Charged Ion Beams Research Articles

Short-pulse ECR: A source of multiply charged ions

Extensive investigation is now under way in CERN (European Organization for Nuclear Research) in the framework of the Beta Beam project with the aim of gaining insight into neutrino oscillations. It is suggested that the decay of 6He nuclei produce neutrino beams accelerated to an energy on the order of 100 GeV/nucleon. To this end, it is necessary to generate short-pulse (30–100 μs) beams of multiply charged ions of this isotope. Conventional ECR-based ion sources seem to be inappropriate for this purpose, since the plasma density grows slowly (for more than a millisecond) in this case compared with the desired pulse duration. A design concept of a short-pulse ECR-based source of multiply charged ions is proposed. In experiments with pumping at frequencies of 37.5 and 75.0 GHz, pulses as short as ∼50 μs were obtained. Good agreement between theory and experiments is demonstrated.

Simulation of the passage of multiply charged ions through crystals

The effect of charge exchange processes on the angular distributions of quasi-isotropic beams of multiply charged ions passed through oriented crystals has been numerically simulated and the recently found effects of cooling and heating of the ion beams have been interpreted.

Generation of a high-current beam of multiply charged ions from a dense plasma produced by high-power millimeter-wave gyrotron radiation under ECR conditions

Experimental data for generating intense beams of multiply charged heavy gas ions are reported. The beams are extracted from the dense plasma of an ECR discharge with quasi-gasdynamic confinement provided by the powerful microwave radiation of a gyrotron in a magnetic trap. The axisymmetric magnetic trap makes it possible to extract uniform (in transverse coordinates) plasma fluxes from it, and the use of a multiple-aperture extraction system makes it possible to increase the beam current by more than an order of magnitude compared with the ECP sources currently available. Multiply charged nitrogen ion beams with a current of 150 mA and a normalized emittance of 0.9π mm mrad are obtained.

Production of highly charged ion beams Kr32+, Xe44+, Au54+ with Electron String Ion Source (ESIS) Krion-2 and corresponding basic and applied studies

Electron String Ion Source (ESIS) Krion-2 (JINR, Dubna) was used for basic and applied research in various aspects of multiply charged heavy ions production. Energy recuperation mode in ESIS has been proofed first and used for production of highly charged ions 84Kr28+÷84Kr32+, 124Xe40÷124Xe44 and Au51+÷ Au54+. Krion-2 ESIS was mounted on high voltage (HV) platform of LU-20 Linac and used as an injector of highly charged ions during Nuclotron run N° 41. Krion-2 ESIS has produced 3.0·107 124Xe42+ ions per pulse of 7 μs duration. This ion beam was injected into LU-20 and Nuclotron, accelerated up to energy of 186 GeV and the extracted Xe beam was used for physics experiments. Electron String Ion Source Krion-2 demonstrated the high reliability and stability running during 30 days on HV platform. We believe that it is due to an extremely low electron beam power, provided by using the electron string mode of operation: 50 W pulse power and about 10 W average power. Other possible application of ESIS could be its use in injection complexes of synchrotrons and cyclotrons for cancer therapy. Slow and fast extraction of C4+ and C6+ beams from Krion-2 ESIS were preliminary studied towards ESIS optimization for medical accelerators requirements.

Global plasma simulation of charge state distribution inside a 2.45 GHz ECR plasma with experimental verification

For the first time, the charge state distribution inside the MEsskammer für FlugzeitInStrumente und Time-Of-Flight (MEFISTO) electron cyclotron resonance (ECR) plasma and in the extracted ion beam was successfully simulated. A self-consistent ECR plasma ionization model (Hohl M 2002 MEFISTO II: Design, setup, characterization and operation of an improved calibration facility for solar plasma instrumentation PhD Thesis University of Bern) was further developed, recomputing the ion confinement time for every ion species and in every time step based on the actual plasma potential rather than using a prescribed constant ion confinement time. The simulation starts with a user defined set of initial conditions and develops the problem in time space by an adaptive step length fourth order Runge–Kutta (RK4) solver, considering particle densities based on ionization rates, recombination rates, ion confinement times and plasma potential. At the simulation end, a steady-state ion charge state distribution is reached, which is in excellent agreement with the measured ion beam charge state distribution of the MEFISTO ion source for Ar1+ to Ar5+ and in good agreement for Ar6+.

