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Various physical and technology-dependent limits are encountered for key performance parameters of accelerators such as high-gradient acceleration, high-field bending, beam size, beam brightness, beam intensity and luminosity. This paper will review these limits and the associated challenges. Possible figures-of-merit and pathways to ultimate colliders will also be explored., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

Optimization of transfer line optics is essential for delivering high quality beams to the experimental areas. This type of optimization is usually done by hand and relies on the experience of operators. The nature of this task is repetitive though highly complex. Besides optimizing the beam quality at the experiments this task is often accompanied by secondary objectives or requirements such as keeping the beam losses below an acceptable threshold. In the past years Deep Learning algorithms have experienced a rapid development and gave rise to various advanced software implementations which allow for straightforward usage of corresponding techniques, such as automatic differentiation and gradient backpropagation. We investigate the applicability and performance of these techniques in the field of transfer line optics optimization, specifically for the HADES beamline at GSI, in form of gradient-based differentiable simulators. We test our setup on results obtained from MADX simulations and compare our findings to different gradient-free optimization methods. Successfully employing such methods relieves operators from the tedious optimization tasks., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

CRYRING@ESR is a heavy ion storage ring, which can cool and decelerate highly charged ions down to a few 100 keV/u. It has been relocated from Sweden to GSI, downstream of the experimental storage ring (ESR), within the FAIR project. The ring will be used as a test facility for FAIR technologies as well as for physics experiments with slow exotic ion beams for several FAIR collaborations: SPARC, BioMat, FLAIR and NUSTAR. CRYRING@ESR is in its commissioning phase since summer 2016. Several ion-optical measurements such as tunes, tune diagram, dispersion, chromaticity and orbit response matrix were performed at the ring. The measurements will be used for several purposes such as improvement of the theoretical model, closed orbit control and correction of unacceptable misalignments, calibration coefficients and field errors., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

CRYRING@ESR is the early installation of the low-energy storage ring LSR, a Swedish in kind contribution to FAIR, which was proposed as the central decelerator ring for antiprotons at the FLAIR facility. An early installation opens the opportunity to explore part of the low energy atomic physics with heavy, highly charged ions as proposed by the SPARC collaboration but also experiments of nuclear physics background much sooner than foreseen in the FAIR general schedule. Furthermore, the ring follows in large parts FAIR standards, and is used to test the FAIR control system. CRYRING@ESR has been installed behind the existing experimental storage ring ESR starting in 2013. It has a local injector that is used for commissioning. In November 2016 the commissioning of the storage ring started and a first turn was achieved. After a complete bake out cycle and substantial developments of control system, diagnosis and others, commissioning was continued in late summer 2017. Stored as well as accelerated beam has been achieved by now. The remaining step is to take the electron cooler into operation, which is planned for November this year., Proceedings of the 11th Workshop on Beam Cooling and Related Topics, COOL2017, Bonn, Germany

The realization of the new Facility for Antiproton and Ion Research, FAIR at GSI, Germany, has advanced significantly. The civil construction process of the Northern part of the building complex, including the excavation of the SIS100 synchrotron tunnel has been launched end of 2017. On site of the GSI campus, major preparations and upgrade measures for the injector operation of the existing accelerator facilities are ongoing and will be completed mid of 2018. The shielding of the SIS18 accelerator tunnel has been enhanced for the booster operation at high repetition rates and high intensity Proton beams. Two new transformer stations were set-up and commissioned which will provide the required pulse and common power for FAIR. All major contracts for series production of SIS100 components have been signed and a large number of the superconducting SIS100 magnets has been produced and accepted. Major testing infrastructures for superconducting magnets of SIS100 and Super-FRS have been set-up at JINR, CERN and GSI. Also for all other FAIR accelerator systems, the procurement of the components is progressing well, Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

