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Chamber propagation physics for heavy ion fusion

Description: Chamber transport is an important area of study for heavy ion fusion. Final focus and chamber-transport are high leverage areas providing opportunities to significantly decrease the cost of electricity from a heavy ion fusion power plant. Chamber transport in two basic regimes is under consideration. In the low chamber density regime ({approx_lt}0.003 torr), ballistic or nearly-ballistic transport is used. Partial beam neutralization has been studied to offset the effects of beam stripping. In the high chamber density regime ({approx_gt}.1 torr), two transport modes (pinched transport and channel transport) are under investigation. Both involve focusing the beam outside the chamber then transporting it at small radius ({approx} 2 mm). Both high chamber density modes relax the constraints on the beam quality needed from the accelerator which will reduce the driver cost and the cost of electricity.
Date: September 1, 1995
Creator: Callahan, D.A.
Partner: UNT Libraries Government Documents Department

Beam charge and current neutralization of high-charge-state heavy ions

Description: High-charge-state heavy-ions may reduce the accelerator voltage and cost of heavy-ion inertial fusion drivers, if ways can be found to neutralize the space charge of the highly charged beam ions as they are focused to a target in a fusion chamber. Using 2-D Particle-In- Cell simulations, we have evaluated the effectiveness of two different methods of beam neutralization: (1) by redistribution of beam charge in a larger diameter, preformed plasma in the chamber, and (2), by introducing a cold-electron-emitting source within the beam channel at the beam entrance into the chamber. We find the latter method to be much more effective for high-charge-state ions.
Date: October 29, 1997
Creator: Logan, B.G. & Callahan, D.A.
Partner: UNT Libraries Government Documents Department

Transport of a partially-neutralized ion beam in a heavy-ion fusion reactor chamber

Description: In a heavy-ion driven, inertial confinement fusion power plant, a space-charge dominated beam of heavy ions must be transported through a reactor chamber and focused on a 2-3 mm spot at the target. The spot size at the target is determined by the beam emittance and space charge, plus chromatic aberrations in the focusing lens system and errors in aiming the beam. The gain of the ICF capsule depends on the focal spot size. We are investigating low density, nearly-ballistic transport using an electromagnetic, r-z particle-in-cell code. Even at low density (n {approx} 5 {times} 10{sup 13} cm{sup {minus}3}), beam stripping may be important. To offset the effects of stripping and reduce the space charge, the beam is partially charge neutralized via a pre-formed plasma near the chamber entrance. Additional electrons for charge neutralization come from ionization of the background gas by the beam. Simulations have shown that stripping can greatly increase the spot size; however, partial neutralization can offset most of this increase.
Date: April 25, 1995
Creator: Callahan, D.A. & Langdon, A.B.
Partner: UNT Libraries Government Documents Department

Manipulation of high-current pulses for heavy-ion fusion

Description: For efficient induction-driven heavy-ion fusion, the current profile along a pulse must be modified in a non-selfsimilar manner between the accelerator and the target. In the accelerator, the pulse should have a duration of at least 50 ns in order to make efficient use of the induction cores, and the current should by nearly uniform along the pulse to minimize the aperture. In contrast, the optimal current profile on target consists of a main pulse of about 10 ns preceded by a longer low-current `foot.` This pulse-shape manipulation must be carried out at the final pulse energy (5-10 GeV for 200 amu ions) in the presence of a large nonlinear longitudinal space-charge field. A straightforward method is presented here for doing the required pulse shaping. Induction-ceU voltages are generated using idealized beam profiles both in the accelerator and on target, and they are verified and checked for error sensitivity using the fluid/envelope code CIRCE.
Date: October 28, 1996
Creator: Sharp, W.M.; Callahan, D.A.; Griedman, A. & Grote, D.P.
Partner: UNT Libraries Government Documents Department

Longitudinal dynamics and stability in beams for heavy-ion fusion

Description: Successful transport of induction-driven beams for heavy-ion fusion requires careful control of the longitudinal space charge. The usual control technique is the periodic application of time-varying longitudinal electric fields, called `ears`, that on the average, balance the space-charge field. this technique is illustrated using a fluid/envelope code CIRCE, and the sensitivity of the method to errors in these ear fields is illustrated. The possibility that periodic ear fields also excite the longitudinal instability is examined.
Date: January 5, 1996
Creator: Sharp, W.M.; Callahan, D.A. & Grote, D.P.
Partner: UNT Libraries Government Documents Department

