Farrokh Najmabadi | University of California, San Diego (original) (raw)

Papers by Farrokh Najmabadi

considered the following four questions: 1. What is the projected market for electrical energy pr... more considered the following four questions: 1. What is the projected market for electrical energy production in the next century? 2. What is fusion's potential for penetrating the energy market in the next century? 3. Is there a potential role for advanced fusion fuels? 4. What is fusion's potential for applications other than conventional power plants? The first two questions were considered together in one session. Questions 3 and 4 were each considered in separate sessions. The following sections summarize the context, session format, and major conclusions emerging from each session.

Proceedings of the 19th IEEE/IPSS Symposium on Fusion Engineering. 19th SOFE (Cat. No.02CH37231)

During the past ten years, the ARIES Team has studied a variety of tokamak power plants with diff... more During the past ten years, the ARIES Team has studied a variety of tokamak power plants with different degrees of extrapolation in plasma physics and technology from present database. Continuation of research has allowed us to apply lessons learned from each ARIES design to the next. The results of ARIES tokamak power plant studies provide a large body of data that highlight the tradeoffs and relative leverage of advanced plasma physics and fusion technology directions. Our results indicate that for the same plasma physics (e.g., firststability) and technology extrapolation, steady state operation is more attractive than pulsed-plasma operation. Dramatic improvement over first-stability operation can be obtained through either utilization of high-field magnets (e.g., hightemperature superconductors) or operation in advancedtokamak modes (e.g., reversed-shear). In particular, if full benefits of reversed-shear operation are realized, as is assumed in ARIES-AT, tokamak power plants will have a cost of electricity competitive with other sources of electricity. In technology area, emerging technologies such as advanced Baryon cycle, hightemperature superconductor, and advanced manufacturing techniques can improve the cost and attractiveness of fusion plants. For blankets, liquid breeder/coolants are the most attractive because most of neutron power is directly deposited in the coolant. This property can be exploited to arrive at a blanket design with a coolant outlet temperature higher than the structure temperature in the radiation zone. The high coolant temperature leads to a high thermal conversion efficiency (as in ARIES-ST and ARIES-AT blankets). The dual-cooled (He and LiPb) ARIES-ST blanket using ferritic steel structural material represents a near-term option for fusion systems and achieves a thermal efficiency of 45%. Development of high-performance SiC composites leads to the high-performance ARIES-AT blanket (SiC composite/LiPb coolant) that achieves 59% thermal conversion efficiency as well as the full potential safety and environmental features of fusion power.

Fusion Technology, 1996

ASSESSMENT OF OPTIONS FOR ATTRACTIVE COMMERCIAL AND DEMONSTRATION TOKAMAK FUSION POWER PLANTS* Fa... more ASSESSMENT OF OPTIONS FOR ATTRACTIVE COMMERCIAL AND DEMONSTRATION TOKAMAK FUSION POWER PLANTS* Farrokh Najmabadi Dept ... for physics operation regime as well engineering de-sign of various components (eg, choice of structural ma-terial, coolant ...

Fusion Technology, 1991

The ARIES research program is a multiinstitutional effort to develop several visions of the tokam... more The ARIES research program is a multiinstitutional effort to develop several visions of the tokamak as an attractive fusion reactor with enhanced economic, safety, and environmental features. The ARIES-I design is a DT-burning, 1000 MW(e) (net) reactor concept based on modest extrapolation from the present physics database and featuring advanced technology such as utilization of very high-field superconducting magnets and a low-activation blanket. This paper describes the helium-cooled ARIE8-I SiC composite low-activation blanket which contributes significantly to enhance thermal-hydraulics performance and safety features of the ARIES-I reactor design.

