Four-Rod RFQ Beam Dynamics Design of PKUNIFTY Upgrade

2007

A high-yield neutron source to screen sea-land cargo containers for shielded Special Nuclear Materials (SNM) has been designed at LBNL [1,2]. The Accelerator-Driven Neutron Source (ADNS) uses the D(d,n)3He reaction to create a forward directed neutron beam. Key components are a high-current radio-frequency quadrupole (RFQ) accelerator and a high-power target capable of producing a neutron flux of >10^7 n/(cm^2•s) at a distance of 2.5 m. The mechanical design and analysis of the four-module, bolt-together RFQ will be presented here. Operating at 200 MHz, the 5.1 m long RFQ will accelerate a 40 mA deuteron beam to 6 MeV. At a 5% duty factor, the timeaverage d + beam current on target is 1.5 mA. Each of the 1.27 m long RFQ modules will consist of four solid OFHC copper vanes. A specially designed 3-D O-ring will provide vacuum sealing between both the vanes and the modules. RF connections are made with canted coil spring contacts. A series of 60 water-cooled pi-mode rods provides quadrupole mode stabilization. A set of 80 evenly spaced fixed slug tuners is used for final frequency adjustment and local field perturbation correction.

Chinese Physics Letters, 2012

A four-rod radio frequency quadruple (RFQ) accelerator is designed, manufactured, installed and commissioned for the Peking University Neutron Imaging Facility (PKUNIFTY). This 2699.6-mm-long RFQ accelerator with the mean aperture radius of 3.88 mm is operating at 201.5 MHz in pulse mode. An inter-electrode voltage of 70 kV is needed to accelerate the injected 50 keV 40 mA D + ions up to 2 MeV. We present the rf system, high rf power feeder design, lower rf measurements and higher rf power test. Especially, the rf commissioning was carried out with rf power up to ∼280 kW and duty factor of 4%. The measured x-ray spectrum shows that the rf inter-electrode voltage reaches 70.7 kV. It is found that the specific shunt impedance of the RFQ cavity reaches 52.7 kΩ•m.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2010

The Peking University Neutron Imaging Facility (PKUNIFTY) is being constructed, which is a compact acceleratordriven neutron source. The accelerator is a radio frequency quadrupole (RFQ) accelerator, which can deliver a 2 MeV deuteron beam. The neutrons are generated by deuterons bombarding beryllium target. The accelerator facility mainly consists of ECR (electron cyclotron resonance) ion source, LEBT (low energy beam transportation), RFQ cavity, HEBT (high energy beam transportation), RF transmitter and control system. This paper will introduce the requirements and design of that accelerator facility.

2018

A new RFQ was successfully installed recently in the SNS linac to replace the old RFQ that was used for more than a decade with certain operational limitations. The new RFQ was completely tested with Hion source in the Beam Test Facility (BTF) at SNS. For robust operation of SNS at 1.4 MW, the full design beam power and to satisfy the beam current requirement of the forthcoming SNS proton power upgrade (PPU) project, an RFQ with enhanced performance and reliability was needed. The new RFQ was built to have the beam parameters identical to those of the first RFQ but with improved RF and mechanical stability and reliability for continuous operation of neutron production. The tests confirmed that the new RFQ can run with high beam transmission efficiency at around 90 % and notably improved operational stability. In this paper, construction, test, installation, and operation of the new RFQ in SNS are discussed with the performance improvements.

Physics Procedia

A 201.5 MHz deuteron four-rod RFQ was designed and operated to generate high flux neutron for the application of neutron radiography at Peking University, which is called as Peking University Neutron Imaging Facility (PKUNIFTY). This paper presents two kinds of tuners to tune the cavity to the designed frequency and reach the needed field unflatness distribution less than 5%; the RFQ intervane voltage 70.7 kV determination by the roentgen spectrum measurement at 237.6 kW; output accelerated deuteron beam energy at 2.0 MeV with energy spread of 2.5% at 300 kW including additional about 60 kW beam power. Although it has been running more than one year, sometimes we have troubles not only for the RFQ, mainly for the RF system. This paper showed some troubles and its shootings methods. Some troubles and shooting methods might be useful for similar projects.

2017

Boron Neutron Capture Therapy (BNCT) [1, 2], promises a bright prospect for future cancer treatment, in terms of effectiveness, safety and less expanse. The PKU RFQ group proposes an RFQ based neutron source for BNCT. A unique beam dynamics design of 162.5 MHz BNCTRFQ, which accelerates 20 mA of H+ from 30 keV to 2.5 MeV in CW operation, has been performed in this study. The Proton current will be about 20 mA. The source will deliver a neutron yield of 1.76 × 10 / / in the , reaction. Detailed 3D electromagnetic (EM) simulations of all components, including crosssection, tuners, pi-rods, and cut-backs, of the resonant structure are performed. The design of a coaxial type coupler is developed. Two identical RF couplers will deliver approximately 153 kW CW RF power to the RFQ cavity. RF property optimizations of the RF structures are performed with the utilization of the CST MICROWAVE STUDIO [3].

2016

The Beam Test Facility (BTF) has been constructed to validate the performance of the new RFQ, to study ion source improvements, and to support neutron moderator development and six-dimensional phase space measurements for SNS. The BTF includes an Hion source, Radio-Frequency Quadrupole (RFQ), and Medium Energy Beam Transport (MEBT) beam diagnostics systems. A spare RFQ was built and fully RF tested in the BTF and will be installed in the SNS linac in the future. The test stand is ready to run with the Hion beam through the new RFQ to fully validate the RFQ performance. The RFQ was designed to have the beam characteristics identical to the existing RFQ with improved operational reliability and stability. The HRF plasma ion source system includes new high power RF components for improved front-end system performance.

The Frankfurt Neutron Source at the Stern-Gerlach-Zentrum [1] is driven by a 2 MeV proton linac (Table 1) consisting of a 4-rod-radio-frequency-quadrupol (RFQ) [2] and an 8 gap IH-DTL [3] structure. RFQ and IH cavity will be powered by only one radio frequency (RF) amplifier to reduce costs. The RF-amplifier of the RFQ-IH combination is coupled into the RFQ. Internal inductive coupling (Fig. 1) along the axis connects the RFQ with the IH cavity ensuring the required power transition as well as a fixed phase relation between the two structures. The main acceleration of 120 keV up to 2.03 MeV will be reached by the RFQ-IH combination with 175 MHz and at a total length of 2.3 m. The losses in the RFQ-IH combination are about 200 kW.

Physics Procedia, 2013

Peking University neutron imaging facility (PKUNIFTY) is a RFQ accelerator based facility, whose design principle is to scale down the size and cost as much as possible while maintaining a basic set of neutron radiography capabilities. The facility has been manufactured, installed and commissioned. As the first stage, lower beam power and neutron flux are employed. The thermal neutron flux is 2.35 × 10 4 n/cm 2 /s on the imaging plane with L/D = 50. Some preliminary experimental results are given.

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