Edward A. Startsev

Physics of neutralization of intense high-energy ion beam pulses by electrons

Neutralization and focusing of intense charged particle beam pulses by electrons form the basis for a wide range of applications to high energy accelerators and colliders, heavy ion fusion, and astrophysics. For example, for ballistic propagation of intense ion beam pulses, background plasma can be used to effectively neutralize the beam charge and current, so that the self-electric and self-magnetic fields do not affect the ballistic propagation of the beam. From the practical perspective of designing advanced plasma sources for beam neutralization, a robust theory should be able to predict the self-electric and self-magnetic fields during beam propagation through the background plasma. The major scaling relations for the self-electric and self-magnetic fields of intense ion charge bunches propagating through background plasma have been determined taking into account the effects of transients during beam entry into the plasma, the excitation of collective plasma waves, the effects of gas ionization, fini...

Nonlinear δf simulation studies of intense charged particle beams with large temperature anisotropy

In this paper, a 3D nonlinear perturbative particle simulation code (BEST) [H. Qin, R. C. Davidson, and W. W. Lee, Phys. Rev. ST Accel. Beams 3, 084401 (2000)] is used to systematically study the stability properties of intense non-neutral charged particle beams with large temperature anisotropy (T⊥b≫T∥b). The most unstable modes are identified, and their eigenfrequencies, radial mode structure, and nonlinear dynamics are determined for axisymmetric perturbations with ∂/∂θ=0.

Two-stream instability for a longitudinally compressing charged particle beam

The electrostatic two-stream instability for a cold, longitudinally compressing charged particle beam propagating through a background plasma has been investigated both analytically and numerically. Small-signal coupled equations describing the evolution of the perturbations are derived, and the asymptotic solutions are obtained. The results are confirmed by direct numerical solution of the linearized fluid equations. It is found that the longitudinal beam compression strongly modifies the space-time development of the instability. In particular, the dynamic compression leads to a significant reduction in the growth rate of the two-stream instability compared to the case without an initial velocity tilt.

Analytical and numerical studies of heavy ion beam transport in the fusion chamber

The propagation of a high-current finite-length ion charge bunch through a background plasma is of interest for many applications, including heavy ion fusion, plasma lenses, cosmic ray propagation, and so forth. Charge neutralization has been studied both analytically and numerically during ion beam entry, propagation, and exit from the plasma. A suite of codes has been developed for calculating the degree of charge and current neutralization of the ion beam pulse by the background plasma. The code suite consists of two different codes: a fully electromagnetic, relativistic particle-in-cell code, and a relativistic Darwin model for long beams. As a result of a number of simplifications, the second code is hundreds of times faster than the first one and can be used for most cases of practical interest, while the first code provides important benchmarking for the second. An analytical theory has been developed using the assumption of long charge bunches and conservation of generalized vorticity. The model predicts nearly complete charge neutralization during quasi-steady-state propagation provided the beam pulse duration τ b is much longer than the inverse electron plasma frequency ω p -1, where ω p = (4πn p e 2 /m e ) 1/2 and n p is the background plasma density. In the opposite limit, the beam head excites large-amplitude plasma waves. Similarly, the beam current is well neutralized provided ω P τ b >>1 and the beam radius is much larger than plasma skin depth δ p = c/ω p . Equivalently, the condition for current neutralization can be expressed in terms of the beam current as I b >>4.25Z b β b (n b /n p )kA, where n b is the beam density, Z b is the ion charge, and V b = β b c is the beam velocity; and the condition for charge neutralization can be expressed as I b >> 4.25β 3 b (n b /n p )(r b /l b ) 2 kA, where l b and r b are the beam length and radius, respectively. For long charge bunches, the analytical results agree well with the results of numerical simulations. The visualization of the data obtained in the numerical simulations shows complex collective phenomena during beam entry into and exit from the plasma.

