X. H. Guo

Dye-sensitized solar cells with NiS counter electrodes electrodeposited by a potential reversal technique

Nickel sulfides have been, for the first time, electrodeposited on transparent conductive glass by a facile periodic potential reversal (PR) technique to supersede Pt counter electrodes (CEs) of dye-sensitized solar cells (DSCs). The composition and electrochemical catalytic activity of the nickel sulfide films prepared by PR technique are different from those of the ones deposited by the commonly used potentiostatic (PS) technique. PR technique produces transparent single-component NiS, while co-deposition of Ni and NiS is found in the opaque films prepared by PS method. The nickel sulfide deposited by PR technique shows high catalytic activity for the reduction of I3− to I− in a DSC. DSC with the CE deposited by PR technique performs much better (6.82%) than that by PS method (3.22%), and is comparable to the device with conventional Pt coated CE (7.00%).

Fibrous CdS/CdSe quantum dot co-sensitized solar cells based on ordered TiO2 nanotube arrays

A new kind of fibrous quantum dot sensitized solar cell has been designed and fabricated by using CdS and CdSe co-sensitized TiO(2) nanotubes on Ti wire as the photoanode and highly active Cu(2)S as the counter electrode. By optimizing the CdSe deposition time and the length of the nanotube, a power conversion efficiency of 3.18% has been obtained under AM 1.5 illumination (100 mW cm(-2)). The potential application of this kind of solar cell has also been discussed in this paper.

Study on the effect of measuring methods on incident photon-to-electron conversion efficiency of dye-sensitized solar cells by home-made setup

An experimental setup is built for the measurement of monochromatic incident photon-to-electron conversion efficiency (IPCE) of solar cells. With this setup, three kinds of IPCE measuring methods as well as the convenient switching between them are achieved. The setup can also measure the response time and waveform of the short-circuit current of solar cell. Using this setup, IPCE results of dye-sensitized solar cells (DSCs) are determined and compared under different illumination conditions with each method. It is found that the IPCE values measured by AC method involving the lock-in technique are sincerely influenced by modulation frequency and bias illumination. Measurements of the response time and waveform of short-circuit current have revealed that this effect can be explained by the slow response of DSCs. To get accurate IPCE values by this method, the measurement should be carried out with a low modulation frequency and under bias illumination. The IPCE values measured by DC method under the bias light illumination will be disturbed since the short-circuit current increased with time continuously due to the temperature rise of DSC. Therefore, temperature control of DSC is considered necessary for IPCE measurement especially in DC method with bias light illumination. Additionally, high bias light intensity (>2 sun) is found to decrease the IPCE values due to the ion transport limitation of the electrolyte.

Highly efficient fibrous dye-sensitized solar cells based on TiO2 nanotube arrays

The structure of fibrous dye-sensitized solar cells, which were constructed by a TiO(2) nanotube array on Ti wire as the photoanode twisted by a Pt wire counter electrode, has been first systematically investigated by accurately controlling the thread pitch distance of screwed Pt wire. It has been revealed that the thread pitch will strongly influence the photovoltaic performance and kinetic processes in fibrous solar cells. The effect of the length of the TiO(2) nanotube on cell performance has also been discussed. After optimization, a relatively universal optimized thread pitch value of 1 mm for fibrous DSCs has been proved and the light-to-electricity conversion efficiency has been remarkably improved to 5.84%.

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 18GHz at initial operation and finally will be extended to 28GHz. 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 3.6T at injection, 2.2T at extraction, and a radial sextupole field of 2.0T 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 so...

Intense beam production of highly charged heavy ions by the superconducting electron cyclotron resonance ion source SECRAL (invited)

There has been increasing demand to provide higher beam intensity and high enough beam energy for heavy ion accelerator and some other applications, which has driven electron cyclotron resonance (ECR) ion source to produce higher charge state ions with higher beam intensity. One of development trends for highly charged ECR ion source is to build new generation ECR sources by utilization of superconducting magnet technology. SECRAL (superconducting ECR ion source with advanced design in Lanzhou) was successfully built to produce intense beams of highly charged ion for Heavy Ion Research Facility in Lanzhou (HIRFL). The ion source has been optimized to be operated at 28 GHz 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. An innovative design 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. For 28 GHz operation, the magnet assembly can produce peak mirror fields on 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. During the commissioning phase at 18 GHz with a stainless steel chamber, tests with various gases and some metals have been conducted with microwave power less than 3.5 kW by two 18 GHz rf generators. It demonstrates the performance is very promising. Some record ion beam intensities have been produced, for instance, 810 e microA of O(7+), 505 e microA of Xe(20+), 306 e microA of Xe(27+), and so on. The effect of the magnetic field configuration on the ion source performance has been studied experimentally. SECRAL has been put into operation to provide highly charged ion beams for HIRFL facility since May 2007.

