Beam Dynamics Newsletter

Electrostatic storage rings operate at very low energies in the keV range and have proven to be invaluable tools for atomic and molecular physics. Because of the mass independence of electric rigidity, these machines are able to store a wide range of different particles, from light ions to heavy singly charged biomolecules, opening up unique research opportunities. However, earlier measurements have shown strong limitations in maximum beam intensity, fast decay of the stored ion current, and reduced beam lifetime. The nature of these effects has not been fully understood and an improved understanding of the physical processes influencing beam motion and stability in such rings is needed. In this paper, a comprehensive study into nonlinear and long-term beam dynamics studies is presented on the examples of a number of existing and planned electrostatic storage rings using the BETACOOL, OPERA-3D, and MAD-X simulation software. A detailed investigation into ion kinetics, under consideration of effects from electron cooling and multiple scattering of the beam on a supersonic gas jet target, is carried out and yields a consistent explanation of the physical effects in a whole class of storage rings. The lifetime, equilibrium momentum spread, and equilibrium lateral spread during collisions with the target are estimated. In addition, the results from experiments at the Test Storage Ring, where a low-intensity beam of ${\mathrm{CF}}^{+}$ ions at $93\text{ }\text{ }\mathrm{keV}/\mathrm{u}$ has been shrunk to extremely small dimensions, are reproduced. Based on these simulations, the conditions for stable ring operation with an extremely low-emittance beam are presented. Finally, results from studies into the interaction of 3--30 keV ions with a gas jet target are summarized.

Nonlinear and long-term beam dynamics in low energy storage rings

The very low momentum spread for small number of particle was reached on different storage rings. When the sudden reduction of the momentum spread ("phase transition") was observed during decreasing of the particle number it was interpreted as ordered state of ion beams. The most extensive study of ordered ion beams was done on storage rings ESR (GSI, Darmstadt) (1) and CRYRING (MSL, Stockholm) (2). Recently, for the first time, the ordered proton beam has been observed on S-LSR (ICR, Kyoto University) (3). This article presents the experimental investigation of low intensity proton beams on COSY (IKP, Juelich) and S-LSR which have the aim to formulate the necessary conditions for the achievement of the ordering state. The experimental studies on S-LSR and numerical simulation with the BETACOOL code (4) were done for the dependence of the momentum spread and transverse emittances on particle number with different misalignments of the magnetic field at the cooler section.

Necessary Condition for Beam Ordering

The ion storage ring, S-LSR has been constructed to study the beam cooling, especially for the physics of the extreme cold ion beam. The magnetic rigidity is 1 Tm and the circumference is 22.557 m. The lattice of the ring was designed to suppress the beam heating as small as possible. The construction was completed in the summer of 2005 and the beam commissioning using 7 MeV protons was started in October, 2005. The electron cooler at S-LSR has an effective cooling length of 0.44 m (2 % of the circumference). The 7 MeV proton beam was successfully cooled in November, 2005. After the improvements and the optimization of the electron cooler, the maximum cooling force of 0.12 eV/m is achieved with the electron energy of 3.8 keV and the electron current of 56 mA. The estimated electron temperature is 25 μeV. Since February, 2006, the one-dimensional ordering experiment of protons has been performed using the electron cooling. The first proton ordering was successfully confirmed in July, 2006. Abrupt drop in the momentum spread and the Schottky noise power have been observed at a proton number of ∼2000 with electron currents of 25 mA, 50 mA and 100 mA. The transition temperatures of the proton ordering are 0.17 meV and 1 meV in the longitudinal and transverse direction, respectively. The transverse proton temperature is much below the transverse electron temperature, which is the result of the magnetized electron cooling. Below the transition, the longitudinal proton temperature is cooled down to 26 μeV, which is close to the longitudinal electron temperature. The transition temperature of the proton ordering is much lower than those of the highly charged heavy ions at ESR because of the weak Coulomb interaction. Nevertheless, the particle reflection model agrees well with the experimental result of the proton ordering. The reflection probability of the proton at the transition is close to those of the heavy ions. It shows that the one-dimensional ordering of the proton occurs by the same mechanism as the highly charged heavy ions. The beam simulations using the molecular dynamics method also agree well with the experimental results.

/pdf/one-dimensional-beam-ordering-of-protons-at-ion-storage-ring-1ftmxrtfnn.pdf

One-dimensional Beam Ordering of Protons at Ion Storage Ring, S-LSR

Investigation of ordered proton beams at S-LSR

This report describes the numerical simulation of the crystalline proton beam formation in COSY using BETACOOL code. The study includes the description of experimental results at NAP‐M storage ring where the large reduction of the momentum spread was observed for first time. The present simulation shows that this behavior of proton beam can not be explained as ordered state of protons. The numerical simulation of crystalline proton beams was done for COSY parameters. The number of protons when the ordering state can be observed is limited by value 106 particles and momentum spread less then 10−6. Experimental results for the attempt to achieve of ordered state of proton beam for COSY is presented. This work is supported by RFBR grant ♯ 05‐02‐16320 and INTAS grant ♯03‐54‐5584.

Studies of Beam Dynamics in Cooler Rings

Recent results of electron cooling of proton beams at COSY-Juelich are reported. Cooling at an electron energy of 70 keV has been studied for the first time. At the injection energy level of COSY, corresponding to 24.5 keV electron energy, the features of the cooled proton beam at extremely low intensities have been investigated in order to find out whether an ordering of the proton beam can be achieved. Such investigations are motivated by the results of a numerical simulation of the ordering process by the BETACOOL code.

New experimental results on electron cooling at cosy

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Studies of Beam Dynamics in Cooler Rings

New experimental results on electron cooling at cosy