Heavy Ion Accelerator Research Articles

Two-proton emission from excited states of proton-rich nuclei

The effective liquid drop model (ELDM) and the generalized liquid drop model (GLDM) are extended to the case of studying the two-proton (2p) radioactivity from the excited states of proton-rich nuclei. It is shown that the experimental 2p decay half-lives are reproduced well by the ELDM and the GLDM. Then, the 2p decay half-lives of excited states of some nuclei that are not yet available experimentally are predicted by the two models, which are useful for searching for the new 2p decay candidates in future. Meanwhile, the above predicted half-lives are analyzed and compared with those given by the unified fission model (UFM). Next, the influence of the uncertainties of the decay energy and the angular momentum on the half-lives are analyzed in the frame of the two models by taking the 2p radioactivity of the 21<sup>+</sup> isomeric state of <sup>94</sup>Ag for example. It is found that the half-lives go up with the increase of the angular momentum, following the law of the quadratic function. Furthermore, the strong dependence of the half-lives on the decay energy suggests that it is important and necessary to measure accurately the mass value of the parent nucleus and the daughter nucleus and the excitation energy. Finally, it is necessary to point out that the existence of the 2p radioactivity in the 21<sup>+</sup> isomeric state of<sup> 94</sup>Ag remains to be a mystery. Moreover, although the 2p radioactivity is observed from the higher excited states of <sup>17</sup>Ne and <sup>18</sup>Ne, the relevant hypotheses have not yet been further tested experimentally. The construction of a new generation of radioactive ion beam facilities, such as the high intensity heavy-ion accelerator facility (HIAF), is expected to be used to uncover the nature of the 2p radioactivity in the 21<sup>+</sup> isomeric state of <sup>94</sup>Ag and further test the hypotheses of the 2p decay from the higher excited states of <sup>17</sup>Ne and <sup>18</sup>Ne. On the other hand, some microscopic models, such as the shell model, need to be further developed by including some necessary physical factors, such as the tensor force, three-body force and accurate pairing force, to describe the mechanism of the 2p emission of the excited states more reasonably. In summary, more nuclear structure information can be extracted by studying the 2p radioactivity of the excited states. It is worth studying further although it is rather difficult to observe.

Production of high intensity highly charged cocktail beams at LEAF

LEAF (Low Energy high intensity highly charged ion Accelerator Facility) is a sophisticated high intensity heavy ion accelerator developed at the Institute of Modern Physics. Various combinations of ion beams have been proposed to study the synergistic effect of irradiating nuclear energy materials with ion beams, and therefore the LEAF has been used to test the feasibility of delivering cocktail beams with precisely controlled timing or dosimetry. Since the requested cocktail beams can be made of ion beams with approximately the same M/q or different M/q, it is important to develop methods for transporting and accelerating ion beams with different M/q with a precisely controlled time structure, as well as to produce and diagnose ion beams of the same M/q. We have performed cocktail beams production on this platform, and have successfully produced and accelerated cocktail beams such as 16O4+ &4He+ with the same M/q ratios and 58Ni15+ &4He+ with different M/q ratios. This paper will present details on how to prepare cocktail beams with a heavy ion linac to meet the research needs of synergistic irradiation of materials. Technical challenges and tricks will be discussed.

Beam dynamics design of HIAF RFQ

The high-intensity heavy ion accelerator facility is a next-generation advanced heavy-ion accelerator facility built by the Institute of Modern Physics, Chinese Academy of Sciences. The RFQ is designed to provide a continuous wave beam and 2[Formula: see text]mA pulse beam with high-quality longitudinal beam distribution for the injection linear accelerator. Two different designs of aiming to suppress the longitudinal emittance were studied, and the optimized scheme which composed of a three-harmonic pre-buncher and an RFQ accelerator with small longitudinal acceptance was chosen. More emphasis is put on the section between pre-buncher and RFQ, where the space charge effect becomes severe with bunched beam. The optimal design and the analysis are presented in this paper.

