Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Here, the potential of the hybrid scenario (first developed as an advanced inductive scenario for high fluence) as a regime for high-beta, steady-state plasmas is demonstrated on the DIII-D tokamak. These experiments show that the beneficial characteristics of hybrids, namely safety factor ≥1 with low central magnetic shear, high stability limits and excellent confinement, are maintained when strong central current drive (electron cyclotron and neutral beam) is applied to increase the calculated non-inductive fraction to ≈100% (≈50% bootstrap current). The best discharges achieve normalized beta of 3.4, IPB98(y,2) confinement factor of 1.4, surface loop voltage of 0.01 V, and nearly equal electron and ion temperatures at low collisionality. A zero-dimensional physics model shows that steady-state hybrid operation with Qfus ~ 5 is feasible in FDF and ITER. The advantage of the hybrid scenario as an Advanced Tokamak regime is that the external current drive can be deposited near the plasma axis where the efficiency is high; additionally, good alignment between the current drive and plasma current profiles is not necessary as the poloidal magnetic flux pumping self-organizes the current density profile in hybrids with an m/n=3/2 tearing mode.
High-beta, Steady-state Hybrid Scenario on DIII-D.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Here, the potential of the hybrid scenario (first developed as an advanced inductive scenario for high fluence) as a regime for high-beta, steady-state plasmas is demonstrated on the DIII-D tokamak. These experiments show that the beneficial characteristics of hybrids, namely safety factor ≥1 with low central magnetic shear, high stability limits and excellent confinement, are maintained when strong central current drive (electron cyclotron and neutral beam) is applied to increase the calculated non-inductive fraction to ≈100% (≈50% bootstrap current). The best discharges achieve normalized beta of 3.4, IPB98(y,2) confinement factor of 1.4, surface loop voltage of 0.01 V, and nearly equal electron and ion temperatures at low collisionality. A zero-dimensional physics model shows that steady-state hybrid operation with Qfus ~ 5 is feasible in FDF and ITER. The advantage of the hybrid scenario as an Advanced Tokamak regime is that the external current drive can be deposited near the plasma axis where the efficiency is high; additionally, good alignment between the current drive and plasma current profiles is not necessary as the poloidal magnetic flux pumping self-organizes the current density profile in hybrids with an m/n=3/2 tearing mode.
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Here, the potential of the hybrid scenario (first developed as an advanced inductive scenario for high fluence) as a regime for high-beta, steady-state plasmas is demonstrated on the DIII-D tokamak. These experiments show that the beneficial characteristics of hybrids, namely safety factor ≥1 with low central magnetic shear, high stability limits and excellent confinement, are maintained when strong central current drive (electron cyclotron and neutral beam) is applied to increase the calculated non-inductive fraction to ≈100% (≈50% bootstrap current). The best discharges achieve normalized beta of 3.4, IPB98(y,2) confinement factor of 1.4, surface loop voltage of 0.01 V, and nearly equal electron and ion temperatures at low collisionality. A zero-dimensional physics model shows that steady-state hybrid operation with Qfus ~ 5 is feasible in FDF and ITER. The advantage of the hybrid scenario as an Advanced Tokamak regime is that the external current drive can be deposited near the plasma axis where the efficiency is high; additionally, good alignment between the current drive and plasma current profiles is not necessary as the poloidal magnetic flux pumping self-organizes the current density profile in hybrids with an m/n=3/2 tearing mode.
Advances in the Physics Basis of the Hybrid Scenario on DIII-D.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 10
Book Description
Recent experiments on DIII-D have extended the hybrid scenario towards the burning plasma regime by incorporating strong electron heating, low torque injection, and edge localized mode (ELM) suppression. Hybrid performance projecting to Q e"10 on ITER at q95=3.1 has been achieved in plasmas with reduced ion/electron temperature ratio or Mach number. Confinement is decreased relative to previous hybrid results, consistent with measurements of increased turbulence at low and intermediate wavenumbers. For the first time, large type-I ELMs have been completely suppressed in a hybrid plasma at q95=3.6 by applying edge resonant magnetic perturbations (RMPs) with toroidal mode number n=3. Additionally, high performance hybrid and steady-state scenario operation has been demonstrated with reduced frequency of wall conditioning with a>95% graphite plasma-facing wall.
