The recent layout of the Julich High Brilliance Neutron Source (HBS) driver linac is based on short crossbar H-mode (CH) cavities operated at a fixed synchronous phase. In the last decades the computing power for the development of linacs, available to physicists and engineers, has been increased drastically. This also enabled the accelerator community to finally carry out the required R&D to generate further the idea of drift tube linacs with alternating phase focusing (APF) beam dynamics, originally proposed in the 1950s. This focusing method uses the electric fields in between the drift tubes (i.e., gaps) to provide subsequent transverse and longitudinal focusing to the beam along multiple gaps. The beam focusing properties within each gap are adjusted individually by means of the synchronous phase. As a result of the alternating phase focusing method, these linacs can operate completely without internal magnetic lenses. The R&D-program for the high brilliance neutron source HBS offered the opportunity to investigate the APF concept further in order to open this advanced concept for high duty-factor, high intensity hadron beam acceleration. Besides, a prototype APF-interdigital H-mode (IH)-cavity has been designed and is going to be build and tested in the next future.

The design and construction of continuous wave (cw) high intensity linacs is a crucial goal of worldwide accelerator technology development. The standalone sc heavy ion linac HELIAC (HElmholtz LInear ACcelerator) is a common project of GSI Helmholtz Centre for Heavy Ion Research and Helmholtz Institute Mainz (HIM) under key support of Goethe University Frankfurt (IAP). In 2017 the first section of the linac has been successfully commissioned and extensively tested with beam at GSI, featuring the capability of 216.816 MHz multi-gap Crossbar H-mode (CH) DTL-structures. At present, the first fully equipped cryomodule of the HELIAC is under construction. In addition, six further superconducting CH cavities are being procured. The HELIAC beam dynamics concept foresees a total of twelve CH-cavities in order to accelerate ions with a mass-to-charge ratio of 6 up to an energy of 7.5 MeV/u. In this paper, an advanced very compact and less complex layout is presented, where the same number of accelerating cavities can be accommodated in three instead of four cryomodules, thus also reducing the number of solenoids and rebunchers. In addition, the integration and linking of the HELIAC to the GSI accelerator UNILAC will be outlined.

The new heavy ion superconducting continuous wave HElmholtz LInear ACcelerator (HELIAC) is under construction at GSI. A normal conducting injector, comprising an ECR ion source, an RFQ and a DTL, is recently in development. The new Interdigital H-mode DTL, presented in this paper, accelerates the heavy ion beam from 300 to 1400 keV/u, applying an Alternating Phase Focusing (APF) beam dynamics scheme. This APF section, consisting of two separately controlled tanks, has to provide for stable routine operation with assistance of dedicated beam diagnostics devices in the Intertank section. The installed quadrupole lenses and beam steerers installed there ensure full transmission in a wide range of input beam parameters.

In the future, a new superconducting (SC) continuous wave (CW) high intensity heavy ion HElmholtz LInear ACcelerator (HELIAC) should provide ion beams with maximum beam energy above the Coulomb barrier for the Super Heavy Element program at GSI (Gesellschaft für Schwerionenforschung, in Engl.: Association for Heavy Ion Research). The HELIAC consists of a SC main accelerator supplied by a normal conducting injector, which comprises an electron cyclotron resonance ion source, a radio-frequency quadrupole, and two separate interdigital H-mode drift-tube linear accelerator cavities, based on an Alternating Phase Focusing (APF) scheme. Together, both cavities will accelerate ions from 300 to 1400 keV/u with only one external quadrupole triplet for transverse focusing in between. Due to the demanding requirements of the APF concept on the voltage distribution along the beam axis on the one hand and the CW operation on the other hand, the optimization of each cavity concerning RF, mechanical, and thermal properties is crucial for the successful operation of the HELIAC injector.

The upcoming commissioning of the superconducting (SC) continuous wave Helmholtz linear accelerators first of series cryomodule is going to demand precise alignment of the four internal SC cavities and two SC solenoids. For optimal results, a beam-based alignment method is used to reduce the misalignment of the whole cryomodule, as well as its individual components. A symmetric beam of low transverse emittance is required for this method, which is to be formed by a collimation system. It consists of two separate plates with milled slits, aligned in the horizontal and vertical direction. The collimation system and alignment measurements are proposed, investigated, and realized. The complete setup of this system and its integration into the existing environment at the GSI High Charge State Injector are presented, as well as the results of the recent reference measurements.