Physics design and scaling of recirculating induction accelerators: from benchtop prototypes to drivers

Description: Recirculating induction accelerators (recirculators) have been investigated as possible drivers for inertial fusion energy production because of their potential cost advantage over linear induction accelerators. Point designs were obtained and many of the critical physics and technology issues that would need to be addressed were detailed. A collaboration involving Lawrence Livermore National Laboratory and Lawrence Berkeley National Laboratory researchers is now developing a small prototype recirculator in order to demonstrate an understanding of nearly all of the critical beam dynamics issues that have been raised. We review the design equations for recirculators and demonstrate how, by keeping crucial dimensionless quantities constant, a small prototype recirculator was designed which will simulate the essential beam physics of a driver. We further show how important physical quantities such as the sensitivity to errors of optical elements (in both field strength and placement), insertion/extraction, vacuum requirements, and emittance growth, scale from small-prototype to driver-size accelerator.
Date: February 6, 1996
Creator: Barnard, J.J.; Cable, M.D. & Callahan, D.A.
Partner: UNT Libraries Government Documents Department

Heavy ion fusion experiments at LLNL

Description: We review the status of the experimental campaign being carried out at Lawrence Livermore National Laboratory, involving scaled investigations of the acceleration and transport of space-charge dominated heavy ion beams. The ultimate goal of these experiments is to help lay the groundwork for a larger scale ion driven inertial fusion reactor, the purpose of which is to produce inexpensive and clean electric power.
Date: February 6, 1996
Creator: Barnard, J.J.; Cable, M.D. & Callahan, D.A.
Partner: UNT Libraries Government Documents Department

Analyses in Support of Z-IFE LLNL Progress Report for FY-05

Description: The FY04 LLNL study of Z-IFE [1] proposed and evaluated a design that deviated from SNL's previous baseline design. The FY04 study included analyses of shock mitigation, stress in the first wall, neutronics and systems studies. In FY05, the subject of this report, we build on our work and the theme of last year. Our emphasis continues to be on alternatives that hold promise of considerable improvements in design and economics compared to the base-line design. Our key results are summarized here.
Date: October 17, 2005
Creator: Moir, R W; Abbott, R P; Callahan, D A; Latkowski, J F; Meier, W R & Reyes, S
Partner: UNT Libraries Government Documents Department

Plastic ablator ignition capsule design for the National Ignition Facility

Description: The National Ignition Campaign, tasked with designing and fielding targets for fusion ignition experiments on the National Ignition Facility (NIF), has carried forward three complementary target designs for the past several years: a beryllium ablator design, a plastic ablator design, and a high-density carbon or synthetic diamond design. This paper describes current simulations and design optimization to develop the plastic ablator capsule design as a candidate for the first ignition attempt on NIF. The trade-offs in capsule scale and laser energy that must be made to achieve a comparable ignition probability to that with beryllium are emphasized. Large numbers of 1-D simulations, meant to assess the statistical behavior of the target design, as well as 2-D simulations to assess the target's susceptibility to Rayleigh-Taylor growth are presented.
Date: December 1, 2009
Creator: Clark, D S; Haan, S W; Hammel, B A; Salmonson, J D; Callahan, D A & Town, R P
Partner: UNT Libraries Government Documents Department

Progress in Heavy Ion Target Capsule and Hohlraum Design

Description: Progress in heavy ion target design over the past few years has focused on relaxing the target requirements for the driver and for target fabrication. We have designed a plastic (CH) ablator capsule that is easier to fabricate and fill than the beryllium ablator we previously used. In addition, 2-d Rayleigh-Taylor instability calculations indicate that this capsule can tolerate ablator surface finishes up to ten times rougher than the NIF specification. We have also explored the trade-off between surface roughness and yield as a method for finding the optimum capsule. We have also designed two new hohlraums: a ''hybrid'' target and a large angle, distributed radiator target. The hybrid target allows a beam spot radius of almost 5 mm while giving gain of 55 from 6.7 MJ of beam energy in integrated Lasnex calculations. To achieve the required symmetry with the large beam spot, internal shields were used in the target to control the P2 and P4 asymmetry. The large-angle, distributed radiator target is a variation on the distributed radiator target that allows large beam entrance angles (up to 24 degrees). Integrated calculations have produced 340 MJ from 6.2 MJ of beam energy in a design that is not quite optimal. In addition, we have done a simple scaling to understand the peak ion beam power required to compress fuel for fast ignition using a short pulse laser.
Date: May 8, 2002
Creator: Callahan, D.A.; Herrmann, M.C. & Tabak, M.
Partner: UNT Libraries Government Documents Department

