, relavely smooth proﬁle

q Perturbaon experiments measure TNTV profile q Aspects of NTV for rotaon control 2 5/2 q Varies as δB ; TNTV ∝ Ti in primary collisionality regime for large tokamaks q No hysteresis on the rotaon profile when altered Rotaon controller using NTV and NBI by non-resonant NTV is key for control q Rotaon controller using NTV and NBI tested for NSTX-U; model-based design saves power q NTV analysis to assess plasma response q Non-resonant NTV quantavely consistent with fully-penetrated field assumpon q Surface-averaged 3D field profile from M3D-C1 single fluid model consistent with field used for quantave NTV agreement in experiment Sen, EXS+EXW+ICC Summary 25th IAEA FEC 13-18 Oct., 2014 21 21 DIII-D and RFX-mod achieved reproducible tokamak operaon at q95<2 thanks to feedback control of 2/1 RWM – for many resisve wall mes using 3D magnec fields EX/P2-41, Marn

q95

2/1 RWM

! ! Blue curve: with feedback control Red curve: w/o feedback control

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 22 13-18 Oct., 2014 Active MHD control has resulted in RWM-stabilized, high-βp, low-A RFP plasmas, and two routes to helical RFP states are identified

Definition: 2 β p = 2µ0 pe0 / Bpa

Central electron pressure vs. Ip2 shows that feedback Using saddle coil array for feedback MHD stabilization of RWM has led to improved performance with control, RWM was suppressed and the attainment of electron poloidal beta10~15%. Density limit RFP discharge duration could be extended studies are becoming important in low-A RFP. to the upper bound determined by the iron core saturation. EX/P3-52, Masamune

Growth of both the resonant (left) and non-resonant (left) mode can lead to self-organized helical RFP with almost Reconstructed magnetic surface shape using SXR identical deformation. Resonant mode accompanies CT during QSH phase shows good agreement with Sen, EXS+EXW+ICC Summary 25th IAEA FEC reconnection (MIPS simulation). helical equi-pressure surface shape in 3-D MHD 23 13-18 Oct., 2014 simulation using the MIPS code. Sen, EXS+EXW+ICC Summary 25th IAEA FEC 24 13-18 Oct., 2014 (R)MHD INSTABILITIES – BASIC STUDIES

Quesons addressed: Triggering mechanisms, Mode Dynamics

FTU &TCV: • 2/1 TM triggered by Ne injecon EX/P2-53, Botrugno • TM onset by central EC power deposion EX/P2-54,Nowak

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 25 13-18 Oct., 2014 HL-2A: LHD: • NTM triggered by intrinsic • Eﬀects of low n MHD modes on error ﬁelds EX/P7-19, Xu achievable beta values EX/P6-37 • NTM triggered by non-local • Bursng Resisve Interchange transport EX/6-4, Ji Modes EX/P6-36 • Interacon between MHD modes EX/P7-25, Yu

Energec-Ion-Driven-Resisve SMBI induced NLT Interchange Mode (EIC) Sen, EXS+EXW+ICC Summary 25th IAEA FEC 26 13-18 Oct., 2014 Energec Parcles / Waves

Main Issues

• Good conﬁnement of EPs crucial for α heang of burning plasmas • Instabilies driven by EPs can degrade their conﬁnement and also alter their energy distribuon; also impact on NB-CD • Characterizaon of stability boundaries • Beer understanding of fast ion transport

Progress since 2012 FEC

• Improved diagnoscs, beer nonlinear modeling have furthered our understanding on a number of issues • Exptal database extended to include STs, stellarators, RFPs etc. • Provide more accurate correlaons between fast ion losses & instabs.

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 27 13-18 Oct., 2014 HL-2A EX/P7-24, Zhang TJ-II EX/P4-46, Cappa

ECRH has a strong inﬂuence on the NBI driven Alfvén modes in TJ-II. A second EC beam can stabilize the AE. Ulizing a new scinllator-based lost fast-ion probe, recent HL-2A experiments have elucidated a variety of neutral beam ion loss behaviors in the presence of MHD instabilies.

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 28 13-18 Oct., 2014 Sen, EXS+EXW+ICC Summary 25th IAEA FEC 29 13-18 Oct., 2014 Fast-ion response to externally applied 3D magnec perturbaons

ASDEX-U EX/P1-22, Garcia DIII-D EX/10-2, Van Zeeland

strong plasma & fast-ions response is observed in H-mode regimes with low collisionality / density and low q95. Pitch angle and energy resolved measurements + wide ﬁeld-of-view infrared imaging show fast ion losses correlated with applied 3D ﬁelds. in L-mode plasmas. Good agreement with model Sen, EXS+EXW+ICC Summary 25th IAEA FEC simulaons. 30 13-18 Oct., 2014 EX/P6-58, Kornev EX/P1-33, Bakharev

TUMAN -3M GLOBUS-M

Plot of neutron ﬂux vs me for • Parcle losses highly correlated with TAE diﬀerent inward shis of column • Sawteeth induced losses >25% • Shi in plasma column inwards can reduce losses

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 31 13-18 Oct., 2014 Noninducve Current Drive

• Studies of LHCD physics and applicaons • ICRH opmizaon in JET • Solenoid-free ST startup

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 32 13-18 Oct., 2014 Near-Field Physics of Lower-Hybrid Wave Coupling

ne0=1.