Publisher:
ISBN:
Category :
Languages : en
Pages : 10
Book Description
Recent experiments on DIII-D have extended the hybrid scenario towards the burning plasma regime by incorporating strong electron heating, low torque injection, and edge localized mode (ELM) suppression. Hybrid performance projecting to Q e"10 on ITER at q95=3.1 has been achieved in plasmas with reduced ion/electron temperature ratio or Mach number. Confinement is decreased relative to previous hybrid results, consistent with measurements of increased turbulence at low and intermediate wavenumbers. For the first time, large type-I ELMs have been completely suppressed in a hybrid plasma at q95=3.6 by applying edge resonant magnetic perturbations (RMPs) with toroidal mode number n=3. Additionally, high performance hybrid and steady-state scenario operation has been demonstrated with reduced frequency of wall conditioning with a>95% graphite plasma-facing wall.
The Franco-American Convention Relative to Double Taxation
Analysis and Modeling of DIII-D Hybrid Discharges and Their Extrapolation to ITER.
Author: M. R. Wade
Publisher:
ISBN:
Category :
Languages : en
Pages : 6
Book Description
Recent experiments on tokamaks around the world [1-5] have demonstrated discharges with moderately high performance in which the q-profile remains stationary, as measured by the motional Stark effect diagnostic, for periods up to several {tau}{sub R}. Hybrid discharges are characterize by q{sub min} {approx} 1, high {beta}{sub N}, and good confinement. These discharges have been termed hybrid because of their intermediate nature between that of an ordinary H-mode and advanced tokamak discharges. They form an attractive scenario for ITER as the normalized fusion performance ({beta}{sub N}H{sub 89P}/q{sub 95}{sup 2}) is at or above that for the ITER baseline Q{sub fus} = 10 scenario, even for q{sub 95} as high as 4.6. The startup phase is thought to be crucial to the ultimate evolution of the hybrid discharge. An open question is how hybrid discharges achieve and maintain their stationary state during the initial startup phase. To investigate this aspect of hybrid discharges, we have used the CORSICA code to model the early stages of a discharge. Results clearly indicate that neoclassical current evolution alone is insufficient to account for the time evolution of the q-profile and that an addition of non-inductive current source must be incorporated into the model to reproduce the experimental time history. We include non-inductive neutral beam and bootstrap current sources in the model, and investigate the difference between simulations with these sources and the experimentally inferred q-profile. Further, we have made preliminary estimates of the spatial structure of the current needed to bring the simulation and experiment into agreement. This additional non-inductive source has not been tied to any physical mechanism as yet. We present these results and discuss the implications for hybrid startup on ITER.
Publisher:
ISBN:
Category :
Languages : en
Pages : 6
Book Description
Recent experiments on tokamaks around the world [1-5] have demonstrated discharges with moderately high performance in which the q-profile remains stationary, as measured by the motional Stark effect diagnostic, for periods up to several {tau}{sub R}. Hybrid discharges are characterize by q{sub min} {approx} 1, high {beta}{sub N}, and good confinement. These discharges have been termed hybrid because of their intermediate nature between that of an ordinary H-mode and advanced tokamak discharges. They form an attractive scenario for ITER as the normalized fusion performance ({beta}{sub N}H{sub 89P}/q{sub 95}{sup 2}) is at or above that for the ITER baseline Q{sub fus} = 10 scenario, even for q{sub 95} as high as 4.6. The startup phase is thought to be crucial to the ultimate evolution of the hybrid discharge. An open question is how hybrid discharges achieve and maintain their stationary state during the initial startup phase. To investigate this aspect of hybrid discharges, we have used the CORSICA code to model the early stages of a discharge. Results clearly indicate that neoclassical current evolution alone is insufficient to account for the time evolution of the q-profile and that an addition of non-inductive current source must be incorporated into the model to reproduce the experimental time history. We include non-inductive neutral beam and bootstrap current sources in the model, and investigate the difference between simulations with these sources and the experimentally inferred q-profile. Further, we have made preliminary estimates of the spatial structure of the current needed to bring the simulation and experiment into agreement. This additional non-inductive source has not been tied to any physical mechanism as yet. We present these results and discuss the implications for hybrid startup on ITER.