Hi’Beam-S: A Monolithic Silicon Pixel Sensor-Based Prototype Particle Tracking System for HIAF

Particle tracking systems, which function either as particle detectors or beam monitors, are the critical elements for the high-intensity heavy-ion accelerator facility (HIAF) complex. The novel Topmetal-M pixel sensor, which combines the features of both monolithic active pixel sensor (MAPS) and the Topmetal sensor, can be used either for a pixel detector or a nondestructive beam monitor. The Topmetal got its name as some part of the pixel&#x2019;s top metal layer is exposed to sense the drifting charge. In this article, a prototype particle tracking system, named Hi&#x2019;Beam-S, has been designed to characterize the Topmetal-M sensor. The laser test shows a spatial resolution of <inline-formula> <tex-math notation="LaTeX">$\sim 9 ~\mu \text{m}$ </tex-math></inline-formula> for the laser spot measurement. The heavy-ion beam test demonstrates that, for a 5-mm track with a &#x007E;20&#x00B0; incident angle, a spatial resolution of <inline-formula> <tex-math notation="LaTeX">$\sim 1.59 ~\mu \text{m}$ </tex-math></inline-formula> could be achieved.

Neutron spectra at a high energy heavy ion accelerator measured with a TLD-based Bonner spectrometer.

A Bonner sphere spectrometer with TLD cards as sensitive elements was constructed and used at the GSI accelerator complex to measure the neutron spectral fluence rates for radiation safety purposes. The neutron spectra were measured in the synchrotron tunnel during 550 MeV/u 40Ar beam operation and in Cave A experimental area with a 1 GeV/u 56Fe beam impinging on a thick aluminum target. Unfolded spectra were compared with those calculated using the Monte Carlo code FLUKA. The measured spectra show a good agreement with the simulations and the set proved itself to be a useful tool for different radiation safety purposes.

Measurement and Protection of Induced Radioactivity in Proton Heavy Ion Accelerator Therapy

Measurement and Protection of Induced Radioactivity in Proton Heavy Ion Accelerator Therapy

Cold Test of a Superconducting Quadrupole-Sextupole Nested CCT Prototype using matrix harmonic coil

IMP (Institute of Modern Physics) has been developing a Quadrupole-Sextupole nested CCT (Canted Cosine Theta Type) prototype for the HFRS (High Energy Fragment Separator) beamline of HIAF (High Intensity Heavy-ion Accelerator Facility) project. Hence a matrix harmonic coil method has been developed for magnetic field quality measurement of multi-pole nested magnets. Furthermore, a whole set of measurement system has been constructed and some special mechanical components, like cold bore, have been set up to cooperate with matrix harmonic coil measurement. After cold test at 4.2 K, the measurement results prove that the prototype property and field quality basically meets our requirement, and matrix harmonic coil also functioning well.

Measurement on the desorption yields of ceramic and Au-coated ceramic irradiated with Bi32+ and Xe23+

The Booster Ring (BRing) is the key part of the High Intensity Heavy Ion Accelerator Facility (HIAF). In order to reduce the eddy current effect, specifically developed stainless steel vacuum chambers with ultra-thin (0.3 mm) walls and ceramic spacers will be used. Desorption yields experiments were carried out on spacers made of zirconia ceramic, on zirconia ceramic coated with different Au thicknesses and coating processes, as well as on zirconia ceramic coated with getter films. A dedicated mass spectrometer was used to analyze the changes in the gas composition during the bombardment. The results show that Au-coated zirconia ceramic can effectively lower the desorption yields, the higher the Au coating thickness, the lower the desorption yield. When the beam impinges on the surface of the zirconia ceramic, the pressure randomly fluctuates, without showing any clear long term beam cleaning effect. As far as the coating process is concerned, samples coated by magnetron sputtering show higher desorption yields than those electroplated. However, the electroplating process is characterized by a low bonding force between the films and the ceramic substrate, which makes possible for the film to peel off under beam bombardment. Finally, TiN-coated zirconia ceramic has better static vacuum performances. However, due to its strong H2 absorption capacity, TiN coated samples will release more H2 under bombardment, thus providing a worse dynamic vacuum conditions. Practical consequences for the BRing vacuum system of the HIAF are given.

