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Computational support for ITS, ECTOR, PIXY, and PHERMEX. Annual report

Description: This report describes calculations carried out in the past year to assist in the design and understanding of experiments on the ITS, ECTOR, PIXY and PHERMEX machines at LANL. The main results are summarized as follows. ITS: Transport calculations were carried out for Milestone 4, modeling the beam all the way from the cathode surface to the target, and gave good agreement with measurements. The LAMDA transport code was upgraded to compute the focusing effect of the accelerating gaps more accurately, and to remove some approximations in the treatment of space-charge. The code is currently being used in the analysis of the Milestone 5 BBU experiments. ECTOR and PIXY: Beam focusing in the gas cell was studied in detail. The focal length was found to progressively shorten during the pulse. As a result, the minimum spot-size was significantly smaller than the time-averaged value. One may be able to exploit this using shaped converters. The beam distribution at the converter was used as input for the MCNP radiation transport code to obtain a radiographic spot-size. The result agrees reasonably well with experimental data from ECTOR. PHERMEX: The new diode using a flat cathode has almost triple the perveance (current/voltage{sup 3/2}) of the old Pierce diode. The current is somewhat lower than that originally predicted by simulation because the cathode has a small inset from the surrounding electrode. When this effect is included, the calculated current agrees quite well with the experiment.
Date: April 1, 1993
Creator: Hughes, T.P.; Welch, D.R. & Carlson, R.L.
Partner: UNT Libraries Government Documents Department

Diode and final-focus simulations for DARHT

Description: Beam dynamics calculations for the injector and final-focus region of a 4 kA, 20 MeV linear induction accelerator are presented. The injector is a low-emittance 4 MeV thermionic or photocathode diode designed to produce four 70 ns pulses over 2 {micro}sec. Due to the long total pule length, the authors have kept the field stress to < 200 kV/cm over the cathode electrode, and to {approx} 50 kV/cm on the radial insulator stacks. The normalized edge emittance produced by the diode is only {approx} 0.019 cm-rad. In the final-focus region, the authors have modeled the effect of ion emission from the target. The intense electric field of the beam at the 1-mm-diameter focal spot produces substantial ion velocities, and, if the space-charge-limited current density can be supplied, significant focal spot degradation may occur due to ion space-charge. Calculations for the existing Integrated Test Stand, which has a larger focal spot, show that the effect should be observable for H{sup +} and C{sup +} ion species. The effect is lessened if there is insufficient ion density on the target to supply the space-charge-limited current density, or if the ion charge-to-mass ratio is sufficiently small.
Date: October 1, 1997
Creator: Hughes, T.P.; Welch, D.R. & Carlson, R.L.
Partner: UNT Libraries Government Documents Department

Formation of Field-reversed-Configuration Plasma with Punctuated-betatron-orbit Electrons

Description: We describe ab initio, self-consistent, 3D, fully electromagnetic numerical simulations of current drive and field-reversed-configuration plasma formation by odd-parity rotating magnetic fields (RMFo). Magnetic-separatrix formation and field reversal are attained from an initial mirror configuration. A population of punctuated-betatron-orbit electrons, generated by the RMFo, carries the majority of the field-normal azimuthal electrical current responsible for field reversal. Appreciable current and plasma pressure exist outside the magnetic separatrix whose shape is modulated by the RMFo phase. The predicted plasma density and electron energy distribution compare favorably with RMFo experiments. __________________________________________________
Date: June 28, 2010
Creator: Welch, D. R.; Cohen, S. A.; Genoni, T. C. & Glasser, A. H.
Partner: UNT Libraries Government Documents Department

Simulations of ion beam neutralization in support of theneutralized transport experiment

