LEIR: TOWARDS THE NOMINAL LEAD ION BEAM
M. ChanelV. BaggioliniP. BelochitskiiA. BlasJ. BorburghChristian CarliKarel CornelisT. FowlerM. Gourber-PaceS. HancockM. HouricanD. KüchlerE. MahnerD. ManglunkiS. MauryM. PaoluzziSergio PasinelliJ. PasternakU. RaichF. RoncaroloC. RossiM. RoyerR. ScrivensL. SermeusG. TranquilleM. Vretenar
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The Low Energy Ion Ring (LEIR) is a central piece for LHC ion operation at CERN, transforming long Linac3 pulses into high density bunches needed for LHC. The first phase of LEIR commissioning successfully attained its goal of providing the so-called “early ion beam” (one bunch of 2.25 10 8 Lead ions) needed for the first LHC ion runs with reduced luminosity. Studies in view of generating the beam needed for nominal ion operation (2 bunches of 4.5 10 8 ions in LEIR) were carried out in parallel with the setting-up of the early beam in the accelerators further downstream in the LHC injector chain. The main characteristics of the machine using a new state of the art electron cooler are discussed together with the latest results.Keywords:
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The Low Energy Ion Ring (LEIR) is central to the “Ions for LHC” project. Its role is to transform a serie of long low intensity ion pulses from Linac 3, into short high density pulses, which will be further accelerated in the PS and SPS rings, before injection into LHC. To do so the injected pulses are stacked and phase space cooled using electron cooling, before acceleration to the ejection energy of 72 MEV/u. This note describes different types of instruments which will be installed in the LEIR ring and transfer lines.
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Electron cooling
Low energy
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The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory is beginning its second year of operation. A cesium sputter ion source injecting into a tandem Van de Graaff provides the gold ions for RHIC. The ion source is operated in the pulsed beam mode and produces a 500-μs-long pulse of Au− with a peak intensity of 290 μA at the entrance of the tandem. After acceleration in the tandem and post-stripping, this results in a beam of Au+32 with an intensity of 80 μA and an energy of 182 MeV. Over the last several years, a series of improvements have been made to increase the intensity of the pulsed beam from the ion source. Details of the source performance and improvements will be presented. In addition, an effort is under way to provide other beam species for RHIC collisions.
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The Low Energy Ion Ring (LEIR) transforms long pulses from Linac 3 into high brilliance ion bunches for LHC by means of multi-turn injection, electron cooling and accumulation. The LEIR injection comprises a magnetic DC septum followed by an inclined electrostatic septum. The electrostatic septum has been newly designed and built. The magnetic septum is mainly recovered from the former LEAR machine, but required a new vacuum chamber. Dynamic vacua in the 10 -12 mbar range are required, which are hard to achieve due to the high desorption rate of ions lost on the surface. A new interlock and displacement control system has also been developed. The major technical challenges to meet the magnetic, electrical and vacuum requirements will be discussed.
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The new CERN Heavy-Ion Accelerating Facility implies besides a new linac also important modifications of existing accelerators. They are imposed by the low speed and the low intensity of the ion beam and, crucially at low energy, by the short lifetime of the partially stripped ions due to charge exchange with the atoms of the residual gas. Once the optimum charge state (Pb/sup 53+/) and energy of the injector (4.2 MeV/u) had been chosen, the operational pulse-to-pulse variability (PPM) of particle species and intensities in the PS and its four-ring Booster (PSB) dictate the main beam parameters.
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With the advent of heavy ion colliders, such as RHIC at BNL and LHC at CERN, the demand for high charge state ion beam intensities was raised by more than an order of magnitude compared to fixed target operation of existing accelerators.(1) RHIC, for example, requires 3.4x10 9 gold 32+ particles per ion source pulse, or about 85 nC total positive charge yield, assu ming a 20% abundance of the selected charge state in the ion source beam. An EBIS is capable of producing the required ion intensities in beams of a low emittance and pulses as short as 10 µs, which is quite advantageous for colliders. However, for the colliders, the EBIS requires electron beam currents on the order of 10 A, about 20 times higher than electron beams utilized in devices at acceler ators at Dubna, Saclay, and Stockholm for fixed target and low intensity atomic physics experiments. At BNL, we have constructed a test EBIS, which is now operating at 10 A, the full electron beam power required for RHIC. Electron and ion beam currents in our test EBIS have exceeded values obtained with previous EBIS devices by more than an order of magnitude, in a stable and quiet mode of operation. For operation with gold, ion spectra with dominant charge state of 34+ have been observed; and, even with only half the trap length required by RHIC, 55 nC ion pulses have been obtained at the source exit after a confinement time of only 30 ms. Simple scaling to RHIC requirements now seems well in hand. In addition, with reasonable extrapolations of several parameters of the RHIC EBIS, one should be able to produce Pb 54+ ions with an intensity which could be of interest for the LHC at CERN. This would eliminate stripping, accumulation, and electron cooling stages from the present LHC injection scheme, which uses an ECR ion source.