5ne0=2 1/ EX/4-2, Goniche Tore Supra P 2 ne0= (103 17m-3) Large data base (~230 points) indicate that L =2mm E scales as (P 1/2) assuming edge n RF coupled L =1.5m density near the cut-oﬀ density (~2×1017m-3) n m

EX/P6-17, Parker Alcator C-MOD

Loss of LHCD efficiency at high density is associated with Excitaon of Parametric Decay Instabilies. PDI are excited near the separatrix and onset can be migated by modifying condions in the scrape-off layer. Launch from HFS may be more efficient – scheme for next machine.

EX/P3-11, Ding High density experiments with LHCD analyzed by simulaon using experimental parameters, show that parametric instability , collision EAST absorpon in the edge region, and density ﬂuctuaons could be Sen, EXS+EXW+ICC Summary responsible for the low current drive eﬃciency at high density. 33 25th IAEA FEC 13-18 Oct., 2014 EX/P6-20, Delgado-Aparacio: Destabilizaon of Internal Kink by Suprathermal Electron Pressure Driven by Lower Hybrid Current Drive (LHCD)

• A new type of periodic ﬁshbone-like instability with a (1,1) internal kink-like structure

• disnct from the sawtooth instability On-axis SXR signatures of a (1,1) internal kink-like (IK) mode in the a) presence or b) absence of Sawtooth precursors (SP) and crashes (SC).

Demonstrate a direct dynamic relaon between LHCD generated fast electrons and a ﬁshbone-like mode

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 34 13-18 Oct., 2014 Sen, EXS+EXW+ICC Summary 25th IAEA FEC 35 13-18 Oct., 2014 Fully Non-inducve Current Drive Experiments using 28 GHz and 8.2 GHz Electron Cyclotron Waves in QUEST H. Idei, et al. 54 kA Plasma Sustainment in Low Aspect Ratio Config. by 28GHz Injection 22870-@3s Plasma current of 54 KA was non- 0.5 inducvely sustained for 0.9 sec by only 28 GHz injecon.

0 Plasma shaping was almost kept for

Z [m] 1.3 sec.

EX/P1-38 Higher current of 66 kA was non- -0.5 inducvely obtained by slow ramp- 0.2 0.4 0.6 0.8 1 up of vercal ﬁeld also. R [m] Non-inducve high current plasma start-up by 2nd ECH/ECCD has been demonstrated. Over Dense Plasma Sustainment by 28 /8.2 GHz Injections after Spont Density Jump Spontaneous density jump across the cutoﬀ density was observed in superposed 28 and 8.2 GHz injecons.

Hα intensity was kept, magnec axis Rax and minor radius a were slightly decreased in the density jump case.

Plasma current Ip was once decreased, but was Sen, EXS+EXW+ICC Summary 25th IAEA FEC recovered aer the plasma shaping became 36 13-18 Oct., 2014 more stable.

Non-inductive Plasma Start-up Experiments on the TST-2 Spherical Tokamak Using Waves in the Lower-Hybrid Frequency Range Y. Takase for the TST-2 Group

• Economically competitive tokamak reactor may be realized at low A = R/a by eliminating the central solenoid

→ Objective: Demonstrate Ip ramp-up by LHW on ST • Three antennas were used: – Combline antenna • Nonlinear excitation of LHW traveling – Grill (dielectric-loaded WG array) antenna wave

• Optimum n|| : 3-4 – CCC (capacitively-coupled combline) antenna

• Highest ηCD achieved (sharp n|| spectrum, good directivity) CCC antenna • Characteristics of LH driven plasma – Pressure dominated by fast electrons 28 kW LH + 4 kW EC I / P = 0.5 A/W • 3-fluid equilibrium being developed p RF

• Importance of Er and flows – Fast electrons are poorly confined at Ip ~ 10 kA • ηCD much smaller than in typical tokamak experiments – Due to poor orbit confinement of fast electrons

• Expected to improve significantly at higher Ip and Bt (need power supply upgrade) • Various diagnostics and analysis tools are being developed Sen, EXS+EXW+ICC Summary 25th IAEA FEC – Wave diagnostics, HX profile, E , flows, j profile, etc. 37 13-18 Oct., 2014 r Innovave Conﬁnement Concepts

