Rearranging a nanoprobe: Line foci,grid shadow patterns and performance tests

After a major modification of the target chamber at the Leipzig high energy ion nanoprobe the probe forming lens system, consisting of two separated quadrupole doublets, had been carefully realigned. This was done by adjusting the line foci position of each individual quadrupole on the centre position defined by the unfocused beam. Using a high magnification microscope the alignment process is very effective and precise. The lens system could be precisely realigned except an intrinsic rotational misalignment which is essentially reduced by a correction lens.Grid shadow patterns have been taken and analysed in order to assess the characteristics of the system. The dominant aberrations are spherical with an additional parasitic octupole.The grid shadow method is also very useful to determine the best position of the aperture diaphragms which minimizes the influence of the aberrations onto the beam spot size.The rearrangement allowed larger aperture diaphragms for higher beam currents at a moderate increase in beam spot sizes. Performance tests yielded proton microbeam currents and half-widths of 4.5 nA at 1.5 μm, 8.3 nA at 1.5 μm and 17.2 nA at 2 μm. For high resolution work the expected beam spots around 0.3 μm at 100 pA were not achieved. The reason is very likely interference on the beam scanner, correlated in x- and y-direction, which results from the insufficiently rectified power supply voltage of the transconductance amplifier.     

Influence of the beam current density distribution on the spatial resolution of a nuclear microprobe

The paper discusses the effect of nonuniform distribution of the ion beam phase density on the nuclear microprobe resolution. The deconvolution of the beam brightness distribution parameters was performed on the base of the beam current distribution measurements in the object collimator plane. This information gives a possibility to define the ion distribution in the phase set for a beam to be transformed by the probe-forming system into the target plane. A criterion for selecting the optimum collimator dimensions was the highest beam current for the fixed beam spot size (FWHM). This approach, with allowance for the initial distribution, makes it possible to obtain a higher beam current intensity at the center of the spot.     

On the Production of Relativistic Runaway Electrons in Damavand Tokamak

Experimental observations in Damavand tokamak show that hard X-ray is produced by either disruption with I _p  < 20 kA or by shots with I _p  > 20 kA. Hard X-ray also persists from the initiation of plasma discharge to the end. Occurrence of multiple spikes in hard X-ray during the discharge is evident. The propagation of hard X-ray is attributed to runaway electrons. We observe runaway electrons in two regimes with different characteristics. Regime (RADI) is similar to the observations of other Tokamak during disruption on that the plasma current is reduced abruptly and interpreted by Dreicer theory. In the regime of RADII, hard X-ray and subsequently runaway electrons are observed from starting of plasma discharge which provides the condition that the most of runaway electrons contain the toroidal plasma current. Runaway electron beam excites whistler waves and scattered electrons in velocity space and prevent growing the runaway electrons beam.     

Numerical Study on the Two-Dimensional Temperature Fields of Titanium/Aluminum Double-Layer Target Irradiated by High-Intensity Pulsed Ion Beam

Interaction between high-intensity pulsed ion beam (HIPIB) and a double-layer target with titanium film on top of aluminum substrate was simulated. The two-dimensional nonlinear thermal conduction equations, with the deposited energy in the target taken as source term, were derived and solved by finite differential method. As a result, the two-dimensional spatial and temporal evolution profiles of temperature were obtained for a titanium/aluminum double-layer target irradiated by a pulse of HIPIB. The effects of ion beam current density on the phase state of the target materials near the film and substrate interface were analyzed. Both titanium and aluminum were melted near the interface after a shot when the ion beam current density fell in the range of 100A/cm2 to 200A/cm2.     

