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Modeling space charge in beams for heavy-ion fusion

Description: A new analytic model is presented which accurately estimates the radially averaged axial component of the space-charge field of an axisymmetric heavy-ion beam in a cylindrical beam pipe. The model recovers details of the field near the beam ends that are overlooked by simpler models, and the results compare well to exact solutions of Poisson`s equation. Field values are shown for several simple beam profiles and are compared with values obtained from simpler models.
Date: May 2, 1995
Creator: Sharp, W. M.
Partner: UNT Libraries Government Documents Department

Effects of longitudinal space charge in beams for heavy-ion fusion

Description: A new analytic model is presented that accurately estimates the radially averaged axial component of the space-charge field of an axisymmetric heavy-ion beam in a cylindrical beam pipe. The model recovers details of the field near the beam ends that are overlooked by simpler models, and the results compare well to exact solutions of Poisson`s equation. Field values are shown for several simple beam profiles and are compared with values obtained from simpler models. The model has been implemented in the fluid/envelope code CIRCE and used to study longitudinal confinement in beams with a variety of axial profiles. The effects of errors in the longitudinal-control fields are presented.
Date: December 27, 1995
Creator: Sharp, W.M.; Friedman, A. & Grote, D.P.
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

Effects of space charge in beams for heavy ion fusion

Description: A new analytic model is presented that accurately estimates the radially averaged axial component of the space-charge field of an axisymmetric heavy-ion beam in a cylindrical beam pipe. The model recovers details of the field near the beam ends that are overlooked by simpler models, and the results compare well to exact solutions of Poisson`s equation. Field values are shown for several simple beam profiles and are compared with values obtained from simpler models. The model has been implemented in the fluid/envelope code CIRCE and used to study longitudinal confinement in beams with a variety of axial profiles. The effects of errors in the longitudinal-control fields are presented.
Date: September 1, 1995
Creator: Sharp, W.M.; Friedman, 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

Accelerator waveform synthesis and longitudinal beam dynamics in a small induction recirculator

Description: A recirculating induction accelerator requires accelerating waveforms that produce current amplification and provide bunch length control throughout the acceleration process. Current amplification occurs because of both an increase in the beam velocity and a shortening of the length of the beam bunch. The pulsed acceleration and control waveforms seen by the beam change in time as the pulse duration shortens. For one acceleration cycle of the small recirculator, each accelerating gap is driven by a burst of 15 pulses. As the beam gains velocity, the time interval between pulses shortens from approximately 20 to 10 {mu}sec. A zero-dimensional design code REC is used to develop the accelerator wave forms. An envelope/fluid code CIRCE and a 3-D particle code WARP3d are used to confirm the REC design and study the effects of errors. The authors find that acceleration errors can lead to space-charge waves launched at the bunch ends that strongly affect or even destroy the current pulse shape. The relation between the rate of longitudinal compression and the velocity of space charge waves is studied.
Date: April 1995
Creator: Fessenden, T.J.; Grote, D.P. & Sharp, W.M.
Partner: UNT Libraries Government Documents Department

Steering algorithms for a small recirculating heavy-ion accelerator

Description: Beam-steering algorithms are proposed for a small recirculating induction accelerator being built at the Lawrence Livermore National Laboratory. The principal problem is that the transverse position and velocity of the beam must be inferred from capacitive position monitors, and this determination is complicated by the limited probe resolution and by the lattice errors within steering modules. The fluid/envelope code CIRCE is used to evaluate these algorithms.
Date: November 7, 1997
Creator: Sharp, W.M.; Grote, D.P. & Hemandez, G.W.
Partner: UNT Libraries Government Documents Department

Acceleration schedules for a recirculating heavy-ion accelerator

Description: Recent advances in solid-state switches have made it feasible to design programmable, high-repetition-rate pulsers for induction accelerators. These switches could lower the cost of recirculating induction accelerators, such as the ''small recirculator'' at Lawrence Livermore National Laboratory (LLNL), by substantially reducing the number of induction modules. Numerical work is reported here to determine what effects the use of fewer pulsers at higher voltage would have on the beam quality of the LLNL small recirculator. Lattices with different numbers of pulsers are examined using the fluid/envelope code CIRCE, and several schedules for acceleration and compression are compared for each configuration. For selected schedules, the phase-space dynamics is also studied using the particle-in-cell code WARP3d.
Date: May 1, 2002
Creator: Sharp, W. M. & Grote, D. P.
Partner: UNT Libraries Government Documents Department