Description: Heavy ion fusion (HIF) requires the acceleration, transport, and focusing of many individual ion beams. Drift compression and beam combining prior to focusing result in {approx}100 individual ion beams with line-charge densities of order 10{sup -5} C/m. A focusing force is applied to the individual ion beams outside of the chamber. For neutralized ballistic chamber transport (NBT), these beams enter the chamber with a large radius (relative to the target spot size) and must overlap inside the chamber at small radius (roughly 3-mm radius) prior to striking the target. The physics of NBT, in particular the feasibility of achieving the required small spot size, is being examined in the Neutralized Transport Experiment (NTX) at Lawrence Berkeley National Laboratory. Interpreted by detailed particle-in-cell simulations of beam neutralization, experimental results are being used to validate theoretical and simulation models for driver scale beam transport. In the NTX experiment, a low-emittance 300-keV, 25-mA K{sup +} beam is focused 1 m downstream into a 4-cm radius pipe containing one or more plasma regions. The beam passes through the first 10-cm-long plasma, produced by an Al plasma arc source, just after the final focus magnet and propagates with the entrained electrons. A second, 10-cm-long plasma (produced with a cyclotron resonance plasma source) is created near focus to simulate the effects of a photo-ionized plasma created by the heated target in a fusion chamber. Given a 0.1-{pi}-mm-mrad beam emittance, two and three-dimensional particle-in-cell (PIC) LSP simulations of the beam neutralization predict a &lt; 2-mm beam rms radius at focus with only the first plasma. The beam radius can be further improved with the addition of the second plasma located further downstream.
Date: September 7, 2003
Creator: Welch, D.R.; Rose, D.V.; Yu, S.S. & Henestroza, E.
Partner: UNT Libraries Government Documents Department

Simulations of neutralized final focus

Description: In order to drive an inertial fusion target or study high energy density physics with heavy ion beams, the beam radius must be focused to &lt; 3 mm and the pulse length must be compressed to &lt; 10 ns. The conventional scheme for temporal pulse compression makes use of an increasing ion velocity to compress the beam as it drifts and beam space charge to stagnate the compression before final focus. Beam compression in a neutralizing plasma does not require stagnation of the compression, enabling a more robust method. The final pulse shape at the target can be programmed by an applied velocity tilt. In this paper, neutralized drift compression is investigated. The sensitivity of the compression and focusing to beam momentum spread, plasma, and magnetic field conditions is studied with realistic driver examples. Using the 3D particle-in-cell code, we examine issues associated with self-field generation, stability, and vacuum-neutralized transport transition and focusing.
Date: January 18, 2005
Creator: Welch, D.R.; Rose, D.V.; Genoni, T.C.; Yu, S.S. & Barnard, J.J.
Partner: UNT Libraries Government Documents Department

Comparison of experimental data and 3D simulations of ion beam neutralization from the neutralized transport experiment

Description: The Neutralized Transport Experiment (NTX) at Lawrence Berkeley National Laboratory has been designed to study the final focus and neutralization of high perveance ion beams for applications in heavy ion fusion (HIF) and high energy density physics (HEDP) experiments. Pre-formed plasmas in the last meter before the target of the scaled experiment provide a source of electrons which neutralize the ion current and prevent the space-charge induced spreading of the beam spot. NTX physics issues are discussed and experimental data is analyzed and compared with 3D particle-in-cell simulations. Along with detailed target images, 4D phase-space data of the NTX at the entrance of the neutralization region has been acquired. This data is used to provide a more accurate beam distribution with which to initialize the simulation. Previous treatments have used various idealized beam distributions which lack the detailed features of the experimental ion beam images. Simulation results are compared with NTX experimental measurements for 250 keV K{sup +} ion beams with dimensionless perveance of 1-7 x 10{sup -4}. In both simulation and experiment, the deduced beam charge neutralization is close to the predicted maximum value.
Date: September 22, 2004
Creator: Thoma, C.; Welch, D.R.; Yu, S.S.; Henestroza, E.; Roy, P.K.; Eylon, S. 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

