Medium Energy Beam Transport Line Research Articles

Measurement and Analysis of the Intensity-dependent Effects on the CSNS Medium Energy Beam Transport line

A power upgrade project (CSNS-II) has been approved in 2021 to increase the beam power to 500 kW for the China Spallation Neutron Source (CSNS), for which the Linac energy will reach 300 MeV and the beam intensity is expected to be 50 mA. In this study, the beam measurement results given by the wire scanners at various current intensities, and the numerical modeling and fitting methods to obtain the evolution of the beam envelope and emittance along the CSNS medium energy beam transfer (MEBT) are given and discussed. Finally, new matching results have been given to control the emittance blowup.

Design, fabrication, and characterization of a drift tube linac type double gap re-buncher cavity.

The Low Energy High Intensity Proton Accelerator (LEHIPA) at Bhabha Atomic Research Centre, India, has recently been commissioned to the target energy of 20MeV by beam acceleration through a 352MHz radio frequency quadrupole (RFQ) and drift tube linac (DTL). The medium energy beam transport (MEBT) line of LEHIPA matches the 3MeV beam from RFQ to the DTL using four electromagnetic quadrupoles and a re-buncher cavity. In the beam transport lines of high frequency linacs, TM010 mode single gap buncher cavities are conventionally used, while a double gap re-buncher cavity was chosen for the short length LEHIPA MEBT based on beam dynamics simulations. The 352MHz double gap re-buncher cavity has been designed in a DTL type geometry with a cell length of βλ. This double gap cavity is found to be more power efficient with a higher shunt impedance and transit time factor than the conventional single gap buncher cavity. Electromagnetic design simulations, fabrication details, low power and high-power RF test results, and beam test results of the re-buncher cavity are presented in this paper.

Beam commissioning of the SARAF Injector and MEBT (protons)

The SARAF Phase II cryogenic linear accelerator (linac) is currently under construction and will be commissioned through collaborative efforts between SNRC and CEA. The linac will accelerate a 5 mA pulsed/continuous wave (CW) proton and deuteron beam, reaching energies of up to 35 MeV and 40 MeV, respectively. The linac injector consists of Phase I components, including an ECR ion source, a Low-Energy Beam Transport (LEBT) line, and a 4-rod Radio Frequency Quadruple (RFQ). Additionally, a new Medium Energy Beam Transport (MEBT) line has been installed and integrated into the injector infrastructure. The MEBT includes three rebuncher resonators, magneto-optical elements, and beam diagnostics. The MEBT beam diagnostics, as well as the Phase I D-plate installed downstream, were used for beam characterization. The downstream-installed Temporary Beam Line (TBL) and a prototype of the Gallium Indium Liquid Target (GALIT) were used for commissioning, operating at high beam duty cycles, including CW mode. The report describes the proton beam commissioning process of the injector prior to the delivery of the cryomodules, scheduled for the second half of 2023.

Improvement of multi-harmonic buncher’s quality factor for RAON

The high-intensity rare-isotope accelerator RAON, a component of the Rare Isotope Science Project, was developed to accelerate heavy ions from elements ranging from proton to uranium. The injector line consists of an Electron Cyclotron Resonance Ion Source, a Low Energy Beam Transport line, a Radio Frequency Quadrupole (RFQ), and a Medium Energy Beam Transport line. To improve beam quality, a multi-harmonic buncher (MHB) was proposed for inclusion before the RFQ. The MHB is needed to efficiently utilize two beams with different mass-to-charge (A/q) ratios. The fundamental frequency of the MHB is half the frequency of the RFQ; as such, a harmonic synthesis is effectively bunching a beam. Electric field simulations of the MHB were conducted using the CST Microwave Studio (MWS). The electrodes were designed as cone- type electrodes so that the electric field can be concentrated between the electrodes through which the beam passes. The electric field was optimized to account for structural changes such as gap length between electrodes, resonator position and other design details. The model optimized in the simulation tool was engineered through the 3D Inventor program.