EBIS charge breeder for radioactive ion beams at ATLAS

The construction of the Californium Rare Isotope Breeder Upgrade (CARIBU) for the Argonne National Laboratory ATLAS facility is completed and its commissioning is being performed. In its full capacity, the CARIBU facility will use fission fragments from a 1 Curie (Ci) 252Cf source. The ions will be thermalized and collected into a low-energy ion beam by a helium gas catcher, mass analyzed by an isobar separator, and charge bred to higher charge states for acceleration in ATLAS. To reach energies E/A 10 MeV/u, one should inject ions with charge-to-mass ratio (q/A) ⩾ 1/7 into the ATLAS linac. In the first stage, the existing Electron Cyclotron Resonance (ECR) ion source will be used as a charge breeder. The maximum intensity of radioactive ion beams at the output of the gas catcher will not exceed 107 ions per second. A charge breeder based on an Electron Beam Ion Source (EBIS) has significant advantages over the ECR option for ion beam intensities up to about 109 ions per second, providing 3-4 times higher efficiency and significantly better purity of highly charged radioactive ion beams for further acceleration. The proposed EBIS project for CARIBU will heavily utilize state-of-the-art EBIS technology recently developed at Brookhaven National Laboratory. This will allow us to reduce both the project cost and timescale, simultaneously insuring reliable technical realization of the cutting-edge technology. Several parameters of the CARIBU EBIS charge breeder (EBIS-CB) will be relaxed with respect to the BNL EBIS in favor of higher reliability and lower cost. Technical performance of the CARIBU charge breeder will not suffer from such a relaxation and will provide high efficiency for a whole range of radioactive ion beams. The goal of this paper is to present the initial design of the EBIS charge breeder for radioactive ion beams at ATLAS.

Some Superconducting Magnets at IMP

Some superconducting magnets research at IMP (Institute of Modern Physics, CAS, Lanzhou) will be described in this paper. Firstly, a superconducting electron cyclotron resonance ion source (SECRAL) was successfully built to produce intense beams of highly charged heavy ions for Heavy Ion Research Facility in Lanzhou (HIRFL). An innovation design of SECRAL is that the three axial solenoid coils are located inside of a sextupole bore in order to reduce the interaction forces between the sextupole coils and the solenoid coils. For 28 GHz operation, the magnet assembly can produce peak mirror fields on axis of 3.6 T at injection, 2.2 T at extraction, and a radial sextupole field of 2.0 T at plasma chamber wall. Some excellent results of ion beam intensity have been produced and SECRAL has been put into operation to provide highly charged ion beams for HIRFL since May 2007. Secondly, a super-ferric dipole prototype of FAIR Super-FRS is being built by FCG (FAIR China Group) in cooperation with GSI. Its superconducting coils and cryostat is made and tested in the Institute of Plasma Physics (IPP, Hefei), and it more 50 tons laminated yoke was made in IMP. This super-ferric dipole static magnetic field was measured in IMP, it reach to the design requirement, ramping field and other tests will be done in the future. Thirdly, a 3 T superconducting homogenous magnetic field solenoid with a ¿70 mm warm bore has been developed to calibrate Hall sensor, some testing results is reported. And a penning trap system called LPT (Lanzhou Penning Trap) is now being developed for precise mass measurements.