Simulation of a Standing-Wave Free-Electron Laser

Description: The standing-wave free-electron laser (FEL) differs from a conventional linear-wiggler microwave FEL in using irises along the wiggler to form a series of standing-wave cavities and in reaccelerating the beam between cavities to maintain the average energy. The device has been proposed for use in a two-beam accelerator (TBA) because microwave power can be extracted more effectively than from a traveling-wave FEL. The standing-wave FEL is modeled in the continuum limit by a set of equations describing the coupling of a one-dimensional beam to a TE{sub 01} rectangular-waveguide mode. Analytic calculations and numerical simulations are used to determine the time variation of the reacceleration field and the prebunching required so that the final microwave energy is the same in all cavities. The microwave energy and phase are found to be insensitive to modest spreads in the beam energy and phase and to errors in the reacceleration field and the beam current, but the output phase appears sensitive to beam-energy errors and to timing jitter.
Date: September 1, 1990
Creator: Sharp, W.M.; Sessler, A.M.; Whittum, D.H. & Wurtele, J.S.
Partner: UNT Libraries Government Documents Department

Phase stability of a standing-wave free-electron laser

Description: The standing-wave free-electron laser (FEL) differs from a conventional linear-wiggler microwave FEL in using irises along the wiggler to form a series of standing-wave cavities and in reaccelerating the beam between cavities to maintain the average energy. The device has been proposed for use in a two-beam accelerator because microwave power can be extracted more effectively than from a traveling-wave FEL. A simplified numerical simulation indicates that, with appropriate prebunching, the standing-wave FEL can produce an output signal that is effectively the same in all cavities. However, changes in the beam energy of less than 1% are found to introduce unacceptably large fluctuations of signal phase along the device. Analytic calculations and single-particle simulations are used here to show that the phase fluctuations result from beam synchrotron motion in the initial signal field, and an approximate analytic expression for the signal phase is derived. Numerical simulations are used to illustrate the dependence of phase fluctuations on the beam prebunching, the beam-current axial profile, and the initial signal amplitude.
Date: January 1, 1991
Creator: Sharp, W.M.; Rangarajan, G.; Sessler, A.M. & Wurtele, J.S.
Partner: UNT Libraries Government Documents Department

Initiation of long, free-standing Z-discharges by CO2 laser gas heating

Description: High current discharge channels can neutralize both current and space charge of very intense ion beams. Therefore they are considered as an interesting alternative for the final focus and beam transport in a heavy ion beam fusion reactor. At the GSI accelerator facility, 50 cm long, stable, free-standing discharge channels with currents in excess of 40 kA in 2 to 25 mbar ammonia (NH{sub 3}) gas are investigated for heavy ion beam transport studies. The discharges are initiated by a CO{sub 2} laser pulse along the channel axis before the discharge is triggered. Resonant absorption of the laser, tuned to the {nu}{sub 2} vibration of the ammonia molecule, causes strong gas heating. Subsequent expansion and rarefaction of the gas prepare the conditions for a stable discharge to fulfill the requirements for ion beam transport. This paper describes the laser-gas interaction and the discharge initiation mechanism. We report on the channel stability and evolution, measured by fast shutter and streak imaging techniques. The rarefaction of the laser heated gas is studied by means of a hydrocode simulation.
Date: April 19, 2004
Creator: Nieman, C.; Tauschwitz, A.; Penache, D.; Neff, S.; Knobloch, R.; Birkner, R. et al.
Partner: UNT Libraries Government Documents Department

Impact of beam transport method on chamber and driver design for heavy ion inertial fusion energy

