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Electron ionization time-of-flight mass spectrometry (EI-TOF-MS) has been widely used in the fields of chemical, environmental, food, medical and pharmaceutical, etc. Coupling gas chromatography (GC) with EI-TOF-MS yields promising qualitative and quantitative results, and the performance is closely related to with the ion guide devices. A good ion guide device for EI ion source can generate a narrow beam of low-energy ions, resulting in high ion transition efficiency. In this study, an ion transition system for EI ion source with radio frequency quadrupole (RFQ) as the collisional focusing ion guide was developed. The ions in the RFQ could be cooled by collisions with buffer gas molecules and focused to near the axis by a RF field. To determine the parameters of the RFQ, including rod length, rod radius, field radius, RFQ exit orifice diameter, RF frequency, RF amplitude, and other transmission electrode voltages, vacuum design theory, RF quadrupole field theory and SIMION software simulations were applied. The performance of a GC-EI-TOFMS instrument was significantly improved using RFQ as collisional focusing ion guide, and the evaluation results showed that the mass resolution was up to 6500 FWHM (m/z 502), the limit of detection (LOD) was 1 pg of OFN (S/N > 30:1), the mass range was 15–968 amu, the mass accuracy was below 0.01 amu, and the relative standard deviation (RSD) was below 1.5% within one week. This study provided an example to build an ion transition system for mass spectrometry, which had important theoretical and practical significance in design and development of new mass spectrometric instrument.

The development of a four vane 3-MeV radio frequency quadrupole is under progress at Raja Ramanna Centre for Advanced Technology, as part of the Indian facility for spallation source. This quadrupole will be powered by four identical 150-kW solid-state amplifiers, each operating at 325 MHz. This article describes the design details, rigorous testing, and measured results of the first such constructed amplifier and its constituent components. Its output power is 150 kW, with variable pulsewidth from 1 to 5 ms, at 50 Hz of pulse repletion rate. Its pulse amplitude droop measured at 1 ms is 0.46 dB. The phase variation around an average value, measured within a single pulse at 1 ms, is less than 2.7°. Its pulse-to-pulse amplitude stability and phase stability are ±0.1 dB and ±2°, respectively. Its main features are its modular and scalable design architecture, comprising of multiple extended continuous class F 1.5-kW amplifiers, energy-efficient two-tier radial power dividers as well as combiners, compact dual-channel power sensors, and aperture-coupled directional couplers.

The eight-chain RF system and radio frequency quadrupole (RFQ) linac were successfully integrated at the facility of the Linear IFMIF Prototype Accelerator (LIPAc). We achieved an unprecedented high current deuteron beam up to 55 mA in pulse operation ( $300~\mu \text{s}$ , 1 Hz). The keys of the success were (1) understanding reflected power from RFQ to RF system, (2) tuning each RF chain individually, (3) intensive RF conditioning for holding the stable RF power in the RFQ, and (4) optimizing the beam loading compensation control. Interestingly, the reflection at the breakdown in RF conditioning was higher than an estimation and reached up to 600 kW so far. In order to avoid damage on tetrodes by the high reflection, the impedance of each circulator was accurately adjusted.

Operation target beam power of China Spallation Neutron Source (CSNS), as the China’s first 100 kW beam power pulsed neutron source, is now larger than 80 kW. During the beam power upgrading process of CSNS to 50 kW from 2018 to 2019, many improvements have been made for the front end of CSNS. The improvements mainly focus on solving the problems of ion source instability and the radio frequency quadrupole (RFQ) sparking caused by the pre-chopped beam into RFQ.

The ISOL facility ALTO, located at Orsay in France, provides stable ion beams from a 15 MV Tandem accelerator and neutron-rich radioactive ion beams (RIB) from the interaction of a γ -flux induced by a 50 MeV 10 μA electron beam in a uranium carbide target. A magnetic dipole mass separator and a resonance ionization laser ion source allow to select the ions of interest. New setups are under preparation to extend the fundamental properties measured at ALTO of ground and excited states of exotic nuclei. For example, high-precision mass measurements for an accurate determination of the nuclear binding energy. To perform these measurements two devices will be hosted at ALTO: a radio frequency quadrupole to cool and bunch (RFQCB) the continuous radioactive beam and the double Penning trap mass spectrometer MLLTRAP, commissioned off-line at the Maier-Leibnitz Laboratory (MLL) in Garching, Germany. The unique production mechanism using photo-fission at the ALTO facility allows for mass measurements in a neutron rich area of nuclides of major interest around 132 Sn with less isobaric contamination than using proton drivers. In this context, we plan to measure neutron-rich silver isotopes (Z = 47, A > 121) to explore the possible weakening of the shell gap for Z

