Design of the IMP microbeam irradiation system for 100 MeV/u heavy ions

Abstract A state-of-the-art high energy heavy ion microbeam irradiation system is constructed at the Institute of Modern Physics of the Chinese Academy of Sciences. This microbeam system operates in both full current intensity mode and single ion mode. It delivers a predefined number of ions to preselected targets for research in biology and material science. The characteristic of this microbeam system is high energy and vertical irradiation. A quadrupole focusing system, in combination with a series of slits, has been designed to optimize the spatial resolution. A symmetrically achromatic system leads the beam downwards and serves simultaneously as an energy analyzer. A high gradient quadrupole triplet finally focuses a C6+ ion beam to 1 µm in the vacuum chamber within the energy range from 10 MeV/u to 100 MeV/u. In this paper, the IMP microbeam system is described in detail. A systematic investigation of the ion beam optics of this microbeam system is presented together with the associated aberrations. Comparison is made between the IMP microbeam system and the other existing systems to further discuss the performance of this microbeam. Then the optimized initial beam parameters are given for high resolution and high hitting efficiency. At last, the experiment platform is briefly introduced.

Experimental results of helicon sources

Helicon plasma source is known as an efficient generator of uniform and high density plasma. A helicon plasma source was developed for the investigation of plasma striping and plasma lens at the Institute of Modern Physics, CAS. In this paper, the characteristics of helicon plasma have been studied by using Langmuir four-probe and a high plasma density up to 3.9×1013 /cm3 has been achieved with the Nagoya type III antenna. In the experiment, several important phenomena have been found: (1) for a given magnetic induction intensity, the plasma density became greater with the increase of RF power; (2) the helicon mode appeared at the RF power between 300 W and 400 W; (3) the plasma density gradually tended to saturation as the RF power increased to the higher power; (4) a higher plasma density can be obtained by a good matching between the RF power and the magnetic field distribution. The key issue is how to optimize the matching between the RF power and the magnetic field. Moreover, some tests on the extraction of ion beam were performed, and the preliminary results were given. The problems which existed in the helicon ion source will be discussed and the increase in beam density will be expected by extraction system optimum.

适合探测较轻粒子的一种多极平行板雪崩计数器

一种高性能多极双维位置灵敏平行板雪崩计数器(multi-plate parallel plate avalanchecounter,MPPAC)在兰州中能重离子加速器放射性次级束流线(radioactive ion beam line in lanzhou,RIBLL)上被应用,由二次雪崩带来的高增益使它很适合探测较高能量的较轻粒子,它主要由1个中心阳极,x,y位置栅极和2个阴极组成,位置信号由x,y位置栅极采用电荷分除法读出,使用异丁烷工作气体,气压650Pa,阳极+400V,阴极-350V时,对于α粒子位置分辨为0.55mm(半高全宽度,fwhm),位置线性色散远好于±0.2mm,探测效率大于99.2％,同时,也研究了位置分辨与阳极、阴极电压的关系,与放大器成形时间常数的依赖,随工作气压变化等。

Characteristics of a 4-fold segmented clover detectore

Four high-purity germanium 4-fold segmented Clover detectors have been applied in the experiment of neutron-rich nucleus N-21. The performance of those, four Clovers have been tested with radioactive sources and in-beam experiments and the main results including energy resolution, peak-to-total ratios, the variation of the hit pattern distribution in difficult crystals of one Clover detector with the energy of gamma ray, and absolute full energy peak detection efficiency curve, were presented.