RF design studies on a 325 MHz rebuncher cavity for high intensity linear accelerators producing neutrons

Two identical Coupled Cavity Linac type (CCL) rebuncher cavities to be integrated in the Medium Energy Beam Transport line (MEBT) of a high intensity linac Accelerator have been studied for matching a 40-mA proton beam accelerated by a 3 MeV Radio-Frequency Quadrupole (RFQ) to a 13 MeV Drift Tube Linac (DTL). The rebuncher operates at 325 MHz, and is designed for β = 0.080. The rebuncher aperture radius is 20 mm required by transverse beam dynamics. It is a single gap structure operating in the TM_010 mode for providing longitudinal beam focusing. The unloaded quality Q0 and the required input power to achieve an effective voltage of 150 kV are 27253 and 20.5 kW, respectively. In this work, we present the RF design studies for the high power rebuncher resonator, as well as the considerations of the tuning scheme and the coupler design.

Beam dynamics design and error study of BISOL deuteron driver linac

The high intensity deuteron linac, one of the drivers of BISOL, aims to accelerate a continuous wave (cw) deuteron beam up to 40 MeV with a beam current of 20 mA, which can also be operated independently as the Multi-Aimed Intense Neutron Source (MAINS). As the high beam power and beam current, high reliability and strict beam loss are demand for the deuteron driver linac. The beam dynamics design of the driver linac, including the radio frequency quadrupole (RFQ), medium energy beam transport line (MEBT) and superconducting rf (SRF) linac, has been designed and optimized to meet the required requirements. In order to prevent halo formation and achieve strict beam losses, beam halo matching is implemented in our design. The simulation results predict a transmission efficiency of above 99% and the beam power losses meet requirements of less than l W/m in the SRF linac. Detailed error studies are performed to evaluate the sensitivity of the bean dynamics design at last. The general design considerations and the overall beam dynamics of the driver linac are presented in this paper.

Longitudinal Measurements and Beam Tuning in the J-PARC Linac MEBT1

The Japan Proton Accelerator Research Complex (J-PARC) linac is operated with design peak current of 50 mA from 2018. For operation with such a high beam current, it is important to understand transverse and longitudinal beam properties especially in low-velocity region. A medium energy beam transport (MEBT1) line between the 3-MeV radio-frequency quadrupole linac (RFQ) and the 50-MeV drift-tube linac (DTL) is a 3-m-long transport line to match the beam to the DTL and produces a macro pulse configuration for a 3-GeV rapid-cycling synchrotron (RCS). In this paper, recent measurements and beam tuning results in MEBT1 will be presented.

A pre-injector upgrade for ISIS, including a medium energy beam transport line and an RF-driven H− ion source

The ISIS spallation neutron and muon facility is undergoing an upgrade to the negative hydrogen (H−) linac preinjector with the addition of a medium-energy beam transport (MEBT) line. A fast electrostatic sweep chopper is included in the MEBT and will notch the linac bunch train at the synchrotron frequency. The MEBT and chopper will increase the beam transport efficiency significantly, reducing the output H− current requirements from the ion source. As such, a long-lifetime, noncesiated, RF-driven, external-antenna H− ion source based on the successful CERN Linac4 and SNS designs is constructed, which will improve facility uptime and reliability. This paper will highlight the latest developments on the MEBT before focusing on the RF ion source. The RF ion source must deliver 35 mA of H− beam current in pulses 400 μs long at a 50 Hz repetition rate, with transverse normalized 4 rms emittances less than 1.2 π mm mrad. The beam current and emittance are within the reach of a noncesiated H− source, whereas operating at relatively high duty cycles presents challenges in terms of thermal management, which this paper will address.

