High Intensity Heavy Ion Research Articles

Design and Simulation of HiGBt, a 5 Gb/s SerDes for Heavy-Ion Physics Experiments

The Heavy Ion Research Facility on Lanzhou (HIRFL) and the High-Intensity heavy-ion Accelerator Facility (HIAF) are the leading heavy-ion physics centers. The increased scale of physics experiments at HIRFL and HIAF has put forward urgent requirements on high-speed serial data transmission links. Also, the intense radiation environment is a significant challenge to commercial ASIC. This paper presents the HiGBt, a general-purpose 5 Gbps SerDes ASIC designed in a 0.13 μm CMOS process for data transmission at HIRFL and HIAF. The HiGBt mainly consists of a Serializer, a Deserializer, and a high-speed clock system. The Serializer includes three stages to realize high-speed serialization. The Deserializer adopts a high linearity phase-interpolator-based structure to avoid coupling multi-VCOs. Finally, the high-speed clock system has a Single Event Upsets (SEUs)-protected divider. The simulation results indicate that the power consumption of the SerDes is 146.3 mW, while the layout area is 310 μm × 310 μm.

Development of Strip-Readout PPAC for high-intensity heavy ions

Strip-Readout Parallel Plate Avalanche Counters (SR-PPACs) have been developed in Center for Nuclear Study (CNS) aiming at high detection efficiency for high-intensity heavy ions based on Delay-line-readout PPAC. A readout circuit board was newly designed for the strip-readout method, and an analysis method using charge difference among two adjacent strips was developed. We achieved high detection efficiency above 99% for 115-MeV/nucleon -132Xe beams with a beam intensity of 700 kppp (particles per pulse). The achieved position resolution was about 240μm (FWHM).

Nitrogen gas scintillation counter for high-intensity heavy ion beams with negligible radiation damage

We developed an N2 gas scintillation counter as a time-of-flight counter for particle identification of radioactive isotope beams. Radiation damage, which often becomes a problem for high-intensity heavy ion beams, can be prevented by a continuous flow of N2 gas. The scintillator, with a volume of 60 mm × 60 mm × 100 mm, was filled with N2 gas at a pressure of approximately 100 kPa. Photons were detected using photomultiplier tubes attached to both sides of the vessel. The main emission wavelength of photons produced in the detector was 300–400 nm. Performance tests confirmed that the detector had sufficient detection efficiency, intrinsic time resolution, and short decay time. Additionally, the detector was demonstrated to be effective for particle identification.

Low beta superconducting cavity system design for HIAF iLinac

A superconducting ion-Linac (iLinac), which is supposed to work as the injector in the High Intensity heavy-ion Accelerator Facility project, is under development at the Institute of Modern Physics (IMP), Chinese Academy of Sciences. The iLinac is a superconducting heavy ion linear accelerator approximately 100 meters long and contains 96 superconducting cavities in two types of 17 cyromodules. Two types of superconducting resonators (quarter-wave resonators with a frequency of 81.25 MHz and an optimal beta β = v/c = 0.07 called QWR007 and half-wave resonators with a frequency of 162.5 MHz and an optimal beta β = 0.15 called HWR015) have been investigated. The cavity design included extensive multi-parameter electromagnetic simulations and mechanical analysis，and its results are described in details. The fundamental power coupler and cavity dynamic tuner designs are also presented in this article. The prototypes are under manufacturing and expected to be ready in 2023.

