10 MeV质子等时性回旋加速器的设计研究

给出10MeV质子等时性回旋加速器的等时性磁场设计,中心区的设计以及加速后最终的束流品质,该加速器可作为正电子断层扫描装置的配套设备,用于生产中短寿命放射性同位素等.它沿半径方向只用一套线圈励磁,等时性磁场的建立完全由磁极形状决定.中心区的设计满足了轨道中心化的要求,并给出较大的横向和纵向接受度,以获得足够的束流强度. 经过172圈加速后,最终的束流品质满足要求.     

Beam Dynamics Simulation in the LINAC-100 Accelerator Driver for the DERICA Project

The results of uranium ion beam dynamics simulation in front-end and superconducting sections of the accelerator-driver LINAC-100 for the new rare isotope facility DERICA (JINR, Dubna) are presented. The optimum parameters are chosen for the buncher accelerator with radiofrequency quadrupole focusing (RFQ) for uranium ion beam acceleration from the ion source up to the energy of 570 keV/nucleon. LINAC-100 modular superconducting part layout for uranium beam acceleration from 3 to 100 MeV/nucleon is obtained. The energies for the stripper section installation are chosen.

     

The continuous energy dependence of pp differential elastic cross sections between 500 and 1200 MeV

Using an internal jet target in the Saturne synchrotron, we have measured the proton-proton differential elastic cross section at 90° c.m. as a continuous function of energy (from 500 to 1200 MeV) during the acceleration of the beam. The energy resolution is about 2 MeV. The results are compared to predictions of phase-shift analyses and discussed in connection with amplitude analyses at 90° c.m. No resonant structure was observed and no evidence for narrow dibaryons was found.     

The58Ni(12C,γ)70Se reaction

The⁵⁸Ni(¹²C,γ)⁷⁰Se capture reaction was studied with beam energies ofE _12C=30 to 42 MeV. The capture events were identified by means of the residual activity produced in the reaction. At a beam energy of 38 MeV the capture cross section has been determined to 1.5±0.7 μb. AtE _12C=30, 34 und 42 MeV we established upper limits of 0.3, 0.5 and 0.6 μb, respectively. The experimental results are compared with a statistical model calculation.     

The excitation functions of complete and incomplete fusion reactions of 6Li with Pt nuclei

Experimental results from measuring the energy dependences of cross sections of fusion and transfer reactions for ⁶Li beams and Pt targets are presented. The experiments were performed using the MSP-144 magnetic analyzer; stacks of platinum foils were installed at the focal plane of this analyzer. In the energy range 22.5–42.5 MeV, the energy resolution of the beam hitting the target stack was not worse than 0.25 MeV and that of the transmitted beam was not worse than 0.40 MeV. The yields of products of neutron and deuteron transfer reaction on target nuclei were measured using the γ activity induced in the platinum targets. Thus, excitation functions for transfer reactions were obtained in a wide energy range, including near the Coulomb barrier. It was shown that the basic reaction channel is the deuteron capture from ⁶Li. In this case, the maximum of the excitation function for ⁶Li breakup and subsequent deuteron capture lies near the Coulomb barrier of the reaction.     

The ISAC post-accelerator

The acceleration chain of the ISAC facility boosts the energy of both radioactive and stable light and heavy ions for beam delivery to both a medium energy area in ISAC-I and a high energy area in ISAC-II. The post-accelerator comprises a 35.4 MHz RFQ to accelerate beams of A/q ≤ 30 from 2 keV/u to 150 keV/u and a post stripper, 106.1 MHz variable energy drift tube linac (DTL) to accelerate ions of A/q ≤ 6 to a final energy between 0.15 MeV/u to 1.5 MeV/u. A 40 MV superconducting linac further accelerates beam from 1.5 MeV/u to energies above the Coulomb barrier. All linacs operate cw to preserve beam intensity.     

HIAF-CRing 中的俘获加速效率研究(英文)

以HIAF-CRing上典型离子238U34+为研究对象,对其纵向俘获和加速的动力学过程进行了研究。累积后的粒子能量为800 MeV/u, 经过绝热俘获和加速后,粒子被加速至1 130 MeV/u。研究结果表明,通过选择适当的俘获时间、绝热参数以及相空间面积因子等参数,应用优化后的高频俘获加速曲线,可以获得更高的俘获和加速效率。通过粒子纵向动力学追踪软件ESME 上进行模拟,得到了优化后的高频相位、高频电压曲线,使得俘获效率达到99.3%,加速效率近乎100%。同时确定出了CRing 高频腔加速U34+ 所需满足的特性参数,即电压需达到40 kV,频率范围是0:31s0:34 MHz。To reduce the beam loss during the capture and acceleration processes of CRing in HIAF project, the longitudinal beam motion is investigated using the typical ion of 238U34+during the two processes mentioned above. The ions will be captured adiabatically firstly and then will be accelerated from 800 to 1130 MeV/u with a high efficiency using optimized RF voltage and RF phase program. After that the bunched beam will be debunched for the later beam compression. Simulation of these processes by tracking appropriate distributions with the longitudinal beam dynamics code ESME has been used tofind optimum parameters such as RF phase, RF voltage. The variation of the parameter during the RF cycle and the character parameters of the RF cavity are presented.      