100 MeV质子回旋加速器二期辐照效应管道设计

针对中国原子能科学研究院100 MeV质子回旋加速器上的单粒子效应辐照装置进行了二期管道设计，采用八极磁铁校正法对束流进行了扩束及均匀化，最终在靶上得到了一个30 cm×30 cm、均匀性好于92%的均匀分布的束斑，满足了单粒子效应实验的需求。为降低靶站处的束流能散及中子本底，采用两级降能的方案，在偏转磁铁前放置1个降能片，将能量分为100 MeV和40 MeV两档，并分别针对这两个能量点进行方案设计，束流利用率均在42%以上。公差分析结果表明，四极磁铁对靶上束斑均匀性的影响大于八极磁铁，安装过程中应优先保证四极磁铁的安装公差。     

A sextupole ion beam guide to improve the efficiency and beam quality at IGISOL

The laser ion source project at the IGISOL facility, Jyväskylä, has motivated the development and construction of an rf sextupole ion beam guide (SPIG) to replace the original skimmer electrode. The SPIG has been tested both off-line and on-line in proton-induced fission, light-ion and heavy-ion induced fusion-evaporation reactions and, in each case, has been directly compared to the skimmer system. For both fission and light-ion induced fusion, the SPIG has improved the mass-separated ion yields by a factor of typically 4-8. Correspondingly, the transmission efficiency of both systems has been studied in simulations with and without space charge effects. The transport capacity of the SPIG has been experimentally determined to be ∼10¹² ions s⁻¹ before space charge effects start to take effect. A direct comparison with the simulation has been made using data obtained via light-ion fusion evaporation. Both experiment and simulation show an encouraging agreement as a function of current extracted from the ion guide.     

Mass spectrometry improvement on an high current ion implanter

The development of accurate mass spectrometry, enabling the identification of all the ions extracted from the ion source in a high current implanter is described. The spectrometry system uses two signals (x-y graphic), one proportional to the magnetic field (x-axes), taken from the high-voltage potential with an optic fiber system, and the other proportional to the beam current intensity (y-axes), taken from a beam-stop. The ion beam mass register in a mass spectrum of all the elements magnetically analyzed with the same radius and defined by a pair of analyzing slits as a function of their beam intensity is presented. The developed system uses a PC to control the displaying of the extracted beam mass spectrum, and also recording of all data acquired for posterior analysis. The operator uses a LabVIEW code that enables the interfacing between an I/O board and the ion implanter. The experimental results from an ion implantation experiment are shown.     

Optimal ion beam,target type and size for accelerator driven systems: Implications to the associated accelerator power

In interactions of different energetic ions with extended targets hydrogen isotopes are the most effective projectiles for the production of spallation neutrons. It is shown that for every target material and incident ion type and energy there is an optimal target size which results in the escape of a maximum number of spallation neutrons from the target. Calculations show that in an ADS, combination of a beam of 1.5 GeV deuteron projectiles and a uranium target results in the highest neutron production rate and therefore highest energy gain. For fast 1.5 GeV d + ²³⁸U ADS with lead or lead–bismuth eutectic moderator, the required ion beam current is only 38% of that for 1 GeV proton projectiles on lead target. It is shown that for a modular ADS with uranium target and output power of 550 MW_th a 1.5 GeV deuteron beam of current 1.8 mA is required, which is easily achievable with today’s technology. For an ADS with k_eff = 0.98 and output power of 2.2 GW_th, the required beam currents for (a) 1 GeV p + Pb and (b) 1.5 GeV d + U systems are 18.5 and 7.1 mA, respectively.     

400 kV强流中子发生器的物理设计

对400 kV强流中子发生器进行了物理设计。采用Poisson/Superfish软件对中子发生器高压电极和加速管的电场分布进行了模拟,结果显示,各关键区域的空间电场最大值远低于击穿电场限值。以强流束旁轴包络方程为基本模型,发展了强流束传输系统束包络的计算机模拟程序IONB1.0,模拟了中子发生器传输系统中40 mA的D束流包络。结果显示,设计方案中所采取的两间隙高梯度加速结构有较强的聚焦性能,能有效抵消强流束空间电荷效应造成的束流发散,加速管出口处的束包络半径约3 cm,由加速管出口处的空间电荷透镜和三重四极磁透镜组成的传输系统能将束流聚焦在约140 cm处的靶上,且束斑直径小于2 cm。     