After two-year's shutdown, the GSI accelerators plus the latest addition of storage ring CRYRING, will be back into operation in 2018 as the FAIR phase 0 with the goal to fulfill the needs of scientific community and the FAIR accelerators and detector development. Even though GSI has been well known for its operation of a variety of ion beams ranging from proton up to uranium for multi research areas such as nuclear physics, astrophysics, biophysics, material science, the upcoming beam time faces a number of challenges in re-commissioning its existing circular accelerators with brand new control system and upgrade of beam instrumentations, as well as in rising failures of dated components and systems. The cycling synchrotron SIS18 has been undergoing a set of upgrade measures for fulfilling future FAIR operation, among which many measures will also be commissioned during the upcoming beam time. This paper presents the highlights of the challenges such as re-establishing the high intensity heavy ion operation as well as parallel operation mode for serving multi users. The status of preparation including commissioning results will also be reported., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The Cooler Synchrotron (COSY) at Forschungszentrum Jülich is currently carrying out the preparation for a direct measurement of the electric Dipole Moment (EDM) of the deuteron using an RF Wien filter*,**. In a magnetic storage ring with the spin vector aligned along the direction of motion, the EDM manifests in a buildup of the vertical spin component. Besides this signal, radial magnetic fields due to a distortion of the vertical closed orbit can produce a similar signal. This signal is a systematic limit of the proposed measurement procedure. Based on simulation studies***, a vertical closed orbit distortion with a RMS smaller than 0.1 mm is required to achieve a sensitivity of 10⁻¹⁹ e.cm or better. In order to accomplish this challenging goal, a slow orbit feedback system was proposed and recently commissioned at COSY. The design and commissioning results will be presented, and the future plan will also be discussed., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

At the Forschungszentrum Jülich (FZJ) the intermediate energy cyclotron JULIC, used as injector of the Cooler Synchrotron (COSY) and COSY itself, have been enabled to perform low to medium current irradiations. Main task is to support the FZJ radionuclide research programme of INM-5. Target holders of the INM-5 were implemented to the external target station of JULIC to obtain reliable irradiations with 45 MeV protons and 76 MeV deuterons for nuclear reaction cross section measurements and medical radionuclide production. For testing of radiation effects, displacement damage DD and single event effects SEE, with energetic protons for electronics used in space and accelerators the beam can be extracted to a dedicated test stand, e.g. used by Fraunhofer INT. To provide these possibilities up to 2.5 GeV as well one external beamline of the cooler synchrotron COSY will be equipped with a new irradiation station and adaption for the dosimetry systems are done. Different dosimetry systems (PTW Farmer® chambers, Bragg Peak chambers, Gafchromic® dosimetry films) are available to monitor and control the ongoing irradiation. This report briefly summarizes the relevant technical activities., Proceedings of the 21st Int. Conf. on Cyclotrons and their Applications, Cyclotrons2016, Zurich, Switzerland

COSY is a versatile racetrack-type synchrotron accelerating protons and deuterons in a range of rigidity between 1 T m and 11 T m. Circulating beam can be slowly extracted on a third order resonance and channeled towards different users. New users of the COSY beam have presented new challenges with specific requests, most notably in term of beam shape. This in turn drove a strong interest to develop and improve characterization and modeling methods in the COSY extraction beam line. In this contribution we will present the different beam characterization methods used and their limitations. We will then discuss the modeling of the line and the importance of an accurate and reliable model of the extraction line. Some of the latest beam measurements are presented and compared to modeled results., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The institute for nuclear physics IKP-4 at the Forschungszentrum Jülich operates the accelerator facility COSY with the isochronous cyclotron JULIC as the pre-accelerator, the cooler synchrotron COSY/Jülich and various experimental facilities for accelerator research and experimental hadron physics developments. The cyclotron has reached in spring 2016, since first beam in 1968, in total about 285000 hours of operation. The ongoing program at the facility foresees increasing usage as a test facility for accelerator research and detector development for realization of FAIR and other novel experiments. In parallel to the operation of COSY the cyclotron beam alone is also used for irradiation and nuclide production for fundamental research. Experience with pulsed ion sources for JULIC enables the development of a dedicated pulsed 100 keV source for protons and negative ions as a contribution to the extra low energy anti-proton synchrotron project ELENA at CERN’s anti proton decelerator AD. A brief overview of the activities at the Forschungszentrum Jülich, the cooler synchrotron COSY and its injector cyclotron JULIC, with focus on recent technical developments, will be presented., Proceedings of the 21st Int. Conf. on Cyclotrons and their Applications, Cyclotrons2016, Zurich, Switzerland

