Increase In Beam Intensity Research Articles

Engineering the optical response of a-Se thin films by employing morphological disorder.

In this article, we experimentally demonstrate for the first time that photobleaching (PB) can be induced in morphologically disordered a-Se thin film, an observation which is opposite of the previously well-known photodarkening (PD) effects in morphologically ordered films. Further, the optical response of the film shows many fold increase with increase in control beam intensity. To explain the observed extraordinary phenomenon, we have proposed a model based on the morphological disorder of a modified surface and its subsequent photo-annealing. Our results demonstrate an efficient and yet simple new method to engineer the optical response of photosensitive thin films. We envision that this process can open up many avenues in optical field-enhanced absorption-based technologies.

Higher-order paraxial theory of the propagation of ring rippled laser beam in plasma: Relativistic ponderomotive regime

This article presents higher-order paraxial theory (non-paraxial theory) for the ring ripple formation on an intense Gaussian laser beam and its propagation in plasma, taking into account the relativistic-ponderomotive nonlinearity. The intensity dependent dielectric constant of the plasma has been determined for the main laser beam and ring ripple superimposed on the main laser beam. The dielectric constant of the plasma is modified due to the contribution of the electric field vector of ring ripple. Nonlinear differential equations have been formulated to examine the growth of ring ripple in plasma, self focusing of main laser beam, and ring rippled laser beam in plasma using higher-order paraxial theory. These equations have been solved numerically for different laser intensities and plasma frequencies. The well established experimental laser and plasma parameters are used in numerical calculation. It is observed that the focusing of the laser beams (main and ring rippled) becomes fast in the nonparaxial region by expanding the eikonal and other relevant quantities up to the fourth power of r. The splitted profile of laser beam in the plasma is observed due to uneven focusing/defocusing of the axial and off-axial rays. The growths of ring ripple increase when the laser beam intensity increases. Furthermore, the intensity profile of ring rippled laser beam gets modified due to the contribution of growth rate.

Scientists and Students from Hong Kong Join a Top Particle Physics Experiment

A team of physicists from Hong Kong has now formally joined one of the most prestigious physics experiments in the world. Following a unanimous vote of approval today by its Collaboration Board, ATLAS has admitted the Hong Kong team as a member. The ATLAS Collaboration operates one of the largest particle detectors in the world, located at the Large Hadron Collider (LHC), the world's highest energy particle accelerator at CERN, Switzerland. In 2012, the ATLAS team — along with the CMS Collaboration — co-discovered the Higgs boson, or so-called 'God Particle'. The gigantic but sensitive and precise ATLAS detector, together with the unprecedentedly high collision energy and luminosity of the LHC, make it possible to search for fundamentally new physics, such as dark matter, hidden extra dimensions, and supersymmetry — a proposed symmetry among elementary particles. The LHC is currently undergoing an upgrade, targeting a substantial increase in beam energy and intensity in a year's time. It is widely expected that the discovery of the Higgs boson is only the beginning of an era of new breakthroughs in fundamental physics. All these exciting opportunities are now opened up to scientists and students from Hong Kong.

Advances in tracking and trigger concepts

Increasing beam intensities and input data rates require to rethink the traditional approaches in trigger concepts. At the same time the advanced many-core computer architectures providing new dimensions in programming require to rework the standard methods or to develop new methods of track reconstruction in order to efficiently use parallelism of the computer hardware. As a results a new tendency appears to replace the standard (usually implemented in FPGA) hardware triggers by clusters of computers running software reconstruction and selection algorithms. In addition that makes possible unification of the offline and on-line data processing and analysis in one software package running on a heterogeneous computer farm.

A study on prevention of an electric discharge at an extraction electrode of an electron cyclotron resonance ion source for cancer therapy

A compact ECR ion source has utilized for carbon radiotherapy. In order to increase beam intensity with higher electric field at the extraction electrode and be better ion supply stability for long periods, electric geometry and surface conditions of an extraction electrode have been studied. Focusing attention on black deposited substances on the extraction electrode, which were observed around the extraction electrode after long-term use, the relation between black deposited substances and the electrical insulation property is investigated. The black deposited substances were inspected for the thickness of deposit, surface roughness, structural arrangement examined using Raman spectroscopy, and characteristics of electric discharge in a test bench, which was set up to simulate the ECR ion source.