Progress in heavy ion fusion research

The U.S. Heavy Ion Fusion program has recently commissioned several new experiments. In the High Current Experiment [P. A. Seidl et al., Laser Part. Beams 20, 435 (2003)], a single low-energy beam with driver-scale charge-per-unit-length and space-charge potential is being used to study the limits to transportable current posed by nonlinear fields and secondary atoms, ions, and electrons. The Neutralized Transport Experiment similarly employs a low-energy beam with driver-scale perveance to study final focus of high perveance beams and neutralization for transport in the target chamber. Other scaled experiments—the University of Maryland Electron Ring [P. G. O’Shea et al., accepted for publication in Laser Part. Beams] and the Paul Trap Simulator Experiment [R. C. Davidson, H. Qin, and G. Shvets, Phys. Plasmas 7, 1020 (2000)]—will provide fundamental physics results on processes with longer scale lengths. An experiment to test a new injector concept is also in the design stage. This paper will describe th...

Finite-β simulation of microinstabilities

A new split-weight perturbative particle simulation scheme for finite-β plasmas in the presence of background inhomogeneities is presented. The scheme is an improvement over the original split-weight scheme, which splits the perturbed particle response into adiabatic and non-adiabatic parts to improve numerical properties. In the new scheme, by further separating out the adiabatic response of the particles associated with the quasi-static bending of the magnetic field lines in the presence of background inhomogeneities of the plasma, we are able to demonstrate the finite-β stabilization of drift waves and ion temperature gradient modes using a simple gyrokinetic particle code based on realistic fusion plasma parameters. However, for βmi/me ≫ 1, it becomes necessary to use the electron skin-depth as the grid size of the simulation to achieve accuracy in solving the resulting equations, unless special numerical arrangement is made for the cancelling of the two large terms on the either side of the governing...

Controlling charge and current neutralization of an ion beam pulse in a background plasma by application of a solenoidal magnetic field: Weak magnetic field limit

Propagation of an intense charged particle beam pulse through a background plasma is a common problem in astrophysics and plasma applications. The plasma can effectively neutralize the charge and current of the beam pulse, and thus provides a convenient medium for beam transport. The application of a small solenoidal magnetic field can drastically change the self-magnetic and self-electric fields of the beam pulse, thus allowing effective control of the beam transport through the background plasma. An analytic model is developed to describe the self-magnetic field of a finite-length ion beam pulse propagating in a cold background plasma in a solenoidal magnetic field. The analytic studies show that the solenoidal magnetic field starts to influence the self-electric and self-magnetic fields when ωce≳ωpeβb, where ωce=eB∕mec is the electron gyrofrequency, ωpe is the electron plasma frequency, and βb=Vb∕c is the ion beam velocity relative to the speed of light. This condition typically holds for relatively sm...

[delta]f simulation studies of the ion–electron two-stream instability in heavy ion fusion beams

Ion‐electron two-stream instabilities in high intensity heavy ion fusion beams, described self-consistently by the nonlinear Vlasov‐Maxwell equations, are studied using a three-dimensional multispecies perturbative particle simulation method. Large-scale parallel particle simulations are carried out using the recently developed Beam Equilibrium, Stability, and Transport ~BEST! code. For a parameter regime characteristic of heavy ion fusion drivers, simulation results show that the most unstable mode of the ion‐electron two-stream instability has a dipole-mode structure, and the linear growth rate decreases with increasing axial momentum spread of the beam particles due to Landau damping by the axial momentum spread of the beam ions in the longitudinal direction.

Heavy ion fusion science research for high energy density physics and fusion applications