The High-Energy Storage Ring (HESR) is one part of the international Facility for Antiproton and Ion Research (FAIR) at GSI Darmstadt. Forschungszentrum Jülich (IKP and ZEA-1) is responsible for the design and development of the HESR. The HESR is designed for antiprotons and heavy ion experiments as well. Therefore the vacuum is required to be 10⁻¹¹ mbar or better. To achieve this also in the curved sections, where 44 bent dipole magnets are installed, NEG coated dipole chambers will be used to reach the needed pumping speed and capacity. For activation of the NEG a bake-out system is needed. Two test benches were installed to investigate the required equipment needed to reach this low pressure: A vacuum test bench to investigate the influence of different types and quantity of vacuum pumps for the straight sections of the HESR A bake-out test bench for checking the achievable end pressure and develop the bake-out system for the NEG coated dipole chambers in the curved sections of the HESR The results of the tests and the bake-out concept including the layout of the control system and the special design of the heater jackets inside the dipoles and quadrupoles are presented., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The COoler SYnchrotron in Jülich is a well suited accelerator for a precursor experiment on the direct measurement of the Electric Dipole Moment (EDM) of the deuteron (see* and references within). It provides polarized and unpolarized proton and deuteron beams in the momentum range between 0.3 GeV/c and 3.65 GeV/c**, allows for phase space cooling and is highly flexible with respect to ion-optical settings***. Unfortunately, a model independent linear optics measurement is not possible and so far the existing MAD-X model of COSY does not provide an agreement with the actual machine parameters that is required by future experiments, such as the EDM experiment. Significant deviations with respect to the working point and linear optics have been reported****. As shown in*****, a MAD-X based LOCO (Linear Optics from Closed Orbits) algorithm in a C++ program was successfully developed and carefully benchmarked. This contribution presents the application of the new program on measured ORM data and its capabilities in calibrating linear optics as well as reconstructing machine imperfections such as gradient errors of quadrupole magnets and calibration factors of BPMs and steerers., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The Research Center Jülich has taken the leadership of a consortium being responsible for the design and manufacturing of the High-Energy Storage Ring (HESR) going to be part of FAIR. The HESR is designed both for antiprotons and for heavy ion experiments. The injection kicker system of the HESR is located directly behind the septum and consists of two pumping crosses for pumps and measurement devices as well as two vacuum tanks housing the four ferrite magnets which will be operated with 40 kV, 4kA. As well as the magnets, the adjustments frames and the electrical feedthroughs will be installed inside the tanks. Due to the large surface of the magnets the injection kicker system will be very sensitive with regard to the achievable vacuum quality that is expected to be in the order of 10⁻¹¹ mbar or better. Thus the vacuum system is designed to heat up to 250°C. In order to investigate the achievable end pressure and to develop the heating system a test facility was constructed. The actual vacuum layout of the injection kicker system as well as the experimental test results will be presented and in similar the layout of the control system of the test facility will be described., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The COoler SYnchrotron in Jülich accelerates and stores unpolarized and polarized proton or deuteron beams in the momentum range between 0.3 GeV/c and 3.65 GeV/c [*,**]. This, in combination with its diverse capabilities of phase space cooling and the flexibility of the lattice with respect to ion-optical settings makes COSY an ideal test facility for accelerator technology development. High demands on beam control and beam based measurements have to be fulfilled for future experiments such as the proposed precursor experiment for a direct measurement of the electric dipole moment of the deuteron (see [***] and references within). The analysis of measured orbit response matrices (ORM), which com- prise the focussing structure of the ring, allows for a better understand- ing of machine imperfections such as gradient errors and misalignments of quadrupole magnets. This contribution presents the development of a MAD-X based LOCO (Linear Optics from Closed Orbits) algorithm [****] in a C++ program aiming to calibrate and correct linear optics as well as improving beam control at COSY., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