In the future a new superconducting (sc) continuous wave (cw) high intensity heavy ion Linac should provide ion beams with a max. beam energy above the coulomb barrier for the Super Heavy Element (SHE) program at GSI Helmholtzzentrum fur Schwerionenforschung. Key features of this new Linac are the acceleration of different ions from protons to uranium as well as a smooth energy variation from 3.5 to 7.3 MeV/u for design ions with a mass-to-charge ratio A/q = 6 and even above for lighter ions. As a first step a newly developed superconducting 15-gap Crossbar H-cavity (CH-cavity) operated at 217 MHz has been successfully tested with heavy ion beam up to the design beam energy of 1.85 MeV/u for the first time. The design energy gain of 3.5 MV within a length of less than 70 cm has been validated with heavy ion beams of up to 1.5 p mu A. The measured beam parameters showed excellent beam quality, while a dedicated beam dynamics layout provides beam energy variation between 1.2 and 2.2 MeV/u. The beam commissioning is a milestone of the R&D work of Helmholtz Institute Mainz (HIM) and GSI in collaboration with Goethe University Frankfurt (GUF) and the first step towards a sc heavy ion cw-Linac with variable beam energy. The first tests under cryogenic conditions of the next two CH-cavities have already been started at GUF in a vertical cryostat. The results of the first successful heavy ion beam acceleration with a superconducting CH-cavity will be presented.

The standalone superconducting continuous wave heavy ion linac HELIAC (HElmholtz LInear ACcelerator) is a common project of GSI Helmholtz Centre for Heavy Ion Research and Helmholtz Institute Mainz (HIM) under key support of Goethe University Frankfurt (IAP) and in collaboration with National Research Nuclear University MEPhI and NRC “Kurchatov Institute” ITEP. In 2017 the first superconducting section of the linac has been successfully commissioned and extensively tested with beam at GSI. The measurements sufficiently present the capability of 216.816MHz multi-gap Crossbar H-mode (CH) DTL-structures. An acceleration of heavy ions up to the design beam energy and beyond has been reached with the setup. The required acceleration gain of 0.5MeV/u was achieved with heavy ion beams even above the design mass-to-charge ratio at maximum available beam intensity and full beam transmission. Recently the HELIAC beam dynamics concept foresees twelve superconducting CH-DTL cavities, assembled in four cryomodules. Each module is equipped with three accelerating CH structures, two superconducting solenoids for transverse beam focusing and a Spoke-type buncher for longitudinal beam matching. The linac is used to accelerate ions with a mass-to-charge ratio up to A∕z=6 from the input energy of 1.4MeV/u up to the smoothly variable output energy between 3.5MeV/u and 7.3MeV/u. The manuscript presents the reference beam dynamics layout of the entire HELIAC facility.

At the GSI Helmholtzzentrum fur Schwerionenforschung (GSI) in Darmstadt, Germany, a prototype cryomodule (advanced demonstrator) for the superconducting (SC) continuous wave (CW) Helmholtz Linear Accelerator (HELIAC) is under construction. A transport line, comprising quadrupole lenses, rebuncher cavities, beam correctors, and adequate beam instrumentation has been built to deliver the beam from the GSI 1.4 MeV/u High Charge Injector (HLI) to the advanced demonstrator, which offers a test environment for SC CW multigap cavities. In order to achieve proper phase space matching, the beam from the HLI must be characterized in detail. In a dedicated machine experiment the bunch shape has been measured with a nondestructive bunch shape monitor (BSM). Therefore, different bunch projections were obtained by altering the voltage of two rebunchers. These measurements were combined with dedicated beam dynamics simulations using the particle tracking code dynamion. The longitudinal bunch shape and density distribution at the beginning of the matching line are fully characterized by a tomographic reconstruction method based on a non-negative least square minimization approach.

The machine beam commissioning is a major milestone of the R&D for the superconducting heavy ion continuous wave linear accelerator HELIAC (HElmholtz LInear ACcelerator) of Helmholtz Institute Mainz (HIM) and GSI, developed in collaboration with IAP Goethe-University Frankfurt . During successful beam commissioning of the superconducting 15-gap Crossbar H-mode cavity at GSI Helmholtzzentrum für Schwerionenforschung heavy ions up to the design beam energy have been accelerated. The design acceleration gain of 3.5 MeV has been reached with full transmission for heavy ion beams of up to 1.5 pμA. Fabrication experiences and results of off-line and on-line cavity performance will be presented. The next step is the procurement and commissioning of so called ’Advanced Demonstrator’ the first of series cryomodule for the entire accelerator HELIAC. Results of further Demonstrator beam tests, as well as the status of the Advanced demonstrator project will be reported.