Accurate Low Current Measurement Electronics With Self-Calibration Function for Ionization Chamber of Slow Extraction in HIAF

The new wide-range readout electronics with a self-calibration function are designed for ionization chambers (ICs) in the slow extraction of high-intensity heavy-ion accelerator facility (HIAF), booster ring (BRing). These electronics consist of a programmable trans-impedance amplifier (TIA), a self-calibration circuit, an 18-bit analog-to-digital converter (ADC), and a ZYNQ-7015 field-programmable gate array (FPGA). It is capable of monitoring weak current signals of 40 pA–4 mA with a sampling rate of 5 MHz. The ZYNQ-7015 FPGA manages the operation mode of the analog front-end (AFE) and the gain of the TIA. It also performs digital signal processing algorithms and data communication with the host computer. The self-calibration circuit uses a combination of a Schmitt trigger and voltage-to-current (V–I) converters to generate two square wave current signals with different peaks ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 \mu \text{A}$ </tex-math></inline-formula> and 2 mA). During offline tests, the effective number of bits (ENOB) is 12.98 bits, and the nonlinearity is less than 0.075% for a full scale. Finally, the readout electronics are deployed for ICs’ slow extraction measurements at the extraction line of the cooling storage ring of the heavy-ion research facility in Lanzhou (HIRFL). With the help of a commercial dc-transformer in the cooling storage ring project of heavy ion research facility in Lanzhou (HIRFL-CSR), these electronics not only execute an accurate current measurement, but also can monitor the extraction efficiency reliably. In a word, these electronics play an important role in the fields of extremely weak and high dynamic current signal measurements.

Study on baking deformation of the thin-walled arc chamber

A large scientific facility, High Intensity heavy-ion Accelerator Facility (HIAF), was being built to study basic and interdisciplinary sciences. To meet the requirements of magnetic rigidity for high-energy heavy ions, pulsed dipole magnets were used in Booster Ring (BRing). Therefore, the ceramic-lined thin-walled arc chambers with 0.3 mm shell were developed to reduce the eddy current resulting from the rapidly changing magnetic field. Furthermore, to satisfy the requirements of the beam lifetime, the pressure of BRing of the HIAF must be lower than 1 × 10−9 Pa. In-situ baking methods were used to obtain ultra-high vacuum. As the stiffness of the thin-walled arc chamber was poorer for evacuation and in-situ baking as a conventional way, it had to be controlled in the deformation and deflection angle. Thus, a deformation control method using springs was adopted. The results show that the longitudinal deformation of both different thin-walled chambers was controlled to within 0.3 mm, the radial deformation was controlled to within 0.8 mm and the variation of deflection angle was within 0.2°.

Eddy current and structural analysis of the beam pipe for the BRing dipole magnet

Fast-ramping magnets will be used in the Booster Ring (BRing) of the High-Intensity Heavy Ion Accelerator Facility (HIAF), which is proposed by the Institute of Modern Physics (IMP), Chinese Academy of Sciences (CAS). The dipole magnet will provide the field quality from the injection field of 0.0496 T up to the maximum value of 1.5786 T, with the maximum ramping rate of 12 T/s. The ramping magnetic field induces eddy currents that give rise to eddy loss and large force on the beam pipe, field delay and sextupole field appear to affect the field quality provided by the BRing dipole. An in-detail understanding of these effects is an essential aspect of the design. Based on the finite-element analysis, a simplified model by use uniform background magnetic field was used to the transient simulations, eddy current and the forces on the pipe at different times on the beam pipe were performed. This paper presents the results obtained for the eddy loss and magnetic field delay for different wall thicknesses. Then, mechanical design details are presented, and also stress distribution, the deformation in the beam pipe. The analysis results revealed that the eddy current and thus the field delay and eddy current-induced Lorentz force scales linearly with the derivative of the magnetic field and the thickness of the pipe. The power losses that cause heating of the pipe is linear with the square of the derivative of the magnetic field and the thickness of the pipe.

