Progress of HL-2A Experiment and HL-2M Program

Summary

This presentation reports on the experimental progress achieved on the HL-2A tokamak and the development of the HL-2M tokamak program at the Southwestern Institute of Physics (SWIP). It details advancements in high-βN operation, impurity transport and confinement, L-H transition physics, ELM mitigation, and MHD instabilities, alongside the design parameters, advanced divertor configurations, and first plasma milestones of the HL-2M device.

Slide 1: Title

Progress of HL-2A Experiment and HL-2M Program Xuru Duan on behalf of SWIP and collaborators Southwestern Institute of Physics, Chengdu, China 28th IAEA Fusion Energy Conference, 10-15th, May, 2021. FEC 2020 - 28th IAEA Fusion Energy Conference CNNC - China National Nuclear Corporation

Slide 2: Outline

Outline • Introduction • Progress of HL-2A Experiment – High βN operation – Impurity effect on transport and confinement – L-H transition and ELM mitigation – Energetic particle and MHD instability • HL-2M Program – Mission – First plasma – Auxiliary System • Summary

Slide 3: Introduction

Introduction Fusion research activities at SWIP: • Tokamak program (HL-2A & HL-2M) Including Engineering, Experiments, Theory & Simulation • Fusion reactor design • Fusion technology relevant activities: Fusion reactor materials R&D of key components (advanced divertor,….) R&D of ITER Procurement Packages at SWIP Helium-cooled solid breeder test blanket module (TBM) • First Wall & Shielding Blanket • Gas Injection & Glow Discharge Cleaning System • Magnet Support • Neutron Flux Monitoring • Langmuir Probe

Slide 4: HL-2A Tokamak

HL-2A Tokamak Parameters: • R: 1.65 m • a: 0.40 m • BT: 1.2~2.7 T • Configuration: Limiter, LSN divertor • Ip: 150 ~ 480 kA

Auxiliary heating: • ECRH/ECCD: 5 MW (6 X 68 GHz/0.5 MW/1 s, 2 X 140 GHz/1 MW/1 s) • NBI (tangential): 3 MW • LHCD: 2 MW (4/3.7 GHz/0.5 MW/2 s)

Fueling system (H2/D2): • Gas puffing (LFS, HFS, divertor) • Pellet injection (LFS, HFS) • SMBI (LFS, HFS) LFS: f = 1~80 Hz, pulse duration > 0.5 ms, gas pressure < 3 MPa

Slide 5: High-βN Operation

High-βN Operation • Integrated modeling for high βN exp. • Two NBI systems for high performance operation • Appropriate configuration and heating power deposition • Hybrid scenarios with double transport barriers achieved. • βN > 2 with duration ~ 15τE

Simulations by OMFIT for HL-2A exp. (W. Chen, this conference)

Slide 6: MHD Instabilities in High-βN Plasmas

MHD Instabilities in High-βN Plasmas • High-frequency coherent mode was induced by LHCD. Strong electrostatic fluctuation components, kθ ~ 1.4 cm⁻¹, can regulates particle and energy transport. • Low frequency global mode: coupling of destabilized internal and external modes with m/n=1/1 and m/n=3/1, respectively. -> Playing a critical role in the triggering onset of ELMs. • NTM: m/n=3/2, f ~ 25kHz (W. Chen, this conference)

Slide 7: Confinement Enhancement with Impurity Seeding

Confinement Enhancement with Impurity Seeding • H-mode confinement is improved by neon impurity seeding in the ELMy H-mode • Ion and electron heat flux exhibits distinct responses to the impurity seeding. • Electron and ion thermal transports are decoupled by the impurity seeding. • Decoupled ion thermal transport contributes to an improved energy confinement. (W.L. Zhong, this conference)

Slide 8: Impurity Transport and its Te Screening Effect

Impurity Transport and its Te Screening Effect • The evidences of impurity mode induced transport such as impurity density peaking factor (PF) are observed in argon injection experiment for the first time. • Theory predicted ITG screening effects on the transport are evidenced in the experiment. • The increment of R/Lne plays a key role in the decrement of PF and sustainment of slightly hollow profile of impurity ions. (M.K. Han, NF 2021)

Slide 9: Impurity Transport and TEM Turbulence

Impurity Transport and TEM Turbulence The strongly hollow impurity density profile observed in experiments arises from the combined effect of the expulsion of impurity by MHD instability in the plasma center and an inward impurity convection driven by TEM turbulence in the outer confinement region. Identification of the unstable modes by the spectra of the (a) growth rate and (b) real frequency. Soft X-ray reconstructions after the injection of Al impurity in discharges with (a) inner- and (b) outer-deposited ECRH. (D. Li, NF 2020)

