E.P. Gilson

Beam dynamics of the Neutralized Drift Compression Experiment-II, a novel pulse-compressing ion accelerator

Intense beams of heavy ions are well suited for heating matter to regimes of emerging interest. A new facility, NDCX-II, will enable studies of warm dense matter at ∼1 eV and near-solid density, and of heavy-ion inertial fusion target physics relevant to electric power production. For these applications the beam must deposit its energy rapidly, before the target can expand significantly. To form such pulses, ion beams are temporally compressed in neutralizing plasma; current amplification factors of ∼50–100 are routinely obtained on the Neutralized Drift Compression Experiment (NDCX) at the Lawrence Berkeley National Laboratory. In the NDCX-II physics design, an initial non-neutralized compression renders the pulse short enough that existing high-voltage pulsed power can be employed. This compression is first halted and then reversed by the beam’s longitudinal space-charge field. Downstream induction cells provide acceleration and impose the head-to-tail velocity gradient that leads to the final neutraliz...

Comparison of experimental data and three-dimensional simulations of ion beam neutralization from the Neutralized Transport Experiment

The Neutralized Transport Experiment at Lawrence Berkeley National Laboratory has been designed to study the final focus and neutralization of high perveance ion beams [E. Henestroza, S. Eylon, P. Roy, S. Yu, A. Anders, F. Bieniosek, W. Greenway, B. Logan, R. MacGill, D. Shuman et al., Phys. Rev. ST-Accel. Beams 7, 083501 (2004)]. Preformed 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. Neutralized Transport Experiment physics issues are discussed and experimental data are analyzed and compared with three-dimensional (3D) particle-in-cell simulations. Along with detailed target images, 4D phase-space data at the entrance of the neutralization region have been acquired. These data are 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 deta...

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...

Short intense ion pulses for materials and warm dense matter research

We have commenced experiments with intense short pulses of ion beams on the Neutralized Drift Compression Experiment-II at Lawrence Berkeley National Laboratory, by generating beam spots size with radius r<1 mm within 2 ns FWHM and approximately 1010 ions/pulse. To enable the short pulse durations and mm-scale focal spot radii, the 1.2 MeV Li+ ion beam is neutralized in a 1.6-meter drift compression section located after the last accelerator magnet. An 8-Tesla short focal length solenoid compresses the beam in the presence of the large volume plasma near the end of this section before the target. The scientific topics to be explored are warm dense matter, the dynamics of radiation damage in materials, and intense beam and beam-plasma physics including selected topics of relevance to the development of heavy-ion drivers for inertial fusion energy. Finally, we describe the accelerator commissioning and time-resolved ionoluminescence measurements of yttrium aluminum perovskite using the fully integrated accelerator and neutralized drift compression components.

Bunching and focusing of an intense ion beam for target heating experiments

An experiment to focus transversely and simultaneously axially bunch a space charge neutralized K+ ion beam has been carried out at LBNL. The principal objectives of the simultaneous bunching and focusing experiments are to control the beam envelope, demonstrate effective neutralization of the beam space- charge, control the velocity tilt on beam, understand effects of net defocusing, field imperfections, limitations on minimal spot size such as emittance and aberrations and to quantify the longitudinal phase space. A demonstration of increased axial compression and a reduction in spot size compared to earlier measurements is presented.

The Paul Trap Simulator Experiment

AbstractThe assembly of the PaulTrap Simulator Experiment~PTSX!is now complete and experimental operations have begun.The purpose of PTSX, a compact laboratory facility, is to simulate the nonlinear dynamics of intense charged particlebeam propagation over a large distance through an alternating-gradient transport system. The simulation is possiblebecause the quadrupole electric fields of the cylindrical Paul trap exert radial forces on the charged particles that areanalogous to the radial forces that a periodic focusing quadrupole magnetic field exert on the beam particles in the beamframe. By controlling the waveform applied to the walls of the trap, PTSX will explore physics issues such as beammismatch, envelope instabilities, halo particle production, compression techniques, collective wave excitations, andbeam profile effects.Keywords: Alternating-gradient transport; Charged particle beam; Nonlinear dynamics; Paul trap 1. INTRODUCTIONConstructionofthePaulTrapSimulatorExperiment~PTSX!is now complete. PTSX is a cylindrical Paul trap ~Paul S Wineland et al., 1983! designed to simu-late the dynamics of intense charged particle beams inalternating-gradient transport systems. The experiment ispredicated on the similarity between the transverse Hamil-tonians for the two systems ~Davidson et al., 2000!. Thetemporally varying forces that the Paul trap exerts on theplasmaparticlesareequivalenttotheperiodicfocusingforcesthat the alternating-gradient quadrupole lattice exerts on thebeam particles in the beam frame. The advantage of thesimulationisthatPTSXisacompactlaboratoryexperiment,whereas a magnetic quadrupole transport system used tostudy the same physics would be kilometers long.Understanding the properties of intense charged beampropagation over large distances is important for a widevarietyofacceleratorapplications~Chao,1993;Reiser,1994;Davidson, 2001! including high energy physics, heavy ionfusion, spallation neutron sources, tritium production, andnuclear waste transmutation. We are especially interested instudying the properties of high-intensity beams, where theself-field effects can significantly alter beam equilibrium,stability, and transport properties.The PTSX trap consists of three cylindrical electrodes ofradius r

