P. Suominen

A new plasma potential measurement instrument for plasma ion sources

A very efficient and fast instrument to measure the plasma potential of ion sources has been developed at the Department of Physics, University of Jyvaskyla (JYFL). The operating principle of this novel instrument is to apply a decelerating voltage into a mesh located in the beamline of the ion source. The plasma potential is determined by measuring the current at the grounded electrode situated behind the mesh as a function of the voltage. In this article, we will introduce the instrument and the first results. In the experiments, the instrument was connected to the beamline of the JYFL 6.4 GHz electron cyclotron resonance ion source. The plasma potential was measured with different source conditions and it was observed to vary between 30–65 V. The plasma potential tended to increase as the microwave power, or the gas feed rate, was increased. These results are consistent with earlier observations and estimations. It was also noticed that the value of the plasma potential changed when the negative voltag...

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...

Electron cyclotron resonance ion source related development work for heavy-ion irradiation tests

The European Space Agency (ESA) uses the facilities at the Accelerator Laboratory (Department of Physics, University of Jyvaskyla: JYFL) for heavy-ion irradiation tests of electronic components. Electron cyclotron resonance ion source related development work has been carried out in order to meet the requirements set by the project. During the irradiation tests several beam changes are performed during the day. Therefore, the time needed for the beam changes has to be minimized. As a consequence, a beam cocktail having nearly the same m∕q ratio is used. This makes it possible a quick tuning of the cyclotron to select the required ion for the irradiation. In addition to this requirement, very high charge states for the heavy elements are needed to reach a penetration depth of 100μm in silicon. In this article we present some procedures to optimize the ion source operation. We also present results of the first three-frequency heating tests. The main frequency of 14GHz was fed from a klystron and both second...

Status report of the multipurpose superconducting electron cyclotron resonance ion source

Intense heavy ion beam production with electron cyclotron resonance (ECR) ion sources is a common requirement for many of the accelerators under construction in Europe and elsewhere. An average increase of about one order of magnitude per decade in the performance of ECR ion sources was obtained up to now since the time of pioneering experiment of R. Geller at CEA, Grenoble, and this trend is not deemed to get the saturation at least in the next decade, according to the increased availability of powerful magnets and microwave generators. Electron density above 10(13) cm(-3) and very high current of multiply charged ions are expected with the use of 28 GHz microwave heating and of an adequate plasma trap, with a B-minimum shape, according to the high B mode concept [S. Gammino and G. Ciavola, Plasma Sources Sci. Technol. 5, 19 (1996)]. The MS-ECRIS ion source has been designed following this concept and its construction is underway at GSI, Darmstadt. The project is the result of the cooperation of nine European institutions with the partial funding of EU through the sixth Framework Programme. The contribution of different institutions has permitted to build in 2006-2007 each component at high level of expertise. The description of the major components will be given in the following with a view on the planning of the assembly and commissioning phase to be carried out in fall 2007. An outline of the experiments to be done with the MS-ECRIS source in the next two years will be presented.

Effect of the gas mixing technique on the plasma potential and emittance of the JYFL 14 GHz electron cyclotron resonance ion source

The effect of the gas mixing technique on the plasma potential, energy spread, and emittance of ion beams extracted from the JYFL 14 GHz electron cyclotron resonance ion source has been studied under various gas mixing conditions. The plasma potential and energy spread of the ion beams were studied with a plasma potential instrument developed at the Department of Physics, University of Jyvaskyla (JYFL). With the instrument the effects of the gas mixing on different plasma parameters such as plasma potential and the energy distribution of the ions can be studied. The purpose of this work was to confirm that ion cooling can explain the beneficial effect of the gas mixing on the production of highly charged ion beams. This was done by measuring the ion-beam current as a function of a stopping voltage in conjunction with emittance measurements. It was observed that gas mixing affects the shape of the beam current decay curves measured with low charge-state ion beams indicating that the temperature and∕or the ...