Fusion Science and Technology, 2005

The rep rate of an inertial fusion energy facility depends on the time-dependent response of the ... more The rep rate of an inertial fusion energy facility depends on the time-dependent response of the chamber environment between target ignitions. The fusion burn following the target ignition releases large quantities of energy into the chamber. This energy should be removed and the environment should be returned to a quiescent state so that the new fusion target can be positioned for the next cycle. Understanding the hydrodynamic transport of this energy through the chamber fill gas is essential because the multidimensional geometry effects become important on the long time scale, as the fluid interacts with the vessel wall containing various beam access ports. This interaction affects several different modes of the chamber species transport, including convection induced by shock waves and secondary flow, molecular diffusion, electron conductivity and radiation. In order to investigate these phenomena, we have developed SPARTAN code as an assembly of algorithms that were the most suitable for an accurate treatment of the computational problem, such as shock wave resolution and tracking, underlying flow physics and complex wall geometry. This study demonstrates that the geometry effects are critical in affecting the flow during the first 50 milliseconds following the target ignition. Thermal diffusion by molecules and free electrons has only a moderate effect in reducing the temperature extrema and is not sufficient to cool down the chamber to the equilibrium with the chamber wall within 100 ms. Radiation of the background plasma was identified as the only transport mechanism that has approached to this goal, making the chamber environment more suitable for inserting the next target.

Fusion Science and Technology, 2011

Fusion Science and Technology, 2005

CS studyour results are described in this paper. We have identified several promising stellarator... more CS studyour results are described in this paper. We have identified several promising stellarator configurations. High particle loss of these configurations is a critical issue. It appears that devices with an overall size similar to those envisioned for tokamak power plants are possible. A novel approach was developed in ARIES-CS in which the blanket at the critical areas of minimum stand-off is replaced by a highly efficient WC-based shield. In this manner, we have been able to reduce the minimum stand-off by ~20%-30% compared to a uniform radial build which was assumed in previous studies. Our examination of engineering options indicates that overall assembly and maintenance procedure plays a critical role in identifying acceptable engineering design and has a major impact on the optimization of a plasma/coil configuration.

Fusion Science & Technology, 2011

Fusion Science and Technology, 2013

Safety, Environmental Impact, and Economic Prospects of Nuclear Fusion, 1990

Controlled fusion energy is one of only a few energy sources available to mankind in the future. ... more Controlled fusion energy is one of only a few energy sources available to mankind in the future. Progress in fusion reactor technology and design is described for both magnetic and inertial confinement fusion energy. The projected economic prospects show fusion will be capital intensive and the historical trend is towards greater mass utilization efficiency and more competitive costs. Recent studies emphasizing safety and environmental advantages show that fusion’s competitive potential can be further enhanced by specific material and design choices. Fusion’s safety and environmental prospects appear to substantially exceed those of advanced fission and coal but will not be achieved automatically. A significant and directed technology effort is necessary. Typical parameters have been established for fusion reactors, and a tokamak at moderately high magnetic field (about 7 T on axis) in the first regime of MHD stability (s ≤ 3.5 I/aB) is closest to present experimental achievement. Directions to further improve economic and technological performance include the development of higher magnetic fields to lower the required plasma current and reactor size, improvement in the beta value in the second stable MHD regime to lower requirements of field and plasma current, and improvement in techniques for plasma current drive to efficiently achieve steady-state plasma operation. For inertial confinement, reactor studies are at an earlier stage but two essential requirements are a high-efficiency (> 10%) repetitively pulsed pellet driver capable of delivering up to 10 MJ of energy on target, and targets capable of yielding an energy gain (ratio of energy produced to energy on target) of 100.

Proceedings of Spie the International Society For Optical Engineering, Mar 1, 2010

Fusion Technology 1990, 1991

Physics of Fluids B: Plasma Physics, 1990

Recently, a set of two fluid equations has been derived that describes the transport of plasmas w... more Recently, a set of two fluid equations has been derived that describes the transport of plasmas with anisotropic pressure along the lines of force and is valid for collisional to weakly collisional regimes [Phys. Fluids 29, 463 (1986); 31, 3280 (1988)]. These transport equations coupled with Poisson’s equation are used to study the structure of the nonquasineutral transition region between the plasma and the material wall. This transition region is defined as the electric sheath region. The Bohm sheath criteria has been derived by various authors by examining behavior of the solution to the plasma-sheath equation. These investigations have shown that only for a supersonic flow would an increasing electric potential (in magnitude) exist in the sheath region to accelerate the ions further toward the wall. For subsonic flows, the behavior of the electric potential is purely oscillatory, which is not physical (electrons would trap in these potential wells and wipe them out). This work s...

