This paper examines the reliability of a widely used method for temperature determination by multi-wavelength pyrometry. In recent warm dense matter experiments with ion-beam heated metal foils, we found that the statistical quality of the fit to the measured data is not necessarily a measure of the accuracy of the inferred temperature. We found a specific example where a second-best fit leads to a more realistic temperature value. The physics issue is the wavelength-dependent emissivity of the hot surface. We discuss improvements of the multi-frequency pyrometry technique, which will give a more reliable determination of the temperature from emission data.

This paper investigates prospects of utilizing a high-power laser-driven target-normal-sheath-acceleration proton beam for the experimental demonstration of the magnetic self-focusing phenomenon in charged particle beams. In the proposed concept, focusing is achieved by propagating a space-charge dominated ion beam through a stack of thin conducting and grounded foils separated by vacuum gaps. As the beam travels through the system, image charges build up at the foils and generate electric field that counteracts the beam's electrostatic self-field — a dominant force responsible for expansion of a high current beam. Once the electrostatic self-field is “neutralized” by the image charges, the beam currents magnetic self-field will do the focusing. The focal spot size and focal length depends on the choice of a number of foils and distance between foils. Considering the typical electrical current level of a target-normal-sheath-acceleration proton beam, we conclude that it is feasible to focus or collimate a beam within tens of millimeters distance, e.g., using 200–1000 Al foils, 0.5 µm thick each, with foil spacing ranging from 25 µm to 100 µm. These requirements are within technical capabilities of modern target fabrication, thus allowing the first possible demonstration of the pinch effect with heavy ion beams.

We describe a funnel cone for concentrating an ion beam on a target. The cone utilizes the reflection characteristic of ion beams on solid walls to focus the incident beam and increase beam intensity on target. The cone has been modeled with the TRIM code. A prototype has been tested and installed for use in the 350-keV K+ NDCX target chamber.

We describe the next set of experiments proposed in the U.S. Heavy Ion Fusion Virtual National Laboratory, the so-called Integrated Beam Experiment (IBX). The purpose of IBX is to investigate in an integrated manner the processes and manipulations necessary for a heavy ion fusion induction accelerator. The IBX experiment will demonstrate injection, acceleration, compression, bending, and final focus of a heavy ion beam at significant line charge density. Preliminary conceptual designs are presented and issues and trade-offs are discussed. Plans are also described for the step after IBX, the Integrated Research Experiment (IRE), which will carry out significant target experiments.

For the High Current Beam Transport Experiment (HCX) at Lawrence Berkeley National Laboratory, an injector is required to deliver up to 1.8 MV of 0.6 A K+ beam with an emittance of ≈1 π-mm-mrad. We have successfully operated a 10-cm-diameter surface ionization source together with an electrostatic quadrupole (ESQ) accelerator to meet these requirements. The pulse length is ≈4 μs, firing at once every 10–15 s. By optimizing the extraction diode and the ESQ voltages, we have obtained an output beam with good current density uniformity, except for a small increase near the beam edge. Characterization of the beam emerging from the injector included measurements of the intensity profile, beam imaging, and transverse phase space. These data along with comparison to computer simulations provide the knowledge base for designing and understanding future HCX experiments.

The High Current Experiment (HCX) is being assembled at Lawrence Berkeley National Laboratory as part of the U.S. program to explore heavy ion beam transport at a scale representative of the low-energy end of an induction linac driver for fusion energy production. The primary mission of this experiment is to investigate aperture fill factors acceptable for the transport of space-charge dominated heavy ion beams at high space-charge intensity (line-charge density ∼ 0.2 μC/m) over long pulse durations (>4 μs). This machine will test transport issues at a driver-relevant scale resulting from nonlinear space-charge effects and collective modes, beam centroid alignment and beam steering, matching, image charges, halo, lost-particle induced electron effects, and longitudinal bunch control. We present the first experimental results carried out with the coasting K+ ion beam transported through the first 10 electrostatic transport quadrupoles and associated diagnostics. Later phases of the experiment will include more electrostatic lattice periods to allow more sensitive tests of emittance growth, and also magnetic quadrupoles to explore similar issues in magnetic channels with a full driver scale beam.

For the intense beams in heavy ion fusion accelerators, details of the beam distribution as it emerges from the source region can determine the beam behavior well downstream. This occurs because collective space-charge modes excited as the beam is born remain undamped for many focusing periods. Traditional studies of the source region in particle beam systems have emphasized the behavior of averaged beam characteristics, such as total current, rms beam size, or emittance, rather than the details of the full beam distribution function that are necessary to predict the excitation of the collective modes. Simulations of the beam in the source region and comparisons to experimental measurements at Lawrence Berkeley National Laboratory and the University of Maryland are presented to illustrate some of the complexity in beam characteristics that has been uncovered as increased attention has been devoted to developing a detailed understanding of the source region. Also discussed are methods of using the simulations to infer characteristics of the beam distribution that can be difficult to measure directly.