High precision Hf ion implantation using a high-current ion implanter

The development of accurate mass spectrometry, enabling the identification of all the ions extracted from the ion source and further precise ¹⁸⁰Hf isotope implantation, in a high current implanter is described. The spectrometry system uses two signals (x-y graphic), one proportional to the magnetic field (x-axes), taken from the high-voltage potential with an optic fiber system, and the other proportional to the beam current intensity (y-axes), taken from a beam-stop. The ion beam mass register in a mass spectrum of all the elements magnetically analyzed with the same radius and defined by a pair of analyzing slits as a function of their beam intensity is presented. Hence, it is possible to implant ¹⁸⁰Hf⁺, with less than 1% contamination from neighboring isotopes, in order to conduct material characterization studies by Perturbed Angular Correlations. The precision of the low fluence ion implantation has been done by neutron activation analysis.     

Beam stability improvement of the HIMAC synchrotron using a feed-forward system for magnet power supplies

In order to realize a precise dose distribution in heavy-ion cancer therapy, high beam stability is required for the accelerator complex. Owing to load fluctuation caused by the upper ring, which is one of the two rings in HIMAC, current dips of ≈5-10 Hz were observed in the power supply for the bending/quadrupole magnet of the other lower ring. The parameters of the beam stability, such as the spill variation, the beam position, and the size, were adversely affected by the current dips. In order to suppress these current dips, we developed a new feed-forward system in the magnet power supply. We verified the performance of the feed-forward system by measuring the suppression of the current dips. We also performed beam experiments to measure the variation of the horizontal tune and the structure of the beam spill, which is slowly extracted by the resonance method. The experimental result showed that the current dips were successfully reduced by the system to ΔI/I ∼ 10⁻⁶. It was also confirmed that the horizontal tune and the spill structure could be stabilized by the current dip suppression.     

Guiding and blocking of highly charged ions through a single glass capillary

Highly charged ions produced in an electron beam ion trap, I^q+, q = 10-50, were transmitted through a tapered glass capillary having diameter of at the end. We found that for a particular beam current, there exists an optimum tilting angle of the capillary in which a steady output of ions is observed, while for smaller angles, the ion counts first rise, then gradually decay on a time scale of minutes. In the case of steady transmission, the charge state distribution is found to be slightly towards the lower side.     

A scoping study of the application of neutral beam heating on the TCV tokamak

The TCV tokamak contributes to the physics understanding of fusion plasmas, broadening the parameter range of reactor relevant regimes, by investigations based on an extensive use of the existing main experimental tools: flexible shaping and high power real time-controllable electron cyclotron heating (ECH) and current drive (ECCD) systems. A proposed implementation of direct ion heating on the TCV by the installation of a 20–35 keV neutral beam injection (NBI) with a total power of 1–3 MW would permit an extension of the accessible range of ion to electron temperatures (T_i/T_e ～ 0.1–0.8) to well beyond unity, depending on the NBI/ECH mix and the plasma density. A NBI system would provide TCV with a tool for plasma study at reactor relevant T_i/T_e ratios ～1 and in investigating fast ion and MHD physics together with the effects of plasma rotation and high plasma β scenarios. The feasibility studies for a NBI heating on TCV presented in this paper were undertaken to construct a specification for the neutral beam injectors together with an experimental geometry for possible operational scenarios.     

Stability and design criterion for cable-in-conduit-conductors with a broad transition to normal state

Stability criterion in cable-in-conduit conductors (CICC) is often associated with heat removal rate higher than heat generated in the normal zone, which requires low current density in the strands. We show that this criterion is not a mandatory requirement for serviceability of CICC and that CICC may work reliably at higher current densities. In conditions of limited and well defined perturbations, sufficient stability is provided not by a large amount of copper and high transient heat transfer, but by a smooth transition to the normal state and easy current redistribution. A strand parameter space in terms of I_c and N-value meeting CICC requirements for stability, limited heat generation, and minimum temperature margin is proposed and discussed. The theory predictions are compared with known experimental data on CICC.     