The N = 126 factory currently under construction at Argonne National Laboratory’s ATLAS facility will make use of multi-nucleon transfer reactions to produce nuclei around the N = 126 shell closure that are of interest for the study of the rapid neutron capture process and are not available in sufficient quantities using common particle-fragmentation, target-fragmentation, or fission production techniques. As part of this facility, a radio frequency quadrupole (RFQ) buncher will cool and accumulate the beam, converting a high-emittance, continuous beam into a low-emittance bunched beam suitable for trapping. Here, the construction of the RFQ cooler-buncher, based on the design used at the National Superconducting Cyclotron Laboratory’s BECOLA and EBIT cooler-bunchers, will be discussed. This design features injection optics optimized to maximize acceptance, separated cooling and bunching regions, and a simplified RFQ electrode construction.

It is difficult to accelerate a high intensity heavy ion beam because the upper limit of the beam current in an RFQ (Radio Frequency Quadrupole) linac depends on the applied voltage at the RFQ electrode and the strength of the space charge effect. A multi-beam RFQ linac, with multiple beam-channels accelerating several beams in parallel in one cavity, and utilizing multiple beams to decrease the space charge effect can be used to achieve a higher beam current. In order to demonstrate that a four-beam IH-RFQ (Interdigital H-type RFQ) linear accelerator is suitable for high-intensity, heavy ion beam acceleration, we have developed a four-beam prototype. A four-beam IH-RFQ cavity was fabricated according to design parameters obtained from our previous detailed simulations. Low-power RF property measurements of the fabricated four-beam IH-RFQ cavity were carried out with a network analyzer. After the low-power RF property measurements, we performed a high-power test and an acceleration test.

Continuous developments in additive manufacturing (AM) technology are opening up opportunities in novel machining, and improving design alternatives for modern particle accelerator components. One of the most critical, complex, and delicate accelerator elements to manufacture and assemble is the radio frequency quadrupole (RFQ) linear accelerator, which is used as an injector for all large modern proton and ion accelerator systems. For this reason, the RFQ has been selected by a wide European collaboration participating in the AM developments of the I.FAST (Innovation Fostering in Accelerator Science and Technology) Horizon 2020 project. The RFQ is as an excellent candidate to show how sophisticated pure copper accelerator components can be manufactured by AM and how their functionalities can be boosted by this evolving technology. To show the feasibility of the AM process, a prototype RFQ section has been designed, corresponding to one-quarter of a 750 MHz 4-vane RFQ, which was optimised for production with state-of-the-art laser powder bed fusion (L-PBF) technology, and then manufactured in pure copper. To the best of the authors’ knowledge, this is the first RFQ section manufactured in the world by AM. Subsequently, geometrical precision and surface roughness of the prototype were measured. The results obtained are encouraging and confirm the feasibility of AM manufactured high-tech accelerator components. It has been also confirmed that the RFQ geometry, particularly the critical electrode modulation and the complex cooling channels, can be successfully realised thanks to the opportunities provided by the AM technology. Further prototypes will aim to improve surface roughness and to test vacuum properties. In parallel, laboratory measurements will start to test and improve the voltage holding properties of AM manufactured electrode samples. Continuous developments in Additive Manufacturing (AM) technologies are opening opportunities in novel machining, and improving design alternatives for modern particle accelerator components. One of the most critical, complex, and delicate accelerator elements to manufacture and assemble is the Radio Frequency Quadrupole (RFQ) linear accelerator, used as an injector for all large modern proton and ion accelerator systems. For this reason, the RFQ has been selected by a wide European collaboration participating in the AM developments of the I.FAST (Innovation Fostering in Accelerator Science and Technology) Horizon 2020 project. RFQ is as an excellent candidate to show how sophisticated pure-copper accelerator components can be manufactured by AM and how their functionalities can be boosted by this evolving technology. To show the feasibility of the AM process, a prototype RFQ section has been designed, corresponding to one-quarter of a 750 MHz 4-vane RFQ, which was optimised for production with state-of-art Laser Powder Bed Fusion (L-PBF) technology, and then manufactured in pure copper. To the best knowledge of the authors, this is the first RFQ section manufactured in the world by AM. Subsequently, geometrical precision and surface roughness of the prototype were measured. The results obtained are encouraging and confirm the feasibility of AM manufactured high-tech accelerator components. It has been also confirmed that the RFQ geometry, in particular the critical electrode modulation and the complex cooling channels, can be successfully realised thanks to the opportunities provided by the AM technology. Further prototypes will aim to improve surface roughness and to test vacuum properties. In parallel, laboratory measurements will start to test and improve the voltage holding properties of AM manufactured electrode samples.