Research on the layout of primary control network and new measurement method for the HIAF survey and alignment

HIAF (High Intensity heavy ion Accelerator Facility) is one of the major national science and technology infrastructure projects in the “12th Five-Year Plan” undertaken by the Institute of Modern Physics, CAS. The primary control network, as the basic framework of the local coordinate system control of the particle accelerator, is the basis for calculating the coordinates in the process of accelerator construction and implementation, and plays a very important role in the survey and alignment during the construction period and the maintenance and monitoring during the operation period. Based on the multi-dissimilar design structure of HIAF and the unique geological conditions of the construction area, a new high-density layout method of the primary control network and a high-precision 3D(three-dimensional) measurement method were studied, and were successfully applied to the survey and alignment of HIAF. Inside and outside the accelerator tunnel, a high-density 3D primary control network that can form a full envelope for the accelerator beam is respectively laid out. All primary control networks are embedded in the bedrock layer with stainless steel reference inner cylinder and outer protective cylinder, and special waterproof filling layer is set up. All primary control network points in the accelerator tunnel are equipped with measuring intervisible holes and measurement platforms that can directly perform 3D measurements on the ground. By setting up the laser tracker on the horizontal attitude of the measurement platform, the 3D coordinates of the primary control network points inside and outside the accelerator tunnel can be measured directly and with high precision, and the simultaneous adjustment of the measurement data can be completed. The HIAF primary control network layout and measurement method proposed in this paper overcomes the problems of heavy pile foundation, poor crack resistance and poor water seepage resistance of the primary control network laid by the traditional method and solves the problem that the traditional primary control network must separate the plane network and the elevation network for independent measurement. The traditional method of tunnel point and forced centering measurement is avoided. By using a laser tracker to directly measure the 3D coordinates of the primary control network points inside and outside the tunnel, the measurement efficiency and measurement accuracy of the primary control network are improved, and the reliability of primary control network measurements is increased. The feasibility and correctness of the HIAF primary control network layout and measurement method are verified by comparing the actual multi-system measurement results in the field. This method has a certain reference value for the layout of the primary control network of the same type of accelerator.

Radiation shielding design for the target area in the pre-separator of HFRS at HIAF

High energy FRagment Separator (HFRS), an essential part of High Intensity heavy-ion Accelerator Facility (HIAF), is used to produce, separate and identify the Radioactive Ions Beams (RIBs). The target area in the pre-separator of HFRS can produce very strong secondary radiation, which seriously threatens the radiation safety of the environment, public and personnel. In this work, the FLUKA code is used to complete the radiation shielding calculation and design of the target area. Firstly, the secondary radiation produced by 25 different typical beam–target combinations are compared. The parameter of 78Kr in fast extraction mode is determined as the basis for the radiation shielding design based on its strongest secondary radiation. Then, the secondary neutron spectrum and the induced radioactivity of the production target and the beam dump are analyzed. The results show that the maximum neutron energy is close to 3 GeV, and special attention should be paid to high-energy neutrons in shielding design, as well as the maximum residual dose rates on the surface of the production target and the beam dump are 3.93 × 107μSv/h and 9.58 × 107μSv/h, respectively, after one month of continuous irradiation. Furthermore, the radiation shielding design is completed using the Q235 steel compact shielding together with the ordinary concrete and sand soil, based on the Monte Carlo simulations and the relevant dose limits. Finally, the radiation effects under this shielding scheme are analyzed. The results show that the shielding design meets the relevant design goals and can provide reliable radiation protection for the environment, public and personnel.

Electro-Thermal Coupling Model of Quench Protection With a Quench-Back for DCT&amp;CCT Superconducting Magnets

As promising magnet types, discrete-cosine-theta and canted-cosine-theta (DCT&CCT) superconducting magnets are designed for the High Energy Fragment Separator (HFRS), a fragment separator of the High Intensity Heavy Ion Accelerator Facility (HIAF). Quench protection is one of the key issues for DCT&CCT superconducting magnets due to low thermal conductivity between each turns and slow transverse quench propagation. Thermal quench-back induced by the center cooper wire as a heater automatically is a feasible quench protection option for the magnet wound with 6+1 type superconducting cables (six superconducting wires and one center cooper wire). In the present paper, an electro-thermal coupling model is developed and validated to deal with the dynamic coupling behaviors of electrical and temperature fields inside the superconducting magnets during quench protection process. The transient evolutions of current and voltage-to-ground are numerically obtained by finite element method, which shows obvious quench-back behaviors and agree well with the experimental measurements of the prototype magnet L800 in first round test. The hot-spot temperature can be reduced significantly considering quench-back effect. Furthermore, the quench protection baselines of temperature and quench integral are analyzed and predicted for L800, indicating that the magnet can be protected properly by the protection method with a quench-back at ultimate current 466A.