15 papers

ü Tokamaks with novel magnec conﬁguraons

ü Advances in Field Reversed Conﬁguraons

ü Spherical Conﬁguraons other than tokamaks (HIT-SI)

• Advances in Spherical Tokamaks (TS4)

ü New ideas/concepts for fusion reactors

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 38 13-18 Oct., 2014 ICC PD/P5-1 S.Yu.Medvedev et al. Negave triangularity tokamak: stability limits and perspecves as fusion energy system

Power and parcle control is an issue in D-shaped (δ > 0 ) cross-secon tokamak with H-mode opmized for core confinement • Assess negave D to solve power and parcle exhaust problem! – Edge stability à different ELM regime (MHD stability) – Geometry of power handling area ß larger Rdiv – SOL flow à slower, wider SOL – Beer confinement: δ < 0 edge transport rather than core – Technical merits: HFS ECCD, lower Posive shear l =0.9: β <3.2 β=0.031; I =0.9; β =3.41 β =3.4;N toroidal mode number n=1 background magnec field for internal PF MHD stability N iN N 6 6 4 coils, larger pumping conductance from 4 4 3 • Beta limit against n=1 external q q 2 2 divertor 0 0 2 mode β >3 for opmized 0 0.5 1 0.5 1 1.5 N 1 1 1 > φ ∇ 0.5 Experimental proposals: φ 0

0.5 j proﬁles 0

-3

0.005 p 0.02 pedestal; high p’ in the 1st p' 0 0 -4 0 0.5 1 0.5 1 1.5 5 6 7 8 9 sqrt(ψ) R/R ω2/ω2=-1.0367e-05 0 A a26xx90_tcvpxx s =0.984 J /J=0.48 p' /p'=0.482 0.5 0 edge edge toroidal mode number n=5 • 1.5 n=0 stability to be migated 4 15 shear reversal -1 30 Normal displacement level lines; n=0; γ=95s 10 3 1.5 20

4 1 1 2 0.5 40 3 3 -1 0 0 Normal displacement level lines, γ = 12 s 1 1 -0.5 2 2 -1

/ 0 1 -1.5 1.5 || J -2 5 61 7 8 9 0 -1 0.5 0.5 -0.5

-1 0 1.5 -2 bootstrap -2 -0.5 -1 5 -3 -3 ballooning -1.5 0.5 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 -4 -1 -4 -2 α 5 6 7 8 9 ω2/ω2=-4.2702e-03 4 5 6 7 8 9 10 A 4 6 8 10 0.6 0.8 1 1.2 Control of Rotaonal Instability in FRC

• Toroidal spin-up in an FRC triggers a centrifugally- driven interchange-like mode n = 2.

• Suppression of Spontaneous ICC/P5-43, Asai Rotaon in a FRC by Magnezed Plasmoid Injecon in NUCTE device Sen, EXS+EXW+ICC Summary 25th IAEA FEC 40 13-18 Oct., 2014 Spherical Conﬁguraon

• Significant progress on Current Drive in HIT-SI • By increasing the frequency of the Imposed Dynamo Current Drive (IDCD) up to 68.5 kHz • Toroidal currents of 90 kA and current gains of nearly 4, a spheromak record, have been achieved. • dynamo current drive does not need plasma-generated fluctuaons -a stable equilibrium with profile control can be sustained with imposed fluctuaons ICC/P4-31, Victor • Extrapolaon to ITER - 80 kHz gives injector powers less than 10 MW and δB/B ≈ 10-4 indicang the effect on 1 Gwe Reactor Dynomak confinement may be acceptable. Jarboe

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 41 13-18 Oct., 2014 Concluding Remarks EXS , EXW: • Focused internaonal eﬀorts on ITER relevant issues has considerably advanced our understanding on ELM physics and disrupon phenomena

• Runaway migaon system not yet ﬁrmly established - but there are promising leads that need to be followed

• Alternate ELM migaon systems that do not require IVCs show considerable promise and may provide an aracve future opon for ITER

• New ideas on disrupon avoidance and control need validaon on larger machines

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 42 13-18 Oct., 2014 Concluding Remarks

ICC: • Heartening to see good scienﬁc progress in alternaves to the tokamak/stellarator approach - e.g. Spheromaks, FRCs ….

• Exploraon and development of such alternate schemes essenal for improving our chances of early fusion power – we need to promote more new ideas

Excing week - wealth of scienﬁc results - wonderful hospitality Thanks to our hosts and IAEA

Sen, EXS+EXW+ICC Summary 25th IAEA FEC 43 13-18 Oct., 2014