Room temperature quarter wave resonator re-buncher development for a high power heavy-ion linear accelerator

In the medium energy beam transport (MEBT) line system of the RAON which consists of several quadrupole magnets, three normal-conducting re-bunchers, and several diagnostic devices, a quarter wave resonator type re-buncher was chosen for minimizing longitudinal emittance growth and manipulating a longitudinal phase ellipse into the longitudinal acceptance of the low energy linac. The re-buncher has a resonant frequency of 81.25 MHz, geometrical beta (βg) of 0.049, and physical length of 24 cm. Based on the result of numerical calculations of electromagnetic field using CST-MWS and mechanical analysis of the heat distribution and deformation, an internal structure of the re-buncher was optimized to increase the effective voltage and to reduce power losses in the wall. The criteria of the multipacting effect was estimated and it was confirmed by the experiment. The position and specification of cooling channels are designed to recover a heat load up to 15 kW with reasonable margin of 25%. The coaxial and loop type RF power coupler are positioned on the high magnetic field region and two slug tuners are installed perpendicularly to the beam axis. The frequency sensitivity as a function of the tuner depth and cooling water temperature is measured and the frequency shift is in all cases within the provided tuner range. The test with a high power of 10 kW and the continuous wave is performed and the reflection power is observed less than 450 W.

MTCA.4-based LLRF control system for the C-ADS proton Linac injector I

The Chinese ADS proton Linac injector I composed of an electron cyclotron resonance ion source, a low-energy beam transport line, a radio frequency quadrupole (RFQ) accelerator, a medium-energy beam transport (MEBT) line, a superconducting section and beam dump with design goal to achieve CW proton beam with beam current 10 mA and energy gain around 10 MeV. In order to maintain the stability of the RF system, to compensate for the beam load effect and to provide the GUI required for the operation of the RF power system, we have established a LLRF control system. This LLRF system for ADS proton Linac injector I in IHEP consists of RF reference system and LLRF controllers for one RFQ cavity, two MEBT bunching cavities and 14 superconductive spoke cavities. We have adopted a new development mTCA.4-based hardware platform, and it has some characteristics such as faster bandwidth, standardized design, easy operation and maintenance and good expansibility. The LLRF system has been improved and optimized and has now been put into operation. It takes into account the pulse and CW beam flow mode, feedforward and feedback control functions. With the help of this system, we achieved stable operation with narrow pulses, long pulses, and CW modes under different beam loads. This article describes the implementation of this system and presents some initial the CW beam acceleration results with the help of this system at the end of 2016.

Start-to-end simulations for beam dynamics in the injector system of the KHIMA heavy ion accelerator

The Korea Heavy Ion Medical Accelerator (KHIMA) project has been developed for cancer therapy. The injector system consists of a low energy beam transport (LEBT) line, a radio-frequency quadrupole, a drift tube linac with two tanks, and a medium energy beam transport (MEBT) line with a charge stripper section. The injector system transports and accelerates the 12C4+ beam that is produced from electron cyclotron resonance ion source up to 7MeV/u, respectively. The 12C6+ beam, which is transformed by a charge stripper from the 12C4+ beam, is injected into a synchrotron and accelerated up to 430MeV/u. The lattice for the injector system was designed to optimize the beam parameters and to meet beam requirements for the synchrotron. We performed start-to-end simulations from the LEBT line to the MEBT line to confirm that the required design goals of the beam and injector system were met. Our simulation results indicate that our design achieves the required performance and a good transmission efficiency of 90%. We present the lattice design and beam dynamics for the injector system in the KHIMA project.

The mechanical design and fabrication of 162.5 MHz buncher for China accelerator driven sub-critical system injector II

Abstract A buncher is one of the main pieces of equipment in the medium energy beam transport line (MEBT) for China accelerator driven sub-critical system (C-ADS) Injector II. To focus the beam longitudinally and match the beam for the acceptance of the superconducting linac section, two room temperature quarter wave resonator (QWR) bunchers with frequency of 162.5 MHz have been designed as parts of the MEBT. According to the beam transmission matching of the MEBT and the geometric parameters requirements of bunchers, the unique mechanical structure and the main processing technology of buncher cavities and their couplers and tuners are described in this paper. The fabrication of bunchers and their parts have been completed and tested at high power, the test results agree well with the design requirements. These bunchers work well for about two years in Institute of Modern Physics, Chinese Academy of Sciences.

