C. E. Hill

Multicharged ion sources for pulsed accelerators (invited)

The relatively low duty cycle of pulsed accelerators can give rise to problems in matching the characteristics of multicharged ion sources to the beam intensity required by the user. Heavy ion physics interests, especially in the heavy ion colliders, demand more and more intensity while the accelerator designers require higher charge states to ease their machine problems. Various options for ion sources for present and future heavy ion accelerators are presented.

Pulsed ECR source in afterglow operation at CERN

A pulsed 14 GHz ECR4 source, adapted to operate in the afterglow mode, was delivered by GANIL to CERN in the framework of the Heavy Ion Facility Project. After four months of operation to commission the facility, it completed its first operational run of nine weeks at the end of 1994, providing lead ions to nuclear physics and ion cooling experiments. A very stable beam, with a useful length of over 1 ms, of 80 eμA of Pb27+ was provided by the source over this period. The operational problems experienced during the commissioning and operation, and the investigations to improve performance for the next experimental physics run are presented.

Experiments on a 14.5 GHz electron cyclotron resonance source

The 14.5 GHz ECR4 source supplied to CERN in the framework of the heavy ion facility collaboration provided Pb27+ operational beams to a new heavy ion linac in 1994. This source, which operates in the pulsed “afterglow” mode, has surpassed its design specification of 80 eμA and now provides currents >120 eμA on an operational basis for this charge state. Early tests showed the existence of extremely stable modes of operation which are fully exploited, and in 1996 the source was operational on a 24 h basis for more than 2400 h. Future operational requirements will benefit from the 10 Hz repetition rate of the source, but will require beam pulse length modulation. In the search for higher intensities a number of experiments were performed on gas composition, rf power matching, extraction, plasma chamber liner, and a biased dynode. The results of these tests will be presented.

Multipurpose superconducting electron cyclotron resonance ion source, the European roadmap to third-generation electron cyclotron resonance ion sources

The major infrastructures of nuclear physics in Europe adopted the technology of electron cyclotron resonance (ECR) ion sources for the production of heavy-ion beams. Most of them use 14GHz electron cyclotron resonance ion sources (ECRISs), except at INFN-LNS, where an 18GHz superconducting ECRIS is in operation. In the past five years it was demonstrated, in the frame of the EU-FP5 RTD project called “Innovative ECRIS,” that further enhancement of the performances requires a higher frequency (28GHz and above) and a higher magnetic field (above 2.2T) for the hexapolar field. Within the EU-FP6 a joint research activity named ISIBHI has been established to build by 2008 two different ion sources, the A-PHOENIX source at LPSC Grenoble, reported in another contribution, and the multipurpose superconducting ECRIS (MS-ECRIS), based on fully superconducting magnets, able to operate in High B mode at a frequency of 28GHz or higher. Such a development represents a significant step compared to existing devices, and...

Modeling of the electron cyclotron resonance sulphur source

A MINIMAFIOS‐type electron cyclotron resonance ion source is being used for S12+ injection into the CERN injector chain for physics experiments at the Super Proton Synchrotron. In this article, charge state distribution spectra obtained from the source are studied and, in addition, the possibility of improving the source performance by various methods is explored.

Studies on ECR4 for the CERN ion program

The CERN heavy ion community, and some other high energy physics experiments, are starting to demand other ions, both heavy and light, in addition to the traditional lead ions. Studies of the behavior of the afterglow for different operation modes of the ECR4 at CERN have been continued to try to understand the differences between pulsed afterglow and continuous operation, and their effect on ion yield and beam reproducibility. The progress in adapting the source and ion beam characteristics to meet the new demands will be presented, as will new information on voltage holding problems in the extraction.

GTS‐LHC: A New Source For The LHC Ion Injector Chain

The ion injector chain for the LHC has to be adapted and modified to reach the design beam parameters. Up to now an ECR4 delivered the ion beam for the SPS fixed target physics programme. This source will be replaced by a higher intensity source to produce the Pb27+ ion current required to fill the Low Energy Ion Ring (LEIR). The new ion source will be based on the Grenoble Test Source which was itself based on empirical scaling laws derived from the Framework 5 “Innovative ECRIS” collaboration. This paper will describe the design principle, the commissioning timetable and the present status of the source development.

Effect of a biased probe on the afterglow operation of an ECR4 ion source

Various experiments have been performed on a 14.5 GHz ECR4 in order to improve the ion yield. The source runs in pulsed afterglow mode, and provides currents ∼120 eμA of Pb27+ to the CERN Heavy Ion Facility on an operational basis. In the search for higher beam intensities, the effects of a pulsed biased disk on axis at the injection side were investigated with different pulse timing and voltage settings. No proof for absolute higher intensities was seen for any of these modifications. However, the yield from a poorly tuned/low-performing source could be improved and the extracted pulse was less noisy with bias voltage applied. The fast response on the bias implies that increases/decreases are not due to ionization processes. A good tune for high yield of high charge states during the afterglow coincides with a high plasma potential.

H- source developments at CERN

Future CERN programs for the large hadron collider (LHC) and the isotope online separator (ISOLDE) require increasing the beam intensity and brightness from the proton synchrotron booster (PSB). This could be achieved by charge-exchange injection with phase-space painting into the PSB acceptance from a higher energy H− linac. A new injector will require a high performance, high reliability, negative hydrogen-ion source. This article will present the results achieved so far with a prototype microwave-driven source operated with three different magnetic structures (multicusp, solenoidal, and a combination of both). The experiments were carried out with different mixing gases, different chamber inserts, and under a wide range of operational conditions.

CHARACTERISATION AND PERFORMANCE OF THE CERN ECR4 ION SOURCE

To optimise the heavy ion injector for the LHC, a good knowledge of the parameters of the ECR4 ion source and the beam transport in the Low Energy Beam Transport (LEBT) for a lead ion beam is necessary. Results of the emittance measurements of the full beam (O + Pb) leaving the source using a scanning slit and profile monitor will be presented. Furthermore, the emittance of a single charge state after the source has been measured using a solenoid scan coupled to a guillotine and spectrometer. The results for last year’s operation for the SPS fixed target physics with indium will also be presented.