A modified permanent magnet structure for a stronger multipole magnetic field

The performance of the electron cyclotron resonance ion source (ECRIS) increases proportionally to the microwave frequency squared. This behavior encourages the use of higher microwave frequencies. However, a higher frequency would require a stronger magnetic field for the efficient operation of ECRIS. A rather complicated magnetic field configuration results from the combination of solenoids for the axial confinement and a multipolar radial field usually provided by permanent magnets. These fields produce the so-called B-minimum structure which is required for a stable and efficient operation of ECRIS. The highest multipole field achieved so far in an ECR ion source by using permanent magnets is about 1.3 T. This makes the efficient operation at a microwave frequency of about 18 GHz possible. We introduce here a new approach to further increase the magnetic multipole field provided by permanent magnets. According to our two-dimensional (2D) simulations, a remarkable improvement in the radial magnetic fie...

Optimization of the Halbach-type magnetic multipole for an electron cyclotron resonance ion source

An efficient electron cyclotron resonance ion source requires microwave frequency as high as possible. At the same time, the magnetic field has to meet experimentally found rules. The magnetic field configuration required for efficient operation is provided by a combination of solenoid and multipole fields. A so-called Halbach array is used to produce as high a magnetic field as possible using permanent magnets. In this work the above-mentioned structure has been studied in detail in order to maximize the strength of the multipole field. Simulations showed that the so-called offset structure, described in this article, gives stronger fields at magnetic poles. As one result of this work, simple equations were developed to easily calculate the value of the magnetic field for different size hexapolar Halbach structures.

Effect of broadband microwave radiation on the performance of a conventional B-minimum geometry electron cyclotron resonance ion source

The performances of electron cyclotron resonance ion sources can be enhanced by increasing the physical sizes or numbers of resonant zones embedded within their plasma volumes. Broadband rf power offers a simple, cost effective alternative for increasing the sizes of electron cyclotron resonance (ECR) zones in conventional minimum-B geometry sources over independently powered narrow bandwidth, multiple discrete frequency schemes. In this report, the charge-state enhancing effects of broadband microwave radiation are first demonstrated by comparing the high charge states of Ar ion beams produced by powering a conventional minimum-B geometry, 6.4 GHz ECR ion source with broadband microwave radiation {200 MHz [full width at half maximum (FWHM)]} with those produced by conventional bandwidth [∼1.5MHz (FWHM)] radiation. The results of these studies show that high-charge-state beams (e.g., Ar11+) can be enhanced by factors >2 with broadband microwave radiation over those powered with narrow bandwidth radiation ...

Emittance and plasma potential measurements in double-frequency heating mode with the 14GHz electron cyclotron resonance ion source at the university of Jyvýskylý

The performance of electron cyclotron resonance ion sources can be improved through the use of multiple-frequency heating. However, the physical processes leading into enhanced production of highly charged ions are still mainly unknown. This gave us a strong motivation to perform a set of emittance and plasma potential measurements with the 14GHz electron cyclotron resonance ion source at the university of Jyvýskylý to compare the results obtained in single- and double-frequency heating modes. The measurements were performed with different microwave frequencies and combinations of primary and secondary powers. It was observed that both the emittance of different ion beams and the plasma potential decreased in the single-frequency heating mode as the microwave frequency was increased. The emittance of highly charged ion beams and the plasma potential was slightly lower in double-frequency heating mode than in single-frequency mode with the same source settings and total power.

The effects of gas mixing and plasma electrode position on the emittance of an electron cyclotron resonance ion source

Gas mixing is a commonly used method to improve the intensities and the charge state distribution of ion beams extracted from an electron cyclotron resonance ion source (ECRIS). At the same time, the emittance of the ion beam should be as small as possible. In this work we have studied the effect of the gas mixing method on the ion beam quality by measuring the emittance and brightness of different ion beams using helium, oxygen, and argon with several gas feeding ratios. All measurements were performed with the JYFL 6.4 GHz ECRIS. At the second stage of the experiments the emittance and the ion beam brightness were studied as a function of the plasma electrode position. The extraction system constructed for this experiment can be moved online.