Beam commissioning for a superconducting proton linac

To develop the next generation of safe and cleaner nuclear energy, the accelerator-driven subcritical (ADS) system emerges as one of the most attractive technologies. It will be able to transmute the long-lived transuranic radionuclides produced in the reactors of today's nuclear power plants into shorter-lived ones, and also it will provide positive energy output at the same time. The prototype of the Chinese ADS (C-ADS) proton accelerator comprises two injectors and a 1.5 GeV, 10 mA continuous wave (CW) superconducting main linac. The injector scheme II at the C-ADS demo facility inside the Institute of Modern Physics is a 10 MeV CW superconducting linac with a designed beam current of 10 mA, which includes an ECR ion source, a low-energy beam transport line, a 162.5 MHz radio frequency quadrupole accelerator, a medium-energy beam transport line, and a superconducting half wave resonator accelerator section. This demo facility has been successfully operating with an 11 mA, 2.7 MeV CW beam and a 3.9 mA, 4.3 MeV CW beam at different times and conditions since June 2014. The beam power has reached 28 kW, which is the highest record for the same type of linear accelerators. In this paper, the parameters of the test injector II and the progress of the beam commissioning are reported.

Beam dynamics and error study of the medium energy beam transport line in the Korea Heavy-Ion Medical Accelerator

The Korea Heavy Ion Medical Accelerator consists of an injector and a synchrotron for an ion medical accelerator that is the first carbon-ion therapy system in Korea. The medium energy beam transport(MEBT) line connects the interdigital H-mode drift tube linac and the synchrotron. We investigated the beam conditions after the charge stripper by using the LISE++ and the SRIM codes. The beam was stripped from C4+ into C6+ by using the charge stripper. We investigated the performance of a de-buncher in optimizing the energy spread and the beam distribution in z-dW/W (direction of beam progress-beam and energy) phase. We obtained the results of the tracking simulation and the error analysis by using the TRACK code. Possible misalignments and rotations of the magnets were considered in the simulations. States of the beam were examined when errors occurred in the magnets by the applying analytic fringe field model in TRACK code. The condition for the beam orbit was optimized by using correctors and profile monitors to correct the orbit. In this paper, we focus on the beam dynamics and the error studies dedicated to the MEBT beam line and show the optimized beam parameters for the MEBT.

High precision capacitive beam phase probe for KHIMA project

In the medium energy beam transport (MEBT) line of KHIMA project, a high precision beam phase probe monitor is required for a precise tuning of RF phase and amplitude of Radio Frequency Quadrupole (RFQ) accelerator and IH-DTL linac. It is also used for measuring a kinetic energy of ion beam by time-of-flight (TOF) method using two phase probes. The capacitive beam phase probe has been developed. The electromagnetic design of the high precision phase probe was performed to satisfy the phase resolution of 1° (@200MHz). It was confirmed by the test result using a wire test bench. The measured phase accuracy of the fabricated phase probe is 1.19ps. The pre-amplifier electronics with the 0.125 ∼ 1.61GHz broad-band was designed and fabricated for amplifying the signal strength. The results of RF frequency and beam energy measurement using a proton beam from the cyclotron in KIRAMS is presented.

Analysis of transverse RMS emittance growth of a beam induced by spherical and chromatic aberration in a solenoidal field

In a medium energy beam transport line transverse rms emittance growth associated with spherical aberration is analysed. An analytical expression is derived for beam optics in a solenoid field considering terms up to the third order in the radial displacement. Two important phenomena: effect of spherical aberrations in axial-symmetric focusing lens and influence of nonlinear space charge forces on beam emittance growth are discussed for different beam distributions. In the second part nonlinear effect associated with chromatic aberration that describes the growth of emittance and distortion of phase space area is discussed.