The 10-MeV Accelerator-Driven Subcritical (ADS) system Injector-I test stand at the Institute of High Energy Physics (IHEP) is a testing facility dedicated to demonstrating the feasibility of the spoke-based superconducting (SC) linear accelerator (linac) for the ADS project in China. The injector adopted a four-vane copper structure radio frequency quadrupole (RFQ) with an output energy of 3.2 MeV and an SC section accommodating 14 $$\beta _{\text{g}}$$ =0.12 single spoke cavities, 14 SC solenoids, and 14 cold beam position monitors (BPMs). A 10-MeV pulsed beam with a beam current of 10 mA and a 2-mA continuous wave (CW) beam were successfully shooting through. The commissioning results confirmed the feasibility of using a 325-MHz spoke-type cavity for accelerating the proton beam in the low $$\beta$$ and medium $$\beta$$ sections. This paper describes the results achieved, the difficulties encountered, and the experiences obtained during commissioning.

In order to facilitate the widespread use of neutrons in industrial applications, it is important to provide a compact, semi-ready-made neutron source that a company and a factory can easily install. We are therefore developing a compact neutron source system utilizing a downsized proton accelerator as an entry level model for industrial use and materials development, which consists of a proton source, a four-vane radio frequency quadrupole linear accelerator (RFQ) and a lithium target for neutron production by the Li ( p,n ) 3 7 Be 4 7 reaction. An RFQ is suitable to accelerate protons in the low energy region because it accepts DC beams extracted from the proton source and accelerates effectively to the design energy with bunching and focusing using the electric fields. Furthermore, it is possible to design the RFQ with a higher frequency than conventionally used owing to technological advances in high power solid-state RF amplifiers. We investigated the specifications for 500 MHz and 650 MHz through beam trajectory and electromagnetic simulations and fabricated a 2.5 MeV prototype of the 500 MHz type with a 2.45 GHz ECR proton source.

We develop a concept of the CW proton linac with the parameters of 13 MeV 162.5 MHz 5 mA. This linac designed for compact neutron source DARIA is based on the linac designed for the project BELA. The different linac layouts were considered. The most perspective linac layout includes Radio Frequency Quadrupole (RFQ) and Drift Tube Linac (DTL) sections with 6D beam matching between them. The drift tube linac section has a modular structure and consists of the separated individually phased IH-cavities with beam focusing by quadrupole magnets between the cavities. This DTL structure provides linac compactness, tuning and commissioning “cavity by cavity”. Results of the beam dynamic simulation and radio frequency parameters of the linac cavities are presented.

Selective laser photodetachment of anions is a novel technique for isobar suppression in Accelerator Mass Spectrometry (AMS). Ion-laser interaction times on the order of ms required for near-complete isobar suppression are achieved by retarding the ions in a gas-filled radio frequency quadrupole cooler. Inside this RFQ, the cooled anion beam is overlapped collinearly with an intense cw-laser beam. Within the Ion Laser InterAction Mass Spectrometry (ILIAMS) project at the University of Vienna, a dedicated injector beamline has been coupled to the VERA-AMS facility to explore and develop this method. In this work, experimental investigations on ion beam transmission, stability and elemental selectivity of the new setup are presented. A 532 nm laser at 10 W transmitted power provides suppression factors larger than ten orders of magnitude for S− and MgO− under AMS conditions with simultaneous beam transmission for the ions of interest of up to 80%. The excellent ion identification capabilities of the subsequent AMS system also facilitate the study of destruction and formation of molecular anions inside the ion cooler. These kinetic and chemical reactions with the buffer gas provide additional elemental selectivity in certain cases, whereas others constitute a source of background.

