T. R. Lockner

Multiframe ion pinhole camera for intense ion beam transport and focusing experiments

We have developed a new ion pinhole camera to obtain energy density profiles of a focused multiterawatt ion beam as a function of ion energy. Beam ions that are elastically scattered from a thin gold foil are imaged through six baffled pinholes onto six separate areas of a sheet of CR‐39 nuclear track detector. Each of the areas is covered by an aluminum range filter and records an image with a different lower bound on the ion energy. Subtracting images with adjacent cutoff energies results in images with upper and lower bounds on the ion energy. Ion images are read from the CR‐39 with VERA, a fully automatic, image‐processor‐based nuclear track counting system. Images of the Particle Beam Fusion Accelerator‐II (PBFA‐II) proton beam have been obtained and show that the beam has been focused to achieve a horizontal FWHM of 5.7 mm and has delivered 9 kJ/cm2 to a target.

Simulation and interpretation of ion beam diagnostics on PBFA‐II

Ion diode and beam focusing experiments are in progress on PBFA‐II working toward an ultimate goal of significant burn of an ICF pellet. Beam diagnostics on these experiments include a Thomson parabola, Kα x‐ray pinhole cameras, filtered ion pinhole cameras, and a magnetic spectrometer. We are developing two new computer programs to simulate and interpret the data obtained from these diagnostics. vida is a VAX‐based program that manipulates and unfolds data from digitized particle and x‐ray diagnostic images. vida operations include: image display, background subtraction, relative‐to‐absolute coordinate transformations, and image projection into the beam reference frame. picdiag allows us to study the effects of time‐dependent ion focusing on the performance of ion beam diagnostics.

Observation of K α. X-ray satellites from a target heated by an intense ion beam

We have made the first observation of K α X-ray satellites from a target heated by an intense ion beam. The satellites are produced when thermal ionization due to beam heating is accompanied by inner-shell ionization from beam ion impact. The Particle Beam Fusion Accelerator II was used to irradiate a conical aluminum target with a proton beam. The nominal beam parameters were 50–75 kJ in a 1-cm spot, 15–20-ns pulse length, and 4–5-MeV protons at peak power. An elliptical crystal X-ray spectrograph inside a 1000-kg tungsten shield was used to record the spectra. The peak ion stage reached by the aluminum target was +8. Collisional radiative calculations were performed, which indicate a peak electron temperature of 20–60 eV.

Intense ion beam diagnostics for particle beam fusion experiments on PBFA II (invited)

A review of the diagnostics used at Sandia National Laboratories to measure the parameters of intense proton and lithium beams generated on the PBFA‐II accelerator will be presented. These diagnostics consist of several types, namely: Kα x‐ray pinhole cameras, a multiframe dE/dx ion pinhole camera, a p‐i‐n array ion pinhole camera, Thomson parabola spectrographs, a Rutherford magnetic spectrograph, plasma visible spectroscopy, and several nuclear activation diagnostics. These components, when taken together, enable a rather thorough description of the 5‐MV, 10‐TW ion beams presently being produced. A unique feature of these diagnostics is that they are capable of operating in hard (several MeV) x‐ray bremsstrahlung backgrounds of some 109–1010 rad/s. Details of each diagnostic, its integration, data reduction procedures, and recent PBFA‐II data will be discussed.

Rutherford magnetic spectrograph for intense ion beam measurements on PBFA‐II

A time‐resolved magnetic spectrograph employing a gold Rutherford‐scattering foil has been constructed to measure the parameters of the intense ion beams generated by Sandia National Laboratories’ PBFA‐II accelerator. The spectrograph operates by allowing the direct intense beam of PBFA‐II to scatter from a thin gold foil to reduce its intensity for magnetic analysis. Details of the spectrograph’s construction, detector package, and recent PBFA‐II proton data are included in the paper.

Intense ion beam Kα measurements on PBFA‐II

Inertial confinement fusion research efforts at Sandia National Laboratories center on generating and focusing high‐intensity light ion beams on the Particle Beam Fusion Accelerator PBFA‐II. A time‐integrating three‐frame ion beam spatial monitor was developed for these experiments to determine proton and lithium ion beam uniformity and orbit characteristics by imaging the ion‐induced Kα line radiation. The three views of the ion beam are made off axis in three diode quadrants at a 3.8‐cm radius. This spatial monitor, in conjunction with other beam diagnostics, allows experimenters to determine the high‐voltage focusing characteristics of the ion diode.

Data analysis for the Rutherford magnetic spectrograph on PBFA‐II

A magnetic spectrograph employing a gold Rutherford scattering foil has been constructed and fielded on Sandia National Laboratories’ PBFA‐II accelerator to diagnose intense ion beams. The instrument simultaneously records time‐integrated data on nuclear track recording film, CR‐39, and time‐resolved data on a set of p‐i‐n diodes. The details of the analysis of these data to provide time‐resolved power density, ion current density, ion energy spectra (including mean ion energy), and ion species identification will be presented.

Lithium fluoride ion source experiments on PBFA II

Lithium fluoride, field‐enhanced ion source experiments are being performed on PBFA II. The source consists of a thin coating of LiF on a microscopically rough substrate. Diagnostics to measure ion beam energy, purity, and transport include electrical monitors, Faraday cups, nuclear activation, ion pinhole camera, Rutherford magnetic spectrograph, and shadowbox aperture array. With PBFA II operating at three‐quarters energy, the source has produced 16 TW of ion power and 550 kJ of ion energy with 70% diode efficiency. Over 26 kJ of lithium beam energy has been focused to the diode center axis with a peak energy density of about 1.3 kJ/cm2 . PICDIAG simulations of the lithium focus indicate the intrinsic source divergence is about 45 mrad with a 20‐μm‐grade porous stainless‐steel substrate.

An integrated diagnostic package for intense proton and lithium-ion beam measurements on the sandia national laboratories' PBFA-II accelerator☆

Abstract A review of the diagnostic packages used at Sandia National Laboratories to measure the parameters of intense proton and lithium beams generated on the PBFA-II accelerator will be presented. These diagnostics consist of several types, namely: K α X-ray pinhole cameras, a multiframe dE/dx ion pinhole camera, a p-i-n diode array ion pinhole camera, Thomson parabola spectrographs, a Rutherford magnetic spectrograph, plasma visible spectroscopy and several nuclear activation diagnostics. These components, when taken together, provide a rather thorough description of the 5 MV, 10 TW ion beams presently being produced. Specifically, the beam parameters measured by the diagnostic array include spatial profile (off and on axis), absolute number, species, voltage, current density and focal power density. A unique feature of these diagnostics is that they are capable of operating in hard (several MeV) X-ray bremsstrahlung backgrounds of some 109–1011rad/s. The operating principles of each diagnostic will be summarized in the paper, along with a discussion of how the diagnostics are integrated together to form a complete system. The paper will close with a discussion of a new nuclear track counting system that has been developed for automatic counting of solid-state nuclear track detectors.

Lithium beam‐driven target experiments at 1015 W/g on PBFA II at Sandia National Laboratories

A lithium beam is focused to an intensity 1–2 TW/cm2. The beam divergencies have been measured as low as 23 mrad. This lithium beam has the specific power deposition of ∼10 W/g, the beam‐driven target experiments have achieved radiation temperature of 58 eV.(AIP)