Production of highly charged ion beams with SECRAL

Superconducting electron cyclotron resonance ion source with advanced design in Lanzhou (SECRAL) is an all-superconducting-magnet electron cyclotron resonance ion source (ECRIS) for the production of intense highly charged ion beams to meet the requirements of the Heavy Ion Research Facility in Lanzhou (HIRFL). To further enhance the performance of SECRAL, an aluminum chamber has been installed inside a 1.5 mm thick Ta liner used for the reduction of x-ray irradiation at the high voltage insulator. With double-frequency (18+14.5 GHz) heating and at maximum total microwave power of 2.0 kW, SECRAL has successfully produced quite a few very highly charged Xe ion beams, such as 10 e microA of Xe(37+), 1 e microA of Xe(43+), and 0.16 e microA of Ne-like Xe(44+). To further explore the capability of the SECRAL in the production of highly charged heavy metal ion beams, a first test run on bismuth has been carried out recently. The main goal is to produce an intense Bi(31+) beam for HIRFL accelerator and to have a feel how well the SECRAL can do in the production of very highly charged Bi beams. During the test, though at microwave power less than 3 kW, more than 150 e microA of Bi(31+), 22 e microA of Bi(41+), and 1.5 e microA of Bi(50+) have been produced. All of these results have again demonstrated the great capability of the SECRAL source. This article will present the detailed results and brief discussions to the production of highly charged ion beams with SECRAL.

New development of advanced superconducting electron cyclotron resonance ion source SECRAL (invited)

Superconducting electron cyclotron resonance ion source with advance design in Lanzhou (SECRAL) is an 18-28 GHz fully superconducting electron cyclotron resonance (ECR) ion source dedicated for highly charged heavy ion beam production. SECRAL, with an innovative superconducting magnet structure of solenoid-inside-sextupole and at lower frequency and lower rf power operation, may open a new way for developing compact and reliable high performance superconducting ECR ion source. One of the recent highlights achieved at SECRAL is that some new record beam currents for very high charge states were produced by 18 GHz or 18+14.5 GHz double frequency heating, such as 1 e microA of (129)Xe(43+), 22 e microA of (209)Bi(41+), and 1.5 e microA of (209)Bi(50+). To further enhance the performance of SECRAL, a 24 GHz/7 kW gyrotron microwave generator was installed and SECRAL was tested at 24 GHz. Some promising and exciting results at 24 GHz with new record highly charged ion beam intensities were produced, such as 455 e microA of (129)Xe(27+) and 152 e microA of (129)Xe(30+), although the commissioning time was limited within 3-4 weeks and rf power only 3-4 kW. Bremsstrahlung measurements at 24 GHz show that x-ray is much stronger with higher rf frequency, higher rf power. and higher minimum mirror magnetic field (minimum B). Preliminary emittance measurements indicate that SECRAL emittance at 24 GHz is slightly higher that at 18 GHz. SECRAL has been put into routine operation at 18 GHz for heavy ion research facility in Lanzhou (HIRFL) accelerator complex since May 2007. The total operation beam time from SECRAL for HIRFL accelerator has been more than 2000 h, and (129)Xe(27+), (78)Kr(19+), (209)Bi(31+), and (58)Ni(19+) beams were delivered. All of these new developments, the latest results, and long-term operation for the accelerator have again demonstrated that SECRAL is one of the best in the performance of ECR ion source for highly charged heavy ion beam production. Finally the future development of SECRAL will be presented.

First results from the new RIKEN superconducting electron cyclotron resonance ion source (invited)

The next generation heavy ion accelerator facility, such as the RIKEN radio isotope (RI) beam factory, requires an intense beam of high charged heavy ions. In the past decade, performance of the electron cyclotron resonance (ECR) ion sources has been dramatically improved with increasing the magnetic field and rf frequency to enhance the density and confinement time of plasma. Furthermore, the effects of the key parameters (magnetic field configuration, gas pressure, etc.) on the ECR plasma have been revealed. Such basic studies give us how to optimize the ion source structure. Based on these studies and modern superconducting (SC) technology, we successfully constructed the new 28 GHz SC-ECRIS, which has a flexible magnetic field configuration to enlarge the ECR zone and to optimize the field gradient at ECR point. Using it, we investigated the effect of ECR zone size, magnetic field configuration, and biased disk on the beam intensity of the highly charged heavy ions with 18 GHz microwaves. In this article, we present the structure of the ion source and first experimental results with 18 GHz microwave in detail.

