The ITER long-pulse and steady-state operations, foreseen in the ITER Research Plan [IRP, 2018 ITER technical report, ITR-18-03], are important steps towards exploration of reactor relevant tokamak operation and research. A few key research areas, such as the operational space with heating mixes and external current drive, access to target plasma states with profile tailoring and control, and...
The Large Helical Device (LHD) started its operation in 1998. One of the main objectives of the LHD project is the comprehensive study for the steady-state operation towards fusion reactors. Since the plasma current is not essential for LHD/stellarator devices to confine plasma, it is free from intensive efforts to drive and sustain plasma current. However, any other issues necessary for...
The Wendelstein 7-X stellarator has a super-conduction coil system, to prove the steady state capabilities of optimized stellarators. After different steps with a limiter (OP1, starting December 2015) and two runs with inertially cooled divertors (OP1.2a, OP1.1b, up to December 2018) the device was completed to fulfill the steady-state capabilities:
- A High-Heat Flux Divertor (HHF) for...
C. Holcomb for the DIII-D Team
Lawrence Livermore National Laboratory
DIII-D is focused on providing the scientific basis of high fusion performance, noninductively-sustained tokamak operation in ITER and pilot plants that will set the stage for commercial energy production. This presentation will highlight recent DIII-D research progress investigating core plasma scenarios ranging from...
Conventional tokamak high-confinement mode (H-mode) scenarios suffer from magnetohydrodynamic (MHD) instabilities and also depend on inductive current from the central solenoid to maintain the plasma current.
Advanced Tokamak (AT) scenarios that feature manipulated non-standard $q$-profiles not only promise to improve the stability and confinement of the discharge by eliminating some of the...
Fuel recycling is one of the key issues for long pulse operation for tokamaks. During long pulse operation in tokamaks, the accumulation of fuel particles on the first wall leads to a decreasing of wall pumping capability, and eventually the wall changes to outgassing from pumping due to the accumulation of fuel retention and the increasing of surface temperature. This enhances fuel recycling...
Effective control of fuel recycling and impurity is very key for achievement of long pulse and high-performance plasmas. High recycling and impurity concentration in the plasma would result in usually degradation of plasma confinement, and uncontrollable plasma density and disruptions. Some advanced vacuum and wall conditioning technologies, have been developed and widely used in EAST to...
Coordinated experiments on DIII-D and EAST are developing the physics basis of fully non-inductive, high poloidal-beta (βP) plasmas for application to steady-state high performance operating scenarios in ITER and Fusion Pilot Plants (FPPs). By optimizing at low plasma current and high plasma pressure, high-βP operation reduces disruption risks and requirements on external current drive, while...
The Advanced Tokamak concept represents a virtuous approach for a fusion reactor, combining improved confinement and stability with reduced heat flux and disruption severity, and the potential for fully stationary “always on” steady state operation to ease engineering and stability challenges. Self-consistent, integrated 1.5D simulations project new paths to a compact fusion pilot plant based...
The UK-based STEP programme aims to develop by 2040 a prototype reactor based on the spherical tokamak (ST) concept, thereby establishing a basis for developing commercial electricity production from fusion [1]. The compact design restricts the possible inductive flux, hence the flat-top plasma current will be entirely non-inductive, enabling long-pulse operation. External current drive will...
Existing magnetically confined plasma devices benefit from an extensive array of diagnostics, commensurate with the R&D function of these plasma devices. While increased diagnostic coverage, and access to information relevant to the plasma, first-wall components, and plasma-material interactions is always desired, the harsh nuclear environment of future fusion reactors is more likely to...
A model has been developed in the transport code ASTRA, which is capable of simulating advanced tokamak discharges, using the density and actuator setup as inputs. The model uses a reduced Gyro-Bohm based core transport, which does include simplified ITG and TEM mode contributions, to achieve a run time of only a few minutes for a full discharge. Edge transport is included via the use of a...
Avoidance of radiative collapse in high-density plasma has been attempted in the Large Helical Device (LHD) with a real-time control system based on a data-driven predictor model. The predictor model has been developed based on machine-learning techniques and high-density experiment data in LHD.
In stellarator-heliotron plasma, radiative collapse is one of the most critical issues that...
Demonstration of long-pulse plasma discharge is one of the critical issues in making fusion reactors true. In the Large Helical Device (LHD), we realized the duration time of 48 min with the electron density of 1.2e19 m-3, the plasma temperature of 2 keV, and the heating power of 1.2 MW using the ICRF and ECRF waves in hydrogen minority helium plasmas He(H). Several feedback systems kept the...