Beam-target interactions in single-and multi-pulse radiography

Description: This report describes calculations concerning the interaction of intense electron beam pulses with a solid target. In Section 2, we treat the propagation of a beam pulse through a dense plasma plume in front of the target, resulting from material blown off from the target by prior pulses. Because of the short magnetic decay-time, the primary effect of the plasma is to shift the focal spot of the beam longitudinally by an amount which is constant over most of the beam pulse. It may be possible to compensate for this effect by changing the upstream focusing elements from one beam pulse to the next. Section 3 describes a mechanism by which lighter ion species can diffuse to the surface of a plasma plume, thereby potentially increasing the concentration of bulk contaminant species such as hydrogen at the leading edge of the plume. These ions could then become a light-ion source for subsequent beam pulses. Based on the calculations, we tentatively recommend bulk contaminant fractions be limited to 10{sup -5}10{sup 4}. In Section 4, we estimate the number of adsorbed monolayers needed to provide a space-charge-limited (SCL) ion source at the target for the initial beam pulse. We find that {approx} 10 monolayers are required for SCL emission of H{sub 2}{sup +} ions. This may explain why there was little evidence of focus disruption in ETA-II target experiments.
Date: April 1, 1999
Creator: Chen, Y.J.; Hughes, T.P.; Oliver, B.V. & Welch, D.R.
Partner: UNT Libraries Government Documents Department

Estimates of energy fluence at the focal plane in beams undergoing neutralized drift compression

Description: The authors estimate the energy fluence (energy per unit area) at the focal plane of a beam undergoing neutralized drift compression and neutralized solenoidal final focus, as is being carried out in the Neutralized Drift Compression Experiment (NDCX) at LBNL. In these experiments, in order to reach high beam intensity, the beam is compressed longitudinally by ramping the beam velocity (i.e. introducing a velocity tilt) over the course of the pulse, and the beam is transversely focused in a high field solenoid just before the target. To remove the effects of space charge, the beam drifts in a plasma. The tilt introduces chromatic aberrations, with different slices of the original beam having different radii at the focal plane. The fluence can be calculated by summing the contribution from the various slices. They develop analytic formulae for the energy fluence for beams that have current profiles that are initially constant in time. They compare with envelope and particle-in-cell calculations. The expressions derived are useful for predicting how the fluence scales with accelerator and beam parameters.
Date: September 2, 2008
Creator: Barnard, J.J.; Seidl, P.A.; Coleman, J.E.; Ogata, D. & Welch, D.R.
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 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

Self-pinched beam transport experiments Relevant to Heavy Ion Driven inertial fusion energy

Description: An attractive feature of the inertial fusion energy (IFE) approach to commercial energy production is that the fusion driver is well separated from the fusion confinement chamber. This ''standoff'' feature means the driver is largely isolated from fusion reaction products. Further, inertial confinement fusion (ICF) target ignition (with modest gain) is now scheduled to be demonstrated at the National Ignition Facility (NIF) using a laser driver system. The NIF program will, to a considerable extent, validate indirectly-driven heavy-ion fusion (HIF) target designs for IFE. However, it remains that HIF standoff between the final focus system and the fusion target needs to be seriously addressed. In fact, there now exists a timely opportunity for the Office of Fusion Energy Science (OFES) to experimentally explore the feasibility of one of the attractive final transport options in the fusion chamber: the self-pinched transport mode. Presently, there are several mainline approaches for HIF beam transport and neutralization in the fusion chamber. These range from the (conservative) vacuum ballistic focus, for which there is much experience from high energy research accelerators, to highly neutralized ballistic focus, which matches well to lower voltage acceleration with resulting lower driver costs. Alternatively, Z-discharge channel transport and self-pinched transport in gas-filled chambers may relax requirements on beam quality and final focusing systems, leading to even lower driver cost. In any case, these alternative methods of transport, especially self-pinched transport, are unusually attractive from the standpoint of chamber design and neutronics. There is no requirement for low chamber pressure. Moreover, only a minuscule fraction of the fusion neutrons can escape from the chamber. Therefore, it is relatively easy to shield sensitive components, e-g., superconducting magnets from any significant neutron flux. Indeed, self-pinched transport and liquid wall protection endow DT fusion with many of the advantages of aneutronic fusion. The question ...
Date: February 6, 1998
Creator: Herrmannsfeldt, W.B.; Bangerter, R.O.; Fessenden, T.J.; Lee, E.P.; Yu, S.S.; Olson, C.L. et al.
Partner: UNT Libraries Government Documents Department

An updated point design for heavy ion fusion

Description: An updated, self-consistent point design for a heavy ion fusion (HIF) power plant based on an induction linac driver, indirect-drive targets, and a thick liquid wall chamber has been completed. Conservative parameters were selected to allow each design area to meet its functional requirements in a robust manner, and thus this design is referred to as the Robust Point Design (RPD-2002). This paper provides a top-level summary of the major characteristics and design parameters for the target, driver, final focus magnet layout and shielding, chamber, beam propagation to the target, and overall power plant.
Date: November 1, 2002
Creator: Yu, S.S.; Meier, W.R.; Abbott, R.P.; Barnard, J.J.; Brown, T.; Callahan, D.A. et al.
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

Results on intense beam focusing and neutralization from the neutralized beam experiment

Description: We have demonstrated experimental techniques to provide active neutralization for space-charge dominated beams as well as to prevent uncontrolled ion beam neutralization by stray electrons. Neutralization is provided by a localized plasma injected from a cathode arc source. Unwanted secondary electrons produced at the wall by halo particle impact are suppressed using a radial mesh liner that is positively biased inside a beam drift tube. We present measurements of current transmission, beam spot size as a function of axial position, beam energy and plasma source conditions. Detailed comparisons with theory are also presented.
Date: October 31, 2003
Creator: Roy, P.K.; Yu, S.S.; Eylon, S.; Henestroza, E.; Anders, A.; Bieniosek, F.M. et al.
Partner: UNT Libraries Government Documents Department

Accelerator and Ion Beam Tradeoffs for Studies of Warm DenseMatter

Description: One approach for heating a target to ''Warm Dense Matter'' conditions (similar, for example, to the interiors of giant planets or certain stages in inertial confinement fusion targets), is to use intense ion beams as the heating source (see refs.[6] and [7] and references therein for motivation and accelerator concepts). By consideration of ion beam phase-space constraints, both at the injector, and at the final focus, and consideration of simple equations of state and relations for ion stopping, approximate conditions at the target foil may be calculated. Thus, target temperature and pressure may be calculated as a function of ion mass, ion energy, pulse duration, velocity tilt, and other accelerator parameters. We connect some of these basic parameters to help search the extensive parameter space including ion mass, ion energy, total charge in beam pulse, beam emittance, target thickness and density.
Date: January 30, 2006
Creator: Barnard, J.J.; Briggs, R.J.; Callahan, D.A.; Davidson, R.C.; Friedman, A.; Grisham, L. et al.
Partner: UNT Libraries Government Documents Department

An integrated mechanical design concept for the final focusingregion for the HIF point design

Description: A design study was undertaken to develop a ''first cut'' integrated mechanical design concept of the final focusing region for a conceptual IFE power plant that considers the major issues which must be addressed in an integrated driver and chamber system. The conceptual design in this study requires a total of 120 beamlines located in two conical arrays attached on the sides of the target chamber 180 degrees apart. Each beamline consists of four large-aperture superconducting quadrupole magnets and a dipole magnet. The major interface issues include radiation shielding and thermal insulation of the superconducting magnets; reaction of electromagnetic loads between the quadrupoles; alignment of the magnets; isolation of the vacuum regions in the target chamber from the beamline, and assembly and maintenance.
Date: November 21, 2002
Creator: Brown, T.; Sabbi, G.-L.; Barnard, J.J.; Heitzenroeder, P.; Chun,J.; Schmidt, J. et al.
Partner: UNT Libraries Government Documents Department

Drift compression of an intense neutralized ion beam

Description: Longitudinal compression of a tailored-velocity, intense neutralized ion beam has been demonstrated. The compression takes place in a 1-2 m drift section filled with plasma to provide space-charge neutralization. An induction cell produces a head-to-tail velocity ramp that longitudinally compresses the neutralized beam, enhancing the beam peak current by a factor of 50 and producing a pulse duration of about 3 ns. this measurement has been confirmed independently with two different diagnostic systems.
Date: October 25, 2004
Creator: Roy, P.K.; Yu, S.S.; Henestroza, E.; Anders, A.; Bieniosek, F.M.; Coleman, J. et al.
Partner: UNT Libraries Government Documents Department