Coulomb dissociation of 8B and solar neutrino problem

We measured the cross section for Coulomb dissociation of ⁸B using a radioactive ⁸B beam of 46.5 MeV/u energy with a ²⁰⁸Pb target. The corss section for the ⁷Be(p,γ)⁸B capture reaction was deduced at E_cm = 0.6 – 1.7 MeV. The extracted astrophysical S₁₇ factors were consistent with the values measured by Vaughn et al. and Filippone et al. Possible corrections due to ⁷Be excited state population, E1 and M2 contribution, nuclear contribution and post acceleration effects are considered.     

Tomography of injection and acceleration of monoenergetic electrons in a laser-wakefield accelerator

A tomographic diagnosis method was developed to systematically resolve the injection and acceleration processes of a monoenergetic electron beam in a laser-wakefield accelerator. It was found that all the monoenergetic electrons are injected at the same location in the plasma column and accelerated from 5 to 55 MeV energy in 200 microm distance. This is a direct measurement of the real acceleration gradient in a laser-wakefield accelerator, and the experimental data are consistent with the model of transverse wave breaking and beam loading for monoenergetic electron injection.     

Initial Part of a Compact Proton Linac for Applied Purposes

Physics of Particles and Nuclei Letters - The initial part (IP) of a compact pulsed proton linac with an output energy of ?230 MeV is intended for the formation and acceleration of a beam...     

Adiabatic plasma buncher

In this paper, we present a new scheme of injection into a plasma accelerator, aimed at producing a high-quality beam while relaxing the demands on the bunch length of the injected beam. The beam dynamics in the injector, consisting of a high-voltage pulsed photodiode, is analyzed and optimized to produce a λ_p/20 long electron bunch at 2.5 MeV. This bunch is injected into a plasma wave in which it compresses down to λ_p/100, while accelerating up to 250 MeV. This simultaneous bunching and acceleration of a high-quality beam requires a proper combination of injection energy and injection phase. Preliminary results from simulations are shown to assess the potentials of the scheme     

Parameters of the electron beam in a betatron with radial comb-type poles

Expressions for the vector potential and components of the magnetic field induction vector of a betatron with radial comb-type poles are derived. The dynamics of the electron beam in the electromagnetic betatron field is investigated in the process of electron injection and acceleration. It is demonstrated that the azimuthally varying field engender beam beats. However, the amplitudes of beam particle oscillations during acceleration do not exceed their values estimated from the symmetric azimuthal component of the betatron magnetic field induction. The energy spectrum of accelerated electrons is not described by a normal law. In the electron energy spectrum, the relative number of electrons whose energy exceeds the average value is large. Application of poles with radial combs improves the efficiency of electron capture in acceleration. Results of investigations can find application in the development and adjustment of electron beam accelerating systems. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 27–34, October, 2005.     

Stuty on the Process of the Fast Neutron Radiative Capture for 40Ca and 208Pb

The pre-equilibrium correction for the nuclear reactions induced by fast neutron is considered as follows: the nuclear reaction processes with the exciton number equal to or larger than five can still be described by the statistical theory of the nuclear reaction. The particle emission processes, in which less than five excitons are involved, are calculated by means of the exciton model and the γ emission of one exciton state is calculated by the direct capture mechanism. For the three-exciton state, only the semidirect capture mechanism, which plays the main role in the researched energy region, is taken into account. The interference effect between the direct and semidirect capture is also considered. The radiative capture cross sections for ⁴⁰Ca and ²⁰⁸Pb in the neutron incident energy region from 3 MeV to 20 MeV are calculated and a better coincidence with the experimental values is obtained. At the same time, the contribution to the (n, γ) reaction cross sections of the γ emissions before and after statistical equilibriums as well as the characteristics of the direct capture, semidirect capture and their interferece terms are discussed.     

High energy gain of trapped electrons in a tapered, diffraction-dominated inverse-free-electron laser

Energy gain of trapped electrons in excess of 20 MeV has been demonstrated in an inverse-free-electron-laser (IFEL) accelerator experiment. A 14.5 MeV electron beam is copropagated with a 400 GW CO2 laser beam in a 50 cm long undulator strongly tapered in period and field amplitude. The Rayleigh range of the laser, approximately 1.8 cm, is much shorter than the undulator length yielding a diffraction-dominated interaction. Experimental results on the dependence of the acceleration on injection energy, laser focus position, and laser power are discussed. Simulations, in good agreement with the experimental data, show that most of the energy gain occurs in the first half of the undulator at a gradient of 70 MeV/m and that the structure in the measured energy spectrum arises because of higher harmonic IFEL interaction in the second half of the undulator.     