In long pulse experiments on ITER and DEMO, pellet injection will need to be used to fuel the core plasma and will likely be the sole actuator available for core density control. The reason is that gas injection will be largely ineffective due to its limited penetration depth towards the core. However, considering the expected 10% lost pellet rate during injection, feedback control will be...
It is estimated that long-pulse fusion devices may experience rates of net erosion and deposition of solid PFC (Plasma Facing Component) material of 10^3 – 10^5 kg/year, whatever the material used [1]. Even if the net erosion (wear) problem can be solved, the redeposition of so much material has the potential for major interference with operation, including disruptions due to so-called ‘UFOs’...
A fusion reactor based on a stellarator design has the advantage of easier access to long pulse scenarios. In fact, one of the main goals of Wendelstein 7-X (W7-X), the largest advanced stellarator in the world, is to demonstrate the steady-state capabilities of the stellarator line. Therefore, in the recent campaign, a number of experiments were performed in order to prepare long pulse...
Attempts using various particle control knobs have been made at Large Helical Device (LHD) to achieve steady-state plasmas in long pulse discharges. Divertor pumping is an important tool to control plasma density in fusion plasmas. In the divertor region, neutral particles shall be compressed and efficiently pumped out. In the LHD, the development of divertor pumping has been strongly...
The new lower tungsten divertor with horizontal and vertical targets has already been developed and installed in EAST for high-power and long-pulse operation in a full metal wall environment. The flexible magnetic configurations allow the position of lower outer strike point located on either horizontal or vertical target with different divertor configurations. Preliminary experimental results...
Plasma-facing materials (PFM) for next generation fusion devices like ITER will be submitted to intense fluxes of He and H isotopes (H, D and radioactive T transmutating as He). This is particularly significant for the divertor components, for which tungsten (W) is the first-choice material thanks to its low sputtering yield, low HI retention and high melting point. Plasma-wall interactions...
The first wall and divertor of a fusion power plant (FPP) will experience heat, particle, and neutron fluences well beyond what has been seen for any existing plasma confinement experiments, and beyond what will be seen in ITER. Each plasma facing component (PFC) must satisfy numerous, often competing, requirements. Among the many challenges that must be addressed in designing these...
In the current, and probably future, fusion devices, divertor is essential to achieve high performance plasma. In conjunction with the generic X-point configuration, its role is to absorb very intense heat flux located at the strike points, as well as keeping plasma impurities at a relatively low level.
For different reasons, such as melting temperature, erosion rate, He retention, tungsten...
There are two lower hybrid current drive (LHCD) systems in EAST with the operating frequencies at 2.45 GHz (source power of 4 MW) and 4.6 GHz (source power of 6 MW), which is the main electron heating and current drive (H&CD) tool. Hot spots issue and anomalous loss of LHCD efficiency at high density are the big challenges in long-pulse and high betap operation with high LH power. By upgrading...
In fusion devices, the first wall will be hit by lost fast ions and release large amounts of impurities into plasmas, which will affect the operation of experiments. Thus, the beam ions needs to be optimized for the safety and long-pulse operation in neutral beam injection (NBI) plasma.
In our research, the beam heating and loss, neutral beam current drive (NBCD) have been numerically...
An efficient current drive method should be developed for future tokamak reactors since bootstrap current is not able to soley fufill the plasma current required for enough confinement for burning plasma and current profile should be carefully controlled for stable operation. Lower Hybrid Current Drive (LHCD) has been typically considered as an current drive method of tokamak due to its...
Abstract—The operation goal of future fusion reactors, such as China Fusion Engineering Experimental Reactor (CFETR), International Thermonuclear Experimental Reactor (ITER) is to realize high-power long-pulse steady-state plasma. The conventional DC busbar occupies too much space, and the large inductance leads to voltage drop, increase EMI (Electromagnetic Interference) and no on-line...
To meet the requirements of continuous improvement of long pulse parameters, it is necessary to build a high-power converter power supply system, and optimize and analyze the power supply system based on the previous EAST (Experimental advanced superconducting Tokamak) and ITER (International Thermonuclear Experimental Reactor) fusion devices. This paper takes the power supply system of CRAFT...
Combined high fusion performance and Long Pulse Operation (LPO) is one of the key integration challenges for fusion energy development in magnetic devices. Solving this problem requires a comprehensive vision of the physical and engineering aspects to simultaneously increase the duration and performance of fusion. Significant progress has been made in tokamaks and stellarators, including very...