Heavy ion fusion science research for high energy density physics and fusion applications* B G Logan 1 , J J Barnard 2 , F M Bieniosek 1 , R H Cohen 2 , J E Coleman 1 , R C Davidson 3 , P C Efthimion 3 , A Friedman 2 , E P Gilson 3 , W G Greenway 1 , L Grisham 3 , D P Grote 2 , E Henestroza 1 , D H H Hoffmann 4 , I D Kaganovich 3 , M Kireeff Covo 2 , J W Kwan 1 , K N LaFortune 2 , E P Lee 1 , M Leitner 1 , S M Lund 2 , A W Molvik 2 , P Ni 1 ,G E Penn 1 , L J Perkins 2 , H Qin 3 , P K Roy 1 , A B Sefkow 3 , P A Seidl 1 , W Sharp 2 E A Startsev 3 , D Varentsov 4 , J-L Vay 1 , W L Waldron 1 , J S Wurtele 1 , D Welch , G. A. Westenskow 1 and S S Yu 1 Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Lawrence Livermore National Laboratory, Livermore, CA, 94551, USA Princeton Plasma Physics Laboratory, Princeton, NJ 08543, USA Gesellschaft fur Schwerionenforschung mbH, Darmstadt, Germany Voss Scientific, Albuquerque, NM, USA Corresponding Author’s E-mail: bglogan@lbl.gov Abstract During the past two years, the U.S. heavy ion fusion science program has made significant experimental and theoretical progress in simultaneous transverse and longitudinal beam compression, ion-beam-driven warm dense matter targets, high brightness beam transport, advanced theory and numerical simulations, and heavy ion target designs for fusion. First experiments combining radial and longitudinal compression of intense ion beams propagating through background plasma resulted in on-axis beam densities increased by 700X at the focal plane. With further improvements planned in 2007, these results will enable initial ion beam target experiments in warm dense matter to begin next year at LBNL. We are assessing how these new techniques apply to low-cost modular fusion drivers and higher-gain direct-drive targets for inertial fusion energy. 1. Introduction A coordinated heavy ion fusion science program by the Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory, and Princeton Plasma Physics Laboratory (the Heavy-Ion Fusion Science Virtual National Laboratory), together with collaborators at Voss Scientific and GSI, pursues research on compressing heavy ion beams towards the high intensities required for creating high energy density matter and fusion energy. Previously, experiments in the Neutralized Drift Compression Experiment (NDCX) and simulations showed increases in focused beam intensities first by transverse focusing [1, 2] and then by longitudinal compression (>50 X) with an induction buncher that imparts increasing ion velocities from the head to the tail of a selected 150 ns slice of beam [3, 4]. Section 2 describes new work on combined radial and longitudinal compression of intense beams within neutralizing plasma. In Section 3 we describe the first joint U.S.-German warm dense matter experiments with porous targets using intense beams from the SIS 18 storage ring at GSI [5], together with plans for initial warm dense matter targets at LBNL next year. Progress in e-cloud research is presented in Section 4, advances in theory and simulations in Section 5, applications to heavy ion fusion in Section 6, and conclusions in Section 7. 2. Combined transverse and longitudinal compression of beams within neutralizing plasma Recent experiments in NDCX have combined neutralized drift compression with a new final focusing solenoid (FFS) and a new target chamber (Figure 1). The FFS was installed with a new beam target chamber, and the plasma density was measured before installing on the NDCX beam line. Two Filtered Cathodic Arc Plasma Sources (FCAPS) streamed aluminum metal plasma upstream toward the exit of the FFS, and a Langmuir probe was driven from the upstream end of the FFS toward the focal plane of the magnet, 18.27 cm downstream of the midplane of the FFS. * This research was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Berkeley and Lawrence Livermore National Laboratories under Contract Numbers DE-AC02-05CH11231 and W-7405-Eng-48, and by the Princeton Plasma Physics Laboratory under Contract Number DE-AC02-76CH03073.

Excitation of transverse dipole and quadrupole modes in a pure ion plasma in a linear Paul trap to study collective processes in intense beamsa)

Transverse dipole and quadrupole modes have been excited in a one-component cesium ion plasma trapped in the Paul Trap Simulator Experiment (PTSX) in order to characterize their properties and understand the effect of their excitation on equivalent long-distance beam propagation. The PTSX device is a compact laboratory Paul trap that simulates the transverse dynamics of a long, intense charge bunch propagating through an alternating-gradient transport system by putting the physicist in the beams frame of reference. A pair of arbitrary function generators was used to apply trapping voltage waveform perturbations with a range of frequencies and, by changing which electrodes were driven with the perturbation, with either a dipole or quadrupole spatial structure. The results presented in this paper explore the dependence of the perturbation voltages effect on the perturbation duration and amplitude. Perturbations were also applied that simulate the effect of random lattice errors that exist in an accelerato...