There are briefly considered physical and medical aspects contemporary development of Boron Neutron Capture Therapy (BNCT) system. Choice of accelerator for neutron produce is discussed. Three of accelerator types are compared: electrostatic accelerator, compact cyclotron and RFQ with working frequency of P-diapason. A few factors determine choice: providing required neutron flux, compactness of accelerator and whole BNCT system, economical power consumption. Our choice is radio-frequency quadrupole. Two of RFQ variants are considered: compact RFQ and universal one, which has possibility to accelerate two of types particles (proton and deuteron) and to use two of types targets (Lithium and Beryllium) for neutron production.

A 325 MHz, 3.0 MeV Radio Frequency Quadrupole (RFQ) is being developed for 1 GeV proton accelerator for proposed Indian Spallation Neutron Source (ISNS) facility at Raja Ramanna Centre for Advanced Technology, Indore. RFQ will be a normal conducting four vane resonating structure made of Oxygen Free Electronic (OFE) copper. During high power operation of RFQ, Radio Frequency (RF) field induced heating results in temperature rise, thermal deformations and shift in resonant frequency from designed values. Therefore thermal stability of RFQ is one of the important design issues. Various RF–thermal–structural coupled multiphysics analysis methodologies for thermal management of RFQ have been attempted in past and reported in literature. However, these efforts are primarily limited to 2D simulations for a thin slice of RFQ cross section and do not addresses for longitudinal temperature rise of cooling water, distribution of frequency tuners, vane tip modulations and vane cut back at the inlet and exit of RFQ structure. This paper proposes a finite element method (FEM) based multiphysics analysis methodology for numerical simulation of RFQ structure. The methodology consists of a complete 3D-RF-fluid–thermal–structural–RF coupled analysis for predicting temperature rise, thermal deformations and frequency shift of RFQ structure due to RF heating. All analysis (electromagnetic, fluid, thermal and structural) and their coupling are carried out using a single code namely ANSYS Mechanical. The simulated results from proposed methodology are compared with published work and a maximum error of less than 7% is obtained. The numerical comparison of described methodology with other multiphysics analysis methodologies (such as importing 2D field maps and using heat transfer coefficient from empirical relations) has been carried out. The described methodology is paving the way for the design and development of ISNS RFQ structure.

We show the design results of beam dynamics on the injector for high-intensity proton accelerators. The injector can be utilized in a medical proton linac and accelerator driven system. The injector system consists of a 325-MHz RFQ (radio-frequency quadrupole) accelerator and a 325-MHz DTL (drift tube linac) accelerator. The injector has been designed to optimize the beam parameters to meet the required design goals. In this paper, we present a design study on the beam dynamics in the injector through beam tracking. We show the results of the beam dynamics study and cavity design study in the RFQ. The high-intensity RFQ accelerates the proton beam from 50 keV to 3 MeV with a peak beam current of 30 mA. The RFQ has a length of 3.839 m and Kilpatrick value of 1.76. We investigated ways to minimize the emittance growth caused by the space-charge effect and optimized achieve a high transmission and a small growth of emittance along the RFQ. The DTL with face angles of 3 degree and 10 degree in one tank accelerates proton beams from 3 MeV to 10 MeV and is 4.3 m long. Electromagnet quadrupoles (EMQs) are used as focusing elements in a Focusing-Defocusing-Focusing-Defocusing (FFDD) lattice scheme in the DTL. A quadrupole between the RFQ and the DTL, and 8 drift tubes (DT) in DTL are used for transverse matching in the DTL. We investigated the beam dynamics to achieve a high transmission and a small growth of emittance along the DTL. We also show the results of beam tracking simulations in the DTL. Our studies show that major parameters affecting on beam dynamics in the injector for a high-intensity proton linac are available.

An 8-MeV linear proton medical accelerator designed with a high RF duty operation is being developed at Ibaraki Neutron Medical Research Center for iBNCT (Ibaraki - Boron Neutron Capture Therapy). The reliability and stability of the cooling water control system has become one of the most important issues in realizing the medical application of the accelerator, which is designed considering high performance and low costs. However the previous cooling water control system with a commercial PID (Proportional–Integral–Differential) controller could not meet the operation requirements of the medical accelerator. Therefore, a new intelligent cooling water controller is successfully developed by application of Fast Feed-forward for Future (FFF). The detailed design of the intelligent cooling water control system and its great efficacy in improving accelerator operation is described in this paper. The stability of the cooling water temperature is improved greatly from the previous ± 0 . 30 ° C to the current ± 0 . 03 ° C. Moreover, the response time of cooling water control is decreased dramatically from the previous 5 min to approximately 20 s. Precise operation and an excellent auto-tuning of the RFQ (Radio Frequency Quadrupole LINAC) cavity are realized by using this stable and intelligent water control system. The beam transmittance is also improved slightly after a fine scan experiment with different settings of RF devices under stable acceleration operation. Finally, the RF startup time is also reduced by using this intelligent cooling water control system. Now the iBNCT accelerator operation is greatly improved with a very high reliability and stability. The accelerator will be operated as a practical medical therapy in late 2019. The technology developed in this intelligent cooling water control system will be very useful for the development of similar accelerators with high performance and low cost.