Heavy-ion-fusion-science: summary of US progress

Over the past two years noteworthy experimental and theoretical progress has been made towards the top-level scientific question for the US programme on heavy-ion-fusion-science and high energy density physics: ‘How can heavy-ion beams be compressed to the high intensity required to create high energy density matter and fusion conditions?’ New results in transverse and longitudinal beam compression, high-brightness transport and beam acceleration will be reported. Central to this campaign is final beam compression. With a neutralizing plasma, we demonstrated transverse beam compression by an areal factor of over 100 and longitudinal compression by a factor of >50. We also report on the first demonstration of simultaneous transverse and longitudinal beam compression in plasma. High beam brightness is key to high intensity on target, and detailed experimental and theoretical studies on the effect of secondary electrons on beam brightness degradation are reported. A new accelerator concept for nearterm low-cost target heating experiments was invented, and the predicted beam dynamics validated experimentally. We show how these scientific campaigns have created new opportunities for interesting target experiments in the warm dense matter regime. Finally, we summarize progress towards heavy-ion fusion, including the demonstration of a compact driver-size high-brightness ion injector. For all components of our high intensity campaign, the new results have been obtained via tightly coupled efforts in experiments, simulations and theory.

Recent results from the Paul Trap Simulator Experiment

The Paul Trap Simulator Experiment (PTSX) is a compact laboratory facility whose purpose is to simulate the nonlinear dynamics of intense charged particle beam propagation over large distances through an alternating-gradient transport system. The simulation is possible because the quadrupole electric fields of the cylindrical Paul trap exert radial forces on the charged particles that are analogous to the radial forces that a periodic focusing quadrupole magnetic field exert on the beam particles in the beam frame. Initial experiments clearly demonstrate the loss of confinement when the vacuum phase advance /spl sigma//sub v/ of the system exceeds 90/spl deg/. Recent experiments show that PTSX is able to successfully trap plasmas of moderate intensity for thousands of equivalent lattice periods.

Modeling Intense Beam Propagation in the Paul Trap Simulator Experiment (PTSX)

The Paul Trap Simulator Experiment (PTSX) is a compact laboratory facility whose purpose is to simulate the nonlinear dynamics of intense charged particle beam propagation over large distances through an alternating‐gradient magnetic transport system. The PTSX device is a 200 cm long, 20 cm diameter cylindrical Paul trap in which a 400 V, 100 kHz signal confines cesium ions to an rms radius of 1 cm. The one‐component cesium plasmas can be confined for hundreds of milliseconds, which would correspond to an equivalent alternating‐gradient transport system many kilometers long. The normalized intensity parameter ŝ = ωp2|r=0/2ωq2, where ωq is the average transverse focusing frequency, describes whether the plasma is emittance‐dominated (ŝ ≪ 1) or space‐charge‐dominated (ŝ → 1). By increasing the amount of charge loaded into the trap, PTSX reaches values of ŝ = 0.8. Thus, the opportunity exists to study important physics topics such as: the conditions necessary for quiescent intense beam propagation over large...

Short-pulse, compressed ion beams at the Neutralized Drift Compression Experiment

We have commenced experiments with intense short pulses of ion beams on the Neutralized Drift Compression Experiment (NDCX-II) at Lawrence Berkeley National Laboratory, with 1-mm beam spot size within 2.5 ns full-width at half maximum. The ion kinetic energy is 1.2 MeV. To enable the short pulse duration and mm-scale focal spot radius, the beam is neutralized in a 1.5-meter-long drift compression section following the last accelerator cell. A short-focal-length solenoid focuses the beam in the presence of the volumetric plasma that is near the target. In the accelerator, the line-charge density increases due to the velocity ramp imparted on the beam bunch. The scientific topics to be explored are warm dense matter, the dynamics of radiation damage in materials, and intense beam and beam-plasma physics including select topics of relevance to the development of heavy-ion drivers for inertial fusion energy. Below the transition to melting, the short beam pulses offer an opportunity to study the multi-scale dynamics of radiation-induced damage in materials with pump-probe experiments, and to stabilize novel metastable phases of materials when short-pulse heating is followed by rapid quenching. First experiments used a lithium ion source; a new plasma-based helium ion source shows much greater charge delivered to the target.