Charged Ion Beams Research Articles

Transport of intense beams of highly charged ions

The new generation of ion sources delivers beams with intensities of several mA. This requires a careful design of the analysing system and the low-energy beam transport (LEBT) from the source to the subsequent systems. At INFN-LNS, high intensity proton sources (TRIPS [L. Celona, G. Ciavola, S. Gammino et al., Rev. Sci. Instrum. 75(5) 1423 (2004)], PM-TRIPS [G. Ciavola, L. Celona, S. Gammino et al., Rev. Sci. Instrum. 75(5) 1453 (2004)]) as well as ECR ion sources for the production of highly charged high-intensity heavy ion beams are developed (SERSE [S. Gammino, G. Ciavola, L. Celona et al., Rev. Sci. Instrum. 72(11) 4090 (2001), and references therein], GyroSERSE [S. Gammino et al., Rev. Sci. Instrum. 75(5) 1637 (2004)], MS-ECRIS [G. Ciavola et al., (2005), 11th Int. Conf. on Ion Sources, Caen, (in press)]). In this paper, we present ion-optical design studies of various LEBT systems for ion-sources devoted to the production of intense beams. Calculations were performed using the computer codes GIOS [H. Wollnik, J. Brezina and M. Berz, NIM A 258 (1987)], GICO [M. Berz, H.C. Hoffmann, and H. Wollnik, NIM A 258 (1987)], and TRANSPORT [K.L. Brown, F. Rothacker and D.C. Carey, SLAC-R-95-462, Fermilab-Pub-95/069, UC-414 (1995)]. Simulations take into account the expected phase space growth of the beam emittance due to space-charge effects and image aberrations introduced by the magnetic elements.

Application of highly charged Ar ion beams to ion beam lithography

Ion beam lithography (IBL) is a very useful tool for the fabrication of nano-structures. In order to expand the applicability of IBL by using highly charged ions (HCI), Ar1+ and Ar9+ ions were irradiated onto spin-on-glass (SOG) through a stencil mask. The step structure was successfully fabricated on SOG by the chemical etching after the irradiation. The depth of etching of the SOG using the Ar9+ ions increases linearly with dose and was greater than the etching depth obtained using Ar1+ ions. The maximum etching depth of the SOG using Ar9+ ions was larger than the range calculated by the SRIM code. The results show the effectiveness of HCI for IBL and indicate the contribution of the damage created by indirect irradiation processes.

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 Jyväskylä (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 spatial distribution of these ions is affected by the mixing gas. The results obtained in the emittance measurements support the conclusion that the ion temperature changes due to the gas mixing. The effect of the energy spread on the emittance of different ion beams was also studied theoretically. It was observed that the emittance depends considerably on the dispersive matrix elements of the beam line transfer matrix. This effect is due to the fact that the dipole magnet is a dispersive ion optical component. The effect of the energy spread on the measured emittance in the bending plane of the magnet can be several tens of percent.

Transfer of spin polarization in ion-surface scattering

Low-energy ion beams impinging under grazing incidence on surfaces interact inherently with the topmost surface layer(s). The method of electron capture spectroscopy in which the degree of polarization of the light emitted by the neutralized projectiles is analyzed has been used to investigate spin polarization effects at Ni(1 1 0) and Fe(1 1 0) surfaces. The results hint at strong spin filtering mechanisms. With multiply charged instead of singly charged ion beams one may obtain access to short range spin ordering at the surface. Progress in the development of this new, so-called multiple electron capture spectroscopy technique is discussed and first results for He 2+ ions interacting with a Ni(1 1 0) surface are presented.

Images of complex interactions of an intense ion beam with plasma electrons

Ion beam propagation in a background plasma is an important scientific issue for many practical applications. The process of ion beam charge and current neutralization is complex because plasma electrons move in the strong electric and magnetic fields of the beam. Computer simulation images of plasma interaction with an intense ion beam pulse are presented.