Design and construction of the MEBT1 for CADS injector scheme II**Supported by National Natural Science Foundation of China (11079001)

A Medium Energy Beam Transport line 1 (MEBT1) has been designed for Injector Scheme II of the China ADS project. To match the beam from RFQ to Superconducting (SC) Half Wave Resonator (HWR) sections with emittance preservation, the MEBT1 has been designed to be mechanically compact. Working at 162.5 MHz, the MEBT1 transports a 10 mA, 2.1 MeV proton beam using seven quadrupoles and two bunching cavities within 2.7 meters. Three collimators are placed between every two adjacent quadrupoles to collimate the beam halo. Design and construction of the MEBT1 are presented in this paper.

Design and RF test of MEBT buncher cavities for C-ADS Injector II at IMP

Abstracts To match the beam from the Radio Frequency Quadrupole (RFQ) accelerator to the Superconducting Half-wave Resonator (HWR) Linac, two room temperature (RT) double-gap Quarter-wave Resonator (QWR) bunchers are designed to be located in the Medium Energy Beam Transport Line (MEBT) for the C-ADS Injector II at IMP. Both cavities work at 162.5 MHz, with β=0.067 and a beam aperture diameter of 40 mm. The effective voltage of these two cavities needs to reach 135 kV in Continuous Wave (CW) mode. In this paper, the RF design and thermal analysis of the cavities will be presented, along with the tuners and coupler consideration. The measured frequencies, Rsh/Q0, Q0 and voltage of the cavities agree well with the simulation result. Details of the RF test results including the full power tests of the cavities will be shown.

Start-to-end simulations for beam dynamics in the RISP heavy-ion accelerator

RAON has been designed as a rare isotope accelerator facility for the Rare Isotope Science Project (RISP). The main accelerator for the in-flight system accelerates uranium and proton beams to 200MeV/u and 660MeV, respectively, with a beam power of 400kW. The front-end system consists of two 28GHz electron cyclotron resonance ion sources (10keV/u), a low-energy beam transport (LEBT) line with two 90° bends, a multi-harmonic buncher with three different rf frequencies, a radio-frequency quadrupole (RFQ), and a medium-energy beam transport line (MEBT) with three rebunchers and eight quadrupoles. A driver linac system consisting of Linac-1 and Linac-2 has been designed to optimize the beam and accelerator parameters so as to meet the required design goals. A charge stripper section is located between Linac-1 and Linac-2. To optimize these designs, we performed start-to-end simulations with the beams from the LEBT to Linac-2 using 1 million macroparticles. We present the resulting beam dynamics to evaluate the performance of the accelerator. Our simulation results predict that the transmission rate of the uranium beam is 85.8% from the LEBT to Linac-2. The designed facility is expected to achieve the required beam loss condition of less than 1W/m. The RAON driver linac lattice design was developed and an overview of the beam dynamics is presented.

Uncoupled achromatic condition of a dog-leg system with the presence of RF cavities

To merge the beam from either of the two injectors to the main linac, a dog-leg system will be employed in the second Medium Energy Beam Transport (MEBT2) line of the China ADS driving accelerator. The achromatic condition has to be guaranteed to avoid beam center excursion against energy jitter. RF cavities were found to be indispensable to control the bunch length growth in the dog-leg system of MEBT2. The full uncoupling between transverse and longitudinal plane is desired to minimize the growth of projected rms emittances. The uncoupled achromatic condition of this dogleg system with the presence of RF bunching cavities will be deduced using the transfer matrices method. It is found that, to fulfill the uncoupling condition, the distance between the bunching cavities is uniquely determined by the maximum energy gain of the RF cavities. The theoretical analysis is verified by the simulation code TraceWin. The space charge effect on the uncoupled achromatic condition and the beam emittance growth will also be discussed.