The thermal stability of the radio frequency quadrupole (RFQ) is an important concern during commissioning. The cooling water takes away the power dissipated on the RFQ internal surface to maintain the thermal stability and limit the structural deformation. In this paper, the thermal-fluid coupled analysis of the RFQ is described and 3D temperature distribution of the RFQ cavity structure is given. The method of adjusting the water temperature is determined through analysis. The heat transfer coefficient for the cooling channels and the outlet water temperature about the water cooling system are obtained. A comparison of the results in simulation and experiment is presented. The cooling system can meet the requirements of RFQ operating.

The proposed Compact Intense Fast NEutron Facility (CIFNEF) will have a wide range of applications, including the investigation of the exotic structure of neutron-rich nuclei, data for the nuclear fission , and the simulation of the neutron field in a star. To satisfy aims of producing high-intensity fast neutrons and forward neutrons with very low environmental background, the CIFNEF linac should have the capacity of accelerating continuous wave (CW) deuteron (D + ), hydrogen ( H 2 + ) and lithium (7Li 3 + ) beams to 2.5 MeV/u with maximum beam currents of 10 mA, 5 mA and 10 uA, respectively. Based on the above requirements, we proposed a novel compact linac using a combination of RFQ and DTL structures. The dynamics of RFQ and DTL are completed to meet all requirements and start-to-end simulation results show that the three ion species can be accelerated to the final energy with transmission efficiency above 99% as well as good beam quality with lower emittance growth. In addition, we performed error sensitivity analysis and combined error study to evaluate the error tolerance limits of the obtained design.

A 162.5 MHz, 7.2 MeV Radio Frequency Quadruples (RFQ) is being designed for the injector of a heavy ion medical machine, which is promoted by the Institute of Modern Physics (IMP), Chinese Academy of Science (CAS). The proposed RFQ will adopt the conventional 4-rod structure, which is most commonly used for the heavy ion linac at low energy section. RF design was based on a new fast-bunching beam dynamics design. Comparing with the conventional beam dynamics design, this design strategy makes the structure more compact and need less power consumption. To meet the requirements of beam dynamics, various methods were used to optimize the electric field distribution. The electric field fluctuation under 3.5% and the dipole field ratio under 3% were obtained simultaneously. Water temperature rise and cavity thermal deformation were also simulated based on the special water-cooling system design. Under the setting of the cooling parameters, the temperature rise of cooling water was kept below 2 °C in theory. Considering the possible frequency shift during assembling and operation, the tuning range of the movable plungers is 500 kHz to compensate frequency shift.

To provide high shunt impendence with low power losses, an 81.25 MHz continuous wave (CW) radio frequency quadrupole (RFQ) accelerator has been designed and machined as parts of the Low Energy Accelerator Facility (LEAF). In this paper, the mechanical structure and the main processing technology of the RFQ cavities are described according to the physical and geometric parameters requirements of the RFQ. The fabrication of the RFQ has been completed and the test results agree well with the design requirements. The RFQ accelerator will work in Institute of Modern Physics, Chinese Academy of Sciences in 2018. Keywords: RFQ, Design, Fabrication, Temperature, Test