At the GSI Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt, Germany, the HElmholtz LInear Accelerator (HELIAC) is currently under construction. The HELIAC comprises superconducting multigap Crossbar H-mode (SC CH) cavities. The input beam is delivered by an already existing High Charge Injector (HLI). For the further development of the accelerator a detailed knowledge of the input beam parameters to the SC section is necessary. A method for beam reconstruction is incorporated, which provides for longitudinal beam characteristics using measurements with a beam shape monitor and a particle simulation code. This finalizes the investigations on 6D beam parameters, following previous measurements in transversal phase space. The reconstruction of the longitudinal phase portrait is presented.

Recently, the first section of a superconducting (SC) continuous wave (CW) linac has been extensively tested with heavy ion beam from the GSI High Charge State Injector (HLI). During this testing phase, the reliable operability of 217 MHz multi-gap crossbar-H-mode (CH) cavities has been successfully demonstrated. The SC 217 MHz CH cavity (CH-0) of the demonstrator setup accelerated heavy ions up to the design beam energy and even beyond at high beam intensities and full transmission. This worldwide first beam test with a SC CH cavity is a major milestone on the way realizing the entire SC CW linac project. In this contribution further RF measurements on the cavity are presented providing full characterization of the RF structure CH-0.

During successful beam commissioning of the superconducting 15-gap Crossbar H-mode (CH) cavity at GSI Helmholtzzentrum für Schwerionenforschung heavy ions up to the design beam energy have been accelerated. The design acceleration gain of 3.5 MeV inside a length of less than 70 cm has been reached with full transmission for heavy ion beams of up to 1.5 pμA. The measured beam parameters confirm sufficient beam quality. The machine beam commissioning is a major milestone of the R&D for the superconducting heavy ion continuous wave linear accelerator HELIAC (HElmholtz LInear ACcelerator) of Helmholtz Institute Mainz (HIM) and GSI, developed in collaboration with IAP Goethe-University Frankfurt (GUF). The next step is the procurement and commissioning of the so called “Advanced Demonstrator” – the first of four cryomodules for the entire accelerator HELIAC. Results of further Demonstrator beam tests, as well as the status of the “Advanced demonstrator” project will be reported.

At the Helmholtz-Institut Mainz (HIM) a cleanroom has been equipped with new tools and installations for the planned treatment of different superconducting RF-cavities. Therefore, the cleanroom had to be shut down and some walls and part of the ceiling had to be dismantled. In its ISO-class 6 area a large ultrasonic and a conductance rinsing bath has been installed. A high pressure rinsing cabinet has been implemented between the ISO-class 6 and 4 cleanroom so that a cavity can be loaded and unloaded from both sides. For drying the ISO-class 4 cleanroom was equipped with a 160°C vacuum oven. Afterwards the cleanroom was sealed again and put back in operation. New cleanroom lift trolleys allow the handling of heavy objects (max. 200 kg). By a rail system in the cleanroom floor it is possible to move entire cold strings through the different clean room classes separated by a roll-up door. This paper reports on the reclassification of the cleanroom after it went back to operation and first experiences with its cleaning. Particle measurements of equipment in operation will be presented as well.

The results of numerical simulations of multipacting discharge in a superconducting accelerating Crossbar H-type (CH) cavity are presented in this paper. The localization of multipactor trajectories in the 15-gap 217 MHz superconducting (sc) CH cavity at various levels of accelerating voltage is considered.