Development of a 1-m plasma source for heavy ion beam charge neutralization

Highly ionized plasmas are being employed as a medium for charge neutralizing heavy ion beams in order to focus to a small spot size. Calculations suggest that plasma at a density of 1–100 times the ion beam density and at a length ∼0.1–1 m would be suitable for achieving a high level of charge neutralization. A radio frequency (RF) source was constructed at the Princeton Plasma Physics Laboratory (PPPL) in support of the joint Neutralized Transport Experiment (NTX) at the Lawrence Berkeley National Laboratory (LBNL) to study ion beam neutralization. Pulsing the source enabled operation at pressures ∼10 −6 Torr with plasma densities of 10 11 cm −3. Near 100% ionization was achieved. The plasma was 10 cm in length, but future experiments require a source 1 m long. The RF source does not easily scale to the length. Consequently, large-volume plasma sources based upon ferroelectric ceramics are being considered. These sources have the advantage of being able to increase the length of the plasma and operate at low neutral pressures. The source will utilize the ferroelectric ceramic BaTiO 3 to form metal plasma. A 1 m long section of the drift tube inner surface of NTX will be covered with ceramic. A high voltage (∼1–5 kV) is applied between the drift tube and the front surface of the ceramic by placing a wire grid on the front surface. Plasma densities of 10 12 cm −3 and neutral pressures ∼10 −6 Torr are expected. A test stand to produce 20 cm long plasma is being constructed and will be tested before a 1 m long source is developed.

Development of a low energy Ne atom scattering system for insulator surface strctural analysis

AbstractWe have been developing a low energy Ne atom scattering system combined with a time-of-flight spectrometer for insulator surface structural analysis. Insulator surface structure is difficult to study because of charging effects during electron or ion beam bombardment. Structural analyses of insulator surfaces are very important in fundamental research as well as technology fields. In our system, charged ion beams of 2 keV-Ne+ are converted into neutral beams by charge exchange with the same element gas after the primary beam passes through a chopper. Other features of this system are pulsed beams, time-of-flight measurements, and a micochannel plate (MCP) detector is coaxially mounted along the primary beam. This is a home made equipment. We will show the detection systems, as well.

Quantum Computer Development with Single Ion Implantation

Spins of single donor atoms are attractive candidates for large scale quantum information processing in silicon. Formation of devices with a few qubits is crucial for validation of basic ideas and development of a scalable architecture. We describe our development of a single ion implantation technique for placement of single atoms into device structures. Collimated highly charged ion beams are aligned with a scanning probe microscope. Enhanced secondary electron emission due tohigh ion charge states (e.g., 31P13+, or 126Te33+)allows efficient detection of single ion impacts. Studies of electrical activation of low dose, low energy implants of 31P in silicon show a drastic effect of dopant segregation to the SiO2/Si interface,while Si3N4/Si retards 31P segregation. We discuss resolution limiting factors in ion placement, and process challenges forintegration of single atom arrays with control gates and single electron transistors.

First optical beam profile measurements on an H −-source in Frankfurt

First non-destructive optical beam profile measurements on low-energy negatively charged hydrogen ion beams have been performed in Frankfurt. The measurements were done to test the diagnostics with H −-beams and to study the extraction performance of an existing cesium free low-current volume ion source. For time-resolved beam profile measurements an intensified CCD camera was used. In the paper the ion source will be briefly introduced and the principles of the measurement device as well as the data analysis method will be described in detail. Time-resolved measurements in both transverse planes for different source parameters will be presented and the results will be discussed.

MONO1001: A source for singly charged ions applied to the production of multicharged fullerene beams

The present article reports on a recent study of the production of multiply charged fullerene beams based on an electron cyclotron resonance (ECR) ion source (ECRIS). As collision studies in fundamental physics are demanding intense beams of multiply charged ions of small molecules, clusters, and particularly of fullerenes, we have further developed the ion source ECRIS MONO1000 [P. Jardin et al., Rev. Sci. Instrum. 73, 789 (2002)], originally devoted to produce singly charged ions, towards the production of multiply charged fullerene beams. In this article, the test measurements performed at the Electrostatic Ion Storage Ring Århus rf power (ELISA) facility will be described. Typical mass spectra (from pure C60 and C70 powder) will be shown and the influence of several source parameters (rf power, support gas, gas pressure,…) will be discussed specifying the conditions necessary for an optimum ion source operation.

