Soreq Nuclear Research Center (SNRC) and CEA collaborate for the upgrade of the existing Soreq Applied Research Accelerator Facility (SARAF) accelerator up to 5mA Continuous Wave (CW) 40 MeV deuteron and proton beams (Phase 2). SNRC is upgrading the injector: the ion source, the low energy beam transport line and the 4-rods Radio Frequency Quadrupole (RFQ). CEA is in charge of the development and commissioning of the medium energy beam transport line and the superconducting linac. This paper presents the status of the SARAF linac development by CEA and the installation and testing of a new set of rods electrodes in the SARAF RFQ.

The original SARAF 3.8 m long 4-rod Radio Frequency Quadrupole (RFQ) has been successful in acceleration of 4 mA ContinuousWave (CW) proton beam and pulsed deuteron beam to 1.5 MeV/u. However, conditions for running CW deuteron beam have not been achieved in the original design. A new 4-rod structure has been designed and implemented, with the goal of reducing the RF power required for CW deuteron operation while slightly compromising the RFQ exit energy to 1.27 MeV/u. The new 4-rod structure was manufactured, and installed in place of the old rod electrodes. Superior field homogeneity was achieved. The RFQ was successfully conditioned to the RF power 200 kW required for CW deuteron operation, with sufficient power margin. The commissioning with proton and deuteron beams showed that most of beam parameters are close to the designed specifications. The first operation with CW RF power of 5 mA deuteron beam was demonstrated. In addition, a 1.1 mA CW deuteron beam was transported through the superconducting module. The future scope of RFQ improvements is discussed.

The MYRRHA (Multi-purpose hYbrid Research Reactor for Hich-tech Applications) Project is a planned accelerator driven system (ADS) which aims to demonstrate the feasibility of large scale transmutation [1]. The first RF structure of the 600 MeV MYRRHA Linac will be a 176.1 MHz 4-Rod RFQ [2] that will accelerate up to 4 mA protons in cw operation from 30 keV up to 1.5 MeV [3]. The voltage along the approximately 4 m long electrodes has been chosen to 44 kV which limits the RF losses to about 26 kW/m. During the design of the structure a new method of dipole compensation has been applied. This paper describes the status of the RFQ and shows the results of the measurements done at IAP Frankfurt such as dipole and flatness measurements and power tests up to 11 kW. FLATNESS MEASUREMENT The frequency and voltage tuning of the RFQ has been performed in several steps. At first tuning plates have been adjusted to a unified height to set the resonance frequency of the structure to the design frequency of 176.1 MHz. After this frequency tuning several iterations of flatness tunings followed, each consisting of flatness measurement and adjusting the heights of individual tuning plates. After finishing a flatness of approximately ±3% could be achieved (see Fig.1). Figure 1: Final voltage distribution after tuning.

The MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) Project is planned as an accelerator driven system (ADS) for the transmutation of long-living radioactive waste. For this project a cw 4-Rod-RFQ with 176 MHz and a total length of about 4 m is required. It is supposed to accelerate protons from 30 keV up to 1.5 MeV*. One of the main tasks during the development of the RFQ is the very high reliability of the accelerator to limit the thermal stress inside the reactor. Another challenge was to compensate the dipole component of the MYRRHA-RFQ which is due to the design principle of 4-Rod-RFQs. This dipole component is responsible for shifting the ideal beam axis from the geometrical center of the quadrupole downwards. Design studies with CST MICROWAVE STUDIO have shown that the dipole component can be almost completely compensated by widening the stems alternately so that the current paths of the lower electrodes are increased.

For electron cyclotron resonance heating of the stellarator W7-X at IPP Greifswald, a 140 GHz/10 MW cw millimeter wave system has been built. Two out of 12 launchers will employ a remote-steering design. This paper describes the overall design of the two launchers, and design issues like input coupling structures, manufacturing of corrugated waveguides, optimization of the steering range, integration of vacuum windows, mitrebends and vacuum valves into the launchers, as well as low power tests of the finished waveguides.

The MYRRHA project requires a proton linac with an energy of 600 MeV with a beam current of 4 mA in cw operation. As first RF structure a 176 MHz 4-Rod RFQ has been chosen because of tuning possibilities, maintenance, lower capital costs and technological risk compared to a 4-Vane-RFQ. The aim of beam dynamics design was to preserve excellent beam quality and to avoid the creation of halo particles especially in the longitudinal plane. Using the NFSP (New Four-Section Procedure) with a soft and symmetric pre-bunching with full 360° acceptance it was possible to reach the requirements. The simulated transmission of the 4 m long RFQ is close to 100%. The electrode voltage has been chosen to 44 kV which gives enough transverse focusing but limits the required RF losses to about 25 kW/m. The cooling has been optimized for reliable operation and a new method of dipole compensation has been applied. The RFQ has been built and tuned with respect to field flatness. The paper describes the status of the RFQ and first measurements.