Description: In heavy ion inertial fusion energy systems, intense beams of ions must be transported from the exit of the final focus magnet system through the target chamber to hit millimeter spot sizes on the target. In this paper, we examine three different modes of beam propagation: neutralized ballistic transport, assisted pinched transport, and self-pinched transport. The status of our understanding of these three modes is summarized, and the constraints imposed by beam propagation upon the chamber environment, as well as their compatibility with various chamber and target concepts, are considered. We conclude that, on the basis of our present understanding, there is a reasonable range of parameter space where beams can propagate in thick-liquid wall, wetted-wall, and dry-wall chambers.
Date: December 1, 2002
Creator: Rose, D.V.; Welch, D.R.; Olson, C.L.; Yu, S.S.; Neff, S. & Sharp, W.M.
Partner: UNT Libraries Government Documents Department

Progress Toward Source-to-Target Simulation

Description: Source-to-target simulation of an accelerator provides a thorough check on the consistency of the design as well as a detailed understanding of the beam behavior. Issues such as envelope mis-match and emittance growth can be examined in a self-consistent manner, including the details of accelerator transitions, long-term transport, and longitudinal compression. The large range in scales, from centimeter-scale transverse beam size and applied field scale-length, to meter-scale beam length, to kilometer-scale accelerator length, poses a significant computational challenge. The ever-increasing computational power that is becoming available through massively parallel computers is making such simulation realizable. This paper discusses the progress toward source-to-target simulation using the WARP particle-in-cell code. Representative examples are shown, including 3-D, along-term transport simulations of Integrated Research Experiment (IRE) scale accelerators.
Date: March 1, 2000
Creator: Grote, D.P.; Friedman, A.; Craig, G.D.; Sharp, W.M. & Haber, I.
Partner: UNT Libraries Government Documents Department

Elise plans and progress

Description: Elise is a heavy ion induction linear accelerator that will demonstrate beam manipulations required in a driver for inertial fusion energy. With a line charge density similar to that of heavy ion drivers, Elise will accelerate a {ge} 1 gs beam pulse of K{sup +} ions from an initial energy of 2 MeV to a final energy {ge} 5 MeV. In the present design, the Elise electrostatic quadrupoles (ESQ) will have a 2.33 cm radius aperture operating at {+-}59 kV. The half-lattice periods range from 21 cm to 31 cm. The entire machine will be approximately 30 m long, half of that is the induction accelerator and the remaining half is the injector (including the Marx generator) and the matching section. Elise will be built in a way that allows future expansion into the full ILSE configuration, therefore it will have an array of four ESQ focusing channels capable of transporting up to a total of 3.2 A of beam current. Elise will also have an active alignment system with an alignment tolerance of less than 0.1 mm. Initially, only one beam channel will be used during nominal Elise operation. At the currently expected funding rate, the construction time will be 4.75 years, with FY95 being an extra year for research and development before construction. Total project cost is estimated to be $25.9 M including contingency cost.
Date: August 1, 1995
Creator: Kwan, J.W.; Bangerter, R.O.; Faltens, A.; Lee, E.P.; Peters, C.; Reginato, L.L. et al.
Partner: UNT Libraries Government Documents Department

Developing acceleration schedules for NDCX-II

Description: The Virtual National Laboratory for Heavy-Ion Fusion Science is developing a physics design for NDCX-II, an experiment to study warm dense matter heated by ions near the Bragg-peak energy. Present plans call for using about thirty induction cells to accelerate 30 nC of Li+ ions to more than 3 MeV, followed by neutralized drift-compression. To heat targets to useful temperatures, the beam must be compressed to a millimeter-scale radius and a duration of about 1 ns. An interactive 1-D particle-in-cell simulation with an electrostatic field solver, acceleration-gap fringe fields, and a library of realizable analytic waveforms has been used for developing NDCX-II acceleration schedules. Axisymmetric simulations with WARP have validated this 1-D model and have been used both to design transverse focusing and to compensate for injection non-uniformities and radial variation of the fields. Highlights of this work are presented here.
Date: August 1, 2008
Creator: Sharp, W.M.; Friedman, A.; Grote, D.P.; Henestroza, E.; Leitner, M.A. & Waldron, W.L.
Partner: UNT Libraries Government Documents Department