Design upgrade of the ISOLDE target unit for HIE-ISOLDE

The High Intensity and Energy HIE-ISOLDE project is a major upgrade of the existing ISOLDE and REX-ISOLDE facilities with the objective of increasing the energy and the intensity of the delivered radioactive ion beams (RIB) [1]. In order to accommodate the future increase of primary beam intensity delivered by the new LINAC4 H− driver to the Proton Synchrotron Booster (PSB) [2] and from this to ISOLDE, a major study is being carried out to upgrade the existing designs of the ISOLDE target and its supporting infrastructure. In particular, the extraction optics plays an important role in the initial beam transport and the quality of the beam supplied to the mass separators. Important factors include the emittance of the beam and the beam profile to avoid beam losses.A new double electrode extraction system has been developed for simplifying and improving the interface between the target unit and the frontend (target coupling table). Numerical and experimental studies have been performed in order to define the new extraction geometry, and the coupling table has been adapted to keep the compatibility. An alternative heating system is under study. An electron bombardment heating system is being developed as an option for avoiding the employment of big cross section cables. The results of these studies and the mechanical models developed are presented and discussed.

A vertical-beam target station and high-power targetry for the cyclotron production of radionuclides with medium energy protons

A vertical-beam target station (VBTS) is described to exploit the high-intensity proton beams delivered by the upgraded separated-sector cyclotron of iThemba LABS for the production of longer-lived, high value radionuclides such as 22Na, 68Ge and 82Sr. Aspects of the targetry are discussed as well as a beam splitter, which makes it possible to perform radionuclide production bombardments simultaneously in two irradiation vaults. With tandem targets in two stations, four targets can be bombarded simultaneously. The delivery of 66MeV proton beams of higher intensity has been realized by installing fixed frequency, flat-top RF resonators on both the main cyclotron and an injector cyclotron. The increase in beam intensity also required new non-destructive diagnostic components in the relevant high-energy beamlines. An overview is given of the current radionuclide production target stations, their similarities and differences and the role of the VBTS in the production programme.

Study of Neutron-Rich Hypernuclei by the (π −, K +) Reaction at J-PARC

We are planning to perform an experiment at J-PARC and produce new neutron-rich Λ hypernuclei by using the (π−, K+) reaction (J-PARC E10). As the first step, we are planning to produce \({^6_{\Lambda}{\rm H}}\) hypernuclei with a 6Li target. To conduct this experiment, we are developing new detectors, those are scintillating fiber tracker, and silicon strip detector, for high rate operation to aim at increasing beam intensity up to 107/spill. As a result of beam test in Jun 2012, we are going to use high-rate beam at least 107/spill.

Property change during nanosecond pulse laser annealing of amorphous NiTi thin film

Nanosecond lasers of different intensities were pulsed into sputter-deposited amorphous thin films of near equiatomic Ni/Ti composition to produce partially crystallized highly sensitive R-phase spots surrounded by amorphous regions. Scanning electron microscopy having secondary and back-scattered electrons, field emission scanning electron microscopy, optical microscopy and X-ray diffraction patterns were used to characterize the laser treated spots. Effect of nanosecond pulse lasering on microstructure, morphology, thermal diffusion and inclusion formation was investigated. Increasing beam intensity and laser pulse-number promoted amorphous to R-phase transition. Lowering duration of the pulse incidence reduced local film oxidation and film/substrate interference.