Correction of longitudinal errors in accelerators for heavy-ion fusion

Description: Longitudinal space-charge waves develop on heavy-ion inertial-fusion pulse from initial mismatches or from inappropriately timed or shaped accelerating voltages. Without correction, waves moving backward along the beam can grow due to the interaction with their resistively retarded image fields, eventually degrading the longitudinal emittance. A simple correction algorithm is presented here that uses a time-dependent axial electric field to reverse the direction of backward-moving waves. The image fields then damp these forward-moving waves. The method is demonstrated by fluid simulations of an idealized inertial-fusion driver, and practical problems in implementing the algorithm are discussed.
Date: June 10, 1993
Creator: Sharp, W. M.; Callahan, D. A.; Barnard, J. J.; Langdon, A. B. & Fessenden, T. J.
Partner: UNT Libraries Government Documents Department

Advances in Target Design for Heavy-Ion Fusion

Description: Over the past few years, the emphasis in heavy ion target design has moved from the distributed radiator target to the 'hybrid' target because the hybrid target allows a larger beam focal spot than the distributed radiator ({approx} 5 mm radius rather than {approx} 2 mm radius). The larger spot relaxes some of the requirements on the driver, but introduces some new target physics issues. Most notable is the use of shine shields and shims in the hohlraum to achieve symmetry rather than achieving symmetry by beam placement. The shim is a thin layer of material placed on or near the capsule surface to block a small amount of excess radiation. While we have been developing this technique for the heavy ion hybrid target, the technique can be used in any indirect drive target. We have begun testing the concept of a shim to improve symmetry using a double-ended z-pinch hohlraum on the Sandia Z-machine. Experiments using shimmed thin wall capsules have shown that we can reverse the sign of a P{sub 2} asymmetry and significantly reduce the size of a P{sub 4} asymmetry. These initial experiments demonstrate the concept of a shim as another method for controlling early time asymmetries in ICF capsules.
Date: June 21, 2005
Creator: Callahan, D A; Tabak, M; Bennett, G R; Cuneo, M E; Vesey, R A; Nikroo, A et al.
Partner: UNT Libraries Government Documents Department

3D particle simulation of beams using the WARP code: Transport around bends

Description: WARP is a discrete-particle simulation program which was developed for studies of space charge dominated ion beams. It combines features of an accelerator code and a particle-in-cell plasma simulation. The code architecture, and techniques employed to enhance efficiency, are briefly described. Current applications are reviewed. In this paper we emphasize the physics of transport of three-dimensional beams around bends. We present a simple bent-beam PIC algorithm. Using this model, we have followed a long, thin beam around a bend in a simple racetrack system (assuming straight-pipe self-fields). Results on beam dynamics are presented; no transverse emittance growth (at mid-pulse) is observed. 11 refs., 5 figs.
Date: November 30, 1990
Creator: Friedman, A.; Grote, D.P.; Callahan, D.A.; Langdon, A.B. (Lawrence Livermore National Lab., CA (USA)) & Haber, I. (Naval Research Lab., Washington, DC (USA))
Partner: UNT Libraries Government Documents Department

Modeling Chamber Transport for Heavy-Ion Fusion

Description: In a typical thick-liquid-wall scenario for heavy-ion fusion (HIF), between seventy and two hundred high-current beams enter the target chamber through ports and propagate about three meters to the target. Since molten-salt jets are planned to protect the chamber wall, the beams move through vapor from the jets, and collisions between beam ions and this background gas both strip the ions and ionize the gas molecules. Radiation from the preheated target causes further beam stripping and gas ionization. Due to this stripping, beams for heavy-ion fusion are expected to require substantial neutralization in a target chamber. Much recent research has, therefore, focused on beam neutralization by electron sources that were neglected in earlier simulations, including emission from walls and the target, photoionization by the target radiation, and pre-neutralization by a plasma generated along the beam path. When these effects are included in simulations with practicable beam and chamber parameters, the resulting focal spot is approximately the size required by a distributed radiator target.
Date: October 1, 2002
Creator: Sharp, W. M.; Callahan, D. A.; Tabak, M.; Yu, S. S.; Peterson, P. F.; Welch, D. R. et al.
Partner: UNT Libraries Government Documents Department