We present multiphysics design studies for thermal management of a 325 MHz 3 MeV Radio Frequency Quadrupole (RFQ) structure for the front end of 1 GeV proton linac for proposed Indian Spallation Neutron Source (ISNS). Physics design of RFQ for ISNS application has been carried out for 10% (maximum) duty factor. During high power operation of RFQ, RF-induced heating would result in temperature rise, thermal deformations and frequency shift of RFQ from designed values. Therefore thermal management is one of the important design considerations for RFQ development. During design studies, electromagnetic analysis of RFQ cavity is performed to compute RF induced heat fluxes on RFQ surfaces using SUPERFISH and ANSYS software. Simulated results for both codes were compared and found in well agreement. A water cooling scheme has been designed to absorb RF induced heat from RFQ structure. Cooling parameters are optimized by employing univariate search method optimization technique. An RF-Thermal-Structural-RF coupled multi-physics analysis methodology is developed to evaluate thermal induced frequency detuning of ISNS RFQ structure. Parametric studies are carried out to investigate the effect of cooling water temperatures on RFQ frequency. Based on analysis results, cooling water temperatures are varied to restore RFQ frequency to designed values. Thus, water cooling will not only remove heat from structure, but it will also be used for online control of resonating frequency during steady state operation of RFQ structure. Results of numerical studies carried out for thermal management of ISNS RFQ are presented in this paper.

A 325 MHz aluminum prototype of a spatially periodic rf quadrupole focusing linac was developed at the Institute of Modern Physics, Chinese Academy of Sciences, as a promising candidate for the front end of a high-current linac. It consists of an alternating series of crossbar H-type drift tubes and rf quadrupole sections. Owing to its special geometry, cavity fabrication is a major hurdle for its engineering development and application. In this paper, we report the detailed mechanical design of this structure and describe its fabrication process, including machining, assembly, and inspection. The field distribution was measured by the bead-pull technique. The results show that the field errors of both the accelerating and focusing fields are within an acceptable range. A tuning scheme for this new structure is proposed and verified. The cold test process and results are presented in detail. The development of this prototype provides valuable guidance for the application of the spatially periodic rf quadrupole structure., 16 pages, 7 figures, 1 table

International audience; Design, development, manufacturing, and test activities of the RF power system (RFPS) for Linear IFMIF Prototype Accelerator (LIPAc) were completed in Europe. Installation and commissioning activities were carried out at the International Fusion Materials Irradiation Facility-Engineering Validation and Engineering Design Activities (IFMIF/EVEDA) site in Rokkasho, Japan. Challenging IFMIF requirements led to a number of innovations during design and development. Commissioning required a major effort on calibration and fine setting and led to development of new functionalities. The RFPS was validated under full power and 125-mA deuteron beam loading conditions, in the radio frequency quadrupole (RFQ), demonstrating good performance. This article is an overview about how technical challenges impacted the prototype RFPS design and its functional evolution during commissioning, cavity conditioning, and beam operation of the RFQ.

Physical review accelerators and beams 24(4), 040101 (2021). doi:10.1103/PhysRevAccelBeams.24.040101, Published by American Physical Society, College Park, MD

The Spallation Neutron Source (SNS) accelerator system includes a 65 keV H- injector, a 2.5 MeV radio frequency quadrupole (RFQ), a 1 GeV linac chain (DTL-CCL-SCL) and an accumulator ring. The H− injector consists of an RF-driven, Cs-enhanced, multi-cusp H− ion source and a compact, two-lens electrostatic low energy beam transport (LEBT). In 2018, a new RFQ was installed in place of the original RFQ along with upgraded ion source support infrastructure. This paper presents the operational performance and some highlights of beam studies with the SNS ion source since the new RFQ was put into operation. SNS routinely operates at 1.4 MW average beam power for three run cycles per year. During the most recently finished run, FY20B, we operated a single source for the entire run spanning ~4 months with a >99.5% availability. A single dose of cesiation was conducted during the ion source startup which yielded ≥54 mA current for the entire run with just few minor adjustments of parameters.

The 500kW tetrode can be used as the radio frequency power supply for a Radio Frequency Quadrupole (RFQ) accelerator. The cathode plays a vital role in reliability and the life of the tetrode. The thermal analysis and structural analysis of the 500kW tetrode were carried out by using the finite element software. Under a given cathode power, the temperature field distribution of the key components of the tetrode is obtained. According to the influence of temperature on the tetrode under working conditions, the axial and radial temperature distributions of the cathode and grid are obtained. It is helpful to optimize the cooling system in the future by analyzing the temperature distribution of key components.