DCT&amp;CCT Superconducting Multiplets for HIAF-HFRS

HIAF (High Intensity heavy ion Accelerator Facility) is the new generation heavy ion accelerator under construction in China. The HFRS (FRagment Separator of HIAF) is a fragment separator and also a transfer-line between the Booster Ring and the Spectrometer ring, which has magnetic rigidity up to 25 Tm. HFRS magnet system is composed of 11 superconducting dipoles and 13 sets of triplets. Several multipole magnets (an octupole coil, a quadrupole coil, and a sextupole coil) are nested together to compact the length of the HFRS-line. All of them feature high field gradients (13 T/m, 25 T/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , 105 T/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) and large bores (320 mm). To reduce the cold mass and ensure the field quality, the whole multipole magnets are all designed with coil-dominated magnets of CCT (Canted Cosine Theta) and DCT (Discrete Cosine Theta). This paper will introduce the general design process of an HFRS multipole module. The development process and test results of the prototype will be presented.

Design and Test of a Half-Aperture Canted-Cosine-Theta Multipole Prototype Magnet for the HIAF FRagment Separator

A novel Canted-Cosine-Theta (CCT) coil technology is first proposed and applied to the HIAF (High Intensity heavy-ion Accelerator Facility) FRagment Separator, which can offer an arbitrary multipole fields and meet the requirements of high magnetic stiffness (25 Tm). In this paper, a half-aperture CCT multipole prototype magnet was built and successfully tested by the Superconducting Magnet Group at Institute of Modern Physics (IMP). This magnet consists of four CCT formers that produces the gradients of 20 T/m@500 A and 120 T/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> @385 A, with a clear bore diameter of 200 mm.Two types of conductor placement methods are chosen and wound into the grooves of formers. The goal of the R&D of prototype is to verify the fabrication process, including coil winding, joints, assembly and impregnation. The detailed design and analysis for the half-aperture prototype magnet will be presented, along with results for the first stage of tests.

Superconducting Magnet Development for the HIAF Accelerator Complex

The High Intensity Heavy-ion Accelerator Facility (HIAF) is a new project under construction in China, which will provide beams of stable and unstable heavy ions with high energies, high intensities, and high quality. This paper discusses the superconducting magnet system for this accelerator complex. It will consist of a Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn magnet with the peak field of 12 Tesla for the ECR ion source operated at 45 GHz, 52 solenoids typically 676 mm long with an operating field of 7.5 Tesla for the superconducting Linac called iLinac, 11 superferric dipoles with 320 mm wide good field region, 13 coil-dominated multiplets with an aperture of 320 mm, gradient 13 T/m for the fragment separator HFRS. This paper reports the design and prototype development status of the main components.

The Study on the Quench Helium Release Process of HFRS Superconducting Magnet

The quench phenomenon of the accelerator superconducting magnet may occur in operation, which will cause the liquid helium in the cryostat to evaporate rapidly and release in the atmosphere. High-pressure helium will result in serious damage on significant components in the transmission line, and the released helium in the tunnel will lead to the ODH (Oxygen Deficiency Hazard), threatening the safety of operators. In this paper, the species transport model was used to study the 2D helium discharge process of fragmentation separator in HIAF (High-Intensity heavy-ion Accelerator Facility) by using the platform of computational fluid dynamics software FLUENT. To verify the effectiveness of the species transport model for the FLUENT in simulating the mixing jet process of different components, a 2D FLUENT simulation results of the LHC helium release process was compared with the experimental results and the 3D OpenFOAM simulation results. The results show that the species transport model based on FLUENT could predict the helium release process effectively. Then the distributions of helium concentration, temperature, and velocity in the HFRS (High energy FRagment Separator) tunnel were studied and obtained by the present work. Based on the above analysis, a reasonable design scheme of the accelerator superconducting magnet relief system can be accomplished for HFRS.

