High Current Radio Frequency Quadrupole Research Articles

Beam dynamics design and irradiation experiment of beam loss for a CW 100-mA proton RFQ

For a high-current Radio Frequency Quadrupole (RFQ) accelerator, space charge will strongly affect the stability of beams, which brings challenges and difficulties to the beam dynamics design. For an in-depth study of this space charge effect, a project has been proposed by Peking University and the Institute of Modern Physics of the Chinese Academy of Sciences. This project requires a 162.5 MHz RFQ to accelerate a 100-mA continuous-wave (CW) proton beam to 3 MeV. The beam dynamics design of this RFQ is based on the four-section procedure with improved radial focusing strength along the RFQ. We have investigated the relationship between limiting current and beam transmission to analyze the reasons for emittance growth and beam loss. We have also carried out an irradiation experiment based on this beam dynamics design to study the irradiation damage of the electrode surface, as this can be one main reason for reduced transmission or unstable operation that most existing high-current RFQs encounter after long-time operation. The results show that low-energy beam losses need to be kept as low as possible to prolong the life of the RFQ electrodes. The final simulated transmission efficiency reached 99.8%, as confirmed by the code toutatis.

Study on shunt impedance and voltage distribution of 4-rod RFQ cavity

A high current RFQ (radio frequency quadrupole) is being studied at the Institute of Modern Physics, CAS for the direct plasma injection scheme. Shunt impedance is an important parameter when designing a 4-rod RFQ cavity, it reflects the RF efficiency of the cavity, and has a direct influence on the cost of the structure. Voltage distribution of a RFQ cavity has an effect on beam transmission, and particles would be lost if the actual voltage distribution is not as what it should be. The influence of cell length, stem thickness and height on shunt impedance and voltage distribution have been studied, in particular the effect of projecting electrodes has been investigated in detail.

Design studies of a high-current radiofrequency quadrupole for accelerator-driven systems programme

A 3 MeV, 30 mA radiofrequency quadrupole (RFQ) accelerator has been designed for the low-energy high-intensity proton accelerator (LEHIPA) project at BARC, India. The beam and cavity dynamics studies were performed using the computer codes LIDOS, TOUTATIS, SUPERFISH and CST microwave studio. We have followed the conventional design technique with slight modifications and compared that with the equipartitioned (EP) type of design. The sensitivity of the RFQ to the variation of input beam Twiss-Courant parameters and emittance has also been studied. In this article we discuss both design strategies and the details of the 3D cavity simulation studies.

Accelerator-driven neutron source for cargo screening

Advanced neutron interrogation systems for screening sea-land cargo containers for shielded special nuclear materials (SNM) require a high-yield neutron source to achieve the desired detection probability, false alarm rate, and throughput. The design of an accelerator-driven neutron source is described that utilizes the D(d,n)3He reaction to produce a forward directed beam of up to 8.5MeV neutrons. The key components of the neutron source are a high-current radio frequency quadrupole (RFQ) accelerator and a neutron production gas target. The 5.1m long, 200MHz RFQ accelerates a 40mA deuteron beam from a microwave-driven ion source coupled to an electrostatic low energy beam transport (LEBT) system to 6MeV. At a 5% duty factor, the time-average D+ beam current on target is 1.5mA. A thin entrance window has been designed for the deuterium gas target that can withstand the high beam power and the gas pressure. The source will be capable of delivering a flux >1×107n/(cm2s) at a distance of 2.5m from the target and will allow full testing and demonstration of a cargo screening system based on neutron stimulated SNM signatures.

Acceleration of high current fully stripped carbon ion beam by direct injection scheme

Acceleration of a 17mA, 100keV∕u C6+ ion beam has been successfully achieved with an radio frequency quadrupole (RFQ) linac by means of “direct injection scheme.” The C6+ beam produced by a laser ion source with a Nd:YAG laser was injected to the high current RFQ linac. It has been experimentally proved that the fully stripped carbon ion beam with a current more than 10mA was accelerated by the RFQ linac.

Design of a high current RFQ for neutron production

A high current Radio Frequency Quadrupole (RFQ) accelerator was designed to produce neutrons by accelerating a 50 mA deuteron beam to 2.0 MeV for the thermal neutron generator project at Peking University. Limited by the 400 kW RF power available only and the demands of radiation protection, beam dynamics studies were performed with the computer code PARMTEQM to achieve both a compact structure and high transmission efficiency. A simulation for varying of input beam parameters has been carried out to check the parameter-sensitivity of the RFQ design.

Interaction of heavy ions with plasma

Abstract The accelerator facilities at GSI, consisting of a high current radio frequency quadrupole (RFQ) accelerator, a rf-linac (UNILAC), a heavy ion synchrotron (SIS), and an experimental storage ring (ESR) provide the unique opportunity to study beam-target interaction phenomena over a wide range of beam energy. This range extends from 45 keV/u up to, and above 1 GeV/u. Thus rf accelerator and beam-target interaction physics issues for heavy-ion-beam driven inertial confinement fusion can be studied. Recent results of the experimental program such as the enhanced energy loss and the increased effective charge state of heavy ions in ionized matter, the generation of dense plasma by intense heavy ion beams, and new advanced focussing methods for intense beams are discussed.