Takeshi Katayama

SPARC experiments at the high-energy storage ring

The physics program of the SPARC collaboration at the Facility for Antiproton and Ion Research (FAIR) focuses on the study of collision phenomena in strong and even extreme electromagnetic fields and on the fundamental interactions between electrons and heavy nuclei up to bare uranium. Here we give a short overview on the challenging physics opportunities of the high-energy storage ring at FAIR for future experiments with heavy-ion beams at relativistic energies with particular emphasis on the basic beam properties to be expected.

Antiproton chain of the FAIR storage rings

In the Modularized Start Version of the Facility of Antiproton and Ion Research (FAIR) at Darmstadt Germany, the 3 GeV antiprotons are precooled in the collector ring and accumulated in the high energy storage ring (HESR). They are further accelerated to 14 GeV or decelerated to 1 GeV for the experiments with a high-density internal target. The powerful beam cooling devices, stochastic cooling and electron cooling will support the provision of a high-resolution antiproton beam. The other option of FAIR is to prepare the low energy, 300 keV antiproton beam connecting the existing storage rings ESR and CRYRING with HESR. Beam physics issues related with these concepts are described.

First Experiences with HESR Stochastic Cooling System

The stochastic cooling system of the HESR (High Energy Storage Ring) is based on completely new structures especially designed for the HESR. Each beam surrounding slot of these so called slot-ring couplers covers the whole image current without a reduction of the HESR aperture and without any plunging system. One pickup (PU) and one kicker (K) system have been already fabricated and installed into the COSY ring to demonstrate stochastic cooling in all three dimensions with only one structure. First results of commissioning with proton beams will be presented. The longitudinal cooling system at HESR is based on filter cooling with an optical notchfilter and ToF cooling. The demanding accuracy concerning phase stability requires dedicated control of the notchfrequency. The optical COSY filter has been modified and can be proven in long term runs together with the new stochastic cooling system. STOCHASTIC COOLING SYSTEM OF HESR Stochastic cooling at HESR is not only used to reduce beam size and momentum spread during the experiment, but also to accumulate antiprotons due to the postponed Recuperated Experimental Storage Ring (RESR) [1, 2] of the modularized start version of the FAIR project. Figure 1: Stacks of slot ring couplers with and without 16:1 combiner-boards and two stacks mounted together including 2:1 combiner with heat-trap. The system is based on dedicated structures. Each beam-surrounding slot of these so called slot-ring couplers covers the whole image current without a reduction of the HESR aperture [3]. Each resonant ring structure is heavily loaded with eight 50 Ω electrodes for a broadband operation. The rings are screwed together to a selfsupporting structure in stacks of 16 rings. Four of these stacks will build the spindle for one tank. Fig. 1 shows these stacks; one without combiner one with combinerboard and a combination of two stacks including additional 2:1 combiner especially designed to minimize the heat flow to the 16:1 combiners. Basic parameters of the main 2 4 GHz system are summarized in Table 1. Table 1: Parameters of the Main Stochastic Cooling System Main system Based on slot-ring couplers Bandwidth 2 4 GHz Cooling methods transverse, longitudinal filter cooling, longitudinal ToF cooling β-range 0.83-0.99 Pickup: 2 tanks No. of rings /tank 64 Shunt impedance Zpu / ring 9 Ohm Total impedance 1152 Ohm Structure temp. 20 K Kicker: 3 tanks 2 tanks for transverse or longitudinal cooling, 1 tank longitudinal cooling only No. of rings /tank 64 Shunt impedance Zk / ring 36 Ohm Impedance /tank 2304 Ohm Installed power/tank 640 (longitudinal cooling) 320 (transverse cooling) W W The same system will be used to cool also heavy ions. Extensive simulations have shown that gain and installed RF-power are sufficient to cool 1*10 heavy ions (limited due to radiation safety) above 740 MeV/u [4].

Stochastic Cooling System for HESR - Theoretical and Simulation Studies

The High-Energy Storage Ring (HESR) is part of the upcoming International Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt. The HESR dedicates to the field of high-energy antiproton physics to explore the research areas of charmonium spectroscopy, hadronic structure, and quark-gluon dynamics with highquality beams over a broad momentum range from 1.5 to 15 GeV/c. High momentum resolution beams are mandatory for internal target experiments which are prepared with the well-established filter method in stochastic momentum cooling. This cooling technique will also be applied for antiproton accumulation in the HESR as well as in heavy ion beam cooling experiments with internal targets. Fast beam cooling is achieved with a (2 – 4) GHz system. In cases when the momentum spread exceeds the filter cooling acceptance the Time-Of-Flight (TOF) method, which is easily set up when filter cooling is already available, is applied to pre-cool the beam prior to filter cooling. To compare both cooling methods the basics of the theory is presented. Beam experiments at COSY are outlined to verify these aspects of the cooling theory.

Stochastic Cooling Experiments at Nuclotron and Application to NICA Collider

Stochastic cooling is obligatory for the NICA accelerator facility that is presently under development at JINR, Russia. Cooling will work with the high-intensity bunched beams in the 3-4.5 GeV energy range; all three dimensions will be treated simultaneously. The preparatory experimental work on stochastic cooling is carried out at accelerator Nuclotron (JINR) since 2010. During this work hardware solutions and automation techniques for system adjustment have been worked out and tested. Based on the gained experience the overall design of the NICA stochastic cooling system was also developed. The report describes the results of cooling experiments at Nuclotron, the developed adjustment automation techniques and presents the design of the NICA stochastic cooling system.

Heavy ion storage and acceleration in the HESR with stochastic cooling and internal target

Heavy ion stochastic momentum cooling is investigated under the constraint of the present concept of the high energy storage ring (HESR). A bare uranium beam is injected from the collector ring into the HESR at 740 MeV u−1 and a beam preparation for an internal target experiment is outlined. Further the acceleration of the ion beam to 4.5 GeV u−1 is considered and an internal target experiment is studied. The simulations include the beam-target interaction involved with a hydrogen target. The capability of momentum filter cooling is envisaged and the possibility of time-of-flight momentum cooling is examined at lower energies where the revolution harmonics begin to overlap.

Application of ion beam cooling in the NICA accelerator complex. Experimental study of stochastic cooling at Nuclotron, JINR (Dubna)

The project of Nuclotron-based Ion Collider fAcility NICA/MPD (MultiPurpose Detector) is under development at JINR (Dubna) now. The general goals of the project are providing of colliding beams for experimental studies of both hot and dense strongly interacting baryonic matter and spin physics (in collisions of polarized protons and deuterons).