Accelerator Physics and Technology
Over a half century, the Institute of Modern Physics has designed, built and operated the leading heavy-ion accelerator research facility in China, the Heavy Ion Research Facility in Lanzhou. Hence, the Institute has a solid technical strength to design and commission next-generation heavy-ion accelerator facility. Presently, the design and engineering team of HIAF is well organized, which constitutes specialized groups of accelerator physics, ion source, cryogenic and superconducting technology, radio frequency technology, power supply technology, magnet and mechanical technology, information technology, vacuum technology, beam diagnosis, and radiation safety and protection.
HIAF aims at producing heavy-ion beams in broad energies with unprecedented intensities as compared with any existing facilities. The low-energy beam intensities from the Linac and high-energy beam intensities from the Booster Ring could compete with and even exceed those from the next-generation facilities planned or under construction. In order to achieve the challenging goals, advanced accelerator techniques have to be developed and adopted to continuously push the limits of beam intensities.
Next-generation Type 45 GHz ECRIS
ECR ion source is capable of producing highly charged heavy ions, and consequently ions can be economically accelerated to high energy by subsequent accelerator. For the very heavy beams, such as Bi and U, the existing highly charged ion sources cannot meet the requirements of HIAF. We have designed a next-generation 45 GHz, 20 KW superconducting ECR ion source with a novel structure shown in the right Figure. Comparing with the best-performance ECR sources presently operated worldwide, the currents of very heavy ions simulated are increased significantly. For example, about 1.0 emA current of 238O34+ion could be delivered by the new ion source, which will not be available elsewhere.
Typical parameters of the new ECR ion source
The structure of the next-generation superconducting ECR ion source. In the right figure, the dashed line shows the simulated currents for highly-charged Bi ions using the new ECR source, and the colored lines represent those available from the existing ECR ion sources worldwide.
Superconducting Cavities and Magnets
A large variety of superconducting cavities and magnets will be used in the Superconducting Linac and the High Energy Fragment Separator. Since the Institute of Modern Physics undertook the long-term project CiADS (China initiative Accelerator Driven Sub-critical System) in 2011, we have been developing superconducting techniques for ion accelerator. After great efforts, we built special laboratories to design, fabricate and test various superconducting cavities and magnets. Importantly, a superconducting 25 MeV proton Linac was commissioned for the CiADS facility. All of the endeavors have enabled us to employ superconducting techniques at HIAF. We will adopt the superconducting quarter-wave cavities with β value of 0.052 and working frequency of 81.25 MHz for the low-energy section of the Linac, and superconducting half-wave cavities with β values of 0.1 and 1.15 and frequency of 162.2 MHz for the high-energy section. Prototypes of the cavities were manufactured and tested successfully in laboratory. The superconducting dipole and quadrupole magnets based on the nuclotron-type cable are used for the High Energy Fragment Separator.
Collimator of Dynamic Vacuum
In a storage ring, circulating ion might collide with the residual gas in the beam pipelines. This might result in change of the charge state of the ion, and consequently the ion deflects its orbit and hits the pipeline. In a case of energetic heavy ion, huge number electrons are produced and released into the pipeline. If the electrons are captured by beam ions, a cascade of ion loss phenomenon might happen, and eventually cause beam collapse suddenly. This phenomenon limits the ion number stored. Therefore, we have to install dynamic vacuum collimators at specific positions at the booster. A dedicated dynamic vacuum simulation software has been developed in collaboration with GSI for the optimization of the collimator design, and a collimator prototype was built and near 100% collimation efficiency could be realized according to simulation. The desorption effect was proved to be as good as expected at the existing facility CSR.
The prototype of collimator of dynamic vacuum.
Thin Walled Vacuum Chamber
Due to fast ramping rate operation of the Booster Ring, thin walled vacuum chambers are needed for all magnets in order to keep eddy currents at a tolerable level. A 0.3 mm thick vacuum chamber prototype was made of stainless steel, which has an elliptical aperture and rib supporters in parallel with the magnetic fields. The prototype was installed at the CSR, and it works very well.
Beam Cooling Devices
In order to obtain high quality radioactive beams for precision measurements, we will install Stochastic cooling device and 450 keV, 2 A electron cooler at the Spectrometer Ring. A prototype of Stochastic cooling device with a novel 2.76 m long slotted pick-up was fabricated and installed at the CSR, and the beam test results show that this cooling device is suitable for the Spectrometer Ring. We have designed electron cooler which can provide hollow electron beams for cooling down ion beams. The hollow electron beam can solve the problem of space charge effect and reduce the recombination between the ions and electrons, and consequently high-quality ion beams would be produced.