The 500kW tetrode can be used as a radio frequency power source for a radio frequency quadrupole (RFQ) accelerator. The cathode is the core component of the tetrode, which can emit a uniform electron column. The electron flow of a tetrode is one of the main factors that determine its life and working stability. These charged particles move among the electrodes under vacuum conditions to achieve energy exchange. In this paper, a three-dimensional solid model is established in the software CST for particle simulation experiments. The whole process from injection to collection of electrons is obtained. It can clearly reflect the energy conversion and collection of the electron flow among the electrodes. The radiation effect between the electrodes is analyzed by analyzing the trajectory of the electron flow, and the thermal analysis is verified by the finite element software ANSYS. In addition, the influence of the electron flow from the cathode on the radiation effect of other components is verified by the heat distribution. The thermal analysis results are basically consistent with the theory of particle simulation analysis.

A 3 MeV proton radio frequency quadrupole (RFQ) accelerator has been designed, built, and commissioned at the Bhabha Atomic Research Centre, India. A compact wide bandwidth strip-line fast Faraday cup (SFFC) has been developed for the beam bunch measurements of the 352 MHz RFQ. The SFFC design is improvised over the standard strip-line FFC designs with a thicker strip, which can withstand larger beam intensities. The absence of the pinhole beam limiting aperture and the provision for a suppressor electrode to suppress secondary electrons on the strip are other improvisations over standard SFFC designs. The SFFC has been characterized using the time domain reflectometry method, and a broad bandwidth of ∼7 GHz is measured. The SFFC has been tested with a 3 MeV RFQ beam at a 4 mA peak current. The time structure of the individual micro-pulses with a FWHM of 297 ps has been measured with a SFFC.

High-frequency linear accelerators are very suitable for carbon ion therapy, thanks to the reduced operational costs and the high beam quality with respect to synchrotrons, which are presently the only available technology for this application. In the framework of the development of a new linac for carbon ion therapy, this article describes the design of a compact 750 MHz Radio Frequency Quadrupole (RFQ) with trapezoidal vanes. A new semi-analytic approach to design the trapezoidal-vane RFQ is introduced together with the relevant beam dynamics properties. The RFQ is split into two decoupled rf cavities, both of which make use of a novel dipole detuning technique by means of length adjustment. The splitting is described both from the rf and the beam dynamics point of view. The paper concludes with the rf design of the full structure, including maximum surface field and thermal studies., Comment: Revised version published in Physical Review Accelerators and Beams on 31 December 2020

The 750 MHz PIXE-RFQ (radio-frequency quadrupole), developed and built at CERN, provides 2 MeV protons over a length of one meter for proton-induced X-ray emission analysis (PIXE) of cultural heritage artwork. In this paper, we report low-power rf measurements and tuning of the PIXE-RFQ, which have been completed mid-2020. Using a novel algorithm based on direct measurements of the response matrix, field and frequency could tuned at the same time in only two steps to satisfying accuracy. Additionally, we report measurements of single modules, quality factors, and coupling strength. In all cases, very good agreement between rf measurement and design values was observed., 13 pages, 15 figures. Submitted to Physical Review Accelerators and Beams

Equipartitioning is an efficient beam-dynamics design scheme also for radio frequency quadrupole (RFQ). To realize an equipartitioned RFQ, it is essential to reproduce the nonuniform intervane voltage profile required from the beam dynamics. We developed a cavity design and tuning method to this end. The dimensions of a voltage-ramped four-vane cavity were determined by a three-dimensional rf simulation. To produce the desired vane voltage profile, the longitudinal variation of the cross-sectional shape was adjusted using the least-squares method based on the simulated responses of the vane-base width to the quadrupole-mode field. In the low-level tuning, slug-tuner positions were determined based also on the least-squares solutions obtained from the simulated tuner responses to the field profile. Finally, the deviation of the quadrupole-mode field was within 1.5% from the design profile, and the mixed dipole modes were 1% of the quadrupole-mode field after only two iterations of tuner adjustment; they are sufficiently smaller than the requirement of 2%.

A 200 MeV, 10 mA, medium energy high intensity proton accelerator (MEHIPA) is proposed to form the second stage of the Indian accelerator-driven system program. The linac consists of a normal conducting 3 MeV radio frequency quadrupole (RFQ) and a 200 MeV superconducting section consisting of three different families of single spoke resonators (SSR-A, SSR-B, and SSR-C). Here we discuss a detailed physics design of MEHIPA, including electro-magnetic design, multipacting analysis, higher-order mode studies, and beam dynamics. We have designed a compact linac, by careful optimization of cavity $\ensuremath{\beta}$ for the superconducting section. We also performed detailed optimization studies on the linac lattice and transport line parameters, aimed at minimizing the emittance and beam halo. Reliability analysis and error studies were performed on this optimized linac, including various beam, cavity, and magnet parameters, to estimate the operation tolerances, and the results are reported for a maximum emittance growth of 50%.