The cw – Linac – demonstrator is a prototype of the first section of the proposed cw-LINAC@GSI, comprising a superconducting CH-cavity embedded by two superconducting solenoids. The sc CH-structure is the key component and offers a variety of research and development. The beam focusing solenoids provide maximum fields of 9.3 T at an overall length of 380 mm and a free beam aperture of 30 mm. The magnetic induction at the fringe is minimized to 50 mT at the inner NbTi-surface of the neighboring cavity. The fabrication of the key components is finished, as well as the cold performance testing of the RF cavity. The cryostat is ready for assembling and the test environment is completely prepared. After successful testing of the RFPower coupler, the components have been assembled to the suspended frame under cleanroom conditions. Alignment, assembly, under cleanroom condition issues will be presented. CW LINAC DEMONSTRATOR Table 1: Main Parameters CH-Cavity

Very compact accelerating-focusing structures, as well as short focusing periods, high accelerating gradients and short drift spaces are strongly required for superconducting (sc) accelerator sections operating at low and medium energies for continuous wave (cw) heavy ion beams. To keep the GSI-super heavy element (SHE) program competitive on a high level and even beyond, a standalone sc cw linac (Helmholtz linear accelerator) in combination with the GSI high charge state injector (HLI), upgraded for cw operation, is envisaged. Recently the first linac section (financed by Helmholtz Institute Mainz (HIM) and GSI) as a demonstration of the capability of 217 MHz multigap crossbar H-mode structures (CH) has been commissioned and extensively tested with heavy ion beam from the HLI. The demonstrator setup reached acceleration of heavy ions up to the design beam energy. The required acceleration gain was achieved with heavy ion beams even above the design mass to charge ratio at high beam intensity and full beam transmission. This paper presents systematic beam measurements with varying rf amplitudes and phases of the CH cavity, as well as phase space measurements for heavy ion beams with different mass to charge ratio. The worldwide first and successful beam test with a superconducting multigap CH cavity is a milestone of the R&D work of HIM and GSI in collaboration with IAP in preparation of the HELIAC project and other cw-ion beam applications.

Recently the first section of a standalone superconducting (sc) continuous wave (cw) heavy ion Linac as a demonstration of the capability of 217 MHz multi gap Crossbar H-mode structures (CH) has been commissioned and extensively tested with beam from the GSI High Charge State Injector (HLI). The demonstrator set up reached acceleration of heavy ions up to the design beam energy and beyond. The required acceleration gain of 0.5 MeV/u was achieved with heavy ion beams even above the design mass to charge ratio at maximum available beam intensity and full beam transmission. This contribution presents systematic beam measurements with varying RF-amplitudes and -phases of the CH-cavity, as well as versatile phase space measurements for heavy ion beams with different mass to charge ratio. The worldwide first and successful beam test with a superconducting multi gap CH-cavity is a milestone of the R&D work of Helmholtz Institute Mainz (HIM) and GSI in collaboration with Goethe University Frankfurt (GUF) in preparation of the sc cw heavy ion Linac project and other cw-ion beam applications.

To keep the ambitious Super Heavy Element (SHE) physics program at GSI competitive a superconducting (sc) continuous wave (cw) high intensity heavy ion LINAC is currently under progress as a multi-stage R&D program of GSI, HIM and IAP [2]. The baseline linac design consists of a high performance ion source, a new low energy beam transport line, an (cw) upgraded High Charge State Injector (HLI), and a matching line (1.4 MeV/u) which is followed by the new sc-DTL LINAC for post acceleration up to 7.3 MeV/u. In the present design the new cw-heavy ion LINAC comprises constant-beta sc Crossbar-H-mode (CH) cavities operated at 217 MHz. The advantages of the proposed beam dynamics concept applying a constant beta profile are easy manufacturing with minimized costs as well as a straightforward energy variation [6]. An important milestone will be the full performance test of the first CH cavity (Demonstrator), in a horizontal cryo module with beam. An advanced Demonstrator setup comprising a string of cavities and focussing elements is proposed to build from 10 short CH-cavities with 8 gaps. The corresponding simulations and technical layout of the new cw heavy ion LINAC will be presented.

For future experiments with heavy ions near the coulomb barrier within the SHE (super-heavy elements) research project a multi-stage R&D program of GSI, HIM and IAP is currently in progress [1]. It aims at developing a superconducting (sc) continuous wave (cw) LINAC with multiple CH cavities as key components downstream the High Charge Injector (HLI) at GSI (Fig. 1). The beam dynamics concept is based on EQUUS (equidistant multigap structure) constant-β cavities. Advantages of its periodicity are a high simulation accuracy, easy manufacturing and tuning with minimized costs as well as a straightforward energy variation. The next milestone will be a full performance beam test of the first LINAC section, comprising two solenoids and a 15-gap CH cavity inside a cryostat (Demonstrator).