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A transverse beam profile monitor that visualizes a two-dimensional beam-induced fluorescent image was developed. The monitor employs a sheet-shaped gas flow formed by a technique of rarefied gas dynamics. A simplified analysis method was developed to reconstruct the beam intensity profile from the obtained image. The developed profile monitor and the analysis method were applied to measure the J-PARC 3 MeV ${\mathrm{H}}^{\ensuremath{-}}$ beam profile. The root mean square values of the profiles were consistent with the ones obtained by a wire-scanning-type beam profile monitor. The beam loss due to the gas sheet injection was measured as a beam-current reduction. The amount of the beam current decreased in proportion to the gas sheet flux and the reduction ranged from 0.004 to 2.5%. The assembled system was capable of reconstructing a beam profile from a single shot beam pulse ($1.7\ifmmode\times\else\texttimes\fi{}{10}^{13}$ protons in $50\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$).

Recent upgrade of the neutral beam system has resulted in considerable improvement of the plasma parameters in the gas dynamic trap experiment. With injection of 5 ms, 20 keV, 4.5 MW neutral beams the electron temperature approaching 250 eV was obtained. At the same time maximal plasma beta attained about 60%. Further progress in plasma temperature and pressure could only be possible with considerable increase of the magnetic field in the central solenoid and re-optimization of its profile to improve stability of highbeta plasma, as well as with extension of the neutral beam pulse. Possible steps in this direction are considered in this paper.

Results of experiments on injection of a sequence of several electron beam pulses (80–90 keV, 20–75 A, ∼30 μs) into 1019–1021 m−3 deuterium plasma are presented. The first beam pulse was injected into deuterium gas, the following pulses propagated through residual plasma that survived the inter-pulse periods. A typical pulse duration was of the order of 106 ω p − 1 that is much longer than most of the interaction-related processes. However, we noticed significant differences in plasma processes between the first pulse and the rest ones. A suggested physical factor behind those differences is longitudinal plasma current that develops during the first beam pulse.

While an intense electron beam passes through the accelerating gaps of a linear induction accelerator, a strong wake field will be excited. In this paper a relatively simple model is established based on the interaction between the transverse magnetic wake field and the electron beam, and the numerical calculation in succession generates a magnetic wake field distribution along the accelerator and along the beam pulse as well. The axial electric wake field is derived based on the relation between field components of a resonant mode. According to some principles in existence, the influence of this field on the high voltage properties of the induction gap is analyzed. The Dragon-I accelerator is taken as an example, and its maximum electric wake field is about 17 kV/cm, which means the effect of the wake field is noticeable.

Near-threshold photodissociation of ${\mathrm{Br}}_{2}$ from a supersonic beam produces slow bromine atoms that are trapped in the magnetic-field minimum formed between two opposing permanent magnets. Here we quantify the dominant trap-loss rate due to collisions with two sources of residual gas: the background limited by the vacuum chamber base pressure and the carrier gas during the supersonic gas pulse. The loss rate due to collisions with residual Ar in the background follows pseudo-first-order kinetics and the bimolecular rate coefficient for collisional loss from the trap is determined by measurement of this rate as a function of the background Ar pressure. This rate coefficient is smaller than the total elastic collision rate coefficient, as it only samples those collisions that lead to trap loss, and is determined to be $\ensuremath{\langle}\ensuremath{\nu}\ensuremath{\sigma}\ensuremath{\rangle}=(1.12\ifmmode\pm\else\textpm\fi{}0.09)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. The calculated differential cross section can be used with this value to estimate a trap depth of $293\ifmmode\pm\else\textpm\fi{}24\phantom{\rule{0.28em}{0ex}}\mathrm{mK}$. Carrier-gas collisions occur only during the tail of the supersonic beam pulse. Using the differential cross section verified by the background-gas collision measurements provides an estimate of the peak molecular-beam density of $(3.0\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, in good agreement with the prediction of a simple supersonic expansion model. Finally, we estimate the trap-loss rate due to Majorana transitions to be negligible, owing to the relatively large trapped-atom phase-space volume.