For the ECRH heating system of the stellarator Wendelstein 7-X, two remote steering antennas are developed and manufactured. The principle of remote steering antennas is based on the imaging characteristics of corrugated rectangular waveguides, which is well understood and can accurately be simulated. Several details, however, require deeper investigation. The antenna needs a miter-bend and a 24 mm gap. The positions of these elements need to be chosen carefully to reduce losses and stray radiation. The antennas are manufactured from copper by electroforming. This allows to integrate all components, including the corrugated inner walls and the cooling channels, in one vacuum-tight piece. This paper reviews the design process of the remote steering antennas for W7-X as well as technological issues and experimental results from test pieces. (C) 2015 Elsevier B.V. All rights reserved.

For electron cyclotron resonance heating of the stellarator W7-X at IPP Greifswald, a 140 GHz/10 MW cw millimeter wave system is in construction. Two out of 12 launchers will employ a remote-steering design. This paper describes design issues like input coupling structures, manufacturing of corrugated waveguides, optimization of the steering range, integration of vacuum windows, mitrebends and vacuum valves into the launchers, as well as tests of prototype parts.

The Beta-Beam is a concept of large-scale facility that aims at providing pure electronic neutrino and antineutrino beams for the measurement of \( \nu_{e}^{}\) \( \rightarrow\) \( \nu_{\mu}^{}\) oscillations. Beta-decaying nuclides are produced in large amounts in a facility of the scale of EURISOL, and are then post-accelerated and stored at large \( \gamma\) in a racetrack decay ring. We present here a conceptual design of the accelerator chain of a Beta-Beam based at CERN.

Accelerator Driven Systems (ADS) for nuclear waste transmutation require proton drivers with energies between 600 and 800 MeV and beam currents of several mA for demonstrators and up to 25 mA for large industrial systems. Within the EUROTRANS project a 600 MeV linac has been designed to meet the stringent requirements regarding reliability, availability and extreme low beam losses. The first accelerating section using the novel CH-cavity accelerates the beam to 17 MeV at the injection point into the main linac. The intermediate energy section (17-100 MeV) of the main linac consists of superconducting independently phased spoke-type cavities followed by the high energy section consisting of 704 MHz superconducting elliptical cavities. The paper covers the development of the linac, prototype testing and reliability considerations of the whole EUROTRANS project.

There is an increasing interest world wide in proton and ion linear accelerators for the low and medium energy range. Many of these accelerators will be operated at high duty cycles up to 100%. Superconducting cavities are favourable or sometimes even technologically necessary. Using conventional low beta cavities (quarter wave, half wave) leads to a large number of cavities and subsystems because of the small number of accelerating cells per cavity. The recently developed superconducting CHcavity is the first multi-cell cavity for low beta applications. A prototype cavity (19 cells, β=0.1) has been tested with effective gradiends of 7 MV/m. Presently two optimized CH-cavities are under construction (β=0.15, 325 MHz, 7cell and β=0.059, 217 MHz, 15 cells). Both cavities will be fully equipped with cryo-module, tuning systems and high power couplers. It is planned to test both cavities with beam at GSI, Darmstadt. The paper covers the development of the superconducting CH-cavity, different applications and future plans.

The Frankfurt Neutron Source at Stern Gerlach Zentrum (FRANZ) will use the Li(p,n) reaction to produce a intense neutron beam. The planned experiments require an adjustable neutron energy between 10 and 250 keV. Hence the energy of primary proton beam should be adjustable between 1.8 MeV and 2.2 MeV. The FRANZ beam line consists of two branches to allow different methods of neutron capture measurements. The compressor mode offer time of flight measurements in combination with a 4πBaF2 detector array. The proton beam of about 150 mA will be compressed to a 1ns pulse with a peak current of about 8 A at the repetition rate of 250 kHz. The activation mode uses a continuous neutron flux. The primary cw proton beam with a low current up to 30 mA will be focussed onto the production target. FRANZ is not only a neutron generator but also a test bench for new accelerator and diagnostic concepts for intense ion beams. The planned proton beam properties on the target leads into a challenge accelerator design to overcome the space charge forces. This presentation emphasises on the ongoing construction of the proton injector.

RFQs as injectors for high power linacs have to deliver high current ion beams at cw operation. The development of the 4-Rod RFQ structure has led to interesting solutions, which will be discussed with actual projects as examples. The properties and limits of our designs will be discussed.