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Electron cooling
Accumulator (cryptography)
Low energy
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A heavy ion fusion driver must be capable of accelerating an intense ion beam to GeV beam energies. The final beam pulse current can be as high as a few kA using beam compression in an induction linac. Combining beamlets at low energy may prove to be economical as long as there is no significant emittance growth. Focusing of the final beam pulse from the reactor chamber wall to the target can be enhanced by using a plasma channel to guide the ion beam. Experiments at LBNL on ion sources, injector, the combiner and plasma channel focusing are discussed. One possible way to reduce the cost of a driver is to use an induction recirculator. Experiments at LLNL are exploring this concept by studying the transport and bending of space-charge-dominated ion beams. At the Univ. of Maryland the behavior of space-charge dominated beams is being simulated with low-energy electrons. They studied emittance growth, halo formation and beam pulse compression.
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After the successful experiments of beam accumulation and stochastic cooling at TARN‐1 ring, it was decided to construct the more powerful heavy ion ring TARN‐2 which has the maximum rigidity of 7 T‐m, corresponding to 1.3 GeV for proton and 0.45 GeV/u for ions of 1/2 charge‐to‐mass ratio. In this ring both the stochastic and the electron beam cooling methods are prepared to obtain the high resolution and small emittance beam. Especially the electron beam cooling has the advantage of low energy heavy ion beam cooling, and then the maximum e‐beam energy 120 keV, corresponding to the 200 MeV/u of ion energy, was selected. At present the injector is the sector focusing cyclotron with K–67 which accelerates ion beams from protons to neon for TARN 2. In parallel with the construction of TARN 2, the heavy ion linac is now being constructed. The first part of the linac is an RFQ with the energy of 800 keV/u which was successfully tested with proton beam acceleration. After boosting up the ion energy to 5 MeV/u by the drift tube linac, this system will take the place of injector for TARN 2. In this case the heavy ions up to Xe will be accelerated and cooled in the ring. In this paper, the status of TARN 2 including the linac system will be presented as well as the possibility of its application to HIF experiments.
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Studies of the beam extraction system of the GTS-LHC electron cyclotron resonance ion source at CERN
The 14.5 GHz GTS-LHC Electron Cyclotron Resonance Ion Source (ECRIS) provides multiply charged heavy ion beams for the CERN experimental program. The GTS-LHC beam formation has been studied extensively with lead, argon, and xenon beams with varied beam extraction conditions using the ion optical code IBSimu. The simulation model predicts self-consistently the formation of triangular and hollow beam structures which are often associated with ECRIS ion beams, as well as beam loss patterns which match the observed beam induced markings in the extraction region. These studies provide a better understanding of the properties of the extracted beams and a way to diagnose the extraction system performance and limitations, which is otherwise challenging due to the lack of direct diagnostics in this region and the limited availability of the ion source for development work.
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Highly charged ion
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The driver linac of RAON heavy ion accelerator based on the superconducting technology, which consists of a 28 GHz ECR ion source, a low energy beam transport line, a RFQ accelerator, a medium energy beam transport line, a low energy linac(SCL1), a charge stripping section and a high energy linac(SCL2), will produce the stable ion beam from proton with 600 MeV to uranium with 200 MeV/u. Many beam dynamics issues such as beam steering effect due to QWR cavities with the peak electric field of 35 MV/m, emittance growth in charge stripper due to the straggling effect, parametric resonance and envelope instability were investigated to design the high power heavy ion machine which can produce the high quality beam. In this presentation, we present our study results for achieving longitudinal acceptance larger than 27 keV/u-ns for the stable operation and minimizing the emittance growth less than 30 % in the superconducting linac for high quality beam at the in-flight target.
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