Absolute efficiency calibration of high-purity germanium detector in the range 120–8500 keV

This article reports the efficiency response curve of the high-purity germanium detector over the wide energy range, covering from 120 to 8500 keV. The efficiencies were measured for different counting geometries by using point radionuclide standards (mono-energetic as well as multi-gamma emitters) supplied by IAEA and the capture gamma-ray facility installed at PINSTECH nuclear reactor PARR-1. The measured efficiencies were required to fit with a suitable fitting function for interpolation within the energy range of interest. Several fitting functions were proposed in the literature covering different energy ranges. The functions giving the best fit to experimental data are presented. The work has successfully extended the response curve beyond 1500–8500 keV, which is the region where the standard calibration radionuclides are not available. The thermal neutron capture gamma-ray facility provided the collimated neutron beam, extracted from the core of the reactor and made to react with ammonium chloride target to produce the capture gamma rays for determining the efficiencies in the extended region. It was found that the capture gamma-ray provides a satisfactory solution to extend the absolute efficiency calibration in the MeV range. It was also found that the fitting function that is linear in its parameter was highly satisfactory up to 1500 keV but proved insufficient upto 8500 keV. The exponential function giving the good fit over the range has been presented. Good agreement has been found between the experimentally measured absolute efficiencies and the predicted result.     

中子辐射俘获反应机制的质量能量相关性研究

对A?<10?0核质量区内的核素,研究中子辐射俘获反应中不同反应机制对辐射俘获截面的贡献随靶核质量数和中子入射能量变化的规律.所考虑的反应机制有复合核统计过程和复合核弹性散射道中的辐射俘获及形状弹性散射道中的直接–半直接辐射俘获两种非统计过程.在中子入射能量0.1—20MeV区间,给出了²⁷Al,⁴⁰Ca,⁶³Cu和⁹³Nb的理论计算结果及与实验数据的比较,并对呈现的变化规律进行了分析讨论     

Generation of high-quality electron beams from a laser-based advanced accelerator

At Shanghai Jiao Tong University (SJTU) we have established a research laboratory for advanced acceleration research based on high-power lasers and plasma technologies. In a primary experiment based on the laser wakefield acceleration (LWFA) scheme, multi-hundred MeV electron beams of reasonable quality are generated using 20-40 TW, 30 femtosecond laser pulses interacting independently with helium, neon, nitrogen and argon gas jet targets. The laser-plasma interaction conditions are optimized for stabilizing the electron beam generation from each type of gas. The electron beam pointing angle stability and divergence angle as well as the energy spectra from each gas jet are measured and compared.     

Enhancement of proton acceleration by hot-electron recirculation in thin foils irradiated by ultraintense laser pulses

MeV-proton production from solid targets irradiated by 100-fs laser pulses at intensities above 1x10(20) W cm(-2) has been studied as a function of initial target thickness. For foils 100 microm thick the proton beam was characterized by an energy spectrum of temperature 1.4 MeV with a cutoff at 6.5 MeV. When the target thickness was reduced to 3 microm the temperature was 3.2+/-0.3 MeV with a cutoff at 24 MeV. These observations are consistent with modeling showing an enhanced density of MeV electrons at the rear surface for the thinnest targets, which predicts an increased acceleration and higher proton energies.     

超强圆偏振激光直接加速产生超高能量电子束

研究表明, 峰值强度为10²²–10²⁵ W/cm²量级的圆偏振激光脉冲的有质动力场可以直接加速并产生GeV–TeV的单能电子束, 其中被加速电子的能量与激光脉冲的峰值强度成线性定标关系. 为了获得更高能量的电子束, 通过对一维解析模型的分析得到: 如果电子束在激光传播的方向上具一个初始能量E₀, 那么这种线性的定标关系可以被打破, 被加速电子束最终的能量可以被放大E₀倍. 这是由于具有一定初始能量的电子束不容易被激光脉冲抛在后面, 进而获得更高的加速距离. 二维粒子模拟结果显示: 当电子束的初始能量E₀为MeV量级时这个方法是有效的, 而当E₀过大时这个方法失效. 这是因为当电子的加速距离远大于激光脉冲的瑞利长度时, 激光强度的衰减使得电子束的加速错过了最佳加速场.     

The Localized Pinch Model as a High Energy Ion Collective Acceleration Mechanism

We present analytic and numerical calculations of the localized pinch model for ion collective acceleration by intense relativistic electron beams. These studies demonstrate the model's postulated synchronous acceleration of the ion clump and beam pinch. However, the configuration is found to be phase unstable, terminating the acceleration process before significant ion energy is acheived. Therefore, although the localized pinch model may be an appropriate explanation for some previous experimental observations of collectively accelerated MeV ions, it does not appear to be a suitable mechanism for high energy ion acceleration.