First Experience of Production and Testing the Superconducting Quadrupole and Corrector Magnets for the SIS100 Heavy Ion Accelerator of FAIR

First Experience of Production and Testing the Superconducting Quadrupole and Corrector Magnets for the SIS100 Heavy Ion Accelerator of FAIR

Conceptual Design of an Electrostatic Trap for High-Intensity Highly Charged Pulsed Beam

Highly charged ion sources play an important role in the advancement of heavy-ion accelerators worldwide. Demands of highly charged heavy ions for new and existing accelerators have driven the performance of ion sources to their limits. A new high charge state ion accumulating trap concept is proposed that converts a dc ion beam from an electron cyclotron resonance (ECR) ion source into a short-pulsed ion beam with suitable compression ratios. With a simple trap composed of an electron gun, a solenoid, and a set of drift tubes (DTs), the injected ions from a dc operation ECR ion source will be trapped radially and axially. By manipulating the potential of the DT, highly charged ions can be accumulated with multiple injections and extracted with augmentation of ion intensity in pulses of tens of μs. This article presents the simulations and design features of the envisioned ion trap.

Electron gun and collector for RAON EBIS charge breeder

A heavy-ion accelerator facility, called RAON, is being constructed in Korea. RAON is a large scale experimental facility for basic science research through nuclear physics experiments using various rare-isotope (RI) beams. An Electron Beam Ion Source (EBIS) will be utilized as a charge breeder in the isotope separation on-line (ISOL) system of RAON. The electron gun (e-gun) and electron collector are essential components of the EBIS to charge-breed the RI beams. The e-gun, a magnetically immersed type, has been designed to generate electron beams with currents up to 3 A. The material of the cathode is IrCe, which provide a higher current density and longer lifetime than the LaB6 cathodes. In addition, the collector which can dissipate electron beam power up to 20 kW has been designed and built. A test bench has been designed and constructed to commission the e-gun and collector sub-systems. The test bench is equipped with a negative high-voltage platform, called a cathode platform, to provide an independent electron beam current loop. The control system was also designed and implemented to be able to control two different platforms, such as the cathode and ground platforms, using the NI LabVIEW hardware and software. The experimental goals of the tests described in this paper are to generate and transport to collector 2 A electron beam, and to demonstrate a stable operation mode with electron beam width of 50 ms and a repetition rate of 10 Hz. These goals have been determined for the first charge breeding experiment, which is to obtain the charge-bred beam of Cs33+, in the future. This paper presents the electron gun and collector sub-system of RAON EBIS, including the cathode tests, the simulation results, and the electron beam experiment.

Magnetic axis measurement of the high precision coil for the High Intensity heavy-ion Accelerator Facility electron cooler

Electron cooling method is used for the High Intensity heavy-ion Accelerator Facility (HIAF), in order to reduce the beam emittance and momentum spread of heavy ion beams, hence to improve the accuracy and luminosity of nuclear physics and atomic physics experiments. The magnetic field homogeneity of the cooling section is the key parameter related to the cooling effect. A new type of cooling section solenoid composed of several coils was used in the HIAF electron cooling device to produce a high parallelism magnetic field. In this paper, a device for the magnetic field axis measurement of high-precision coils is presented. The geometric symmetrical axis of the coil is measured by a positioning device. The radial and axial magnetic field distribution in the center plane of the coil is measured by the rotating Hall probes. Finally, the relative angle between the coil magnetic field axis and the geometric symmetrical axis is calculated by the measurement results. The accuracy of the measured angle is within ±0.10 mrad. The measured angle of the prototype coil is (1.28±0.10) mrad, which satisfies the physics requirement.

Discriminative detection of laser-accelerated multi-MeV carbon ions utilizing solid state nuclear track detectors

A new diagnosis method for the discriminative detection of laser-accelerated multi-MeV carbon ions from background oxygen ions utilizing solid-state nuclear track detectors (SSNTDs) is proposed. The idea is to combine two kinds of SSNTDs having different track registration sensitivities: Bisphenol A polycarbonate detects carbon and the heavier ions, and polyethylene terephthalate detects oxygen and the heavier ions. The method is calibrated with mono-energetic carbon and oxygen ion beams from the heavy ion accelerator. Based on the calibration data, the method is applied to identify carbon ions accelerated from multilayered graphene targets irradiated by a high-power laser, where the generation of high-energy high-purity carbon ions is expected. It is found that 93 ± 1% of the accelerated heavy ions with energies larger than 14 MeV are carbons. The results thus obtained support that carbon-rich heavy ion acceleration is achieved.

Certification testing of production superconducting quarter-wave and half-wave resonators for FRIB

The Facility for Rare Isotope Beams (FRIB) is designed to accelerate ion beams to ≥ 200 MeV per nucleon with 46 superconducting radio-frequency cryomodules. The FRIB driver linac uses quarter-wave resonators and half-wave resonators; with a total of 324 resonators, the linac is currently the largest heavy ion accelerator in the world. Production of jacketed resonators began in January 2014 and was completed in December 2019. Dewar certification testing of all the cavities was done before they were installed into cryomodules. The experience and lessons from more than 5 years of FRIB resonator production and certification testing are analyzed and summarized in this paper.

Design and implementation of module fault interlock and protection system of HIAF-BRing power supply prototype

Power supply prototype in High Intensity heavy ion Accelerator Facility-Booster Ring (HIAF-BRing) adopts the scheme of full energy and fast cycle storage pulse power supply topology. Its multi modules are connected in series and parallel pattern, and the power reaches megawatt level. Due to the high power and large scale of the power supply, a module fault interlock protection system based on Programmable Logic Controller (PLC), interlock boards and Field Programmable Gate Array (FPGA) is designed and implemented to protect the power supply in operation. In this paper, first, a design of double redundant module fault interlock is introduced. Second, the logic implemented in PLC is described. Third, the work about FPGA is given. Finally, the system is tested in three aspects: the responsive time of the power supply interlock loop, the total time from controller error occurrence to interlock finish, and the equipment fault response. The result shows that the module fault interlock system can action sensitively, timely and reliably in case of fault occurrence, which meets the requirements of the power supply prototype in HIAF-BRing.

Proposal and design of an 81.25 MHz interdigital H-mode dual-beam drift tube linac

A novel type dual-beam drift tube linac (DB-DTL) was proposed at the Institute of Modern Physics for ultra-high intensity heavy-ion acceleration. With two identical beam apertures located in the vertical direction with the same off-set from the cavity axis, two beams could be accelerated simultaneously by the DB-DTL and then be merged to one, thus double the current beam intensity limit, which is of great significance for ultra-high intensity heavy-ion acceleration. An 81.25 MHz proof-of-principle cavity was developed to demonstrate this new concept. Designed and optimized with the alternative phase focusing (APF) scheme, this prototype cavity was supposed to accelerate 10 mA protons beam from 0.56 MeV to 2.5 MeV in one meter with transmission efficiency more than 90%. Inter-digital H-mode (IH) structure was adopted by this DB-DTL, thus high shunt impedance could be achieved which significantly reduce the power loss. With efficient cooling, this cavity was capable to work at the pulsed mode with a maximum duty cycle of 10%. Beam dynamics simulations, electromagnetic design and optimization of the prototype cavity, and multi-physics analyses of this DB-DTL will be presented in this paper.