В статье описываются результаты исследования воздействия сверхзвуковой газовой струи, сформированной внутри цилиндрического канала и пропущенной через источник электронной ионизации, на выход дейтерозамещённых ионов из жидкости, подаваемой через капилляр внутрь радиочастотного квадруполя, сопряжённого с времяпролётным масс-спектрометром с ортогональным вводом ионов. При увеличении потока анализируемого раствора не наблюдалось явной зависимости изменения относительных вкладов дейтерированных ионов в жидкой фазе от скорости подачи образца. Полученные результаты подтверждают перспективность использования сверхзвуковой струи для создания высокоэффективного источника дейтерозамещённых ионов из растворов при остаточном давлении на уровне 10-4 Торр и в отсутствие сильных электрических полей., The article describes the results of a study of the effect of a supersonic gas jet on the formation and extraction of the deuterosubstituted ions from a liquid supplied through a capillary into a radio-frequency quadrupole coupled to a time-of-flight mass spectrometer with orthogonal ion injection the supersonic gas jet being formed inside a cylindrical channel and passed through the ion source with electron ionization. With an increase in the flow of the analyzed solution, there was no steady trend in the relative contributions of deuterated ions from liquid phase. The results confirm the prospects of using a supersonic jet to create a high-performance source of deuterosubstituted ions from a liquid supplied into a vacuum region under conditions of 10-4 Torr residiual pressure and absence of strong electric fields., №2 (2020)

It is well known that the tuning of a long radio-frequency quadrupole accelerator is demanding. This study investigated how to realize efficient long RFQ accelerators with multiple shorter and independent cavities. From the RF point of view, the use of shorter cavities has many advantages e.g. enlarged mode separation and simplified RF tuning, but the beam matching between cavities will become an issue, especially at high current and low energy. Taking a more than 9 m long, high current machine as an example, this paper presents the design concepts and methods leading to good beam quality and high beam transmission throughout a multi-stage RFQ accelerator., Comment: 26 pages, 16 figures

A laser ion source coupled with a radio frequency quadrupole linac accelerator is being proposed as a suitable system for the production of a low energy, high-current stable lithium beam. In order to maximize the lithium yield, plasmas generated by laser ablation of different materials based on lithium (Li, LiOH, and LiNbO3) have been characterized by using a Faraday cup and an electrostatic ion analyzer in the time of flight configuration. A wide range of laser power density has been investigated (109–1012 W/cm2) using two Nd:YAG lasers operating at different wavelengths (1064 nm and 532 nm), pulse durations (6 ns and 17 ns), and maximum energies (1400 mJ and 210 mJ). This paper outlines the pros and cons of the investigated materials by studying how the ion energy, yields, and charge state distributions are modified when the laser power density is changed. Considerable attention has been paid to the higher charge states of oxygen, which may occur with the same mass-to-charge ratio of Li3+. The analysis has evidenced that LiNbO3 represents a valid target since it allows minimizing the O6+/7Li3+ ratio down to 2.5% by using a laser power density of 1.8 × 1010 W/cm2. For such a condition, a Li3+ current of 1.4 mA/cm2 has been measured.

An analytical and cold model study of a prototype extended vane rod-type RFQ (radio frequency quadrupole linac) is presented. The bead-pull measurement allowed us to experimentally determine the effect of shaping of the vane-supporting posts and, most interestingly, the size of the vacuum enclosure in the dipolar and quadrupolar field asymmetry. Disk shaped beads of BaTiO3 have been tailor made for this purpose. The special shape of the beads has allowed precise measurements of frequency shifts all along the length of the RFQ. The measured quadrupolar asymmetry and dipole component at a radial distance of 7 mm from the beam axis are within ±1% for the optimized structure. Particle tracking of a 10 mA proton beam with a simulated 3D field for the optimized full scale RFQ with modulated vanes has been carried out. Simulation shows vertical and horizontal shifts of only 0.01 mm and 0.03 mm, respectively, for the accelerated beam at the exit of RFQ. The percentage of accelerated particles lying within an energy width of ±40 keV about 800 keV is increased from 86% for the original enclosure to 88% for the reduced enclosure, whereas the transmission efficiency is 100% for both the cases.