Bio-Nano ECRIS: An electron cyclotron resonance ion source for new materials production

We developed an electron cyclotron resonance ion source (ECRIS) for new materials production on nanoscale. Our main target is the endohedral fullerenes, which have potential in medical care, biotechnology, and nanotechnology. In particular, iron-encapsulated fullerene can be applied as a contrast material for magnetic resonance imaging or microwave heat therapy. Thus, our new ECRIS is named the Bio-Nano ECRIS. In this article, the recent progress of the development of the Bio-Nano ECRIS is reported: (i) iron ion beam production using induction heating oven and (ii) optimization of singly charged C(60) ion beam production.

Study of ion beam extraction and transport from an electron cyclotron resonance ion source

We have started an experimental and theoretical program to better understand the extraction and transport of intense multiply charged ion beams from an electron cyclotron resonance ion source (ECRIS). In this paper we present the first results of this program concerning a simple, monocomponent He(+) beam extracted from an ECRIS. We have calculated the ion trajectories starting from the ECRIS plasma electrode up to the image plane of the analyzing magnet taking into account space-charge effects and fringe fields. The initial phase-space distribution of the He(+) beam at the extraction aperture has been calculated with a particle-in-cell code. To check the simulations we have measured beam profiles with a viewing screen both before and after the analyzing magnet. In addition also measurements with a pepperpot emittance meter located behind the analyzing magnet have been performed. We find good agreement between these measurements and simulations showing that (i) there is a significant compensation of the space charge and that (ii) our analyzing magnet causes a severe increase in effective beam emittance.

Effect of electron cyclotron resonance ion source frequency tuning on ion beam intensity and quality at Department of Physics, University of Jyväskylä

Ion beam intensity and quality have a crucial effect on the operation efficiency of the accelerator facilities. This paper presents the investigations on the ion beam intensity and quality after the mass separation performed with the Department of Physics, University of Jyväskylä 14 GHz electron cyclotron resonance ion source by sweeping the microwave in the 14.05-14.13 GHz range. In many cases a clear variation in the ion beam intensity and quality as a function of the frequency was observed. The effect of frequency tuning increased with the charge state. In addition, clear changes in the beam structure seen with the beam viewer were observed. The results confirmed that frequency tuning can have a remarkable effect on ion beam intensity and quality especially in the case of highly charged ion beams. The examples presented here represent the typical charge state behavior observed during the measurements.

Laser plasma in a magnetic field

Laser ion source (LIS) is a candidate among various heavy ion sources. A high density plasma produced by Nd:yttrium aluminum garnet laser with drift velocity realizes high current and high charge state ion beams. In order to obtain higher beam current, we made experiments using the LIS with a magnetic field by which a confinement effect can make higher beam current. We measured total current by Faraday cup and analyzed charge distribution by electrostatic ion analyzer. It is shown that the ion beam charge state is higher by a permanent magnet.

Acceleration of Macroscopic Particle to Hypervelocity by High-Intensity Beams

Hypervelocity (~1000-km/s) impact of a macroscopic particle (macron) has profound influences in high energy density physics and inertial fusion energy researches. As the charge-mass ratio of macrons is too low, the length of an electrostatic accelerator can reach hundreds to thousands of kilometers, rendering macron acceleration impractical. To reduce the accelerator length, a much higher electric field than what the most powerful klystrons can provide is desired. One practical choice may be the high-intensity charged particle beam ldquoblowing-piperdquo approach. In this approach, a high-intensity (~10-kA) medium-energy (0.5-2-MeV) long-pulse (10-1000-mus) positively charged ion beam shots to a heavily charged millimeter-size macron to create a local high-strength electric field (~1010 V/m), accelerating the macron efficiently. We will discuss the physics and challenges involved in this concept and give an illustrative simulation.