New development of advanced superconducting electron cyclotron resonance ion source SECRAL (invited)

Superconducting electron cyclotron resonance ion source with advance design in Lanzhou (SECRAL) is an 18-28 GHz fully superconducting electron cyclotron resonance (ECR) ion source dedicated for highly charged heavy ion beam production. SECRAL, with an innovative superconducting magnet structure of solenoid-inside-sextupole and at lower frequency and lower rf power operation, may open a new way for developing compact and reliable high performance superconducting ECR ion source. One of the recent highlights achieved at SECRAL is that some new record beam currents for very high charge states were produced by 18 GHz or 18+14.5 GHz double frequency heating, such as 1 e microA of (129)Xe(43+), 22 e microA of (209)Bi(41+), and 1.5 e microA of (209)Bi(50+). To further enhance the performance of SECRAL, a 24 GHz/7 kW gyrotron microwave generator was installed and SECRAL was tested at 24 GHz. Some promising and exciting results at 24 GHz with new record highly charged ion beam intensities were produced, such as 455 e microA of (129)Xe(27+) and 152 e microA of (129)Xe(30+), although the commissioning time was limited within 3-4 weeks and rf power only 3-4 kW. Bremsstrahlung measurements at 24 GHz show that x-ray is much stronger with higher rf frequency, higher rf power. and higher minimum mirror magnetic field (minimum B). Preliminary emittance measurements indicate that SECRAL emittance at 24 GHz is slightly higher that at 18 GHz. SECRAL has been put into routine operation at 18 GHz for heavy ion research facility in Lanzhou (HIRFL) accelerator complex since May 2007. The total operation beam time from SECRAL for HIRFL accelerator has been more than 2000 h, and (129)Xe(27+), (78)Kr(19+), (209)Bi(31+), and (58)Ni(19+) beams were delivered. All of these new developments, the latest results, and long-term operation for the accelerator have again demonstrated that SECRAL is one of the best in the performance of ECR ion source for highly charged heavy ion beam production. Finally the future development of SECRAL will be presented.

Intense heavy ion beam production from IMP LECR3 and construction progress of a superconducting ECR ion source SECRAL

Intense heavy ion beams have been produced from IMP 14.5 GHz LECR3 by optimization of the ion source conditions and transmission efficiency. Highly charged stable beams, such as 325 eμA of Ar11+, 95 eμA of Xe26+, 7 eμA of Xe30+, 140 eμA of Fe13+, and 75 eμA of Ni12+, were obtained by 14.5 GHz rf power 800–1000 W. Furthermore, an advanced superconducting ECR ion source named SECRAL is being constructed. SECRAL is designed to operate at rf frequency 18–28 GHz with axial mirror magnetic fields 4.0 T at injection, 2.2 T at extraction, and sextupole field 2.0 T at the plasma chamber wall. The unique feature of this superconducting ECR source is that the sextupole is located outside of the three axial solenoid coils to reduce the interaction force and make the source more compact. Fabrications of the superconducting coils, cryostat, beam transmission line, and other components are almost completed. Tests of the superconducting magnet with sextupole and solenoid coils are under way.

Performance and operation of advanced superconducting electron cyclotron resonance ion source SECRAL at 24 GHz

SECRAL (superconducting ECR ion source with advanced design in Lanzhou) ion source has been in routine operation for Heavy Ion Research Facility in Lanzhou (HIRFL) accelerator complex since May 2007. To further enhance the SECRAL performance in order to satisfy the increasing demand for intensive highly charged ion beams, 3-5 kW high power 24 GHz single frequency and 24 GHz +18 GHz double frequency with an aluminum plasma chamber were tested, and some exciting results were produced with quite a few new record highly charged ion beam intensities, such as (129)Xe(35+) of 64 eμA, (129)Xe(42+) of 3 eμA, (209)Bi(41+) of 50 eμA, (209)Bi(50+) of 4.3 eμA and (209)Bi(54+) of 0.2 eμA. In most cases SECRAL is operated at 18 GHz to deliver highly charged heavy ion beams for the HIRFL accelerator, only for those very high charge states and very heavy ion beams such as (209)Bi(36+) and (209)Bi(41+), SECRAL has been operated at 24 GHz. The total operation beam time provided by SECRAL up to July 2011 has exceeded 7720 hours. In this paper, the latest performance, development, and operation status of SECRAL ion source are presented. The latest results and reliable long-term operation for the HIRFL accelerator have demonstrated that SECRAL performance for production of highly charged heavy ion beams remains improving at higher RF power with optimized tuning.

ECR ion sources at the Institute of Modern Physics: From classical to fully superconducting device

Electron cyclotron resonance (ECR) ion sources are used for cyclotron complex and atomic physics research at the Institute of Modern Physics (IMP). Intense beams of highly charged gaseous and metallic ions could be produced by the IMP 14.5 GHz ECR ion source (LECR2-Lanzhou Electron Cyclotron Resonance Ion Source No. 2). A particular emphasis has been put on the production of metallic ion beams recently. Metallic ion beams of Mg, Ca, Fe, Ni, Cu, Zn, and Pb were tested at the IMP 14.5 GHz ECR ion source (LECR2) to improve beam intensities and long-term stability. A new ECR ion source (Lanzhou Electron Cyclotron Resonance Ion Source No. 3), an upgraded version of the IMP 14.5 GHz ECR (LECR2) but with double-frequency wave heating (10 GHz + 14.5 GHz), is under commissioning. The preliminary results of this new source will be presented. To satisfy the requirements of the heavy ion cooling storage ring that is under construction at IMP, a fully superconducting ECR ion source (Lanzhou Electron Cyclotron Resonance Ion Source with Superconducting Coils) with a completely new structure is being developed for the production of intense heavy ion beams of very high charge states, such as Xe30+ and U40+. The superconducting magnet consists of three axial solenoid coils and six saddle-curved sextupole coils with a cold iron structure as field booster and clamp. At full excitation, this magnet assembly will produce maximum peak fields on axis of 4.0 T at the injection, 2.2 T at the extraction region, and a radial sextupole field of 2.0 T at plasma chamber wall. The design features and status of this new superconducting ECR ion source will be presented