Slide 10: Edge Velocity Shear for L-I-H Transition

Edge Velocity Shear for L-I-H Transition Threshold of Edge Velocity Shear for L-I-H Transitions • Velocity shear increases before the L-I and L-H transitions. Significant decrease of turbulence and increase of density gradient were observed at the L-H transition, mainly due to the pressure gradient term • L-H transition occurred only when the velocity shear exceeded some threshold, which is independent of the plasma density or the heating power. (A.S. Liang, NF 2020)

Slide 11: Effect of SMBI on L-H transition

Effect of SMBI on L-H transition • Mechanism of SMBI on L-H transition is demonstrated. Two dynamic processes:

GAM intensity increases with the turbulence intensity owing to the SMBI
Interaction between GAM and turbulence indicates that the turbulence is quenched by the GAM • Nonlinear regulation dynamics between the turbulence and shear flows is externally enhanced by SMBI. The enhancement plays a key role in facilitating the L-H transition.

Slide 12: Mechanism of ELM Mitigation by RMP

Mechanism of ELM Mitigation by RMP • Edge coherent oscillation (2–25 kHz), caused by the three-wave interaction of turbulence enhanced by RMP, is observed in the steep-gradient pedestal region of ELM mitigated H-mode plasmas. • The mode drives a significant outflows of particles and heat, providing a channel for continuous particle transport across the pedestal during the mitigation of ELM. • ECO caused by nonlinear wave coupling among turbulence • ECO induced continuous particle transport • Type I ELM mitigation with RMP

Slide 13: LBO Impurity Seeding for ELM Mitigation

LBO Impurity Seeding for ELM Mitigation • ELM mitigation and suppression has been achieved by LBO impurity seeding. • Pedestal turbulence is governed by the turbulence wavenumber shift process. • Dual effect of the impurity on the turbulence behavior interact in the pedestal, result in the turbulence enhancement during ELM mitigation and turbulence suppression during ELM suppression

Slide 14: Evidence of EPM Avalanche Dynamics

Evidence of EPM Avalanche Dynamics • In a successive chirping process (a strong single burst) t=618.60-618.76 ms: – The frequency of the mode sweeps down from 55 to 43 kHz; – Poloidal mode number changes from m=2 to 3, and then from 3 to 4. – Toroidal mode number keeps at n=1. • Additionally, radial propagation of EPM can also be proved by: – m=2 elements are dominant at first, then the mode propagates outward. At last, the m=4 elements are dominant. (L.M. Yu, submitted to NF 2021)

Slide 15: Influence of Large Magnetic Island Structures

Influence of Large Magnetic Island Structures Influence of large magnetic island structures on turbulence and quasi-coherent modes The influence of the rotating m/n = 2/1 magnetic islands: • Both the QCM (100–175 kHz) and broadband turbulence (40–100 kHz and 175–300 kHz) outside the island are significantly enhanced during the O-point phase in comparison with that of the X-point. • The QCM magnitude increases with the island size.

Slide 16: LBO for Disruption Mitigation

LBO for Disruption Mitigation • With LBO system, the avoidance of runaway current generation during disruptions has been successfully achieved. • With the impurity injection, strong m/n=2/1 mode was excited about 5 ms after LBO. • The ‘seed’ electrons for the runaway current are ‘killed’ by strong magnetic fluctuation. (Y.P. Zhang, this conference)

Slide 17: Disruption Predicted by Deep Learning

Disruption Predicted by Deep Learning • Disruption prediction algorithms developed based on deep learning. • Accuracy: 96.8%, by assembling convolutional neural network (CNN) and long short-term memory (LSTM) neural network. • Disruption alarms: 30 ms before current quench. (Z.Y. Yang, this conference)

Slide 18: Outline (HL-2M Focus)

Slide 19: HL-2M Mission

HL-2M Mission Addressing critical physics and technology issues for ITER and next-step fusion devices: • High performance, high βN scenarios compatible with flexible advanced divertor configurations, including Snow Flake (SF) and Tripod • Tests and validation of high heat flux plasma-facing components • Investigation of advanced plasma physics with high performance

Main Parameters: • Major radius R = 1.78 m • Minor radius a = 0.65 m • Plasma current Ip = 2.5 (3) MA • Aspect ratio R/a = 2.8 • Elongation Κ = 1.8-2 • Triangularity δ > 0.5 • Toroidal field BT = 2.2 (3) T • Flux swing ΔΦ = 14 Vs • Heating power 25 (27) MW (NBI 15 + EC 8 + LH 2(4))

Slide 20: Magnets System and Vacuum Vessel

Magnets System and Vacuum Vessel Demountable TF coils: – 20 TF coils – Maximum 3T at 190kA