PROGRESS TOWARD FULLY NONINDUCTIVE, HIGH BETA DISCHARGES IN DIII-D.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
OAK-B135 Advanced Tokamak (AT) research in DIII-D focuses on developing a scientific basis for steady-state, high performance operation. For optimal performance, these experiments routinely operate with[beta] above the n= 1 no-wall limit, enabled by active feed-back control. The ideal wall[beta] limit is optimized by modifying the plasma shape, current and pressure profile. Present DIII-D AT experiments operate with f[sub BS][approx] 50%-60%, with a long-term goal of[approx] 90%. Additional current is provided by neutral beam and electron cyclotron current drive, the latter being localized well away from the magnetic axis ([rho][approx] 0.4-0.5). Guided by integrated modeling, recent experiments have produced discharges with[beta][approx] 3%, [beta][sub N][approx] 3, f[sub BS][approx] 55% and noninductive fraction f[sub NI][approx] 90%. Additional control is anticipated using fast wave current drive to control the central current density.
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
OAK-B135 Advanced Tokamak (AT) research in DIII-D focuses on developing a scientific basis for steady-state, high performance operation. For optimal performance, these experiments routinely operate with[beta] above the n= 1 no-wall limit, enabled by active feed-back control. The ideal wall[beta] limit is optimized by modifying the plasma shape, current and pressure profile. Present DIII-D AT experiments operate with f[sub BS][approx] 50%-60%, with a long-term goal of[approx] 90%. Additional current is provided by neutral beam and electron cyclotron current drive, the latter being localized well away from the magnetic axis ([rho][approx] 0.4-0.5). Guided by integrated modeling, recent experiments have produced discharges with[beta][approx] 3%, [beta][sub N][approx] 3, f[sub BS][approx] 55% and noninductive fraction f[sub NI][approx] 90%. Additional control is anticipated using fast wave current drive to control the central current density.
Scientific and Technical Aerospace Reports
Production and Stability of High-beta DIII-D Discharges with Reversed Magnetic Shear
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Plasma configurations with reversed magnetic shear have been proposed for steady-state tokamak operation since the plasma profiles can be made consistent with good confinement, high bootstrap current fraction, and stability at very high beta. The stability of reversed magnetic shear discharges with beta up to 11% has previously been demonstrated in DIII-D. Reversed magnetic shear (RMS) refers to a safety factor profile, q([rho]), which is a non-monotonic function of minor radius, [rho]. The magnetic shear S[equivalent-to] ([rho]/q) dq/d[rho] is negative within the plasma core and positive at the edge. When S
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Plasma configurations with reversed magnetic shear have been proposed for steady-state tokamak operation since the plasma profiles can be made consistent with good confinement, high bootstrap current fraction, and stability at very high beta. The stability of reversed magnetic shear discharges with beta up to 11% has previously been demonstrated in DIII-D. Reversed magnetic shear (RMS) refers to a safety factor profile, q([rho]), which is a non-monotonic function of minor radius, [rho]. The magnetic shear S[equivalent-to] ([rho]/q) dq/d[rho] is negative within the plasma core and positive at the edge. When S
Systems Approaches to Nuclear Fusion Reactors
Author: Frederick B. Marcus
Publisher: Springer Nature
ISBN: 3031177118
Category : Science
Languages : en
Pages : 484
Book Description
This book offers an overall review, applying systems engineering and architecture approaches, of the design, optimization, operation and results of leading fusion experiments. These approaches provide a unified means of evaluating reactor design. Methodologies are developed for more coherent construction or evaluation of fusion devices, associated experiments and operating procedures. The main focus is on tokamaks, with almost all machines and their important results being integrated into a systems design space. Case studies focus on DIII-D, TCV, JET, WEST, the fusion reactor prototype ITER and the EU DEMO concept. Stellarator, Mirror and Laser inertial confinement experiments are similarly analysed, including reactor implications of breakeven at NIF. The book examines the engineering and physics design and optimization process for each machine, analysing their performance and major results achieved, thus establishing a basis for the improvement of future machines. The reader will gain a broad historical and up-to-date perspective of the status of nuclear fusion research from both an engineering and physics point of view. Explanations are given of the computational tools needed to design and operate successful experiments and reactor-relevant machines. This book is aimed at both graduate students and practitioners of nuclear fusion science and engineering, as well as those specializing in other fields demanding large and integrated experimental equipment. Systems engineers will obtain valuable insights into fusion applications. References are given to associated complex mathematical derivations, which are beyond the scope of this book. The general reader interested in nuclear fusion will find here an accessible summary of the current state of nuclear fusion.
