Small Energy Spread Research Articles

Generation and Propagation of High Quality Proton Beams Produced by Laser Plasma Interactions

The acceleration of proton beams during the interaction of an ultra short and ultra intense laser pulse with matter is possibly the most important application of compact laser systems with multi-terawatt and petawatt power. High quality beams with a small energy spread are required for applications where spatially accurate energy deposition is important. For some specific applications the target may be located far from the acceleration region, in which case space charge effects and the interaction with an ambient plasma may deteriorate the beam quality during its propagation.Here, first we review a recently proposed method for producing high quality proton beams using short laser pulses and a target made of a layer of heavy ions followed by a thin proton layer with a transverse size smaller than the pulse waist. Subsequently, we investigate the effects of the beam propagation through a plasma slab in a simplified one-dimensional model.

Some fundamental considerations in resonance imaging using fast neutrons

Resonance imaging with mono-energetic (or quasi-mono-energetic) fast neutrons is able to map features in bulk samples in a way that is sensitive to their elemental composition. It has a number of potential applications, for example, in mining and in the detection of contraband substances such as drugs and explosives. The realisation of these applications depends on the availability of intense neutron sources with a narrow energy distribution and also the development of position-sensitive fast neutron detectors that have adequate efficiency and resolution. Both of these topics present many challenges for research in applied physics. Developments in the use of the reaction D(d,n) 3He as an intense, accelerator-based source of neutrons with a reasonably small energy spread over a wide energy range will be described. In addition, the physics of neutron detection will be discussed in relation to resolution and efficiency using position-sensitive detectors based on a proton radiator and a scintillator. In this case, both the use of image intensifiers coupled to CCDs as well as the use of TFT imaging screens (for example as developed by Varian) will be described. These will be contrasted with recent developments using channel plates.

Development of a low-energy monoenergetic neutron source for applications in low-dose radiobiological and radiochemical research

The McMaster University 3 MV KN Van de Graff accelerator facility primarily dedicated to in vivo neutron activation measurements has been used to produce moderate dose rates of monoenergetic fast neutrons of energy ranging from 150 to 600 keV with a small energy spread of about 25 keV (1 σ width of Gaussian) by bombarding thin lithium targets with 2.00–2.40 MeV protons. The calculated dose rate of the monoenergetic neutrons produced using thin lithium targets as functions of beam energy, target thickness, lab angle relative to beam direction, and the solid angle subtended by the sample with the target has also been reported.

Equilibrium and low-frequency stability of a uniform density, collisionless, spherical Vlasov system

Equilibrium and stability of a collisionless, spherical Vlasov system with uniform density are considered. Such an electron system is useful for the Periodically Oscillating Plasma Sphere (POPS) fusion system. In POPS the space charge of a uniform-density spherical electron cloud provides a harmonic well for an under-dense thermal ion population. Previous special solutions [D. C. Barnes, Phys. Plasmas 6, 4472 (1999)] are extended to arbitrary energy dependence. These equilibrium distribution functions and their first derivatives may be made nonsingular, in contrast to the previous solutions. Linear stability of general spherical equilibria is considered, and reduced to a one-dimensional calculation by the introduction of a spherical harmonic decomposition. All azimuthal mode numbers are degenerate. Using this formalism, the low-frequency stability of a collisionless, spherical Vlasov electron system coupled to a minority ion cloud is studied for the class of uniform-density electron equilibria found. In the low-frequency (adiabatic) limit, the general kinetic stability formalism can be integrated to find a closed form for the response of electron number density. The adiabatic response operator is shown to be self-adjoint. Computation of its eigenvalues proves the constant-density electrons/thermal ions system in POPS to be mostly stable to ion-electron electrostatic modes. Unstable modes are avoided unless central electrons have an extremely small energy spread. These results may also be useful for the consideration of gravitational and beam systems.

Trapping, compression, and acceleration of an electron bunch in the nonlinear laser wakefield.

A scheme of laser wakefield acceleration, when a relatively rare and long bunch of nonrelativistic or weakly relativistic electrons is initially in front of the laser pulse, is suggested and considered. The motion of test electrons is studied both in the one-dimensional (1D) case (1D wakefield) and in the case of three-dimensional laser wakefield excited in a plasma channel. It is shown that for definite parameters of the problem the bunch can be trapped, effectively compressed both in longitudinal and transverse directions, and accelerated to ultra-relativistic energies in the region of first accelerating maximum of the wakefield. The accelerated bunch has sizes much less than the plasma wavelength and relatively small energy spread.

Characteristics of a large diameter reactive ion beam generated by an electron cyclotron resonance microwave plasma source

A new ion source with a large beam diameter generated by an electron cyclotron resonance microwave plasma source is presented. Ion beams with a beam diameter of >160 mm and a maximum argon-ion current density of 2.1 mA/cm2 are obtained. For this large two-electrode silicon-ion extraction optics are mounted into an electron cyclotron resonance microwave plasma source. With ion extraction optics installed an electron temperature up to three times higher than without optics was observed. Due to this high electron temperature (up to 12 eV) the O+ concentration as compared to the O2+ concentration is enhanced in an oxygen plasma. Therefore, a very reactive oxygen ion beam with an ion current density of 1.1 mA/cm2 can be generated. Ion energies of 1 keV corresponding to the screen grid voltage are obtained with a small energy spread of 10 eV full width at half maximum or less. The low working pressure (about 10−4 mbar) is well suited for low-pressure ion-beam processes.

Performance of multicusp plasma ion source for focused ion beam applications

The multicusp plasma ion source has found many uses such as in ion implanters, ion projection lithography, and injectors for particle accelerators. This source is favorable for such applications because of its low ion temperature, small energy spread, and good stability. These properties also offer the tantalizing possibility of utilizing such a source to create a noncontaminating focused ion beam (FIB) system for semiconductor fabrication line use and advanced photomask repair applications. We have made measurements of the brightness of this ion source and have done some preliminary applications work with a Kr+-enabled FIB system for mask repair and ion milling. A specially designed multicusp plasma ion source has been used to measure focused beam spot size versus current relationships for several inert gas ion species. From these data the axial brightness of the ion source was ascertained. For the extraction of Kr+ from the source we find an angular intensity of 12 μA/sr and a virtual source size of 16.9 μm, giving an approximate value for the image-side brightness (at 30 keV) of 1650 A/cm2 sr. We find good sputtering rates for the Kr+ beam, and the Aerial image measurement system measurements show essentially 100% transmission of 193 nm light through photomask quartz that had been implanted with a significant dose of krypton.

Analysis of the longitudinal collective behavior in a50GeV×50GeVmuon collider ring

Simulations of the longitudinal instability in the $50\mathrm{GeV}\ifmmode\times\else\texttimes\fi{}50\mathrm{GeV}$ muon collider ring have been performed. Operation of the ring close to the slippage factor ${\ensuremath{\eta}}_{1}\ensuremath{\simeq}{10}^{\ensuremath{-}6}$, such that synchrotron motion is frozen, minimizes the need for rf to maintain the bunch length. However, there is still an energy spread due to the bunch wake. For design parameters of the ring, this induced energy is too large and must be controlled. This paper demonstrates that the bunch wake may be compensated for by two rf cavities with low rf voltages. These studies were made at the nominal design point, and sensitivities to errors were explored. It is seen that the small energy spread of the beam ($\ensuremath{\delta}E/E=3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$) in the $50\mathrm{GeV}\ifmmode\times\else\texttimes\fi{}50\mathrm{GeV}$ muon collider ring can be maintained during the 1000 turn lifetime of the muons. Controlled beam dynamics requires proper choice of rf parameters (rf voltage, rf frequency, and phase offset) for two cavities; these parameters depend on the ring design through the impedance, beam pipe radius, and momentum compaction. The simulation also shows that the computation of wake field using bins of variable width (each with a constant number of macroparticles in each bin) gives an accurate wake and also yields reduced computing time compared to an evaluation of the wake as the direct sum over the wakes of all preceding macroparticles.

Laser-induced electron trapping in plasma-based accelerators

Trapping of plasma electrons in the self-modulated laser wakefield accelerator (LWFA) via the coupling of Raman backscatter to the wake is examined analytically and with three-dimensional (3-D) test particle simulations. The trapping threshold for linear polarization is much less than for circular and occurs for wake amplitudes of δn/n∼25%, which is well below wave breaking. Self-channeling provides continuous focusing of the accelerated electrons which, along with relativistic pump laser effects, can enhance the energy gain by a factor ⩾2. The colliding pulse method for injecting electrons in the standard LWFA is examined. Simulations of test electrons in 3-D fields indicate the production of relativistic (⩾25 MeV) high-quality electron bunches with ultrashort durations (a few femtoseconds), small energy spreads (a few percent), and low normalized emittances (1 mm mrad).

Simulation of ultrarelativistic beam dynamics in the plasma wake-field accelerator

With two-dimensional hybrid code LCODE, the long-term dynamics of two drivers in plasma is studied. The bunch train is shown to produce a well-controlled wake-field good for particle acceleration. In this wake-field, a narrow witness bunch can be accelerated with a small energy spread (several percent), a high energy gain (exceeding the initial driver energy), and the driver-witness efficiency about 20%. The long shaped bunch is unusable for particle acceleration, since it is rapidly destroyed by the transverse two-stream instability.

Conical beams from open nanotubes

Electron guns are indispensable devices that are widely used in household and industrial appliances. Field electron-emitting sources (which emit electrons by tunnelling effects in electric fields), with their small size, small energy spread, high current density and no requirement for heat, have distinct advantages over thermionic emitters. We have made a field electron emitter from hollow, open-ended carbon nanotubes.

Slow Positron Beam with Small Energy Spread in the Magnetic Field Using Reflection Type Remoderator

Slow Positron Beam with Small Energy Spread in the Magnetic Field Using Reflection Type Remoderator

High-brightness photoelectric field-emission cathodes for free-electron laser applications

Field emission from very fine needles in an electric field is characterized by a very small energy spread, less than 1 eV, and emittance of the order of 10 −8π m rad, normalized. In microsecond pulses, total currents in excess of 6 A have been observed, corresponding to normalized brightness of the order of 10 15 A/m 2 str, which is four orders of magnitude higher than conventional sources. Recently, photoemission has been observed from needles operating in fields too small for significant field emission. Total currents as high as 10 A have been observed in nanosecond pulses. The quantum efficiency is of the order of unity. Using e-beams of such high brightness, single-pass FELs can operate at very long and very short wavelengths, with very low total e-beam current. In the FIR, it is possible to construct Cerenkov FELs with enough gain ( e 20) to reach saturation in a single pass using only 10 mA total electron-beam current. In the UV, it is possible to build single-pass Compton-backscatter FELs operating at total current less than 300 mA.

Ultra-High Resolution with The Jem-2010F Field-Emission Tem

Historically, high probe current in small probes has been the principal virtue of the field emission TEM. Analytical performance is greatly enhanced[1] and fine probe mapping an important analytical tool for trace element segregation and very fine scale high resolution chemical imaging. Less appreciated is the enhanced high resolution capability due to the small energy spread of the electron source and higher coherency due to reduced primary and virtual source size. The envelope function of the phase contrast transfer function (PCTF) is drastically improved reducing image blurring due to both chromatic aberration and specimen illumination angle. This is especially true for the high spatial frequencies beyond the first zero. Intensities sufficient for image formation can be obtained from these higher frequency regions. Since the PCTF does not change its form, photographing images at the Scherzer condition will yield higher resolution with higher coherency, however, the transfer of the specimen potential corresponding to contrast enhanced regions is in the oscillations form beyond the first zero. Changes in the defocus will lead to changes in transferred frequencies beyond the first zero and possible extinctions of otherwise transferred information since the oscillations will pass through zero contrast. Interpretation of images under these conditions will, therefore, require accurate measurement of the optical parameters of the microscope and especially accurate measurements of the defocus conditions. It is also important to calculate images under these conditions for comparison with measured images which give the insurance of defocus conditions supposed to be presented.

Beam emittance measurements on multicusp ion sources

Multicusp ion sources are used for various applications. Presently, the implementation of this type of ion source is planned for the development of an ion beam lithography machine, which will be used for the projection of sub-0.2 μm patterns onto a wafer substrate. Since, for this application, a very good beam quality and a small ion energy spread are required, emittance measurements have been performed on a multicusp ion source for various source conditions. It is shown that the installation of proper capacitors between the extraction electrodes is necessary to avoid rf pickup, which otherwise leads to a distortion of the beam emittance. The influence of the magnetic filter field on the beam emittance has been investigated, and the beam emittance of a dc filament-discharge plasma has also been compared to that of a rf-generated plasma.