Characterization of a flat-panel detector for ion beam spot measurements

Dynamic beam delivery techniques are being increasingly used for cancer therapy. Scanning ion beams require extensive and time-demanding quality assurance procedures and beam tuning. Accordingly, fast measurement techniques improving the efficiency of the procedures and accommodating the safety requirements are highly desirable. Major requirements for a detector used for beam-shape measurements are high spatial resolution in two dimensions, reusability, online readout and easy handling. At the Heidelberg Ion Beam Therapy Facility (Germany), we examined the performance of the RID 256 L flat-panel detector for beam spot measurements. The two-dimensional beam profiles of proton and carbon ion beams measured were compared to measurements with radiographic films at intermediate energies using the Γ index. The difference to the beam width measured with radiographic films of less than 3% demonstrates sufficient accuracy of ion beam width measurements possible with this detector for both proton and carbon ion beams. The beam shapes were also measured at different beam intensities. At both the highest and lowest energies available at the HIT, no beam spot-shape deformation was found with increasing beam intensities, as long as the boundary of the dynamic range was not exceeded. The signal leak along the readout direction was identified as an undesirable effect. However, due to small amplitudes and static beams, this effect is of minor importance for beam spot measurements. Distortion of results due to detector radiation damage was monitored. No detector radiation damage was observed over the experiments. Moreover, the observed short-time detector response stability (within ±0.1%) as well as medium term stability (within 0.5% in 15 months) was excellent. This flat-panel detector is compact and easy to use. Together with its low weight, this helps to speed up measurement procedures substantially. All these properties make this an ideal detector for the fast, high-resolution imaging of static ion beam spots needed for constancy measurements in daily beam quality assurance and for accelerator tuning. For daily use, radiation damage has to be monitored continuously and corrected for if necessary.

Ar beam induced desorption from different materials at TSL

This paper describes new experiments on the heavy ion desorption yield measurements with 5 MeV/u Ar 8+ and summarizes all results of experiments with 5 MeV/u Ar 8+ performed at The Svedberg Laboratory in Uppsala (Sweden). These results are important for the update and design of the FAIR facility at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt (Germany) where the required increase in beam intensity is limited by ion induced pressure instability. It was shown that lowest desorption yields can be achieved with gold coatings, whereas grazing incident loss increases the desorption yield by roughly an order of magnitude compared to perpendicular loss. The desorption yield of saturated NEG samples was measured to be higher compared to any non pumping samples. The desorption yield of copper can be lower and higher compared to stainless steel depending on cleaning procedure and sample history. Additionally the secondary electron and ion yield was measured to be a few tens of electrons and ions emitted per projectile impact in backward direction. Their influence on the desorption yield due to secondary effects was less than 5% compared to the primary desorption by the high energetic projectile.

Increase in Irradiation Beam Intensity by Using a Hybrid Target System in Cyclotron-Based Neutron Capture Therapy

A cyclotron-based epithermal neutron generator has been expected to achieve the early realization of hospital-based boron neutron capture therapy. The system using a hybrid target composed of a thin tungsten (W) layer and a thick beryllium (Be) one with 30MeV protons and a beam-shaping assembly was previously proposed as a better generator candidate than the system using only a thick W or Be layer. In this study, to clearly show that the hybrid target system is more clinically useful than the other two, all three target systems were compared using epithermal neutron intensity as a figure of merit under an equal condition of the harmful effect of fast neutron dose. We found that the hybrid system using a W layer of appropriate thickness increased the epithermal neutron intensity by 107 and 32% compared with systems using only W or Be, respectively, with the same harmful fast neutron component. It is concluded that the hybrid target system is more useful in terms of epithermal neutron intensity than systems with either W or Be as a generator using the 30MeV proton accelerator and beam-shaping assembly.

Funnel cone for focusing intense ion beams on a target

AbstractWe 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.

Highlights of heavy ion fusion induced by neutron-rich radioactive nuclei near the Coulomb barrier

The use of neutron-rich radioactive isotope beams for synthesizing heavy elements is a subject of continuing interest. Current experiments utilize low intensity beams to study reaction mechanisms for fusion induced by neutron-rich radioactive nuclei. Enhanced fusion cross sections were observed near and below the Coulomb barrier. A lowering of the barrier height was observed for heavy mass compound systems. Future experiments will benefit from improving detectors and increasing beam intensities.

Increase in Irradiation Beam Intensity by Using a Hybrid Target System in Cyclotron-Based Neutron Capture Therapy

A cyclotron-based epithermal neutron generator has been expected to achieve the early realization of hospital-based boron neutron capture therapy. The system using a hybrid target composed of a thin tungsten (W) layer and a thick beryllium (Be) one with 30MeV protons and a beam-shaping assembly was previously proposed as a better generator candidate than the system using only a thick W or Be layer. In this study, to clearly show that the hybrid target system is more clinically useful than the other two, all three target systems were compared using epithermal neutron intensity as a figure of merit under an equal condition of the harmful effect of fast neutron dose. We found that the hybrid system using a W layer of appropriate thickness increased the epithermal neutron intensity by 107 and 32% compared with systems using only W or Be, respectively, with the same harmful fast neutron component. It is concluded that the hybrid target system is more useful in terms of epithermal neutron intensity than systems with either W or Be as a generator using the 30MeV proton accelerator and beam-shaping assembly.