Advanced superconducting electron cyclotron resonance ion source SECRAL: Design, construction, and the first test result

Superconducting electron cyclotron resonance (ECR) ion source with advanced design in Lanzhou (SECRAL) is a next generation ECR ion source and aims for developing a very compact superconducting ECR ion source with a structure and high performances for highly charged ion-beam production. The ion source was designed to be operated at 18 GHz at initial operation and finally will be extended to 28 GHz. The superconducting magnet confinement configuration of the ion source consists of three axial solenoid coils and six sextupole coils with a cold iron structure as field booster and clamping. At full excitation, this magnet assembly can produce peak mirror fields on the axis of 3.6 T at injection, 2.2 T at extraction, and a radial sextupole field of 2.0 T at plasma chamber wall. What is different from the traditional design, such as LBNL VENUS and LNS SERSE, is that the three axial solenoid coils are located inside of the sextupole bore in order to reduce the interaction forces between the sextupole coils and the solenoid coils. SECRAL may open the way for building a compact and high-performance 18-28 GHz superconducting ECR ion source. Very preliminary commissioning results are promising. Detailed design, construction issues and very preliminary test results of the ion source at 18 GHz are presented.

Study on charge equilibration time of highly charged ions in carbon foils

Charge state distribution of 0.8MeV/u uranium ions after transmission through a thin carbon foil has been studied. It is observed that the charge state distribution is equilibrated after the uranium ions have passed through a 15 mu g/cm(2) carbon foil. The equilibrated average charge state is 33.72 and the charge equilibration time of uranium ions in carbon foil is less than 5.4fs.

First results of SECRAL at 18GHz for intense beam production of highly charged ions

A Superconducting ECR ion source with Advanced design in Lanzhou (SECRAL) was successfully built to produce intense beams of highly charged ions for Heavy Ion Research Facility in Lanzhou (HIRFL). The ion source has been optimized to be operated at 28GHz for its maximum performance. The superconducting magnet confinement configuration of the ion source consists of three axial solenoid coils and six sextupole coils with a cold iron structure as field booster and clamping. For 28GHz operation, the magnet assembly can produce peak mirror fields on axis 3.6T at injection, 2.2T at extraction and a radial sextupole field of 2.0T at plasma chamber wall. A unique feature of SECRAL is that the three axial solenoid coils are located inside of the sextupole bore in order to reduce the interaction forces between the sextupole coils and the solenoid coils. During the ongoing commissioning phase at 18GHz with a stainless steel chamber, tests with various gases and some metals have been conducted with microwave power less than 3.2kW and it turned out the performance is very promising. Some record ion beam intensities have been produced, for instance, 810e mu A of O7+, 505e mu A of Xe20+, 306e mu A of Xe27+, 21e mu A of Xe34+, 2.4e mu A of Xe38+ and so on. To reach better results for highly charged ion beams, further modifications such as an aluminium chamber with better cooling, higher microwave power and a movable extraction system will be done, and also emittance measurements are being prepared.

Preliminary results of the updated LECR2 source-LECR2M

The Latest developed LECR2M (Lanzhou ECR No. 2 Modified) source is the updated one of LECR2 (Lanzhou ECR No. 2) source at IMP. It has been assembled on the low energy ion beam experimental platform to produce MCI beams for atomic physics and material physics experimental research. In our updating program, the structure of injection and extraction components has been modified to make the source structure more simple and effective. The hexapole magnet has also been replaced by a new hexapole magnet with higher radial field and larger inner diameter. With this updating, stronger magnetic field confinement of the ECR plasma is possible and better base vacuum condition is also achieved. LECR2M was designed to be operated at 14.5GHz. During the preliminary test, 1.3emA O6+ beam was extracted with the injected rf power of 1.1kW. The source has been used to deliver intense MCI beams for different experiments. After some discussion of the main features of this newly updated source, some of the typical commissioning test results of LECR2M will be presented.

High sensitivity beam phase measurement system for isochronous cyclotron

The beam phase measurement system in the HIRFL is introduced. Based on the double-balanced mixer principle using rf-signal mixing and filtering techniques, a stable and sensitive phase measurement system has been developed. The phase history of the ion beam is detected by using a set of capacitive pick-up probes installed in the cyclotron. The phase information of the measurement is necessary for tuning to obtain a optimized isochronous magnetic field which induces to maximize the beam intensity and to optimize the beam quality. The result of the phase measurement is reliable and the accurancy reaches +/- 0.5 degrees.