Information limit of a 300kV field emission TEM

The use of an FEG on a high resolution microscope will increases the spacial and temporal coherence of the microscope due to the improvement in coherence of the electron source. Additionally, the improved energy spread will extend the envelope of the phase contrast transfer well beyond the first zero point at Sherzer focus. Between the Sherzer point and the ultimate point of zero contrast (the information limit) there is useful information for the analysis of high-resolution images. We have already obtained a resolution of 0.194nm and an information limit of 0.14nm by using the 200kV FETEM (JEM-2010F). In the present experiment, we attempted to obtain a higher resolution and information limit by using the 300kV FE TEM (JEM-3000F).The electron gun is configured with a ZrO/W Shottky emitter which has a small energy spread with a stable emission. The objective lens has a spherical and chromatic aberration of 0.6mm and 1.3mm respectively. The specimen used was gold islands on an amorphous Ge thin film.

Production of a spinpolarized keV Sr + ion beam by laser-optical pumping

Using a well collimated Sr + ion beam with very small energy spread in combination with collinear laser-optical pumping, we have obtained a beam with high electron spin polarization. The Sr + ions were produced with μA intensity by surface ionisation in a point-like hot iridium-plated Ta tube and extraction into a beam guiding system. The 5 2S 1 2 5 2P 1 2 transition was pumped by circularly polarized laser light (421.6 nm) propagating antiparallel to the ion beam. The laser is actively stabilized to the SP transition by means of a newly developed method. The final electron spin polarisation of the ground state for the most abundant 88Sr + isotope was measured to be greater than 90%.

Neutron generator at Hiroshima University for use in radiobiology study.

A neutron generator (HIRRAC) for use in radiobiology study has been constructed at the Research Institute for Radiation Biology and Medicine, Hiroshima University (RIRBM). Monoenergetic neutrons of which energy is less than 1.3 MeV are generated by the 7Li(p,n)7 Be reaction at proton energies up to 3 MeV. The protons are accelerated by a Schenkel-type-accelerator and are bombared onto the 7Li-target. An apparatus for the irradiation of biological material such as mice, cultured cells and so on, was designed and will be manufactured. Neutron and gamma-ray dose rates were measured by paired (TE-TE and C-CO2) ionization chambers. Contamination of the gamma ray was less than about 6% when using 10-microns-thick 7Li as a target. Maximum dose rates for the tissue equivalent materials was 40 cGy/min at a distance of 10 cm from the target. Energy distributions of the obtained neutrons have been measured by a 3He-gas proportional counter. The monoenergetic neutrons within an energy region from 0.1 to 1.3 MeV produced by thin 7Li or 7LiF targets had a small energy spread of about 50 keV (1 sigma width of gaussian). The energy spread of neutrons was about 10% or less at an incident proton energy of 2.3 MeV. We found that HIRRAC produces small energy spread neutrons and at sufficient dose rates for use in radiobiology studies.

A low-energy-spread rf accelerator for a far-infrared free electron laser

A high electron current and a small energy spread are essential for the operation of a free electron laser (FEL). In this paper we discuss the design and performance of the accelerator for FELIX, the free electron laser for infrared experiments. The system consists of a thermionic gun, a prebuncher, a buncher and two standard commercial linac sections. The gun is operated with a pulse duration of 280 ps and a bunch charge of 200 pC. After compression to 35 ps by the prebuncher, the bunches are accelerated to 4 MeV in the buncher and simultaneously compressed to 6 ps. The principle of the method is that the order of the electrons is conserved in the buncher, so that the resulting more or less linear energy-phase relationship along each bunch can be compensated effectively against space charge forces and the accelerating field gradient in the linacs, via an appropriate choice of the phase of the rf wave. Behind the linacs an rms energy spread of 0.30% has been measured.

Design study of the secondary-beam line at RCNP

A beam line for use with the new RCNP ring cyclotron ( K = 400) has been designed to separate unstable nuclei produced in high energy heavy-ion reactions. The separation principle takes advantage of A- and Z-dependence of the energy loss of ions in matter (energy degrader), and enables us to obtain the reaction products in the form of a secondary beam. Ion-optical consideration has been made for the separator by treating the degrader as one of the ion-optical elements. By this new treatment it has been made possible to optimize the optics of the system according to experimental requirements. The methods (i) to achieve an achromatic focusing of the secondary beams and (ii) to obtain beams with small energy spread are discussed. The effects of energy straggling in the degrader are shown to be the principal factor to limit the isotopic resolution of the separator. Ion-optical calculations have been performed for the secondary-beam line taking into account the transfer matrix elements up to third order. The design specifications are described and the expected profiles of the secondary beams are presented.