Charge States Of Heavy Ions Research Articles

Acceleration sites of energetic ions upstream of the Earth's bow shock and in the magnetosheath: Statistical study on charge states of heavy ions

In order to identify acceleration sites of energetic ions upstream of the Earth's bow shock and in the dayside magnetosheath, we investigated energetic ion events observed by the Energetic Particles and Ion Composition (EPIC) instrument on board the Geotail spacecraft from 1995 to 2001. Energetic ion data obtained by the Ion Composition System (ICS) sensor were used to select “events,” that is, intervals when the 77–107 keV ion flux increased by more than two orders of magnitude within 10 min, and examine their spatial distribution and its geomagnetic activity dependence. Heavy ions with energy range of 9–210 keV/e detected by the Suprathermal Ion Composition Spectrometer (STICS) sensor were chosen to calculate the percentage of low‐charge‐state heavy ions (PLCS = (O+ + N+)/(O+ + N+ + O6+ + O7+)) in each event, and the events were classified into three groups: high‐charge‐state (HCS) events (PLCS ≤ 25%), intermediate (IM) events (25% < PLCS < 75%), and low‐charge‐state (LCS) events (PLCS ≥ 75%). The HCS and LCS events occurred at almost the same rate in geomagnetically quiet conditions (SYM‐H ≥ 0 nT), while the LCS events were observed more frequently than the HCS events in geomagnetically disturbed conditions (SYM‐H ≤ −30 nT). The percentage of the IM and LCS events summed was higher in disturbed conditions than in quiet conditions. The HCS and LCS events were frequently observed in the dawnside upstream region and in the duskside magnetosheath, respectively. The IM events occurred both in the dawnside upstream region and in the magnetosheath around noon. We conclude that energetic ion events including ions accelerated in the magnetosphere are dominant. Ions accelerated in the magnetosphere leak out from the duskside magnetopause, in particular when geomagnetic activity is high, and then most likely mix with ions accelerated at the bow shock on the way to the dawnside upstream region. The acceleration site of the HCS events is also discussed.

Solar wind stream interaction regions without sector boundaries

During periods of high solar activity when there are many sources of solar wind on the solar disk, a spacecraft occasionally encounters consecutive solar wind streams with the same magnetic polarity. The low‐speed wind in the region of interaction between the two streams exhibits many of the same features as, but has some differences from, the low‐speed wind that includes crossings of the heliospheric current sheet (HCS) where the direction of the heliospheric magnetic field reverses. The non‐HCS slow wind exhibits many of the same small‐scale structures usually associated with the slow wind around the HCS; these include discontinuous stream interfaces and other discontinuities, magnetic holes, and low‐entropy structures. These entropy holes do not appear to have the same origin as the plasma sheets observed near the HCS, however. The helium abundances and heavy ion charge states in the non‐HCS regions are not significantly different from those in HCS‐associated regions. Some of the dynamical properties of the non‐HCS regions differ from those found near the HCS; the regions between leading and trailing stream interfaces have a shorter duration or scale size, greater minimum speed, and lower peak and average densities. No correlation could be found between the non‐HCS slow wind and visible coronal streamers.

The influence of nonthermal particles and radiation on the charge state of heavy ions in solar cosmic rays

The influence of various types of nonthermal electron and proton distributions and photoionization on the charge state of energetic heavy elements moving in a plasma is investigated. The mean charges of Mg, Si, and Fe are calculated for a bi-Maxwellian distribution of the background electrons and for electron and neutral beams with power-law energy distributions. An anomalously high density of the nonthermal component is required to obtain substantial deviations of the equilibrium mean charges of these elements (a few charge units) from the case when they interact with a purely Maxwellian plasma. In this context, the mean charges for O, Ne, Mg, Si, and Fe ions are also calculated for a model with charge-consistent acceleration. The results indicate that photoionization does not significantly influence the charge state of solar cosmic rays if the parameters of the plasma are those characteristic of impulsive solar events.

Review of laser ion sources developments in Prague and production of q over 50+ ions at Prague Asterix Laser System (invited)

The high-power iodine laser systems PERUN and Prague Asterix Laser System, with a maximum attainable laser intensity IL of up to about 6×1016 W/cm2, were used to generate highly charged ions of various elements (Al,Co,Ni,Cu,Ag,Sn,Ta,W,Pt,Au,Pb,Bi). The properties of ions were investigated mainly on the basis of time-of-flight method using ion collectors, cylindrical electrostatic ion energy analyzer, Thomson parabola spectrometer, and track detectors. Simultaneous x-ray and interferometric measurements were also implemented. Maximum ion charge states of heavy ions above z=50+ were recorded and the maximum energy of emitted ions exceeded Ei=22 MeV. Using laser intensities of about 1×1016 W/cm2 can produce such ions. Due to the convenient pulse length of the iodine laser, part of the pulse may interact with the self-created expanding plasma. It was proved that in this case the conditions for an appearance of the relativistic self focusing may be fulfilled (position of minimum focus spot in front of the target surface and the threshold laser intensity about 3×1014 W/cm2) and the highest charge states above 50+ may be generated, too.