A storage ring provides an attractive option for directly measuring the electric dipole moment~(EDM) of charged particles. To reach a sensitivity of 10^-29 e x cm, it is critical to mitigate the systematic errors from all sources. This daunting task is pushing the precision frontier of accelerator science and technology beyond its current state of the art. Here, we present a unique idea of a magnetic dipole moment~(MDM) spin transparent quadrupole that can significantly reduce the systematic errors due to the transverse electric and magnetic fields that particle encounters., Comment: 10 pages

COSY is a cooler synchrotron designed for internal target hadron physics experiments, equipped with both electron cooling system and stochastic cooling system. During the past couple of years, COSY has been evolved into an ideal test facility for accelerator technology development as well as detector development for the Facility of Anti-proton and Ion Research at Darmstadt (FAIR). In addition, COSY has been the test ground for exploring the feasibility of a storage ring based Electric Dipole Moment (EDM) measurement. The proposed precursor experiment of a direct measurement of the EDM of the deuteron at COSY using an RF wien filter by the Jülich Electric Dipole moment Investigation (JEDI) requests significant improvement of beam based measurements as well as beam control. In this paper, first results of measured linear optics based on AT-LOCO are reported. Simulation studies are also discussed., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

For the planned Electric Dipole Moment (EDM) precursor experiment at the COSY synchrotron and storage ring an accurate control of the beam orbit is crucial. The required beam position measurement accuracy demands an upgrade of the BPM readout electronics. The BPM system currently in operation is described. The required performance and the possible upgrade scenarios are discussed., Proceedings of the 4th International Beam Instrumentation Conference, IBIC2015, Melbourne, Australia

As the last missing step in phase 1 of the beam energy scan (BES-I), aimed at the search for the critical point in the QCD phase diagram, RHIC collided gold ions at a beam energy of 7.3 GeV/nucleon during the FY 2014 run. While this particular energy is close to the nominal RHIC injection energy of 9.8 GeV/nucleon, it is nevertheless challenging because it happens to be close to the AGS transition energy, which makes longitudinal beam dynamics during transfer from the AGS to RHIC difficult. We report on machine performance, obstacles and solutions during the FY 2014 low energy run., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

Future RHIC physics program calls for polarized He3 beam. The He3 beam from the new EBIS source has a relative low rigidity which requires delicate control of injection and RF setup in the Booster. The strong depolarization resonance strength in both AGS and AGS Booster requires careful consideration of beam energy range and optics setup. Recently, the He3 beam was accelerated to 11GeV/n in the AGS. The near term goal fo 3*10¹⁰ at RHIC requires several RF bunch merges in both AGS and the Booster. The beam test results are presented in this paper., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

High energy polarized proton beams are desired for exploring the proton spin structure as well as other spin dependent measurements. However, depolarizing mechanisms due to the interaction between the spin motion and the magnetic fields challenges accelerating polarized protons to high energy in circular accelerators. Several decades of efforts in developing techniques to preserve polarization to high energy have finally led to the success of the polarized proton program at the Brookhaven Relativistic Heavy Ion Collider (RHIC). Designed to provide polarized proton collisions up to 250GeV, RHIC is equipped with two Siberian snakes to avoid both intrinsic and imperfection depolarizing resonances. Currently, polarization has been preserved up to 100 GeV at RHIC with precise control of orbit and betatron tunes. The polarized protons were first brought into collisions at 250GeV in RHIC in 2009, and depolarizations were observed between 100 GeV to 250 GeV. This presentation reports the progress of RHIC polarized proton program. Strategies of how to preserve the polarization through the RHIC injectors are also presented., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