Vacuum system for EBIS charge breeder of the RAON heavy ion accelerator

An Electron Beam Ion Source (EBIS) will be utilized for charge breeder in the RAON heavy ion accelerator facility. The vacuum system for the RAON EBIS charge breeder is crucial part for the achievable charge state, breeding efficiency, and purity of the charge-bred beam. A strict vacuum level of about 10−11 mbar is required in the ion trap. The pumping system of the RAON EBIS charge breeder consists of turbo pumps (TMPs), cryo-pumps, and non-evaporable getter (NEG) ZAO modules. The material for the ion trap structures and vacuum chamber was chosen and handled carefully to satisfy the vacuum requirements in the manufacturing step with vacuum firing at 1050 °C for 2 h. A vacuum test of the ion trap section has been performed with baking, and final vacuum level reached 2.3 × 10−11 mbar. In this paper, the vacuum system of the RAON EBIS and test procedures and results are presented and discussed.

Highly Efficient Heavy Ion Acceleration from Laser Interaction with Dusty Plasma

Energetic heavy ions with short duration can be generated in the interaction of ultrashort ultraintense (USUI) laser pulse with solid matter. However, the energy conversion efficiency from laser to heavy ions is usually very low. Herein, a novel scheme for efficient transfer of USUI laser energy to the heavy ions of microscopic dust grains in dusty plasma is proposed. Due to the resulting ultraintense space‐charge field, the heavy ions expand isotropically together with the laser heated and expelled grain electrons as a plasma cloud on roughly the ion acoustic timescale. It is found that with 3.1 × 1020 W cm−2 USUI laser, one can produce hundreds‐megaelectronvolt C6+ ions with ≈60% energy transfer efficiency. In fact, up to 300 GeV Au79+ ions with ≈30% energy transfer efficiency can be obtained by using 8.8 × 1023 W cm−2 laser. This result suggests the possibility of using hundreds‐petawatt laser facility to investigate heavy‐ion collisions for nuclear state detection and quantum cardiodynamics phase transition.

Design study of reflection time-of-flight mass spectrometer for EBIS charge breeder

In this study, a time-of-flight mass spectrometer is developed to analyze the mass-to-charge ratio of ion beams generated from an electron beam ion source (EBIS) at the RAON heavy ion accelerator facility. The time-of-flight mass spectrometer comprises a Bradbury–Nielson gate, steerer, mirror electrode, and microchannel plate detector. The Bradbury–Nielson gate is applied to generate a bunch beam with a 5-ns pulse width at the front end of the time-of-flight system. A double-stage reflector is employed to obtain a beam chromatic correction from the energy spread of the ion beam generated from the EBIS. The design is created through optics simulation using the SIMION code, with 133Cs as the reference ion. Consequently, the charge state of 27+ separated from neighboring states at a maximum voltage of 20 kV is obtained. By utilizing ion sources of Cs1+ (m/z 133) and Rb1+ (m/z 85 and m/z 87) to perform the performance test on the designed TOFMS system, the spectral peak of the ion sources and a relatively high mass resolution are obtained. This paper introduces the development process and test results of the time-of-flight mass spectrometer in detail.

A new type of ground-based simulator of radiation field inside a spacecraft in deep space

The problem of full-scale ground-based modeling of cosmic radiation on heavy-ion accelerators for space radiobiology is very urgent. A new type of space radiation simulator at the 56Fe ion beam with energy 1 GeV/n is proposed. The simulator uses rotating converters consisting of segmented targets with varying thicknesses. When a flat uniform field of primary 56Fe ions is used, this design ensures the uniformity of the fields of all secondary particles behind the targets. The proposed setup with four replaceable converters makes it possible to simulate not only the distribution of linear energy transfers of cosmic radiation but also reproduce continuous energy spectra of all charged fragments of the projectile ion from protons to Co. The results of simulation of the internal radiation field inside the habitable module of a spacecraft with a shell of 15 g/cm2 Al, generated by particles of galactic cosmic rays in the solar activity range from 0 to 190 Wolf numbers, are presented.