Physics of Fluids B: Plasma Physics, 1991

The comments of Riemann and van den Berg represent a misinterpretation of what was presented by Z... more The comments of Riemann and van den Berg represent a misinterpretation of what was presented by Zawaideh et al. [Phys. Fluids B 2, 647 (1990)]. Namely, they claim that the oscillations in the electric field in the presheath region are a result of incorrect boundary conditions. To disprove their claim, both the sheath and presheath region with no assumption about quasineutrality have been solved self-consistently. To eliminate the issue of incorrect boundary conditions, a symmetrically confined plasma between two floating electrodes was considered. From the self-consistent solution, it is shown that, for subsonic flow, the oscillations in the electric field do exist in the absence of external particle sources and are not due to an incorrect boundary condition.

Fusion Science & Technology, 2013

ARIES-ACT1 power plant has been designed and configured to allow for rapid removal of full power ... more ARIES-ACT1 power plant has been designed and configured to allow for rapid removal of full power core sectors followed by disassembly in hot cells during maintenance operation. To achieve high availability and maintainablity of a fusion power plant, power core components of a sector, including inboard and outboard FW/blankets, upper and lower divertor, structural ring or high temperature shield were integrated into one replacement unit to minimize time comsuming handling inside plasma chamber. In this paper, the overall power core configuration and system integration, as well as the definitions of major power core components are described and main design features are highlighted.

Fusion Science and Technology, 2015

ARIES-ACT1 is the latest in a series of tokamak power plant designs that capitalize on the high-t... more ARIES-ACT1 is the latest in a series of tokamak power plant designs that capitalize on the high-temperature capabilities and attractive safety and environmental characteristics of SiC composites coupled with a self-cooled lead-lithium breeder. This combination offers both design simplicity and high performance, capable of operating at very high coolant outlet temperature in a moderately highpower-density device. Blankets are supported within a poloidally continuous He-cooled steel structural ring, which adds robustness and minimizes loads on the SiC modules. In order to withstand high local surface heat flux in the divertor (of the order of 14 MW/m 2 time averaged), a helium-cooled tungsten-alloy divertor was adopted. About 25% of the total ''high-grade'' heat is thus removed by helium, to be combined with the blanket heat in order to feed the power cycle. In addition to the in-vessel power-producing elements of the design, this paper also summarizes the key features and analysis of the vacuum vessel and power conversion system.

Fusion Science and Technology, 2013

considered the following four questions: 1. What is the projected market for electrical energy pr... more considered the following four questions: 1. What is the projected market for electrical energy production in the next century? 2. What is fusion's potential for penetrating the energy market in the next century? 3. Is there a potential role for advanced fusion fuels? 4. What is fusion's potential for applications other than conventional power plants? The first two questions were considered together in one session. Questions 3 and 4 were each considered in separate sessions. The following sections summarize the context, session format, and major conclusions emerging from each session.

Proceedings of the 19th IEEE/IPSS Symposium on Fusion Engineering. 19th SOFE (Cat. No.02CH37231)

During the past ten years, the ARIES Team has studied a variety of tokamak power plants with diff... more During the past ten years, the ARIES Team has studied a variety of tokamak power plants with different degrees of extrapolation in plasma physics and technology from present database. Continuation of research has allowed us to apply lessons learned from each ARIES design to the next. The results of ARIES tokamak power plant studies provide a large body of data that highlight the tradeoffs and relative leverage of advanced plasma physics and fusion technology directions. Our results indicate that for the same plasma physics (e.g., firststability) and technology extrapolation, steady state operation is more attractive than pulsed-plasma operation. Dramatic improvement over first-stability operation can be obtained through either utilization of high-field magnets (e.g., hightemperature superconductors) or operation in advancedtokamak modes (e.g., reversed-shear). In particular, if full benefits of reversed-shear operation are realized, as is assumed in ARIES-AT, tokamak power plants will have a cost of electricity competitive with other sources of electricity. In technology area, emerging technologies such as advanced Baryon cycle, hightemperature superconductor, and advanced manufacturing techniques can improve the cost and attractiveness of fusion plants. For blankets, liquid breeder/coolants are the most attractive because most of neutron power is directly deposited in the coolant. This property can be exploited to arrive at a blanket design with a coolant outlet temperature higher than the structure temperature in the radiation zone. The high coolant temperature leads to a high thermal conversion efficiency (as in ARIES-ST and ARIES-AT blankets). The dual-cooled (He and LiPb) ARIES-ST blanket using ferritic steel structural material represents a near-term option for fusion systems and achieves a thermal efficiency of 45%. Development of high-performance SiC composites leads to the high-performance ARIES-AT blanket (SiC composite/LiPb coolant) that achieves 59% thermal conversion efficiency as well as the full potential safety and environmental features of fusion power.