According to the Unilac upgrade program for the SHE research at GSI, a new high energy part of the High Charge State Injector (HLI) has to be worked out. One of the versions of this linac foresees the acceleration of the highly stripped ions with charge-to-mass ratio of 1/6 delivered from the existing HLI at 1.4 MeV/u. The output beam energy should allow experiments at the Coulomb barrier and is assumed to be variable from 3.5 MeV/u to 7.5 MeV/u. These capabilities would allow for a competitive research in the field of radiochemistry and for the production of super heavy elements (SHE). Since high luminosities are strongly desirable on the target, the superconducting linac operated at 100% duty factor seems to be a very attractive solution for this machine. A preliminary linac design based on superconducting CHcavities is presented. Superconducting CH-Cavities The CH-cavity is a multi-cell cavity suitable for the efficient acceleration of low and medium energy ions. It combines the advantages of more conventional multi-cell cavities like IH-structures and superconducting operation. Superconducting cavities can be operated at significant higher acceleration gradients especially with high duty cycles. A superconducting CH-prototype cavity has been developed and tested with gradients of 7 MV/m in cw operation [1],[2]. Figure 1: Optimized CH-cavity geometry. Recently the cavity geometry has been optimized based on the experience with the prototype cavity. The new design has reduced drift sections in the end-cells which leads to very compact cavities with improved beam dynamics. Additionally, the new geometry is capable to handle more RF power and it has an innovative tuning concept using internal membrane tuners. It is planned to build a 325 MHz prototype cavity optimized for a particle β of 0.15. This cavity will be fully equipped with cryo module, power coupler and tuner system. It is also planned to test this cavity with beam behind the Unilac at GSI. Figure 1 shows the new cavity which can be considered as the prototype for the cw heavy ion linac.

The Frankfurt Neutron Source at the Stern-GerlachZentrum (FRANZ) [1] will comprise a short 175 MHz linac sequence consisting of a 1.75 m long 700 keV 4-rod type RFQ [2] followed by a 60 cm IH-DTL [3] for proton acceleration up to 2 MeV. The beam current is 200 mA at pulsed and up to 30 mA at c.w. operation. The aim is to have a very compact device driven by only one rfamplifier to reduce costs and required installation space. A strong coupling between the RFQ and the IH resonators will be realized by a direct connection between the last stems of each resonator through the common end wall. The accelerators could also be driven separately by just removing the coupling. The distance between the end of the RFQ electrodes and the midplane of the first DTL gap is only 5 cm leaving some place for a x-y-steerer. Preliminary rf-simulations have been carried out together with accompanying measurements on rf-models.

After the successful tests of the superconducting CH-prototype including the piezo tuners inside of a vertical cryostate, the CH-prototype is now beeing installed into a horizontal cryostate with a slow mechanical tuning device. In parallel a second generation is now beeing designed for dedicated high current projects such as IFMIF or EUROTRANS. The tuning concept has been innovated leading to an even more compact device. Test of the CH-prototype Tuning System All parts of the horizontal cryostat are now assembled and aligned. A first vacuum test of the inner cold mass has been performed successfully. The liquid nitrogen cooling system is prepared and closed now; it has been extended by an additional cooling loop at the pump port of the cavity. A first cold test is currently performed. A driver for the slow mechanical tuner has now been designed and constructed and allows either a manual or a computerized operation. This device has passed a first test run. The driving speed of the stepping motor can easily be changed and will be adjusted during the first performance test with the cavity. Before that there will be a cold test of the cryostat without cavity, to check for cold leaks and thermal issues. Figure 1: Cold test of the horizontal cryostat with liquid nitrogen. The New Superconducting CH Tuning Concept The most obvious change is the inclining of the outermost stems to homogenize the field distribution along beam axis. That was realized at the prototype by lengthening the drifttubes which are embedded in the tank wall, with the acceptance of longer drifts which is rather disadvantageous especially at high beam currents where the next focusing element should not be to far away. Figure 1: fast Membrane tuner for the new CH-structure at 325 MHz, β = 0.154. The design of the stems has been changed in a second way: The ratio between logitudinal and transversal stem diameter has been inverted, giving more space inbetween to locate the power coupler and the new membrane tuners. This change has been done by accepting a slightly higher magnetic peak field at the basis of each stem. The magnetic peak fields are a limiting factor regarding the maximum achievable accelerating field. Figure 2: Performance of the membrane tuner. References [1] A. Bechtold, M. Busch, H. Liebermann, H. Podlech, U. Ratzinger, "A tuner for a Superconducting CH-Prototype Cavity", SRF2007, Peking. [2] H. Podlech, A. Bechtold, M. Busch, H. Klein, H. Liebermann, U. Ratzinger, “Development of the superconducting CH-cavity and Applications to Proton and Ion Acceleration”, SRF2007, Peking.. GSI-ACCELERATORS-25 GSI SCIENTIFIC REPORT 2008

Worldwide there is an increasing interest in new high intensity proton and ion driver linacs with beam powers up to several MW. A very challenging part of these accelerators is the low and medium energy section up to 100 MeV. Depending on the duty cycle room temperature or superconducting options are favoured. In both cases the Crossbar-H-mode (CH)-structure developed at the IAP in Frankfurt is an excellent candidate. Room temperature as well as superconducting prototype cavities have been developed and tested successfully. A superconducting 19 cell low energy CH-cavity at 360 MHz reached effective gradients of 7 MV/m corresponding to an accelerating voltage of 5.6 MV. This cavity could be used for high intensity, cw operated linacs like accelerator driven systems (ADS, EUROTRANS) or the international fusion material irradiation facility (IFMIF). Recent developments of this new type of a multi-cell drift tube cavity, tests of the prototypes and future plans will be presented.