PF coils: – 17 PF coils – Between VV and TFC

Vacuum Vessel: – Double-shell structure – Baking at 300 °C – 42 m³

Coils System of HL-2M & VV of HL-2M

Slide 21: Flexible Configurations

Flexible Configurations • Standard divertor with 14 MW/m² heat flux • Advanced divertor configurations with Mega-Ampere plasma • Heat flux width λq: 1~10mm Configurations displayed: – Standard divertor – Snow flakes (SF) – SF- – Tripod – Double null – NT

Slide 22: Advanced Scenarios with Ip≥1MA

Advanced Scenarios with Ip≥1MA In support of ITER pre-fusion phase operation (Hybrid and Steady State): • Hybrid scenario: Ip = 1.0~1.4MA, fG ~ 0.5 by combining NBCD with ECCD or ECCD+LHCD • In Hybrid regimes, the fractions of bootstrap current fBS and total non-inductive current fni are between 30%~45% and 70%~90%, respectively; βN can reach 2.5 with H98(y,2) ~ 1.1 • Full non-inductive regimes, such as the hybrid steady state regime and the regime with a reversed magnetic shear, can reach 1MA plasma current with fBS > 60%, H98(y,2) ~ 1.3, βN > 3.

Scenario parameter table comparison: Hybrid vs Full non-inductive across Ip, Bt, κ/δ, a/R, fG, heating power allocations, q95, βp, βN/4li, fBS/fni, Te0/Ti0, Wth, and H98(y,2).

Slide 23: High Performance at Ip=2.5MA / Bt=2.2T

High Performance at Ip=2.5MA / Bt=2.2T • High performance operation with βN ~ 3 (Pheat ~ 25MW(27MW)) • n(0) τ Ti(0) can reach about 10²⁰ m⁻³·s·keV • Central plasma temperature can reach around 10keV, with fG = 0.5

Waveform and profiles of plasma parameters in the regime of Ip=2.5MA / Bt=2.2T with Pheat=27MW and fG=0.5.

Slide 24: HL-2M First Plasma

HL-2M First Plasma • First plasma achieved in 2020. • Close-loop feedback control of plasma current and position was successfully implemented • Divertor configuration realized. First frame of tangential-view, equilibrium reconstruction at 70 ms (Shot: 901), and experimental waveforms.

Slide 25: H&CD and Diagnostic System

H&CD and Diagnostic System Auxiliary Heating: • NBI: Present 5MW | Plan 15MW • ECRH: Present 5MW | Plan 8MW • LHW: Present 2MW | Plan 4MW

Diagnostics: • Density: CO2, MW interferometers • Electron temperature: ECE, Soft X-ray • Radiation: Hα, bolometer, Hard X-ray… • Impurity: VUV… • Neutral gas pressure: Vacuum gauge… • Magnetic field: magnetic coils… • … CCD…

More diagnostics such as profile measurements (MSE, CXRS…), fast particles (SLIP, NPA, Neutron camera, FIDA…), turbulence measurement (BES, Doppler reflectometry…) and so on are in progress.

Slide 26: Summary

Summary HL-2A experiment: • High βN operation with DTB; • Impurity effect on transport and confinement (H-mode enhancement, impurity mode, TEM); • L-H transition and ELM mitigation (Velocity shear and SMBI on L-H, RMP and LBO on ELM mitigation) • Energetic particle and MHD instability (Interaction EP, MHD and turbulence, Disruption prediction and mitigation)

HL-2M tokamak, with R=1.78m, a=0.65m, BT=2.2~~3 T, Ip=2.5~~3MA, achieved its first plasma in 2020; Aiming at critical physics and technology issues for ITER & fusion reactors, provide the platform for: • High performance plasmas study for next-step fusion devices; • Flexible divertor configuration (snowflake, tripod, etc.); • Test and validation of PFC under high heat and particle flux; • Key issue such as mitigation of ELM, disruption, VDE, etc.

For further details relevant to this talk please refer to: • M. Jiang: EX/4 13/05, 14:20 • G.Z. Hao: TH/2 11/05, 11:48 • Z.Y. Yang: TH/7 15/05, 08:30 • N. Wu: P3 12/05, 08:30 • T. Long: P3 12/05, 08:30 • H.L. Du: P4 12/05, 14:00 • N. Zhang: P3 12/05, 08:30 • D. Li: P3 12/05, 08:30 • L. Xue: P2 11/05, 14:00 • Y.P. Zhang: P3 12/05, 08:30 • Y. Liu: P3 12/05, 08:30 • G.L. Xiao: P3 12/05, 08:30 • L.M. Yu: P3 12/05, 08:30 • W.L. Zhong: P3 12/05, 08:30 • L.G. Zang: P3 12/05, 08:30 • J. Wen: P3 12/05, 08:30 • W. Chen: P3 12/05, 08:30

Slide 28: Conclusion

Thank you all for your attention!