Longcheng Wu

H− cusp source development for 100 MeV compact cyclotron at China Institute of Atomic Energy

As a part of the Upgrade Project of Beijing Tandem Accelerator Laboratory, a 100 MeV compact cyclotron was designed for the generation of high intensity proton beams. Due to the limit of acceptance by the cyclotron central region, a new H− cusp source was developed at China Institute of Atomic Energy. The design of this new source is based on TRIUMF’s experience. More than 10 mA of H− beam with a measured emittance of 0.65 π mm mrad are obtained at a voltage of 28 kV from an extraction hole of 11 mm in diameter. In this article, the structure of the source, the magnetic field configuration of the multicusp and virtual filter, the extraction optics, the test results, and future improvements will be described.

Experimental study for 15–20 mA dc H- multicusp source

Recently, a new H- source and test stand was developed at CIAE. The design of this new source is based on the experience on our previous 10-15 mA H(-) ion source and the source at TRIUMF. Major efforts include the study of the virtual filter magnetic field, confining magnetic field, filament shape and location, the vacuum improvement on the extracting area, the extraction optics, new control and interlock system of the power supplies. More than 15 mA of H-beam was obtained for 36 h with stability of +/-0.5%. The normalized emittance of 0.48pi mm mrad (4 rms normalized emittance) were measured with approximately 8 mA dc beam. Further experimental studies are proceeding in an effort to reach 20 mA with reasonable emittance at this moment. More study plans are conducted, e.g., building a longer source body and using cesium injection to get better emittance, which will be presented as a separate paper at this conference.

Design of a compact, permanent magnet electron cyclotron resonance ion source for proton and H2(+) beam production.

A 2.45 GHz microwave ion source was developed at China Institute of Atomic Energy (CIAE) for proton beam production of over 60 mA [B.-Q. Cui, Y.-W. Bao, L.-Q. Li, W.-S. Jiang, and R.-W. Wang, Proceedings of the High Current Electron Cyclotron Resonance (ECR) Ion Source for Proton Accelerator, APAC-2001, 2001 (unpublished)]. For various proton beam applications, another 2.45 GHz microwave ion source with a compact structure is designed and will be built at CIAE as well for high current proton beam production. It is also considered to be used for the test of H(2)(+) beam, which could be injected into the central region model cyclotron at CIAE, and accelerated to 5 MeV before extraction by stripping. The required ECR magnetic field is supplied by all the permanent magnets rather than electrical solenoids and six poles. The magnetic field distribution provided by this permanent magnets configuration is a large and uniformly volume of ECR zone, with central magnetic field of a magnitude of approximately 875 Gs [T. Taylor and J. S. C. Wills, Nucl. Instrum. Methods Phys. Res. A 309, 37 (1991)]. The field adjustment at the extraction end can be implemented by moving the position of the magnet blocks. The results of plasma, coupling with 2.45 GHz microwave in the ECR zone inside the ion source are simulated by particle-in-cell code to optimize the density by adjusting the magnetic field distribution. The design configuration of the ion source will be summarized in the paper.

Fabrication of thermal-resistant gratings for high-temperature measurements using geometric phase analysis

Grating fabrication techniques are crucial to the success of grating-based deformation measurement methods because the quality of the grating will directly affect the measurement results. Deformation measurements at high temperatures entail heating and, perhaps, oxidize the grating. The contrast of the grating lines may change during the heating process. Thus, the thermal-resistant capability of the grating becomes a point of great concern before taking measurements. This study proposes a method that combines a laser-engraving technique with the processes of particle spraying and sintering for fabricating thermal-resistant gratings. The grating fabrication technique is introduced and discussed in detail. A numerical simulation with a geometric phase analysis (GPA) is performed for a homogeneous deformation case. Then, the selection scheme of the grating pitch is suggested. The validity of the proposed technique is verified by fabricating a thermal-resistant grating on a ZrO2 specimen and measuring its thermal strain at high temperatures (up to 1300 °C). Images of the grating before and after deformation are used to obtain the thermal-strain field by GPA and to compare the results with well-established reference data. The experimental results indicate that this proposed technique is feasible and will offer good prospects for further applications.

Ion source and low energy injection line for a central region model cyclotron

At CIAE, a 100 MeV H(-) cyclotron (CYCIAE-100) is under design and construction. A central region model (CRM) cyclotron was built for various experimental verifications for the CYCIAE-100 project and for research and development of high current injection to accelerate milliampere H(-) beam. The H(-) multicusp source built in 2003 has been improved recently to make the source operation more stable. A new injection line for axial low energy high current injection has been designed and constructed for the CRM cyclotron.

The injection efficiency measurement and analysis for central region model cyclotron.

At the China Institute of Atomic Energy, a central region model cyclotron has been constructed, which is dedicated for various experimental verifications to study beam properties. The design features of the ion source and injection line have already been described in other papers. We shall report here the results of the initial beam tests. A wire scanner is employed in the injection line to measure beam transverse sizes and these data can be used to fit the phase plane parameters after the ion source. Based on the beam tests results, the ion source built in 2003 has been improved recently. The improvement is mainly due to the repair of the multicusp field. From the ion source to the exit of the inflector, a transmission efficiency of 93% has been obtained for a continuous and low current input beam. It is also described here the experimental arrangement and the results.

Development of Specially Designed Small Doublet for Compact Cyclotron Beam Injection

A number of compact cyclotrons accelerating H- ions to energies between 10 MeV and 100 MeV have recently been constructed for research and medical diagnostics/therapy in several countries. However limitations in extracted beam intensity are brought up by inadequate injection efficiency from the ion source into the machine. To improve the optics matching from the external source to machine acceptance, a specially designed small doublet has been developed to replace the traditionally used solenoid in the vertical injection line before the spiral inflector. Due to the narrow space inside the compact cyclotron, the doublet is designed based on the following special consideration: 1) To use the central plug of the main magnet as a part of the return yoke of the doublet; 2) To use the capillary water-cooling conductor for the coil to keep the doublet sufficiently small; 3) To adopt an integral design of the two quadrupoles into one assembly so that they could be installed in the channel of the central plug in high vacuum environment. In this paper, the design of the doublet is introduced. The outer diameter of 118 mm is precisely fit to the central plug of the Verification Facility of High Intensity Cyclotron at CIAE. Its inner diameter is 50 mm for beam injection. It can provide a maximal magnetic field gradient of 2.6 T/m from the measurement. Various kinds of detailed techniques for the doublet fabrication, e.g. the enwinding of capillary water-cooling conductor with outer diameter of 3 mm and inner diameter of 2 mm, the poles and yoke assembling, will be presented. The beam test results will be given as well.