A prototype of beam profile measurement system for HIAF-HFRS beam line

ABSTRACT A prototype of beam profile measurement system developed by the Institute of Modern Physics, which can work in the proportional region and ionization region, respectively, by adjusting the pressure and voltage, has been tested several times and achieved the design expectation. When the working pressure of the detector is low enough, the system can work in the secondary electron mode to measure the fast extraction beam profile too. The measurement system has been used to measure the profile of carbon ion beam in the Second Radioactive Ion Beam Line in Lanzhou in slow extraction mode and fast extraction mode, respectively. It is confirmed that the measurement system can measure the profile of carbon ion beam with a dynamic range of beam intensity up to six orders of magnitude. We used the X-ray beam to simulate the Gaussian-like distribution for laboratory testing, and the results show that the measurement system has a better resolution than 0.1 mm for the beam position with a Sigma of about 1.6 mm. This measurement system, together with the harps measurement system, will be able to meet needs of most beam profile measurements in High energy Fragment Separator (HFRS) at High Intensity heavy-ion Accelerator Facility (HIAF).

Design of a radio frequency quadrupole for a high intensity heavy-ion accelerator facility

We report a design work of a continuous-wave (cw) radio frequency quadrupole (RFQ) for the injector linac of the High Intensity heavy-ion Accelerator Facility project. The rf design and multiphysics analysis were conducted to enhance the long-term stability and reliability of the cavity. To minimize the peak modified Poynting vector and peak surface electric field associated with the rf breakdown rate, the cross section and the vanes segmentation of the RFQ cavity were optimized. Pi-mode stabilizing loops (PISLs) were adopted for the cavity to increase the mode separation between the quadrupole and the neighboring dipole modes, intending to reduce the emittance growth and beam loss caused by the field asymmetry of the quadrupole mode. Due to the lack of a universal criterion of acceptable mode separation, the field asymmetry of the quadrupole mode was directly used as the design criterion for the PISL. Tuners were designed to tune the cavity frequency and longitudinal field flatness. Thermal distributions on tuners with and without rf sealing were investigated, and we found that rf sealing was indispensable in decreasing the tuner's temperature. A multiphysics analysis was carried out to maintain the cavity frequency while running with different rf power, in an attempt to avoid frequently adjusting the cooling water temperature when accelerating different ions. The analysis also verified that a large wall thickness could make the cavity possess a low stress and a minor deformation.

An engineering geological suitability comprehensive evaluation index (EGSCEI) for large-scale infrastructure site selection

The purpose of this paper is to present a quantitative method for evaluating the engineering geological suitability of potential sites in order to select the optimal site for large-scale infrastructure. Based on the fuzzy comprehensive evaluation decision method and analytic hierarchy process (AHP), an engineering geological suitability comprehensive evaluation index (EGSCEI) model was applied in the selection of a site for the construction of the China Initiative Accelerator-Driven System (CiADS) and the High-Intensity Heavy-Ion Accelerator Facility (HIAF). In this model, seven parameters, including land use, geomorphology, geological structure, lithology, hydrogeology, geological disaster and rock weathering, were selected as the evaluation factors. The factor evaluation matrices were established, and the weight vector of the seven factors was determined using the AHP. The engineering geological suitability fuzzy comprehensive evaluation vectors were then computed. Finally, according to the normalized engineering geological suitability comprehensive evaluation vectors and the quantified evaluation ranking vector, the EGSCEI values were calculated. As a result, site No. 3 was evaluated as the most optimal site of the three potential sites for the construction of the CiADS and HIAF. The result was adopted by the Chinese government, and site No. 3 became the selected location. This case study shows that the EGSCEI model is scientific, reasonable and applicable in providing a reference for similar large-scale infrastructure site selection.