Publisher: Springer Nature
ISBN: 3031177118
Category : Science
Languages : en
Pages : 484
Book Description
This book offers an overall review, applying systems engineering and architecture approaches, of the design, optimization, operation and results of leading fusion experiments. These approaches provide a unified means of evaluating reactor design. Methodologies are developed for more coherent construction or evaluation of fusion devices, associated experiments and operating procedures. The main focus is on tokamaks, with almost all machines and their important results being integrated into a systems design space. Case studies focus on DIII-D, TCV, JET, WEST, the fusion reactor prototype ITER and the EU DEMO concept. Stellarator, Mirror and Laser inertial confinement experiments are similarly analysed, including reactor implications of breakeven at NIF. The book examines the engineering and physics design and optimization process for each machine, analysing their performance and major results achieved, thus establishing a basis for the improvement of future machines. The reader will gain a broad historical and up-to-date perspective of the status of nuclear fusion research from both an engineering and physics point of view. Explanations are given of the computational tools needed to design and operate successful experiments and reactor-relevant machines. This book is aimed at both graduate students and practitioners of nuclear fusion science and engineering, as well as those specializing in other fields demanding large and integrated experimental equipment. Systems engineers will obtain valuable insights into fusion applications. References are given to associated complex mathematical derivations, which are beyond the scope of this book. The general reader interested in nuclear fusion will find here an accessible summary of the current state of nuclear fusion.
Steady State Scenario Development with Elevated Minimum Safety Factor on DIII-D.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
On DIII-D (Luxon 2005 Fusion Sci. Technol. 48 828), a high [beta] scenario with minimum safety factor (qmin) near 1.4 has been optimized with new tools and shown to be a favourable candidate for long pulse or steady state operation in future devices. Furthermore, the new capability to redirect up to 5 MW of neutral beam injection (NBI) from on- to off-axis improves the ability to sustain elevated qmin with a less peaked pressure profile. The observed changes increase the ideal magnetohydrodynamics (MHD) n = 1 mode [beta]N limit thus providing a path forward for increasing the noninductive current drive fraction by operating at high [beta]N. Quasi-stationary discharges free of tearing modes have been sustained at [beta]N = 3.5 and [beta]T = 3.6% for two current profile diffusion timescales (about 3 s) limited by neutral beam duration. The discharge performance has normalized fusion performance expected to give fusion gain Q H"5 in a device the size of ITER. Analysis of the poloidal flux evolution and current drive balance show that the loop voltage profile is almost relaxed even with 25% of the current driven inductively, and qmin remains elevated near 1.4. Our observations increase confidence that the current profile will not evolve to one unstable to a tearing mode. In preliminary tests a divertor heat flux reduction technique based on producing a radiating mantle with neon injection appears compatible with this operating scenario. 0D model extrapolations suggest it may be possible to push this scenario up to 100% noninductive current drive by raising [beta]N. Similar discharges with qmin = 1.5-2 were susceptible to tearing modes and off-axis fishbones, and with qmin> 2 lower normalized global energy confinement time is observed.
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
On DIII-D (Luxon 2005 Fusion Sci. Technol. 48 828), a high [beta] scenario with minimum safety factor (qmin) near 1.4 has been optimized with new tools and shown to be a favourable candidate for long pulse or steady state operation in future devices. Furthermore, the new capability to redirect up to 5 MW of neutral beam injection (NBI) from on- to off-axis improves the ability to sustain elevated qmin with a less peaked pressure profile. The observed changes increase the ideal magnetohydrodynamics (MHD) n = 1 mode [beta]N limit thus providing a path forward for increasing the noninductive current drive fraction by operating at high [beta]N. Quasi-stationary discharges free of tearing modes have been sustained at [beta]N = 3.5 and [beta]T = 3.6% for two current profile diffusion timescales (about 3 s) limited by neutral beam duration. The discharge performance has normalized fusion performance expected to give fusion gain Q H"5 in a device the size of ITER. Analysis of the poloidal flux evolution and current drive balance show that the loop voltage profile is almost relaxed even with 25% of the current driven inductively, and qmin remains elevated near 1.4. Our observations increase confidence that the current profile will not evolve to one unstable to a tearing mode. In preliminary tests a divertor heat flux reduction technique based on producing a radiating mantle with neon injection appears compatible with this operating scenario. 0D model extrapolations suggest it may be possible to push this scenario up to 100% noninductive current drive by raising [beta]N. Similar discharges with qmin = 1.5-2 were susceptible to tearing modes and off-axis fishbones, and with qmin> 2 lower normalized global energy confinement time is observed.