Overview of WARP, a particle code for Heavy Ion Fusion

Description: The beams in a Heavy Ion beam driven inertial Fusion (HIF) accelerator must be focused onto small spots at the fusion target, and so preservation of beam quality is crucial. The nonlinear self-fields of these space-charge-dominated beams can lead to emittance growth; thus a self-consistent field description is necessary. We have developed a multi-dimensional discrete-particle simulation code, WARP, and are using it to study the behavior of HIF beams. The code`s 3d package combines features of an accelerator code and a particle-in-cell plasma simulation, and can efficiently track beams through many lattice elements and around bends. We have used the code to understand the physics of aggressive drift-compression in the MBE-4 experiment at Lawrence Berkeley Laboratory (LBL). We have applied it to LBL`s planned ILSE experiments, to various ``recirculator`` configurations, and to the study of equilibria and equilibration processes. Applications of the 3d package to ESQ injectors, and of the r, z package to longitudinal stability in driver beams, are discussed in related papers.
Date: February 22, 1993
Creator: Friedman, A.; Grote, D. P.; Callahan, D. A.; Langdon, A. B. & Haber, I.
Partner: UNT Libraries Government Documents Department

Using Laser Entrance Hole Shields to Increase Coupling Efficiency in Indirect Drive Ignition Targets for the National Ignition Facility (NIF)

Description: Coupling efficiency, the ratio of the capsule absorbed energy to the driver energy, is a key parameter in ignition targets. The hohlraum originally proposed for NIF coupled {approx}11% of the absorbed laser energy to the capsule as x-rays. We describe here a second generation of hohlraum target which has higher coupling efficiency, {approx}16%. Because the ignition capsule's ability to withstand 3D effects increases rapidly with absorbed energy, the additional energy can significantly increase the likelihood of ignition. The new target includes laser entrance hole (LEH) shields as a principal method for increasing coupling efficiency while controlling symmetry in indirect-drive ICF. The LEH shields are high Z disks placed inside the hohlraum to block the capsule's view of the cold LEHs. The LEH shields can reduce the amount of laser energy required to drive a target to a given temperature via two mechanisms: (1) keeping the temperature high near the capsule pole by putting a barrier between the capsule and the pole, (2) because the capsule pole does not have a view of the cold LEHs, good symmetry requires a shorter hohlraum with less wall area. Current integrated simulations of this class of target couple 140 kJ of x-rays to a capsule out of 865 kJ of absorbed laser energy and produce {approx}10 MJ of yield. In the current designs, which are not completely optimized, the addition of the LEH shields saves {approx}95 kJ of energy (about 10%) over hohlraums without LEH shields.
Date: November 3, 2005
Creator: Callahan, D A; Amendt, P A; Dewald, E L; Haan, S W; Hinkel, D E; Izumi, N et al.
Partner: UNT Libraries Government Documents Department

Design Calculations For NIF Convergent Ablator Experiments

Description: The NIF convergent ablation tuning effort is underway. In the early experiments, we have discovered that the design code simulations over-predict the capsule implosion velocity and shock flash rhor, but under-predict the hohlraum x-ray flux measurements. The apparent inconsistency between the x-ray flux and radiography data implies that there are important unexplained aspects of the hohlraum and/or capsule behavior.
Date: October 25, 2011
Creator: Olson, R E; Hicks, D G; Meezan, N B; Callahan, D A; Landen, O L; Jones, O S et al.
Partner: UNT Libraries Government Documents Department

Update on specifications for NIF ignition targets and their rollup into an error budget

Description: Targets intended to produce ignition on NIF are being simulated and the simulations are used to set specifications for target fabrication. Recent design work has focused on designs that assume only 1.0 MJ of laser energy instead of the previous 1.6 MJ. To perform with less laser energy, the hohlraum has been redesigned to be more efficient than previously, and the capsules are slightly smaller. The main-line hohlraum design now has a SiO2 foam fill, a wall of U-Dy-Au, and shields mounted between the capsule and the laser entrance holes. Two capsule designs are being considered. One has a graded doped Be(Cu) ablator, and the other graded doped CH(Ge). Both can perform acceptably with recently demonstrated ice layer quality, and with recently demonstrated outer surface roughness. Smoothness of the internal interfaces may be an issue for the Be(Cu) design, and it may be necessary either to polish partially coated shells or to improve process control so that the internal layers are smoother. Complete tables of specifications are being prepared for both targets, to be completed this fiscal year. All the specifications are being rolled together into an error budget indicating adequate margin for ignition with the new designs.
Date: July 11, 2005
Creator: Haan, S W; Herrmann, M C; Amendt, P A; Callahan, D A; Dittrich, T R; Edwards, M J et al.
Partner: UNT Libraries Government Documents Department

