Side Coupled Drift Tube Linac Research Articles

Magnetically focused 70MeV proton minibeams for preclinical experiments combining a tandem accelerator and a 3GHz linear post-accelerator.

Radiotherapy plays an important role for the treatment of tumor diseases in two-thirds of all cases, but it is limited by side effects in the surrounding healthy tissue. Proton minibeam radiotherapy (pMBRT) is a promising option to widen the therapeutic window for tumor control at reduced side effects. An accelerator concept based on an existing tandem Van de Graaff accelerator and a linac enables the focusing of 70MeV protons to form minibeams with a size of only 0.1mm for a preclinical small animal irradiation facility, while avoiding the cost of an RFQ injector. The tandem accelerator provides a 16MeV proton beam with a beam brightness of as averaged from 5µs long pulses with a flat top current of 17µA at 200Hz repetition rate. Subsequently, the protons are accelerated to 70MeV by a 3GHz linear post-accelerator consisting of two Side Coupled Drift Tube Linac (SCDTL) structures and four Coupled Cavity Linac (CCL) structures [design: AVO-ADAM S.A (Geneva, Switzerland)]. A 3GHz buncher and four magnetic quadrupole lenses are placed between the tandem and the post-accelerator to maximize the transmission through the linac. A quadrupole triplet situated downstream of the linac structure focuses the protons into an area of (0.1×0.1)mm2 . The beam dynamics of the facility is optimized using the particle optics code TRACE three-dimensional (3D). Proton transmission through the facility is elaborated using the particle tracking code TRAVEL. A study about buncher amplitude and phase shift between buncher and linac is showing that 49% of all protons available from the tandem can be transported through the post-accelerator. A mean beam current up to 19nA is expected within an area of (0.1×0.1)mm2 at the beam focus. An extension of existing tandem accelerators by commercially available 3GHz structures is able to deliver a proton minibeam that serves all requirements to obtain proton minibeams to perform preclinical minibeam irradiations as it would be the case for a complete commercial 3GHz injector-RFQ-linac combination. Due to the modularity of the linac structure, the irradiation facility can be extended to clinically relevant proton energies up to or above 200MeV.

Beam commissioning of the 35 MeV section in an intensity modulated proton linear accelerator for proton therapy

This paper presents the experimental results on the Terapia Oncologica con Protoni-Intensity Modulated Proton Linear Accelerator (TOP-IMPLART) beam that is currently accelerated up to 35 MeV, with a final target of 150 MeV. The TOP-IMPLART project, funded by the Innovation Department of Regione Lazio (Italy), is led by Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) in collaboration with the Italian Institute of Health and the Oncological Hospital Regina Elena-IFO. The accelerator, under construction and test at ENEA-Frascati laboratories, employs a commercial 425 MHz, 7 MeV injector followed by a sequence of 3 GHz accelerating modules consisting of side coupled drift tube linac (SCDTL) structures up to 71 MeV and coupled cavity linac structures for higher energies. The section from 7 to 35 MeV, consisting on four SCDTL modules, is powered by a single 10 MW klystron and has been successfully commissioned. This result demonstrates the feasibility of a ``fully linear'' proton therapy accelerator operating at a high frequency and paves the way to a new class of machines in the field of cancer treatment.

First acceleration of a proton beam in a side coupled drift tube linac

We report the first experiment aimed at the demonstration of low-energy protons acceleration by a high-efficiency S-band RF linear accelerator. The proton beam has been accelerated from 7 to 11.6 MeV by a 1 meter long SCDTL (Side Coupled Drift Tube Linac) module powered with 1.3 MW. The experiment has been done in the framework of the Italian TOP-IMPLART (Oncological Therapy with Protons-Intensity Modulated Proton Therapy Linear Accelerator for Radio-Therapy) project devoted to the realization of a proton therapy centre based on a proton linear accelerator for intensity modulated cancer treatments to be installed at IRE-IFO, the largest oncological hospital in Rome. It is the first proton therapy facility employing a full linear accelerator scheme based on high-frequency technology.

The radiation fields around a proton therapy facility: A comparison of Monte Carlo simulations

