Fabrication and cold test of prototype of spatially periodic radio frequency quadrupole focusing linac
Peiyan YuBin ZhangFengfeng WangChen-Xing LiGuozhen SunZhijun WangLubei LiuChenzhang YuanYuan HeHu-Shan Xu
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Radio-frequency quadrupole
Radio-frequency quadrupole (RFQ) linear accelerators appeared on the accelerator scene in the late 1970s and have since revolutionized the domain of low-energy proton and ion acceleration. The RFQ makes the reliable production of unprecedented ion beam intensities possible within a compact radio-frequency (RF) resonator which concentrates the three main functions of the low-energy linac section: focusing, bunching and accelerating. Its sophisticated electrode structure and strict beam dynamics and RF requirements, however, impose severe constraints on the mechanical and RF layout, making the construction of RFQs particularly challenging. This lecture will introduce the main beam optics, RF and mechanical features of a RFQ emphasizing how these three aspects are interrelated and how they contribute to the final performance of the RFQ.
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Radio-frequency quadrupole
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PIGMI (Pion Generator for Medical Irradiations) is a compact linear proton accelerator design, optimized for pion production and cancer treatment use in a hospital environment. Technology developed during a four-year PIGMI Prototype experimental program allows the design of smaller, less expensive, and more reliable proton linacs. A new type of low-energy accelerating structure, the radio-frequency quadrupole (RFQ) has been tested; it produces an exceptionally good-quality beam and allows the use of a simple 30-kV injector. Average axial electric-field gradients of over 9 MV/m have been demonstrated in a drift-tube linac (DTL) structure. Experimental work is underway to test the disk-and-washer (DAW) structure, another new type of accelerating structure for use in the high-energy coupled-cavity linac (CCL). Sufficient experimental and developmental progress has been made to closely define an actual PIGMI. It will consist of a 30-kV injector, an RFQ linac to a proton energy of 2.5 MeV, a DTL linac to 125 MeV, and a CCL linac to the final energy of 650 MeV. The total length of the accelerator is 133 meters. The RFQ and DTL will be driven by a single 440-MHz klystron; the CCL will be driven by six 1320-MHz klystrons. The peak beam current is 28 mA. The beam pulse length is 60 ps μs at a 60-Hz repetition rate, resulting in a 100-μA average beam current. The total cost of the accelerator is estimated to be ~$10 million.
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Radio-frequency quadrupole
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RF Acceleration in Linacs Periodic Accelerating Structures Standard Linac Structures Microwave Topics for Linacs Longitudinal Particle Dynamics Transverse Particle Dynamics Radio-Frequency Quadrupole Linac Multiparticle Dynamics with Space Charge Beam Loading Wakefields Special Structures and Techniques Index.
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The new proton linear accelerator (linac) with output energy 13 MeV and 100 mA current is under development at NRC “Kurchatov Institute” - ITEP for DARIA project. The linac consists of Radio-Frequency Quadrupole (RFQ) and Drift Tube Linac (DTL) with operating frequency 162.5 MHz. The RFQ is based on 4-vanes structure with shifted coupling windows. DTL has a modular structure and consists of separated individually phased cavities with focusing magnetic quadrupoles located between the cavities. The DTL is based on interdigital H-mode (IHDTL) 5-gaps cavities. The 6D beam matching between RFQ and DTL is provided by magnetic quadrupole lenses and RF-bunchers. The paper presents results of the radio-frequency (RF) design, thermal analyses and RF tuning of RFQ linac accelerating structure.
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After extensive upgrading, our radio-frequency quadrupole (RFQ) linac is again installed on the accelerator test stand (ATS). The measured parameters of the RFQ, such as the output transverse emittance, transmitted beam, average energy, and energy spread is presented.
Radio-frequency quadrupole
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Summary form only given. The Spallation Neutron Source (SNS) accelerator system includes a nominally 1000 MeV, 1.4 mA average current linac consisting of a radio frequency quadrupole (RFQ), drift tube linac (DTL), coupled cavity linac (CCL), a medium and high beta super conducting (SC) linac, and two buncher cavities for beam transport to an accumulator ring. The average proton beam power of the accelerator is 1.4 MW. Los Alamos is responsible for the RF systems for all sections of the linac. The SNS linac is a pulsed proton linac and the RF system must support a 1 msec beam pulse at up to a 60 Hz repetition rate. The RFQ and DTL utilize seven, 2.5 MW klystrons and operate at 402.5 MHz. The CCL,SC, and buncher cavities operate at 805 MHz. Six, 5 MW klystrons are utilized for the CCL and buncher cavities while eighty-one 550 kW klystrons are used for the SC cavities.
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At RIKEN, a transportable accelerator-driven compact neutron source (RANS-III) is under development for an on-site nondestructive inspection of the degradation of old concrete and reinforcing steel. RANS-III consists of an ion source, a low-energy beam transport, a radio frequency quadrupole linear accelerator (RFQ linac), a radio frequency (RF) system, a high-energy beam transport, a target station and a neutron measurement system. Because the inner diameter of the RFQ linac is inversely proportional to the resonance frequency, the resonance frequency of the RANS-III RFQ linac in this study was chosen to be 500 MHz, which is 2.5 times that of the RANS-II RFQ linac. Therefore, the inner diameter and weight of the RANS-III RFQ linac were reduced to approximately half and one third, respectively, of those of the RANS-II RFQ linac. The RANS-III RFQ linac was designed to accelerate a proton beam with a 10 mA peak current and 100 μA average beam current from 30 keV to 2.49 MeV (Journal of Disaster Research 12(3) (2017) 585–592). Based on the evaluations, an RFQ linac for RANS-III was fabricated, and the RF characteristics of the cavity, such as the resonant frequency and electric-field distribution, were measured using a low-power test and tuned using fixed tuners. In addition, RF couplers and RF systems were constructed to inject RF power into the RANS-III RFQ linac, and RF input tests were performed.
Radio-frequency quadrupole
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In many Laboratories, great emphasis now is placed on the development of linear accelerators with very large ion currents. To achieve this goal, a primary concern must be the low-velocity part of the accelerator, where the current limit is determined and where most of the emittance growth occurs. The use of magnetic focusing, the conflicting requirements in the choice of linac frequency, and the limitations of high-voltage dc injectors, have tended to produce lowvelocity designs that limit overall performance. The radio-frequency quadrupole (RFQ) linear accelerator, invented in the Soviet Union and developed at Los Alamos, offers an attractive solution to many of these low-velocity problems. In the RFQ, the use of RF electric fields for radial focusing, combined with special programming of the bunching, allows high-current dc beams to be captured and accelerated with only small beam loss and low radial emittance growth. Advantages of the RFQ linac include a low injection energy (20-50 keV for protons) and a final energy high enough so the beam can be further accelerated with high efficiency in a Wideröe or Alvarez linac. These properties have been confirmed at Los Alamos in a highly successful experimental test performed during the past year. The success of this test and the advances in RFQ design procedures have led to the adoption of this linac for a wide range of applications. The beam-dynamics parameters of three RFQ systems are described.
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Quadrupole magnet
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In linear accelerators the particles are accelerated by either electrostatic fields or oscillating Radio Frequency (RF) fields. Accordingly the linear accelerators are divided in three large groups: electrostatic, induction and RF accelerators. Overview of the different types of accelerators is given. Stability of longitudinal and transverse motion in the RF linear accelerators is briefly discussed. The methods of beam focusing in linacs are described.
Accelerator physics
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