Standing-Wave Free-Electron Laser Two-Beam Accelerator

Description: A free-electron laser (FEL) two-beam accelerator (TBA) is proposed, in which the FEL interaction takes place in a series of drive cavities, rather than in a waveguide. Each drive cavity is 'beat-coupled' to a section of the accelerating structure. This standing-wave TBA is investigated theoretically and numerically, with analyses included of microwave extraction, growth of the FEL signal through saturation, equilibrium longitudinal beam dynamics following saturation, and sensitivity of the microwave amplitude and phase to errors in current and energy. It is found that phase errors due to current jitter are substantially reduced from previous versions of the TBA. Analytic scalings and numerical simulations are used to obtain an illustrative TBA parameter set.
Date: February 1, 1991
Creator: Sessler, Andrew M.; Whittum, D.H.; Wurtele, Jonathan S.; Sharp, W.M. & Makowski, M.A.
Partner: UNT Libraries Government Documents Department

Progress Toward Source-to-Target Simulation

Description: Source-to-target simulation of an accelerator provides a thorough check on the consistency of the design as well as a detailed understanding of the beam behavior. Issues such as envelope mismatch and emittance growth can be examined in a self-consistent manner, including the details of accelerator transitions, long-term transport, and longitudinal compression. The large range in scales, from centimeter-scale transverse beam size and applied field scale-length, to meter-scale beam length, to kilometer-scale accelerator length, poses a significant computational challenge. The ever-increasing computational power that is becoming available through massively parallel computers is making such simulation realizable. This paper discusses the progress toward source-to-target simulation using the WARP particle-in-cell code. Representative examples are shown, including 3-D, long-term transport simulations of Integrated Research Experiment (IRE) scale accelerators.
Date: March 1, 2000
Creator: Grote, D.P.; Friedman, A.; Craig, G.D.; Sharp, W.M. & Harber, I.
Partner: UNT Libraries Government Documents Department

SIMULATING AN ACCELERATION SCHEDULE FOR NDCX-II

Description: The Virtual National Laboratory for Heavy-Ion Fusion Science is developing a physics design for NDCX-II, an experiment to study warm dense matter heated by ions. Present plans call for using 34 induction cells to accelerate 45 nC of Li+ ions to more than 3 MeV, followed by neutralized drift-compression. To heat targets to the desired temperatures, the beam must be compressed to a millimeter-scale radius and a duration of about 1 ns. A novel NDCX-II acceleration schedule has been developed using an interactive one-dimensional particle-in-cell simulation ASP to model the longitudinal physics and axisymmetric WARP simulations to validate the 1-D model and add transverse focusing. Three-dimensional Warp runs have been used recently to study the sensitivity to misalignments in the focusing solenoids.
Date: May 1, 2009
Creator: Sharp, W.M.; Friedman, A.; Grote, D.P.; Henestroza, E.; Leitner, M.A. & Waldron, W.L.
Partner: UNT Libraries Government Documents Department

Chamber transport of ''foot'' pulses for heavy-ion fusion

Description: Indirect-drive targets for heavy-ion fusion must initially be heated by ''foot'' pulses that precede the main heating pulses by tens of nanoseconds. These pulses typically have a lower energy and perveance than the main pulses, and the fusion-chamber environment is different from that seen by later pulses. The preliminary particle-in-cell simulations of foot pulses here examine the sensitivity of the beam focusing to ion-beam perveance, background-gas density, and pre-neutralization by a plasma near the chamber entry port.
Date: February 20, 2002
Creator: Sharp, W.M.; Callahan-Miller, D.A.; Tabak, M.; Yu, S.S. & Peterson, P.F.
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

Simulation of integrated beam experiment designs

Description: Simulation of designs of an Integrated Beam Experiment (IBX) class accelerator have been carried out. These simulations are an important tool for validating such designs. Issues such as envelope mismatch and emittance growth can be examined in a self-consistent manner, including the details of injection, accelerator transitions, long-term transport, and longitudinal compression. The simulations are three-dimensional and time-dependent, and begin at the source. They continue up through the end of the acceleration region, at which point the data is passed on to a separate simulation of the drift compression. Results are be presented.
Date: June 11, 2004
Creator: Grote, D.P. & Sharp, W.M.
Partner: UNT Libraries Government Documents Department