Microwave plasma source as an ion beam neutralizer

A 13.56 MHz radio-frequency (rf) driven multicusp ion source has been developed at the Fast Neutron Research Facility. An argon ion current density of 29 mA cm−2 can be obtained for argon gas at a pressure of 0.4 Pa, rf power of 500 W and extraction voltage of 3 kV. For such a low energy and high current of several milliampere ion beam, additional low energy electrons are needed to suppress the unwanted beam broadening by the low energy Ar+ ions. This can be achieved by injecting additional electrons into the Ar+-ion beam. An in-waveguide microwave plasma source, operating at a frequency of 2.45 GHz, has been constructed based on the design of Korzec et al. [D. Korzec, A. Muller, and J. Engemann, Rev. Sci. Instrum. 71, 800 (2000)], at Wuppertal. An electron current of up to 250 mA can be extracted from the source, at an absorbed microwave power of 90 W, a pressure of 8×10−2 Pa, and an extraction voltage of 50 V. The neutralization source is installed downstream close to the beam line. By electrostatic interaction the plasma electrons are attracted to the positively charged ion beam forming a beam envelope. To investigate the neutralization effect, the ion extractor is modified to produce a parallel beam. A fluorescent beam profile monitor is used to measure the beam size in both cases; with and without the neutralizer. The profile of the beam can give information about the effect of the neutralizer on the ion beam. The beam current was also measured by using a Faraday cup. Results of the measurements will be presented and discussed.

Numerical simulation multicomponent ion beam transport from ECR ion source

We are developing a multicharged ion beam transport program. The program is dedicated to numerical simulation of the behavior of highly charged ion beam and optimization of beam optics in transport lines and is realized on a PC with Windows user interface of Microsoft Visual Basic. Among all the ions with different charge states in the beam, the exchange of electrons between highly charged ions and low charged ions or neutral atoms of residual gas are taken into account using classical molecular over-barrier model and Monte Carlo method. Therefore, the code is able to describe the changing charge state distribution along the transmission line. The initial charged state distribution of ions may be input from experimental data or calculated from some classical density distribution such as uniform, Gaussian, water bag, or parabolic. The main advantage of the code is the ability to simultaneously simulate a number of ions with different masses and charge states, particularly the decrease of the highly charge ions and the increase of low charged ions due to electron capture. Some simulation results for a transmission line of a highly charged ECR ion source are presented.

Formation of a high intensity low energy positron string

The possibility of a high intensity low energy positron beam production is discussed. The proposed Positron String Trap (PST) is based on the principles and technology of the Electron String Ion Source (ESIS) developed in JINR during the last decade. A linear version of ESIS has been used successfully for the production of intense highly charged ion beams of various elements. Now the Tubular Electron String Ion Source (TESIS) concept is under study and this opens really new promising possibilities in physics and technology. In this report, we discuss the application of the tubular-type trap for the storage of positrons cooled to the cryogenic temperatures of 0.05 meV. It is intended that the positron flux at the energy of 1–5 eV, produced by the external source, is injected into the Tubular Positron Trap which has a similar construction as the TESIS. Then the low energy positrons are captured in the PST Penning trap and are cooled down because of their synchrotron radiation in the strong (5–10 T) applied magnetic field. It is expected that the proposed PST should permit storing and cooling to cryogenic temperature of up to 5×109 positrons. The accumulated cooled positrons can be used further for various physics applications, for example, antihydrogen production.

First operation of ECR ion source at Kochi University of Technology

To study nano-scale manufacturing using highly charged ion beams, a facility to produce and irradiate heavy ion beams has been installed at Kochi University of Technology (KUT). The facility includes an ECR ion source (ECRIS), a beam transport and analysis system, and an irradiation system. The first beam was extracted from ECRIS in January 2003. To evaluate the performance of ECRIS, the measurements of the current and mass spectrum of ion beams as a function of the voltage for the beam extraction and of the rf power have been carried out. It is concluded from the present results that the combined use of the ECRIS and acceleration system with the transport and analysis system build at KUT works normally.

X-ray-induced fluorescence spectroscopy with highly charged ion beam produced by a laser ion source

We designed and tested a beam line for transport of highly charged ions produced by a laser ion source. The ion beam is prepared for an x-ray spectroscopy experiment based on a laser-induced fluorescence spectroscopy. A C4+ beam which has a peak current of 160 μA and bunch width of 500 ns was obtained. It corresponds to 1.3×108 ions/pulse, and the quantity enables the x-ray spectroscopy experiment.