Polarized proton beams are accelerated in RHIC to 250 GeV energy with the help of Siberian Snakes. The pair of Siberian Snakes in each RHIC ring holds the design spin tune at 1/2 to avoid polarization loss during acceleration. However, in the presence of closed orbit errors, the actual spin tune can be shifted from the exact 1/2 value. It leads to corresponding shift of locations of higher-order ("Snake") resonances and limits available betatron tune space. The largest closed orbit effect on the spin tune comes from the horizontal orbit angle between the two snakes. During RHIC Run in 2009 dedicated measurements with polarized proton beams were taken to verify the dependence of the spin tune on the local orbits at the Snakes. The experimental results are presented along with the comparison with analytical predictions., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

We report recent experimental results on linear optics measurements and corrections using ac dipole. In RHIC 2009 run, the concept of the SVD correction algorithm is tested at injection energy for both identifying the artificial gradient errors and correcting it using the trim quadrupoles. The measured phase beatings were reduced by 30% and 40% respectively for two dedicated experiments. In RHIC 2010 run, ac dipole is used to measure β^{*} and chromatic beta function. For the 0.65m β^{*} lattice, we observed a factor of 3 discrepancy between model and measured chromatic function in the yellow ring., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

During the second half of Run-9, the Relativistic Heavy Ion Collider (RHIC) provided polarized proton collisions at two interaction points with both longitudinal and vertical spin direction. Despite an increase in the peak luminosity by up to 40%, the average store luminosity did not increase compared to previous runs. We discuss the luminosity limitations and polarization performance during Run-9., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

Imperfection and vertical intrinsic depolarizing resonances have been overcome by the two partial Siberian snakes in the AGS. The relatively weak but numerous horizontal resonances are the main source of polarization loss in the AGS. A pair of horizontal quads have been used to overcome these weak resonances. This technique needs very accurate jump timing. Fast roll-over magnet cycle has been used and it improves the polarization transmission efficiency near extraction when acceleration usually is slowing down. Emittance preservation is also important to mitigate polarization loss. Recent experimental results including jump quad timing and emittance preservation are presented in this paper., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

The Relativistic Heavy Ion Collider (RHIC) has two main operating modes with heavy ions and polarized protons respectively. In addition to a continuous increase in the bunch intensity in all modes, two major new systems were completed recently mitigating the main luminosity limit and leading to significant performance improvements. For heavy ion operation stochastic cooling mitigates the effects of intrabeam scattering, and for polarized proton operation head-on beam-beam compensation mitigated the beam-beam effect. We present the performance increases with these upgrades for heavy ions and polarized protons, as well as an overview of all operating modes past and planned., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

After running uranium-uranium and copper-gold collisions in 2012, the high energy heavy ion run of the Relativistic Heavy Ion Collider (RHIC) for Fiscal Year 14 (Run14) is back to gold-gold (Au-Au) collisions at 100 GeV/nucleon. Following the level of performance achieved in Run12, RHIC is still looking to push both instantaneous and integrated luminosity goals. To that end, a new 56 MHz superconducting RF cavity was installed and commissioned, designed to keep ions in one RF bucket and improve luminosity by allowing a smaller beta function at the interaction point (IP) due to a reduced hourglass effect. The following presents an overview of these changes and reviews the performance of the collider., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

Commissioning of spin flipper in the RHIC (Relativistic Heavy Ion Collider) Blue ring during the 2009 RHIC polarized proton run showed significant global vertical coherent betatron oscillations induced by a two AC dipole plus four DC dipole configuration. These global orbital coherent oscillations affected collision rates and Yellow beam polarization when beams were in collision. The measured depolarizing strength of of the two AC dipoles at a phase difference of 180 degrees at injection with a different spin tune also confirmed that a single isolated spin resonance can not be induced in the presence of this global vertical coherent betatron oscillation. Hence, a new design was proposed to eliminate the coherent orbital oscillation outside the spin flipper with three additional AC dipoles. This paper presents the new design and supporting numerical simulations. In the RHIC 2010 Au run, only one AC dipole was inserted between the two original AC dipoles; and the measured closure of this AC dipole bump is also presented., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan