The beam loss control and the minimization of the emittance growth are considered to be the main issues while optimizing the linac configuration and the operating parameters. The beam dynamics design of an RFQ is performed keeping in view a given ion species, input energy, beam current and emittances, operating frequency, interelectrode voltage, through choosing proper dynamics parameters, to reach the requirement of output energy, beam current and emittances. The various studies which were performed for the design of the RFQ are described in the following sections. The design specifications of the RFQ.Īnd Accelerating Section. We have followed the generalized method of RFQ beam dynamics proposed by LANL in which the RFQ is divided in four sections namely Radial Matching Section (RMS), Shaper Section, Gentle Bunching (GB) Section The structure of RFQ is selected to be four-vane type because of higher efficient at higher frequency. Considering these facts as well as due to the availability of high power RF sources, the operating frequency of RFQ is selected to be 352.2 MHz. The RFQ is decided to be pulsed with the duty factor of 1.25%, hence, the constraint of higher power dissipation capability of the structure can be relaxed in pulsed operation. Requirement from spallation neutron source leads to the choice of injector linac and hence RFQ to be operated in pulsed mode. Additionally the machining and alignment tolerances become too stringent at higher frequencies. But the power dissipation capability of the structure is higher for low frequency structures. The choice of higher frequency is preferred from rf power economy point of view because of the improved shunt impedance at higher frequencies due to reduction in cavity dimensions.
To meet the demand for 20 mA beam current in the synchrotron, the RFQ is decided to be designed for 30 mA. The design specifications of the RFQ are listed in Table 1. A special feature of RFQ is that it adiabatically bunches, strongly focuses and efficiently accelerates the charged particles simultaneously with the help of RF electric field set inside. Being very much efficient accelerator for ions in low energy region, Radio Frequency Quadrupole (RFQ) is one of the main components in the front-end system which accelerates 30 mA beam current of H - particles at 50 keV from ion source to 3 MeV.
Presently RRCAT is building a low energy front-end upto 3 MeV as a first phase development for the linac. The front-end 100 MeV linac will serve as an injector to the synchrotron facility. The physics design of RFQ consisting of the beam dynamics design near the beam axis and the electromagnetic design for the RFQ resonator is described here.Ī 1 GeV proton synchrotron facility is envisaged for ISNS (Indian Spallation Neutron Source) project at RRCAT, India. The electromagnetic studies for the two-dimensional and three-dimensional cavity design are performed using computer codes SUPERFISH and CST Microwave Studio.
The beam dynamics design of RFQ and the error analysis of the input beam parameters are done by using standard beam dynamics code PARMTEQM. The physics design of a 3 MeV, 30 mA, 352.2 MHz Radio Frequency Quadrupole (RFQ) is done for the future Indian Spallation Neutron Source (ISNS) project at RRCAT, India. Keywords: Radio Frequency Quadrupole (RFQ), Beam Dynamics, Error Analysis, Cavity Design, End-Cells Raja Ramanna Centre for Advanced Technology, Indore, IndiaĮmail: June 30 th, 2010 revised August 13 th, 2010 accepted August 13 th, 2010