Some major system features are not stated but can be inferred. For example this is probably an engineering test facility, not a power plant driver, because the standoff from target to final magnet is only 5.0 m. The fusion target takes two-sided illumination with indirect drive using a total of 60 beam pulses: 10 pre-pulses (3.0 GeV) + 20 main pulses (4.0 GeV) from each side. On page 12 it's stated that the charge per beam pulse is 26.8 {micro}C, so we calculate pre-pulse: 20 x 3 GeV x 26.8 {micro}C = 1.608MJ, main pulse: 40 x 4 GeV x 26.8 {micro}C = 4.288MJ, total beam energy 5.896MJ. The beam ion mass ks 200 amu, so the species is Hg{sup +}. Therefore the mid-pulse velocities are: pre-pulse v = .1773c = 5.316 x 10{sup 7} m/s, main pulse v = .2040c = 6.114 x 10{sup 7} m/s, On page 12 it is stated that the pre-compression pulse length is L{sub 0} = 10.0m, and compression is by a 'factor of order 20'. They infer a final pulse length of about .5 m and final durations pre-pulse {tau} {approx} .5/5.316 x 10{sup 7} = 9.4 ns; main pulse {tau} {approx} .5/6.114more » x 10{sup 7} = 8.2 ms. The magnetic rigidity of the beam ions is [B{rho}] = {gamma}m v/e = {l_brace} 112.0 T-m - prepulse/129.5 T-m - mainpulse{r_brace}.« less

A proposed, high charge, fixed target experiment (E-158) is planned to run with the highest possible energies available at the Stanford Linear Accelerator Center (SLAC), at 45 and 48 Gev. The charge is up to 6 {center_dot} 10{sup 11} particles in a 370 ns long beam pulse. The SLAC Energy Development (SLED) rf system generates an increasing no-load beam energy, with a linearly decreasing slope. We show how to obtain a current variation that tracks the no-load voltage, resulting in zero energy spread. We discuss the results of a lower energy experiment that verifies the predicted charge and current at the energies required for E-158.

It has been observed that H- current could be improved by adding Ar to H2 plasma. But due to a slower pumping speed for Ar with the existing pumping scheme, the tank pressure will increase quickly during the length of a beam pulse. Since H- stripping loss depends on the tank pressure and gas species, part of the H- beam can be converted to H0 and then H0 can be converted into H+ with background H2 and Ar gas thickness. Therefore, the H- beam current, measured by a Faraday cup, situated at a distance L from GG (ground grid), will decrease because it will be converted into a H+ current. This gives a ratio of the Faraday cup net current to the H- beam current before stripping at background partial pressure of Ar.

Improvement in focusing the proton beam onto the antiproton production target necessitates the development of a higher resolution beam profile monitor. Two designs for the construction of a multiwire profile monitor grid are presented. The first is a conventional strung and tensioned Ti wire design. The second is a photo etched Ti grid of wires bonded to a ceramic substrate. Both have a central wire spacing of 125 /spl mu/m. The completed beam profile monitors are designed to operate in a 120 GeV beam pulse of 5/spl times/10/sup 12/ protons with a 1.5 /spl mu/s duration and will be installed in late 1993. >

Summary form only given. A 1-MV accelerator column composed of aperture lenses that focus and accelerate K/sup +/ ions from a hot-plate is being studied experimentally at Lawrence Berkeley Laboratory. The source must provide adequate current with a sufficiently low temperature so that the beam can be focused to the required small spot at the target. Time-independent codes provide design insight but fail to give any information about beam transients. HIF applications require careful control of the entire beam pulse. Continued refinement of the time-dependent code GYMNOS now allows detailed comparison with experiment and provides guidance for the evolution of the column design.

Two-stage autoacceleration was experimentally realized by passing an annular electron beam through a two-stage passive cavity structure. The kinetic energies of the last quarter part in the beam pulse were increased. Possibility of compression of an intense beam using multistage autoacceleration is discussed.

Brillouin amplifier was numerically simulated by using the theoretic model of transient stimulated Brillouin scattering. Wehave oblained the depleted pump energy extract efficiency, Stokes seed amplification factor, seed beam pulse\|width compression ratio and pump beam pulse\|width compression ratio versus the ratio of seed to pump energy. Experiment was done so as to verify the theory. The theoretical calculation was in good agreement with experimental results.