Production of intense pulsed beams of highly charged ions from a superconducting electron cyclotron resonance ion source

An experimental study of the afterglow mode was performed with a third generation electron cyclotron resonance ion source, SECRAL-II (Superconducting ECR ion source with Advanced design in Lanzhou No. II), under double frequency heating. The experimental results show that intense pulsed beams of highly charged ions (e.g., $266\text{ }\text{ }\mathrm{e}\ensuremath{\mu}\mathrm{A}$ of ${^{129}\mathrm{Xe}}^{34+}$ and $169\text{ }\text{ }\mathrm{e}\ensuremath{\mu}\mathrm{A}$ of ${^{129}\mathrm{Xe}}^{38+}$) could be produced at high frequency ($24+18\text{ }\text{ }\mathrm{GHz}$) and high power ($\ensuremath{\sim}8\text{ }\text{ }\mathrm{kW}$), even compared with the beam intensity records of SECRAL-II obtained in continuous wave (cw) mode at higher microwave frequency ($28+18\text{ }\text{ }\mathrm{GHz}$) and higher power ($\ensuremath{\sim}10\text{ }\text{ }\mathrm{kW}$), the gain factor is also up to $\ensuremath{\sim}3$. Meanwhile, it is found that the afterglow decay time in our study is much longer than that obtained with the second generation ECR ion sources typically operating at 10--18 GHz, and the corresponding peak duration is greater than 2 ms. This study provides a viable solution for heavy ion synchrotron accelerator complex such as High Intensity Heavy Ion Accelerator Facility project that requires intense pulsed beams of highly charged ions with long peak duration.

Continuous wave interdigital H-mode cavities for alternating phase focusing heavy ion acceleration.

In the future, a new superconducting (SC) continuous wave (CW) high intensity heavy ion HElmholtz LInear ACcelerator (HELIAC) should provide ion beams with maximum beam energy above the Coulomb barrier for the Super Heavy Element program at GSI (Gesellschaft für Schwerionenforschung, in Engl.: Association for Heavy Ion Research). The HELIAC consists of a SC main accelerator supplied by a normal conducting injector, which comprises an electron cyclotron resonance ion source, a radio-frequency quadrupole, and two separate interdigital H-mode drift-tube linear accelerator cavities, based on an Alternating Phase Focusing (APF) scheme. Together, both cavities will accelerate ions from 300 to 1400 keV/u with only one external quadrupole triplet for transverse focusing in between. Due to the demanding requirements of the APF concept on the voltage distribution along the beam axis on the one hand and the CW operation on the other hand, the optimization of each cavity concerning RF, mechanical, and thermal properties is crucial for the successful operation of the HELIAC injector.

A new digital beam position and phase measurement implementation based on a field programmable gate array for the high intensity heavy-ion accelerator iLinac.

A new digital beam position and phase measurement (BPM) system was designed for the ion-Linac accelerator at the high intensity heavy ion accelerator facility. The fundamental and second harmonic signals are retrieved from the BPM electrodes to simultaneously calculate their respective beam positions and phases. All data acquisition and digital signal processing algorithm routines are performed in a field programmable gate array (FPGA). The position and phase information are obtained by using the in-phase and quadrature demodulation method. A practical and straightforward method is used to generate the second harmonic reference signal for processing the second harmonic beam signal. The reconfigurable filters are integrated into the FPGA to allow the measurement of short beam pulse length. The laboratory test results show that the achieved phase resolution is better than 0.2° and 0.03° when the input signal is -60 and -45 dBm, respectively. A position resolution better than 30 μm was achieved for an input power level of approximately -60 dBm, and it can reach 7 μm with the input power higher than -45 dBm. The entire execution time of the algorithm is accomplished within 3.4 µs, which provides a sufficient reaction time for the fast beam interlock signal to the machine protection system. The performance of this newly designed prototype BPM electronics was evaluated with the online proton beam.