A proton therapy test facility with a beam current lower than 10nA in average, and an energy up to 150MeV, is planned to be sited at the Frascati ENEA Research Center, in Italy. The accelerator is composed of a sequence of linear sections. The first one is a commercial 7MeV proton linac, from which the beam is injected in a SCDTL (Side Coupled Drift Tube Linac) structure reaching the energy of 52MeV. Then a conventional CCL (coupled Cavity Linac) with side coupling cavities completes the accelerator. The linear structure has the important advantage that the main radiation losses during the acceleration process occur to protons with energy below 20MeV, with a consequent low production of neutrons and secondary radiation. From the radiation protection point of view the source of radiation for this facility is then almost completely located at the final target. Physical and geometrical models of the device have been developed and implemented into radiation transport computer codes based on the Monte Carlo method. The scope is the assessment of the radiation field around the main source for supporting the safety analysis. For the assessment independent researchers used two different Monte Carlo computer codes named FLUKA (FLUktuierende KAskade) and MCNPX (Monte Carlo N-Particle eXtended) respectively. Both are general purpose tools for calculations of particle transport and interactions with matter, covering an extended range of applications including proton beam analysis. Nevertheless each one utilizes its own nuclear cross section libraries and uses specific physics models for particle types and energies. The models implemented into the codes are described and the results are presented. The differences between the two calculations are reported and discussed pointing out disadvantages and advantages of each code in the specific application.

Sensitivity study in a compact accelerator for laser-generated protons

AbstractA sensitivity study is presented here on a compact hybrid postacceleration scheme coupling laser-generated protons to a high frequency Linac based on the use of a SCDTL (Side Coupled Drift Tube Linac) structure. The study analyzes the main laser-generated beam characteristics and the most important parameters linked to the accelerating structure. We show that the required tolerances regarding alignment and field uniformity, although challenging, are within the reach of actual technology. Regarding the laser-generated proton beam parameters (spot size and divergence), we show that they have only a little influence on the final emittance that is mainly determined by the capturing and accelerating structure. However, these parameters can sensitively affect the final transmission of the proton beam current.

Status of the TOP Linac project

The TOP Linac (Oncological Therapy with Protons), under development by ENEA and ISS is a sequence of three pulsed (5 μs 300 Hz) linear accelerators: a 7 MeV, 425 MHz RFQ+DTL (AccSys Model PL-7), a 7–65 MeV, 2998 MHz Side Coupled Drift Tube Linac (SCDTL) and a 65–200 MeV, variable energy 2998 MHz Side Coupled Linac (SCL). The status of the project will be presented. The 7 MeV injector is installed at ENEA-Frascati laboratories. The first SCDTL module structure, composed by nine DTL tanks coupled by eight side cavities, has been built and tested on RF bench, so that it is ready for proton acceleration. The results of the measurements done will be also shown.

RF behaviour of 3 GHz SCDTL structures

The 3 GHz linac section designed for the low energy (7–65 MeV) part of TOP (Therapy Oncological Protons) linac consists of eight modules of the structure SCDTL (Side Coupled Drift Tube Linac). The non axisymmetric cavities required a full 3D modelling. Electromagnetic calculations carried out by using MAFIA code gave the full mode spectrum, power losses, the coupling coefficients distribution and some indications for the tuning procedure. This paper reports a comparison between the results of this study and some RF measurements on the first module (7–13.4 MeV).

Numerical studies and measurements on the side-coupled drift tube linac (SCDTL) accelerating structure

The 3 GHz linac section designed for the low energy (7–65 MeV) part of TOP (therapy oncological protons) linac (Picardi et al., 1997, 1996), operating at 3 GHz frequency and in π/2 mode, consists of eight modules of the structure SCDTL (side-coupled drift tube linac). The first module is designed to accelerate 7 MeV protons up to 13.4 MeV, and a prototype is presently under construction. Electromagnetic field calculations of the non-axisymmetric cavities carried out by using MAFIA 3D code (Weiland, 1986) gave the RF wall losses and the full mode spectrum. Two prototypes, an aluminium model of the first quintuplet and a copper model of the last triplet of the module, were built in order to check the complex 3D properties of the structure, and to refine the tuning procedure. This paper reports the results of the 3D numerical simulations about the RF properties of the first module and of some RF measurements on the prototypes. The beam dynamics study results in the SCDTL section are discussed as well.

Design development of the SCDTL structure for the TOP linac

The Side Coupled Drift Tube Linac (SCDTL) is an attractive 3 GHz accelerating structure composed of short DTL tanks coupled together by side coupling cavities, in the course of development of the 200 MeV proton linear accelerator for proton therapy planned for the Terapia Oncologica con Protoni (TOP) program of the Italian National Institute of Health (Istituto Superiore di Sanità, ISS). The TOP Linac will be used to boost to 70 MeV the 7 MeV proton beam from a linac injector. Our main concern is to investigate in detail the characteristics of the structure in terms of RF properties of the accelerating mode, like longitudinal and transverse shunt impedance and quality factor, and of the other modes that cause the origin of the tank dispersion curve, in order to stabilize the behaviour under operating conditions. Calculations performed with the computer three-dimensional (3D) codes MAFIA and SOPRANO on the smallest unit of the system (a single DTL tank without coupling cavities) and experimental measurements made on a prototype have shown good agreement. Two possible supporting stem configurations (single stem and two stems 180° apart for each drift tube) were examined and a comparison of the results in both cases are discussed.