Search

In rf linacs the longitudinal focalization is done by si-nusoidal forces and at high accelerating fields the zero-current longitudinal phase advance per longitudinal fo-cusing period σ0l_l can be high. The nonlinear compo-nents of the sinusoidal rf field (sextupolar, octupolar and higher order components) can then excite parametric resonances, including the 4th-order resonance (σl_l = 90°) when σ0l_l is higher than 90°, inducing strong longitudinal emittance growths and acceptance reductions. As pointed out in previous papers, the longitudinal beam dynamics is therefore complex, even when the space-charge forces are ignored. The parametric resonance excitation by the rf field is analyzed before discussing the additional effect of the space-charge forces, in particular to explain why the zero-current longitudinal phase advance per trans-verse focusing period σ0l_t is not a relevant parameter. Examples are given in the SPIRAL2 linac case.

International audience; The single bunch selector of the SPIRAL2 accelerator allows reducing the bunch rate to the target of the Neutron For Science (NFS) facility in view of time of flight experiments. It involves two processes: a static dipole magnet deviates the beam on a 7.3 kW scraper, while the electric field of two high voltage travelling wave pulses maintains the selected bunch on axis at the required repetition rate. This original principle, named “inverted duty cycle”, was chosen to provide reasonable power requirement for the pulse generators, high rejection of the side bunches, and safe operation for the experimental target. This paper gives an overview of the whole system, recalls the main component design issues and performances and reports the successful commissioning results with the first 0.2 and 5 mA proton beams.

Les accelerateurs de particules sont des outils tres utilises. Parmi eux, les accelerateurs de protons de haute intensite et d'energie autour du gigaelectrons- Volt (GeV) ont des applications tres variees, s'etendant de la recherche pure a l'incineration des dechets radioactifs dans des systemes hybrides. Ces machines sont a l'extreme pointe de la technologie des accelerateurs et font l'objet d'une R&D importante partout dans le monde. De nombreux projets existent, dont certains sont deja en cours de realisation.

The accelerator system of the International Fusion Materials Irradiation Facility (IFMIF) provides the 250-mA, 40-MeV continuous-wave deuteron beam at one of the two lithium target stations. It consists of two identical linear accelerator modules, each of which independently delivers a 125-mA beam to the common footprint of 20 cm × 5 cm at the target surface. The accelerator module consists of an ion injector, a 175 MHz RFQ and eight DTL tanks, and rf power supply system. The requirements for the accelerator system and the design concept are described. The interface issues and operational considerations to attain the proposed availability are also discussed.

The angular dependece of the pp elastic scattering spin correlation parameter was measured in the angular range from 60° to 97° CM at 14 energies between 1.96 and 2.23 GeV. A rapid decrease of the energy dependence of this observable at 90° CM is observed around 2.11 GeV kinetic energy. This agrees with the behavior of Aoonn predicted on the basis of an exotic six-quark structure. The Aoonn (90° CM), together with the known differential cross section, allows the determination of the absolute value of the pure spin-singlet amplitude. The energy dependence of this amplitude shows a shoulder centered at 2.11 GeV, corresponding to a total mass of 2.735 GeV and an estimated width of 17 MeV.

Reliable high intensity H− ion source development is now part of the CEA/Saclay work in the field of high intensity linear accelerators. A 2.45 GHz electron cyclotron resonance (ECR) H− ion source and test bench have been built. This new source has been designed taking into account our experience on the French high intensity ECR proton source. For H− ion production, the high-energy electrons created in the ECR zone are trapped by a dipole magnetic filter. A rectangular 210 mm long plasma chamber and an intermediate iron shield are used to minimize the magnetic field in the extraction region. A second magnetic dipole separates electrons and negative ions in a 10 kV extraction system. To reduce the electron/H− ratio, the plasma electrode is biased by a power supply. The first helium plasma allowed us to verify the satisfactory electron separator behavior. Pulsed hydrogen plasma is currently produced. The first plasma characterization is under progress as a function of ion source parameters by using Langmuir...

