Volume 71, Issue 2, February 2000
Index of content:
- PROTON ION SOURCES AND ECR SOURCES (III)
Status and new developments of the high intensity electron cyclotron resonance source light ion continuous wave, and pulsed mode (invited)71(2000); http://dx.doi.org/10.1063/1.1150306View Description Hide Description
The high intensity light ion source (SILHI) is the electron cyclotron resonance (ECR) source constructed and tested at CEA-Saclay. The first aim is to produce up to 100 mA cw proton beams at 95 keV for the proton injection high intensity (IPHI) beams [5 MeV radio frequency quadrupole (RFQ) and 10 MeV drift tube linac (DTL)]. This prototype is developed by a CEA–CNRS-IN2P3 collaboration for applications such as accelerator driven systems for nuclear waste transmutation, production of radioactive ion beams or secondary particles. SILHI is also used to study the production of deuteron and beams for the International Fusion Material Irradiation Facility and European spallation source projects, respectively. The present status of SILHI and the experiments planned for the near future in both cw and pulsed modes are presented in this article. 80 mA cw proton beams are now currently produced at 95 keV with a high availability (∼1 spark/day). The proton fraction is around 90% and the typical rms normalized emittance after transport through a single solenoid low energy beam transport (LEBT) without beam losses is 0.3 πmm mrad. The best beam characteristics are obtained when an ECR zone is created at the frontier between the plasma chamber and the rf ridged transition. Extensive emittance measurements performed with different gas injection in the LEBT have shown a factor of three emittance reduction. Space charge compensation measurements in cw mode will be undertaken with a four-grid analyzer to understand this behavior. Time resolved space charge compensation measurements in pulsed mode are also discussed. The highest total beam current of 120 mA (240 mA/cm2) can be extracted with two ECR zones located at the plasma chamber extremities. Nevertheless a new electrode design must be done for this configuration to avoid excessive beam losses in the extraction system.
71(2000); http://dx.doi.org/10.1063/1.1150307View Description Hide Description
For the International Fusion Materials Irradiation Facility (IFMIF) scenario, a 140 mA deuterium beam in continuous wave (cw) mode with an atomic yield of above 85% is required. The normalized root-mean-square emittance should be less than 0.2 π mm mrad at the entrance of a RFQ. As part of a conceptual design for IFMIF, a new ion source has been developed and is tested at the Institut für Angewandte Physik in Frankfurt. The ion source is of the volume type with a tungsten cathode driving the discharge. Both cw and pulsed mode are possible and were studied. First experiments were carried out with deuterium. 80 mA deuterons with a fraction of above 90% were extracted [A. Maser et al., Rev. Sci. Instrum. 67, 1054 (1996)]. In order to avoid neutron generation by the reaction, hydrogen was used instead of deuterium later on. As far as the ion source and plasma production processes are concerned, the use of hydrogen instead of deuterium is equivalent because of their similar atomic shells. Recently, a 200 mA protonbeam at 55 kV was extracted in cw mode (according to Child–Langmuir, 200 mA corresponds to 140 mA with a fraction of 93%. This article will give a detailed description of the ion source and the essential experimental results. Especially, the influence of important physical parameters (such as discharge current and strength of the filter field) on the fraction was studied. By using different kinds of auxiliary gases, the influence on the fraction and the noise level were investigated, too.
Fundamental aspects of electron cyclotron resonance ion sources: From classical to large superconducting devices (invited)71(2000); http://dx.doi.org/10.1063/1.1150308View Description Hide Description
Electron cyclotron resonanceion sources (ECRIS) of highly charged ions are widely used for many applications. Depending on the application, ECRIS now have to cope with new beam requirements: intense flux of medium charge states and/or very high charge states are demanded by users. In addition, these sources have to be stable and reliable. These requirements lead to large volume/high magnetic fielddevices. Through a discussion of the main parameters of an ECRIS, we deal with the present state of the art of ECRIS in this article. The evolution from “classical” sources to superconducting devices is presented.
Dynamic simulations of the interchange instability, ion production, and electron heating processes in an electron cyclotron resonance ion source plasma71(2000); http://dx.doi.org/10.1063/1.1150309View Description Hide Description
Simulations hitherto performed with electron cyclotron resonance (ECR) ion sources (ECRIS) were mostly to predict physical quantities in their steady states. This article explores the time-dependent phenomena such as: interchange instability, ion production, and electron heating in order to simulate the time variations of hot-electron density, ion-trapping potential well, and core-electron temperature. This study has identified that the oscillations of around 1 Hz observable for these plasma parameters are a consequence of the interchange instability suffered by the hot electrons in the outer radial edge of an ECR shell. A pulsation of the ion-trapping potential well was found to take place under the unstable regime, thereby increasing the extractable ion current whenever the depth of the well is reduced due to the instability-triggered loss of electrons from the confinement. This finding may be exploited as a new method to obtain pulsed ion beams without pulsing the rf power. This article presents a formula for the best operating condition to achieve the highest steady ion beam currents out of an ECRIS. A self-consistent core-electron temperature was also predicted as a function of time.
71(2000); http://dx.doi.org/10.1063/1.1150310View Description Hide Description
The development of a model of electron and ion accumulation and production in the electron-cyclotron resonance (ECR) ion source is presented. Any kind of experimental or analytical electron distribution function can be approximated with a series of Maxwellian distributions with different temperatures and partial weights. A main positive plasma potential with negative potential dip is introduced into consideration. The first test of a new model and code with recent experimental data of the RIKEN 18 GHz ECR source has shown some new opportunities for investigators to study the ECR ion sources.