Characterization of signs change of nonlinear refraction in ZnSe based on a modified double 4 f imaging system with a phase object

Signs change of nonlinear refractive index in ZnSe is observed by employing a modified double 4 f imaging system at the wavelength of 800 nm using picosecond pulses with different pulse energies. This process results from the competition of the bound electronic nonlinear refraction and the free carrier refraction. At low intensity, positive nonlinear refraction is obtained, which is attributed to bound electrons. As the increase of laser beam intensity, the nonlinear refractive index become small, and changes to negative. This is ascribed to free carriers generated by two-photon absorption. Additionally, the nonlinear refractive index of bound electron and the refractive index change of free carrier are determined unambiguously by a simple method.

Measurement of femtosecond electron pulse length and the temporal broadening due to space charge

The temporal width of ultrashort electron pulses as a function of beam intensity was measured on the femtosecond time scale with a customized streak camera. The results show that the temporal profile of an electron pulse is Gaussian at low beam intensity and progressively evolves to a top-hat shape due to space charge broadening as the beam intensity increases. The strong correlation between the pulse width and beam intensity observed in our streaking measurements agrees very well with the mean-field calculation and supports the main conclusion of previous theoretical studies that the space charge broadening plays a determinant role.

Basic features of a charged particle dynamics in a laser beam with static axial magnetic field

AbstractIn this paper, the trajectory and kinetic energy of a charged particle, subjected to interaction from a laser beam containing an additionally applied external static axial magnetic field, have been analyzed. We give the rigorous analytical solutions of the dynamic equations. The obtained analytical solutions have been verified by performing calculations using the derived solutions and the well known Runge-Kutta procedure for solving original dynamic equations. Both methods gave the same results. The simulation results have been obtained and presented in graphical form using the derived solutions. Apart from the laser beam, we show the results for a maser beam. The obtained analytical solutions enabled us to perform a quantitative illustration, in a graphical form of the impact of many parameters on the shape, dimensions and the motion direction along a trajectory. The kinetic energy of electrons has also been studied and the energy oscillations in time with a period equal to the one of a particle rotation have been found. We show the appearance of, so-called, stationary trajectories (hypocycloid or epicycloid) which are the projections of the real trajectory onto the (x, y) plane. Increase in laser or maser beam intensity results in the increase in particle’s trajectory dimension which was found to be proportional to the amplitude of the electric field of the electromagnetic wave. However, external magnetic field increases the results in shrinking of the trajectories. Performed studies show that not only amplitude of the electric field but also the static axial magnetic field plays a crucial role in the acceleration process of a charged particle.At the authors of this paper best knowledge, the precise analytical solutions and theoretical analysis of the trajectories and energy gains by the charged particles accelerated in the laser beam and magnetic field are lacking in up to date publications. The authors have an intention to clarify partly some important aspects connected with this process. The presented theoretical studies apply for arbitrary charged particle and the attached figures-for electrons only.

On beam intensity upgrade in the commercial cyclotrons of negative hydrogen ions

Compact isochronous cyclotrons to accelerate negative hydrogen ions of up to 30 MeV are widely used for production of medical isotopes and other applications. The physical and technical parameters of different accelerators are analyzed and compared. Measures to improve performance and to increase beam intensity are discussed.

Photoinduced two-dimensional gratings based on dye-doped cholesteric liquid crystal films

This work elucidates photoinduced two-dimensional (2D) gratings in dye-doped cholesteric liquid crystal films. The helical pitch is increased by green-beam-induced trans-cis isomerization and a concomitant thermal effect. Two-dimensional gratings appear when the green beam is turned off. Grating formation results from elastic instability caused by restored strain arising from helical pitch reduction. Grating lifetime increases as green beam intensity increases and declines under irradiation with a strong red beam. Variation in grating spacing with green intensity with various pitches is also examined.