3D Simulations of the NIF Indirect Drive Ignition Target Design

Description: The radiation hydrodynamics code Hydra is used to quantify the sensitivity of different NIF ignition point designs to several 3D effects. Each of the 48 NIF quads is included in the calculations and is allowed to have different power. With this model they studied the effect on imploded core symmetry of discrete laser spots (as opposed to idealized azimuthally-averaged rings) and random variations in laser power.
Date: January 5, 2010
Creator: Jones, O S; Milovich, J L; Callahan, D A; Edwards, M J; Landen, O L; Salmonson, J D et al.
Partner: UNT Libraries Government Documents Department

Simulation of chamber transport for heavy-ion fusion

Description: Beams for heavy-ion fusion (HIF) are expected to require substantial neutralization in a target chamber. Present targets call for higher beam currents and smaller focal spots than most earlier designs, leading to high space-charge fields. Collisional stripping by the background gas expected in the chamber further increases the beam charge. Simulations with no electron sources other than beam stripping and background-gas ionization show an acceptable focal spot only for high ion energies or for currents far below the values assumed in recent HIF power-plant scenarios. Much recent research has, therefore, focused on beam neutralization by electron sources that were neglected in earlier simulations, including emission from walls and the target, photoionization by radiation from the target, and pre-neutralization by a plasma generated along the beam path. The simulations summarized here indicate that these effects can significantly reduce the beam focal-spot size.
Date: October 4, 2002
Creator: Sharp, W.M.; Callahan, D.A.; Tabak, M.A.; Yu, S.S.; Peterson, P.F.; Rose, D.V. et al.
Partner: UNT Libraries Government Documents Department

Realistic modeling of chamber transport for heavy-ion fusion

Description: Transport of intense heavy-ion beams to an inertial-fusion target after final focus is simulated here using a realistic computer model. It is found that passing the beam through a rarefied plasma layer before it enters the fusion chamber can largely neutralize the beam space charge and lead to a usable focal spot for a range of ion species and input conditions.
Date: May 1, 2003
Creator: Sharp, W.M.; Grote, D.P.; Callahan, D.A.; Tabak, M.; Henestroza, E.; Yu, S.S. et al.
Partner: UNT Libraries Government Documents Department

A 3d particle simulation code for heavy ion fusion accelerator studies

Description: We describe WARP, a new particle-in-cell code being developed and optimized for ion beam studies in true geometry. We seek to model transport around bends, axial compression with strong focusing, multiple beamlet interaction, and other inherently 3d processes that affect emittance growth. Constraints imposed by memory and running time are severe. Thus, we employ only two 3d field arrays ({rho} and {phi}), and difference {phi} directly on each particle to get E, rather than interpolating E from three meshes; use of a single 3d array is feasible. A new method for PIC simulation of bent beams follows the beam particles in a family of rotated laboratory frames, thus straightening'' the bends. We are also incorporating an envelope calculation, an (r, z) model, and 1d (axial) model within WARP. The BASIS development and run-time system is used, providing a powerful interactive environment in which the user has access to all variables in the code database. 10 refs., 3 figs.
Date: June 8, 1990
Creator: Friedman, A.; Bangerter, R.O.; Callahan, D.A.; Grote, D.P.; Langdon, A.B. (Lawrence Livermore National Lab., CA (USA)) & Haber, I. (Naval Research Lab., Washington, DC (USA))
Partner: UNT Libraries Government Documents Department

Modeling the longitudinal wall impedance instability in heavy ion beams using an R-Z PIC code

Description: The effects of the longitudinal wall impedance instability in a heavy ion beam are of great interest for heavy ion fusion drivers. We are studying this instability using the R-Z thread of the WARP PIC code. We describe the code and our model of the impedance due to the accelerating modules of the induction LINAC as a resistive wall. We present computer simulations which illustrate this instability. 2 refs., 2 figs., 1 tab.
Date: February 22, 1991
Creator: Callahan, D.A.; Langdon, A.B.; Friedman, A.; Grote, D.P. (Lawrence Livermore National Lab., CA (USA)) & Haber, I. (Naval Research Lab., Washington, DC (USA))
Partner: UNT Libraries Government Documents Department