Source of light ions with high intensities The (SILHI) source has been producing proton beams since 1996. The first aim is to produce up to 100 mA cw beams at 95 keV for the injector of protons for high intensity demonstrator. This prototype is developed by a CEA/DSM–CNRS/IN2P3 collaboration for applications such as accelerator driven systems for nuclear waste transmutation, production of radioactive ion beams, or secondary particles. To measure installation reliability, continuous 5 day long runs have been performed. In October 1999, a 99.96% availability was achieved with a single short beam off and a 103 H uninterrupted beam. A new extraction system leads to lower beam losses and higher LEBT transparency. SILHI now produces a 95 keV–130 mA total beam with a proton fraction higher than 80%. Up to a 157 mA (247 mA/cm2) total cw beam has been extracted. The new EPICS control system, electromagnetic interference hardened devices and automatic control procedures now allow us to do longer runs. To analyze th...

A computer code has been developped in order to make the tuning of the injection process easier in the Saturne synchrotron accelerator and search for sets of new values of parameters leading to the optimum of any criterion. The usual criterion being mainly the beam intensity given by current transformers or any non-destructive measurement device. Acquisition of the criterion is made at each cycle of the acceleration. The technique used has many advantages

International audience; Robert R. Wilson, an accelerator pioneer working with E.O. Lawrence at Berkeley, made the first proposal to treat cancer using proton beams more than 60 year ago (1946). In a first period, many accelerators built for nuclear and particle physics research have been progressively used to treat patients all over the word. It was the time of the hadrontherapy “first generation”. As it has been the case for the evolution of the synchrotron radiation sources, starting with Loma Linda in 1990, a “second generation” of dedicated facilities has then been built to treat cancer without the constraints imposed to “parasitic users”. The total number of patients treated with protons was about 10.000 in 1993 and 50.000 in 2006, the progression looks to be exponential. Hadrontherapy is today part of the medical business landscape, several companies sell turnkey protontherapy centres and the fight is started for carbon centres. The status of some hadrontherapy projects in Europe (existing facilities and future projects) as well as the industrial aspects will be presented in this framework.

The assembly of a laser driven photo-injector and an RF linear accelerator offers the advantage of a versatile machine in order to produce multi-pulse electron beams. A train of 20 bunches (micro-pulses) carrying each a 100 nC charge would be extracted from a photo-cathode and accelerated in a DC voltage to 2.5 MV. The electron beam is then injected into superconducting radio frequency cavities operating at 352 MHz. They accelerate the beam as a relativistic linear accelerator. The 55 ns pulse duration electron beam (macro-pulse) is accelerated at 51 MeV through this structure. If this process is repeated at short given time delays, it enables to deliver multi-pulse or/and multi-axe electron beams. This machine has been proposed for radiographic applications and a design has been completed. It led to a proposal for a demonstrator of photo-injector which would be built shortly. Detailed simulations of the electron beam generation, acceleration and transport will be presented along with present experimental studies for validations of the numerical simulation codes.

A 2.45 GHz electron cyclotron resonance (ECR) ion source for producing a 100 mA H+ beam is under study. The microwave power is coupled through a quartz window and a water‐cooled 90° waveguide bend in order to avoid the heating of the electrons backstreaming from the source. The ECR condition is obtained with dc magnetic coils. Preliminary results reported here show that a beam current density of 75 mA/cm2 can be extracted at 10 kV from a 3‐mm‐diam aperture, with 1.2 kW of microwave power at 1×10−3 mbar of hydrogen pressure. The proton fraction is 75% with an alumina‐coated plasma electrode and 85% with a nitride coating.

A simple model has been built to study the evolution of high-current electron or ion beams in axially symmetric extraction systems (electron guns or ion sources). Both electric and magnetic field components induced by a HV diode and a focusing solenoid respectively are computed using analytical formulas. The space-charge forces are computed using a ring method. In a first step, the individual effects of the 3 nonlinear forces (electric, magnetic and space charge) on the emittance evolution are presented. We then discuss how the knowledge acquired in the first step can be used to understand and optimize the emittance evolution in systems combining these effects.

Beginning with the TRISPAL project, halo formation has been extensively studied at CEA last 10 years. Effect of mismatching, non‐linear forces, resonances, longitudinal‐transverse coupling, intrabeam scattering, and interaction with the residual gas have been explored. They have been studied theoretically from both analytical models and dedicated simulation codes and, for some of them, experimentally from proton beam profile measurements over a high dynamic range in a 26 periods FODO channel. Our knowledge, strongly improved through collaborations with our worldwide colleagues, has been applied to the design of several linac projects, whose last are SPIRAL2 and RX2. The goal of this presentation is to summarise the contribution of the CEA teams to the understanding of the halo formation.