Fusion Technology, 1996

ASSESSMENT OF OPTIONS FOR ATTRACTIVE COMMERCIAL AND DEMONSTRATION TOKAMAK FUSION POWER PLANTS* Fa... more ASSESSMENT OF OPTIONS FOR ATTRACTIVE COMMERCIAL AND DEMONSTRATION TOKAMAK FUSION POWER PLANTS* Farrokh Najmabadi Dept ... for physics operation regime as well engineering de-sign of various components (eg, choice of structural ma-terial, coolant ...

Fusion Technology, 1991

The ARIES research program is a multiinstitutional effort to develop several visions of the tokam... more The ARIES research program is a multiinstitutional effort to develop several visions of the tokamak as an attractive fusion reactor with enhanced economic, safety, and environmental features. The ARIES-I design is a DT-burning, 1000 MW(e) (net) reactor concept based on modest extrapolation from the present physics database and featuring advanced technology such as utilization of very high-field superconducting magnets and a low-activation blanket. This paper describes the helium-cooled ARIE8-I SiC composite low-activation blanket which contributes significantly to enhance thermal-hydraulics performance and safety features of the ARIES-I reactor design.

Fusion Science and Technology, 2005

The rep rate of an inertial fusion energy facility depends on the time-dependent response of the ... more The rep rate of an inertial fusion energy facility depends on the time-dependent response of the chamber environment between target ignitions. The fusion burn following the target ignition releases large quantities of energy into the chamber. This energy should be removed and the environment should be returned to a quiescent state so that the new fusion target can be positioned for the next cycle. Understanding the hydrodynamic transport of this energy through the chamber fill gas is essential because the multidimensional geometry effects become important on the long time scale, as the fluid interacts with the vessel wall containing various beam access ports. This interaction affects several different modes of the chamber species transport, including convection induced by shock waves and secondary flow, molecular diffusion, electron conductivity and radiation. In order to investigate these phenomena, we have developed SPARTAN code as an assembly of algorithms that were the most suitable for an accurate treatment of the computational problem, such as shock wave resolution and tracking, underlying flow physics and complex wall geometry. This study demonstrates that the geometry effects are critical in affecting the flow during the first 50 milliseconds following the target ignition. Thermal diffusion by molecules and free electrons has only a moderate effect in reducing the temperature extrema and is not sufficient to cool down the chamber to the equilibrium with the chamber wall within 100 ms. Radiation of the background plasma was identified as the only transport mechanism that has approached to this goal, making the chamber environment more suitable for inserting the next target.

Fusion Science and Technology, 2011

Fusion Science and Technology, 2005

CS studyour results are described in this paper. We have identified several promising stellarator... more CS studyour results are described in this paper. We have identified several promising stellarator configurations. High particle loss of these configurations is a critical issue. It appears that devices with an overall size similar to those envisioned for tokamak power plants are possible. A novel approach was developed in ARIES-CS in which the blanket at the critical areas of minimum stand-off is replaced by a highly efficient WC-based shield. In this manner, we have been able to reduce the minimum stand-off by ~20%-30% compared to a uniform radial build which was assumed in previous studies. Our examination of engineering options indicates that overall assembly and maintenance procedure plays a critical role in identifying acceptable engineering design and has a major impact on the optimization of a plasma/coil configuration.