Cross-section for D(p,p)D elastic scattering from 1.8 to 3.2 MeV at the laboratory angles of 155° and 165°

The D(p,p)D cross-sections for elastic scattering of proton on deuterium over incident proton energy range from 1.8 to 3.2 MeV at both laboratory angles of 155° and 165° were measured. A thin solid state target Ni/TiD_x/Ta/Al used for cross-section measurement was fabricated by firstly depositing layers of Ta, Ti and Ni film on the Al foil substrate of about 7 μm in turn using magnetron sputtering and then deuterating under the deuterium atmosphere. The areal density of metal element in each layer of film was measured with RBS analysis by using a 4.0 MeV ⁴He ion beam, while the areal density of the deuterium absorbed in the Ti film was measured with ERD analysis by using a 6.0 MeV ¹⁶O ion beam. The results show that the cross-sections of p-D scattering under this experimental circumstance were much enhanced over the Rutherford cross-section value. It was found that the enhancement increases linearly as the energy of the incident beam increases. The total uncertainty in the measurements was less than 7.5%.     

Surface oxidation of Si assisted by irradiation with large gas cluster ion beam in an oxygen atmosphere

Surface oxidation of Si assisted by Ar cluster impact with a current density of a few μA/cm² under O₂ atmosphere was investigated. Thin-film formation by cluster ion beam presents a number of advantages such as atomic-scale surface smoothing, high density and precise stoichiometry. We used an Ar cluster ion beam with 20 keV and a mean size of 1000 atoms per cluster and measured the emission yields of Si⁺ and SiO⁺ after Ar cluster ion irradiation in O₂ atmosphere using a quadrupole mass spectrometer to investigate the dependence of Si surface oxidation on oxygen partial pressure. It was found that the Si surface was oxidized by Ar cluster ion irradiation in O₂ atmosphere.     

Investigation of thermally stimulated properties of SHI beam irradiated polycarbonate/polystyrene double layered samples

The double layered samples of polycarbonate/polystyrene (PC/PS) have been prepared by solvent casting method and irradiated with 55 MeV C⁵⁺ beam at different ion fluences range from 1 × 10¹¹ to 1 × 10¹³ ion/cm². The effect of swift heavy ion (SHI) beam in interfacial phenomena, phase change, dielectric relaxation, degradation temperature, stability, charge storage and transport mechanism of PC/PS pristine and irradiated double layered samples have been investigated by thermally stimulated discharge current (TSDC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). TSDC show α, β-relaxation peaks shifted to the lower temperatures side with increase of fluence. The activation energy and relaxation time decrease, while the depolarization current and charge released increase with increase in the ion fluences. DSC curve show the glass transition temperature (T_g) and heat capacity decreases with increase in the ion fluences. The TGA characteristics represent the thermal stability, which is found to be decreased with increase in the ion fluences.     

Results of Predictive Fokker?CPlanck Modelling of NBI Deuterons in ITER

First an analytical formalism is presented for calculating the source distribution of ions generated by neutral beam injection (NBI) in tokamak plasmas. A general NBI ion source term, applicable to studies in the phase space up to 6 dimensions, is provided for neutral beams with finite thickness and divergence. Further, using this source term for the envisaged NBI in ITER, we carry out 3D Fokker?CPlanck modelling of the steady-state deuteron distribution function of NBI produced fast deuterons relaxing on bulk plasma components. For two basic ITER scenarios we demonstrate the poloidal profiles of the beam deuteron density, of the NBI generated current as well as of the NBI power deposition to bulk electrons and ions. Further, we evaluate the capability of gamma and NPA diagnostics of NBI ions in ITER and demonstrate the sensitivity of the distributions of NBI generated ions to different ITER operation scenarios.     

Change in magnetic properties of MgB2 thin films after irradiation by 200 MeV Au ion beam

The SHI irradiation induced effects on magnetic properties of MgB₂ thin films are reported. The films having thickness 300-400 nm, prepared by hybrid physical chemical vapor deposition (HPCVD) were irradiated by 200 MeV Au ion beam (S_e ∼ 23 keV/nm) at the fluence 1 × 10¹² ion/cm². Interestingly, increase in the transition temperature T_c from 35.1 K to 36 K resulted after irradiation. Substantial enhancement of critical current density after irradiation was also observed because of the pinning provided by the defects created due to irradiation. The change in surface morphology due to irradiation is also studied.