High-power accelerators are being studied for several projects based on high-flux neutron sources driven by proton or deuteron beams. Since the front end is the most critical part of such accelerators, it has been decided to build a high-intensity proton injector (IPHI) designed to accelerate a CW 100 mA beam up to 11 MeV. The aim is to validate design codes, test technical choices, demonstrate operational reliability and measure the beam parameters in order to optimize the high-energy part of the accelerator. The design chosen for IPHI (ECR source, RFQ, DTL and diagnostic line) and the construction schedule are presented.

A study is progress to prepare an experiment on the transport of an intense proton beam, with high optical qualities, through a periodic magnetic quadrupole FODO channel (29 periods). It is intended to provide a better understanding of how halo develops and can be controlled as a crucial issue for the design of high-intensity linear accelerators. Simulations were done showing that this experiment can be performed with a high-brightness proton beam produced by a duoplasmatron source, with an energy of 500 keV and a current of tens of mA. Beam pulse length will be less than 1 ms and normalized emittance better than 1./spl pi/ mm.mrad (90% of total beam). Thus, transverse tune can be sufficiently depressed in the transport channel to allow instabilities to grow and halo to develop or stay under control. The overall experiment is divided in two phases. Phase 1, the subject of this paper, is dedicated to precise measurements on initial beam conditions, such as emittance, for the beam entering the FODO channel. Phase 2, concerning the halo formation phenomena will be carried on latter, if results of phase 1 are satisfactory.

A significant breakthrough in the understanding of the space-charge dominated beam dynamics has been achieved with the introduction of the particle-core model at the previous PAC (O'Connell, Wangler, Mills and Crandall, May 1993). Using this model, we have shown the chaotic behaviour of the particles for mismatched beams in continuous focusing channels (August 1993 and August 1991) and for matched beams in FODO channels (December 1993 and June 1994). In these studies, it has been settled that the recent theories developed for the analysis of nonlinear dynamic systems ("chaotic dynamics") are very useful to understand charge redistribution and halo formation phenomena. They are now used to describe the behaviour of mismatched beams in FODO channels. It is shown that a mismatch adds perturbing forces which can deeply modify the dynamics. The particle diffusion far from the beam core is studied.

A CW RFQ, designed to accelerate 100 mA proton beams from 100 keV to 4 MeV, is being studied by the GECA in Saclay. A preliminary design leading to a beam transmission larger than 97% is presented. A logical approach, based on both the choice of transverse and longitudinal phase advances at the end of the gentle buncher and an adiabatic variation of the RFQ parameters in this region is described.

The International Fusion Materials Irradiation Facility (IFMIF) requires generation, by a linear accelerator (linac), of 250 mA continuous current of deuterons at a nominal energy of 35 MeV, with provision for operation at 30 MeV and 40 MeV. Our basic approach is to provide two linac modules, each delivering 125 mA to a common target for a total of 10 MW of continuous beam power. The deuterons would be stripped in a molten lithium target to two neutrons, with a neutron energy spectrum peaked at /spl sim/14 MeV as would be found in a fusion device.

The 1.3 GeV linac of the CONCERT multi-users facility has to accelerate protons and H/sup -/ ions in a series of current pulses distributed over each 20 ms period. The peak current is identical for all pulses to keep the space charge forces about constant apart from a slight emittance change between H/sup +/ and H/sup -/ bunches. The beam power required for a given application is then obtained by adjusting the pulse duration. Because of their high acceleration efficiency, superconducting cavities of elliptical shape and working at 704 MHz have been selected. The overall architecture - transition energy, number of cavities per module, cavity design and number of families - results from linac length/cost optimisation and does not depend on the duty cycle which can vary from 5% to 25%, typical values for a stand-alone and multi-users facilities, respectively. RF power generation is based on individual klystrons and pulsed IGBT high voltage power supplies. Each cavity is fed by two symmetrical couplers to achieve the required peak power and to reduce the RF kicks. With adequate beam matching between the different sections, beam dynamics 3D simulations in the absence of errors and with various realistic errors show stable beam behaviour, as well as moderate halo enhancement and emittance growths.