Drift compression of an intense neutralized ion beam

Description: Longitudinal compression of a velocity-tailored, intense neutralized K{sup +} beam at 300 keV, 25 mA has been demonstrated. The compression takes place in a 1-2 m drift section filled with plasma to provide space-charge neutralization. An induction cell produces a head-to-tail velocity ramp that longitudinally compresses the neutralized beam, enhancing the beam peak current by a factor of 50 and producing a pulse duration of about 3 ns. This measurement has been confirmed independently with two different diagnostic systems.
Date: September 8, 2005
Creator: Roy, P.K.; Yu, S.S.; Henestroza, E.; Anders, A.; Bieniosek, F.M.; Coleman, J. et al.
Partner: UNT Libraries Government Documents Department

Toward a physics design for NDCX-II, an ion accelerator for warm dense matter and HIF target physics studies

Description: The Heavy Ion Fusion Science Virtual National Laboratory (HIFS-VNL), a collaborationof LBNL, LLNL, and PPPL, has achieved 60-fold pulse compression of ion beams on the Neutralized Drift Compression eXperiment (NDCX) at LBNL. In NDCX, a ramped voltage pulse from an induction cell imparts a velocity&quot;tilt&quot; to the beam; the beam's tail then catches up with its head in a plasma environment that provides neutralization. The HIFS-VNL's mission is to carry out studies of Warm Dense Matter (WDM) physics using ion beams as the energy source; an emerging thrust is basic target physics for heavy ion-driven Inertial Fusion Energy (IFE). These goals require an improved platform, labeled NDCX-II. Development of NDCX-II at modest cost was recently enabled by the availability of induction cells and associated hardware from the decommissioned Advanced Test Accelerator (ATA) facility at LLNL. Our initial physics design concept accelerates a ~;;30 nC pulse of Li+ ions to ~;;3 MeV, then compresses it to ~;;1 ns while focusing it onto a mm-scale spot. It uses the ATA cells themselves (with waveforms shaped by passive circuits) to impart the final velocity tilt; smart pulsers provide small corrections. The ATA accelerated electrons; acceleration of non-relativistic ions involves more complex beam dynamics both transversely and longitudinally. We are using analysis, an interactive one-dimensional kinetic simulation model, and multidimensional Warp-code simulations to develop the NDCX-II accelerator section. Both LSP and Warp codes are being applied to the beam dynamics in the neutralized drift and final focus regions, and the plasma injection process. The status of this effort is described.
Date: August 1, 2008
Creator: Friedman, A.; Barnard, J.J.; Briggs, R.J.; Davidson, R.C.; Dorf, M.; Grote, D.P. et al.
Partner: UNT Libraries Government Documents Department

PROGRESS IN BEAM FOCUSING AND COMPRESSION FOR WARM-DENSE MATTER EXPERIMENTS

Description: The Heavy-Ion Fusion Sciences Virtual National Laboratory is pursuing an approach to target heating experiments in the Warm Dense Matter regime, using spacecharge-dominated ion beams that are simultaneously longitudinally bunched and transversely focused. Longitudinal beam compression by large factors has beendemonstrated in the Neutralized Drift Compression Experiment (NDCX) with controlledramps and forced neutralization. Using an injected 30-mA K+ ion beam with initialkinetic energy 0.3 MeV, axial compression leading to ~;;50-fold current amplification andsimultaneous radial focusing to beam radii of a few mm have led to encouraging energy deposition approaching the intensities required for eV-range target heating experiments. We discuss the status of several improvements to our Neutralized Drift Compression Experiment and associated beam diagnostics that are under development to reach the necessary higher beam intensities, including: (1) greater axial compression via a longer velocity ramp using a new bunching module with approximately twice the available voltseconds; (2) improved centroid control via beam steering dipoles to mitigate aberrations in the bunching module; (3) time-dependent focusing elements to correct considerable chromatic aberrations; and (4) plasma injection improvements to establish a plasma density always greater than the beam density, expected to be&gt;1013 cm-3.
Date: September 25, 2008
Creator: Seidl, P.A.; Anders, A.; Bieniosek, F.M.; Barnard, J.J.; Calanog, J.; Chen, A.X. et al.
Partner: UNT Libraries Government Documents Department