Fusion Science & Technology, 2011

Fusion Science and Technology, 2013

Safety, Environmental Impact, and Economic Prospects of Nuclear Fusion, 1990

Controlled fusion energy is one of only a few energy sources available to mankind in the future. ... more Controlled fusion energy is one of only a few energy sources available to mankind in the future. Progress in fusion reactor technology and design is described for both magnetic and inertial confinement fusion energy. The projected economic prospects show fusion will be capital intensive and the historical trend is towards greater mass utilization efficiency and more competitive costs. Recent studies emphasizing safety and environmental advantages show that fusion’s competitive potential can be further enhanced by specific material and design choices. Fusion’s safety and environmental prospects appear to substantially exceed those of advanced fission and coal but will not be achieved automatically. A significant and directed technology effort is necessary. Typical parameters have been established for fusion reactors, and a tokamak at moderately high magnetic field (about 7 T on axis) in the first regime of MHD stability (s ≤ 3.5 I/aB) is closest to present experimental achievement. Directions to further improve economic and technological performance include the development of higher magnetic fields to lower the required plasma current and reactor size, improvement in the beta value in the second stable MHD regime to lower requirements of field and plasma current, and improvement in techniques for plasma current drive to efficiently achieve steady-state plasma operation. For inertial confinement, reactor studies are at an earlier stage but two essential requirements are a high-efficiency (> 10%) repetitively pulsed pellet driver capable of delivering up to 10 MJ of energy on target, and targets capable of yielding an energy gain (ratio of energy produced to energy on target) of 100.

Proceedings of Spie the International Society For Optical Engineering, Mar 1, 2010

Fusion Technology 1990, 1991

Physics of Fluids B: Plasma Physics, 1990

Recently, a set of two fluid equations has been derived that describes the transport of plasmas w... more Recently, a set of two fluid equations has been derived that describes the transport of plasmas with anisotropic pressure along the lines of force and is valid for collisional to weakly collisional regimes [Phys. Fluids 29, 463 (1986); 31, 3280 (1988)]. These transport equations coupled with Poisson’s equation are used to study the structure of the nonquasineutral transition region between the plasma and the material wall. This transition region is defined as the electric sheath region. The Bohm sheath criteria has been derived by various authors by examining behavior of the solution to the plasma-sheath equation. These investigations have shown that only for a supersonic flow would an increasing electric potential (in magnitude) exist in the sheath region to accelerate the ions further toward the wall. For subsonic flows, the behavior of the electric potential is purely oscillatory, which is not physical (electrons would trap in these potential wells and wipe them out). This work s...

Physics of Fluids B: Plasma Physics, 1991

The comments of Riemann and van den Berg represent a misinterpretation of what was presented by Z... more The comments of Riemann and van den Berg represent a misinterpretation of what was presented by Zawaideh et al. [Phys. Fluids B 2, 647 (1990)]. Namely, they claim that the oscillations in the electric field in the presheath region are a result of incorrect boundary conditions. To disprove their claim, both the sheath and presheath region with no assumption about quasineutrality have been solved self-consistently. To eliminate the issue of incorrect boundary conditions, a symmetrically confined plasma between two floating electrodes was considered. From the self-consistent solution, it is shown that, for subsonic flow, the oscillations in the electric field do exist in the absence of external particle sources and are not due to an incorrect boundary condition.

Fusion Science & Technology, 2013

ARIES-ACT1 power plant has been designed and configured to allow for rapid removal of full power ... more ARIES-ACT1 power plant has been designed and configured to allow for rapid removal of full power core sectors followed by disassembly in hot cells during maintenance operation. To achieve high availability and maintainablity of a fusion power plant, power core components of a sector, including inboard and outboard FW/blankets, upper and lower divertor, structural ring or high temperature shield were integrated into one replacement unit to minimize time comsuming handling inside plasma chamber. In this paper, the overall power core configuration and system integration, as well as the definitions of major power core components are described and main design features are highlighted.

Fusion Science and Technology, 2015

ARIES-ACT1 is the latest in a series of tokamak power plant designs that capitalize on the high-t... more ARIES-ACT1 is the latest in a series of tokamak power plant designs that capitalize on the high-temperature capabilities and attractive safety and environmental characteristics of SiC composites coupled with a self-cooled lead-lithium breeder. This combination offers both design simplicity and high performance, capable of operating at very high coolant outlet temperature in a moderately highpower-density device. Blankets are supported within a poloidally continuous He-cooled steel structural ring, which adds robustness and minimizes loads on the SiC modules. In order to withstand high local surface heat flux in the divertor (of the order of 14 MW/m 2 time averaged), a helium-cooled tungsten-alloy divertor was adopted. About 25% of the total ''high-grade'' heat is thus removed by helium, to be combined with the blanket heat in order to feed the power cycle. In addition to the in-vessel power-producing elements of the design, this paper also summarizes the key features and analysis of the vacuum vessel and power conversion system.

Fusion Science and Technology, 2013