The 1.3 GeV linac of the CONCERT multi-users facility has to accelerate protons and H/sup -/ ions in a series of current pulses distributed over each 20 ms period. The peak current is identical for all pulses to keep the space charge forces about constant apart from a slight emittance change between H/sup +/ and H/sup -/ bunches. The beam power required for a given application is then obtained by adjusting the pulse duration with a total maximum power of 20 MW and 5 MW for the proton and H/sup -/ beams respectively. The reference design of the low-energy part of this linac is made-up of two separate proton and H/sup i/njectors up to 23 MeV, the H/sup -/ one using a funnelling system. These injectors are followed by a series of copper cavities up to the transition with superconducting cavities at about 185 MeV. The overall architecture, the technical choices and the beam dynamics in this high-power proton linac front end are presented and discussed.

Experimental results are presented for the $\mathrm{pp}$ elastic-scattering single spin observable ${A}_{\mathrm{oono}}{=A}_{\mathrm{ooon}}{=A}_{N}=P,$ or the analyzing power, at 19 beam kinetic energies between 1795 and 2235 MeV. The typical c.m. angular range is $60--100\ifmmode^\circ\else\textdegree\fi{}.$ The measurements were performed at Saturne II with a vertically polarized beam and target (transverse to the beam direction and scattering plane), a magnetic spectrometer and a recoil detector, both instrumented with multiwire proportional chambers, and beam polarimeters.

The polarization of extracted SATURNE II proton beam as a function of different ion source configurations was studied. Two distinct experiments were necessary for this purpose. In the first one, the LEFT-RIGHT instrumental asymmetry of the beam polarimeter was determined using an unpolarized beam. In the second one this correction factor was applied to asymmetries measured with the beam from the polarized ion source in all polarization states. The measurements were carried out at the proton beam kinetic energy 0.80 GeV, where the pp-elastic scattering analyzing power is near its maximum. The results confirmed that the two so-called “unpolarized states” of the source were polarized to several percent, whereas the absolute values of the beam polarizations in the so-called “polarized states” were equal and opposite. It was observed that the hexapole lens of the ion source produced beam polarization in the absence of any transition. The beam polarization as a function of hexapole current, transition field attenuation, and spin rotation solenoid current was measured. It was also shown how to obtain a strictly unpolarized beam using the polarized source only. The results obtained with the SATURNE II ion source HYPERION may also be relevant to similar sources at other accelerators.

A significant breakthrough in the understanding of the mechanisms leading to charge redistribution and halo formation in space‐charge dominated beams has been achieved in the past few years. The first aim of this paper is to summarize the main results which have been obtained in recent studies. The nonlinear resonances excited by space charge forces are analyzed, then it is shown that they can induce chaotic trajectories, therefore halo formation. The second objective is to present some ideas in order to try to promote new successful studies, as well as to point out the ambiguous character of some theories used in this field without any serious justification.

SILHI is the ECR high intensity light ion source studied in France at C.E.A. Saclay. This is the source for the injector of the high intensity proton injector prototype developed by a CNRS-IN2P3 collaboration. 80 mA at 95 keV beams with a rms normalized r–r′ emittance lower than 0.3 π mm mrad and a proton fraction better than 85% are currently produced. Recently, it has been found that the injection in the low energy beam transport of a buffer gas had a strong effect on the emittance measured 1 m downstream of the focusing solenoid. By adding several gases (H2, N2, Ar, Kr), improvements as great as a factor of 3 have been observed. The emittance has been measured by means of an r–r′ emittance measurement unit equipped with a sampling hole and a wire profile monitor, both moving across the beam. Simultaneously, the space charge compensation factor is measured using a four-grid analyzer unit. In this article all results of these experiments are presented and discussed. A first explanation of the emittance r...

The high intensity light ion source (SILHI) is the electron cyclotron resonance (ECR) source constructed and tested at CEA-Saclay. The first aim is to produce up to 100 mA cw proton beams at 95 keV for the proton injection high intensity (IPHI) beams [5 MeV radio frequency quadrupole (RFQ) and 10 MeV drift tube linac (DTL)]. This prototype is developed by a CEA–CNRS-IN2P3 collaboration for applications such as accelerator driven systems for nuclear waste transmutation, production of radioactive ion beams or secondary particles. SILHI is also used to study the production of deuteron and H− beams for the International Fusion Material Irradiation Facility and European spallation source projects, respectively. The present status of SILHI and the experiments planned for the near future in both cw and pulsed modes are presented in this article. 80 mA cw proton beams are now currently produced at 95 keV with a high availability (∼1 spark/day). The proton fraction is around 90% and the typical r–r′ rms normalized...