Improving the Yield and Turn-Around Time of Focused Ion Beam Microsurgery of Integrated Circuits by LCVD Method

Tungsten conductor lines deposited by focused ion beam (FIB) from W(CO) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> precursor gas quite often have too high a resistivity (typically 100-200 mu Omega cm) in practical integrated circuit edit work. Even if the high resistivity of the deposited conductor line can be tolerated the FIB deposition process of conductor lines with length over 100 mum can take several hours. This can cause serious problems in analogue or mixed signal type integrated circuit (IC) microsurgery often encountered in RF-band circuits. We present a method for the reduction of the FIB deposited tungsten conductor line resistance by subsequent laser chemical vapor deposition (LCVD) of copper from an organometal Cu(hfac)tmvs precursor. In this way, the resistance of the FIB deposited tungsten line can be reduced by order of magnitude from its original value by subsequent LCVD process. LCVD takes place selectively only on the FIB deposited tungsten line with high spatial resolution. As another practical application LCVD can be used to fabricate charge dissipation routes before FIB operations and thus protect transistors from charged ion beam induced discharge damages. Furthermore, the feasibility of the FIB/LCVD process in circuit edit work is discussed in this paper. Examples of both technologies used successfully in a combined way and the developed process flow for the circuit edit are presented. We applied the combined method to over different 200 circuit edit cases manufactured by various semiconductor processes. We found that the developed combined method could be used in about 20%-30% of the circuit edit cases to either improve the yield in circuit edit or speed up the total turnaround time.

Laser ion source for low-charge heavy ion beams

For heavy ion inertial fusion application, a combination of a laser ion source and direct plasma injection scheme into a radio frequency quadrupole (RFQ) is proposed. The combination might provide more than 100 mA of singly charged heavy ion beam from a single laser shot. A planned feasibility test with moderate current is also discussed.

Discharging dynamics of insulator surfaces irradiated by highly charged ions

Guiding and focusing of keV to MeV ions by insulator micro-capillaries offer exciting perspectives for the production of low divergence micro-sized beams and the spatial control over the irradiated zone. These effects result from the local charging of the capillary inner wall and depend strongly on the charging/discharging dynamics of the insulating material. This dynamics has been studied on various glass insulator surfaces (borosilicate, fused silica and quartz) by grazing incidence highly charged ion beams. We propose simple experimental methods to derive the relevant time constant and study the influence of temperature and different material properties to the charging process.

X-ray spectroscopy characterization of Ar17+ produced by an ECRIS in the afterglow mode

An electron-cyclotron-resonance ion source (ECRIS) operating in the afterglow mode allows to produce pulsed highly charged ion beams. We present a characterization of the first production of pulsed Ar17+ ions from an ECRIS using X-ray spectroscopy techniques. An ion current increase of a factor 3-4 compared to the continuous operating mode with a short rise time (< 100 μ s) and a full width at half maximum of 500 μ s has been obtained.

Long plasma source for heavy ion beam charge neutralization

Plasmas are a source of unbound electrons for charge neutralizing intense heavy ion beams to focus them to a small spot size and compress their axial length. The plasma source should operate at low neutral pressures and without strong externally applied fields. To produce long plasma columns, sources based upon ferroelectric ceramics with large dielectric coefficients have been developed. The source utilizes the ferroelectric ceramic BaTiO 3 to form metal plasma. The drift tube inner surface of the Neutralized Drift Compression Experiment (NDCX) is covered with ceramic material. High voltage (∼8 kV) is applied between the drift tube and the front surface of the ceramics. A BaTiO 3 source comprised of five 20-cm-long sources has been tested and characterized, producing relatively uniform plasma in the 5×10 10 cm −3 density range. The source was integrated into the NDCX device for charge neutralization and beam compression experiments, and yielded current compression ratios ∼120. Present research is developing multi-meter-long and higher density sources to support beam compression experiments for high-energy-density physics applications.