Recent results with the mVINIS ion source

The mVINIS ion source is a part of the TESLA Accelerator Installation, in Belgrade. It is an ECR ion source used as a stand-alone machine delivering multiply charged ion beams to a low energy experimental channel for modification of materials (the L3A channel). In the future, it will be also used as a heavy ion injector for the VINCY Cyclotron. In this article we present the recently introduced hardware and software changes resulting in an improved operation of the mVINIS: the emittance measurement system, the inlet system for precious gases, the improved control system of the microwave generator, a new power supply for the injection stage coil, and the improved program for recording and analysis of the ion beam spectra.

Production of highly charged ion beams with the Grenoble test electron cyclotron resonance ion source (plenary)

Grenoble Test Source (GTS) is a room temperature electron cyclotron resonance ion source whose purpose is to deepen the knowledge of this type of device. GTS was designed according to magnetic scaling laws determined with the SERSE source [Hitz et al., Rev. Sci. Instrum. 73, 509 (2002); Gammino et al., ibid. 72, 4090 (2001)] while keeping enough flexibility in terms of magnetic confinement and rf heating to determine best conditions for the production of intense beams of any charge state. First results were presented 1 year ago [Hitz et al., 8th European Particle Accelerator Conference, 2002; 15th International Workshop on ECR Ion Sources, 2002]. Since then, some improvements have been performed mostly in the magnetic confinement, beam extraction and analysis. Updated ion beam intensities are presented: e.g., 0.5 mA of Ar11+ at 18 GHz, 20 μA of Ar16+ and 1.8 μA of Ar17+ when GTS is operated at 14.5 GHz. On the other hand, charge coupled device imagers have been installed to diagnose and monitor the ion beam and some beam images are shown.

Milling of submicron channels on gold layer using double charged arsenic ion beam

The capability of using a focused ion beam (FIB) for milling of submicron channel structures on a gold layer is investigated. A double-charged arsenic (As2+) FIB is adopted to assess the effect of the dwell time on the final profiles of the milled structures. A single-pass milling, which creates relatively shallow microchannels, is conducted in order to estimate the corresponding milling yields. The condition to provide a uniform ion flux in milling is first studied. The procedure on conducting the milling experiment is then presented. The atomic force microscope (AFM) is applied for measuring the profiles of the milled channels. Based on the AFM measurements, the milling yields have been estimated and compared with the sputtering yields predicted by a more sophisticated numerical simulation. The milling yield for the relatively shallow microchannels presently considered has been discovered to be roughly equal to the predicted normal-incidence sputtering yield. Consistence has also been found as the present findings have been compared with other channel milling studies, which had used different ion beams and target materials. FIB milling has been shown to be an effective tool for making submicron channels in gold layers.

Highly charged ion beams from the Tokyo EBITfor applications to nano-science and -technology

We report present status of a beam line for transportation of highly charged ions(HCIs) extracted from the Tokyo EBIT. We have produced continuous beams of 2.5 × 105 cps forXe44+ through a 1 mm aperture. With slightly high energy operation (electron beam energy: 78keV) of the Tokyo EBIT, we have also obtained 103 ions/pulse for Ta70+ HCIs extracted by apulse mode (trapping time: 3 sec). We are going to apply such HCI beams to nano-processes onsolid surfaces by utilizing some useful characteristics of the HCI-interactions. Future perspectiveof HCI-based nano-science and -technology is presented.

Analytical and Numerical Studies of the Complex Interaction of a Fast Ion Beam Pulse with a Background Plasma

Plasma neutralization of an intense ion beam pulse is of interest for many applications, including plasma lenses, heavy ion fusion, high energy physics, etc. Comprehensive analytical, numerical and experimental studies are underway to investigate the complex interaction of a fast ion beam with a background plasma. The positively charged ion beam attracts plasma electrons, and as a result the plasma electrons have a tendency to neutralize the beam charge and current. A suite of particle-in-cell codes has been developed to study the propagation of an ion beam pulse through the background plasma. For quasi-steady-state propagation of the ion beam pulse, an analytical theory has been developed using the assumption of long charge bunches and conservation of generalized vorticity. The analytical results agree well with the results of the numerical simulations. The visualization of the data obtained in the numerical simulations shows complex collective phenomena during beam entry into and exit from the plasma.