A comparison of two advanced accelerator concepts, the plasma wakefield accelerator (PWA) and the dielectric wakefield accelerator (DWA), is presented. Emphasis focuses on the peak accelerating gradients and transformer ratios that can be achieved in these two devices. The effect of finite plasma size on the PWA is also analyzed. For the same cavity geometry and drive beam current, it is found that the dielectric wakefield accelerator can generate a peak field that is comparable to the field that can be generated in the plasma wakefield accelerator. Provided that ideal beam pulse shaping can be achieved, the transformer ratio for the PWA is ten times larger than that for the DWA. A change in this ideal pulse shape results in closer agreement for the transformer ratios. Given these encouraging preliminary results for the DWA it is concluded that the simplicity of employing a passive structure as an accelerating medium warrants further experimental testing of the dielectric wakefield accelerator.

Life-time measurements were carried out by using time to amplitude conversion methods, the information being classified in a two- or three-dimensional spectrum by means of an on-line IBM 360-50 computer. In the first case, the zero time corresponds to the compound nucleus formation and is defined by a fast coincidence between a prompt γ-ray and the beam pulse detected by a thin plastic foil. In this way, the time distributions of all the γ-rays associated with a given reaction are simultaneously measured and can be extracted from the resulting 1024 (Eγ) × 256 (time) channels spectrum. The random coincidence peaks shown by all the curves with the same repetition rate as that of the cyclotron frequency (150–200 ns) can be eliminated by computing the difference between the contributions of a γ-ray and of the continuous background. However, as it is rather difficult to resolve the components of a complex decay curve, when several half-lives of intermediate levels interfere, we turned to a three-dimensional analysis in order to estimate these components. The pulse starting the TAC is due to the same type of coincidence as before but the γ-rays taken into account are now delayed relative to the compound nucleus formation. The size of this delayed γ spectrum is limited by the computer memory and only eight energy regions can be selected (four peaks and the backgrounds nearby, for example). By treatinf the 8 (Eγ2) × 1024 (Eγ2) × 256 (time) channels spectrum obtained, we can derive the decay curves of all the γ-rays with respect to each of the delayed γ transitions.

The modification of a low energy electrostatic accelerator for terminal pulsing is described. Beam pulse durations as low as 3.7 nsec have been obtained at the target after acceleration. Under typical operating conditions the beam pulse duration is 4–5 nsec with peak currents of 100–200 μA and a pulse repetition period of 200 nsec.

The intriguing aspect of these experiments is that as little as one sixth of the elec- tron beam pulse is used to bunch and accelerate the ions at which time the acceleration appears to be rattler abruptly terminated. In this paper we address possible reasons for the cutoff of the acceleration process and suggest experi- ments to check the speculations. Also, we briefly men- tion recent developments in the technology of intense electron beam generation and transport, and indicate their relevance to other ion acceleration proposals using linear electron beam geometries. experi~~~~?r~~$~~ '-' however acceleration in the lontext of we shall consider the tl;e LPM.' This model, although speculative, does agree with presently estab- lished features of the experimental data. Keferring to Figure 2, we trace the history of the acceleration pro- cess.

The distribution of the charges contained in the individual beam pulse of the external beam of the Hamburg Isochronous Cyclotron has been studied.

Intense and sharply pulsed muons with 50 ns pulse width and 50 ms pulse distance are now available in our laboratory (UT-MSL) at KEK Booster Utilization Facilityl1,2. Strong backward muons with a focussing property are generated by the superconducting muon channel with 0° take-off angle from the pion production target, while surface muons can be obtained simultaneously by the parasite pion channel with 102.5° take-off angle from the same target. With the aid of multi-telescope and multi-stop TDC system, we are able to measure decay e+ time spectrum from instantaneously intense stopped μ+ with a rate of 104 μ+/pulse. Using beam pulse as a start pulse and multiple e+ as a stopping signal, one can measure μSR time spectrum. Thus, μSR time spectrum can be observed with 50 ns time resolution, so that muon spin rotation can be straightly measured for the frequency up to 10 MHz.

Diamagnetic loop measurements of the heating of a hydrogen plasma by a pulsed, relativistic electron beam indicate strong heating during the decaying part of the beam pulse.

An accelerator timing signal and a logic signal derived from an accelerator-produced nuclear event are used to gate on and off, respectively, a train of crystal-controlled oscillator pulses. The frequency distribution of the number of gated oscillator pulses yields detailed information about the accelerator beam pulse shape.