Overview of the U.S. rare isotope accelerator proposal

The Rare Isotope Accelerator (RIA) is the highest priority of the nuclear physics community in the United States for a major new facility. RIA is a next generation facility for basic research with radioactive beams that utilizes both standard Isotope-separator On-line (ISOL) and in-flight fragmentation methods with novel approaches to handle high primary-beam power and remove existing limitations in the extraction of short-lived isotopes. A versatile primary accelerator, a 1.4-GV, CW superconducting linac designed to simultaneously accelerate several heavy-ion charge states, will provide beams from protons at 900 MeV to uranium at 400 MeV/u at power levels of 400 kW. The wide variety of primary beams allows various production and extraction schemes to be used to optimize production of specific isotopes. These isotopes, at unprecedented intensities, are available for research at a broad range of energies. They can be delivered at ion source energy for stopped-beam studies, reaccelerated by a second superconducting linac, or directly separated in-flight for use at energies up to 500 MeV/u. The post accelerator uses a unique injection scheme, based on CW low-frequency RFQs, for efficient acceleration of singly charged heavy ions with masses up to 240 amu from ion source energy.

A charge-consistent model for the acceleration of iron in the solar corona: Nonisothermal injection

A charge-consistent numerical model for the joint (regular and stochastic) acceleration of iron by a spherical shock wave propagating in the solar corona is proposed. Large-scale irregularities of the plasma density and the nonisothermal injection of ions are taken into account. For the case of iron, the energy dependence of the mean charge qFe(E) is determined by the relationships between the characteristic acceleration time, the charge-variation time for the accelerated ions, and the time for their trapping in regions of high plasma density. Due to the global inhomogeneity of the medium, these relationships depend on the shock speed. Our calculations indicate that photoionization by soft X-rays from flare regions can substantially change the charge states of heavy ions only in the most powerful solar events (both impulsive and gradual).

Upstream magnetospheric ion flux tube within a magnetic cloud: Wind/STICS

[1] We present a case study of a remarkable upstream O+ and N+ ion outflow event. We present observational evidence for spatially structured outflow of these Low Charge State Heavy Ions (LCSHIs) of magnetospheric origin along a small reconnected field line region within the framework of a magnetic cloud of an ICME. From the particles' in situ 3D distribution function we conclude that in this case the interaction of the outflow with the bow shock is small. We conclude further that the gyrophases of outflowing ions at the reconnection point are randomly distributed. This leads to the formation of a flux tube with a specific geometry. In particular, the outflow reveals spatial dispersion and non-gyrotropy. This result has implications for the size of the dayside reconnection site.

Effect of minimum strength of mirror magnetic field (Bmin) on production of highly charged heavy ions from RIKEN liquid-He-free super conducting electron–cyclotron resonance ion source (RAMSES)

We measured the beam intensity of highly charged heavy ions (O, Ar and Kr ions) as a function of the minimum strength of mirror magnetic field (Bmin) of the RIKEN liquid-He-free super conducting electron–cyclotron resonance ion source. In this experiment, we found that the optimum value of Bmin exists to maximize the beam intensity of highly charged heavy ions and the value was almost the same (∼0.49T) for various charge state heavy ions.

Development of a medium-energy superconducting heavy-ion linac

The Rare Isotope Accelerator (RIA) facility project includes a cw 1.4 GeV driver linac and a 100 MV postaccelerator both based on superconducting (SC) cavities operating at frequencies from 48 to 805 MHz. In these linacs more than 99% of the total voltage is provided by SC cavities. An initial acceleration is provided by room temperature radio frequency quadrupoles. The driver linac is designed for acceleration of any ion species, from protons up to 900 MeV to uranium up to 400 MeV/u. The novel feature of the driver linac is an acceleration of multiple charge-state heavy-ion beams in order to achieve 400 kW beam power. This paper presents design features of a medium-energy SC heavy-ion linac taking the RIA driver linac as an example. The dynamics of single and multiple charge-state beams are detailed, including the effects of possible errors in rf field parameters and misalignments of transverse focusing elements. The important design considerations of such linac are presented. Several new conceptual solutions in beam dynamics in SC accelerating structures for heavy-ion applications are discussed.

Determination of charge states of single swift heavy projectiles by high-energy delta-electrons

The effective charge state is an important particle parameter which is required for the calculation of many effects concerning the interaction between radiation and matter such as an estimate of the radial dose of swift heavy projectiles, stopping power and so on. A new method for the determination of effective charge states of heavy ions is based on the measurement of the number of high-energy delta-electrons which are ejected from a target by the penetrating ion. These electrons are detectable with a CCD-detector and their number can be correlated to the effective charge state of the projectile for known particle velocities. This method is even applicable to operation with single swift heavy ions within statistical bounds.

The three‐dimensional solar wind at solar activity minimum

In early 1998 the Ulysses spacecraft made history by completing an orbit around the Sun inclined to the solar equator by 80°. It observed the properties of the high‐latitude heliosphere at a time of low solar activity when the configuration of the solar magnetic field was relatively simple. The solar wind data acquired by Ulysses have placed firm observational constraints on theories of the acceleration of the fast wind from the polar regions. The speed of the polar solar wind was in the range 750–800 km s−1, with a slow increase toward the poles. The polar proton flux of ∼2 × 108 cm−2 s−1 was only two‐thirds the low‐latitude flux but still sufficiently high to require energy sources in addition to the conduction of heat from the hot solar corona. In comparison with the slow, low‐latitude solar wind, the heavy ions in the fast, high‐latitude wind had less elemental fractionation relative to the solar surface and a lower state of ionization. Fine structures in the polar solar wind, named microstreams, exhibited a correlation between speed, proton temperature, and alpha particle abundance. The absence of a latitude dependence of the widths of the microstreams suggests that they are caused by temporal, rather than purely spatial variations at the Sun. Magnetic field observations revealed a latitude‐independent radial field strength of ∼3 nT (normalized to 1 AU) and a large flux of outward propagating Alivén waves. The most probable direction of the interplanetary magnetic field was close to the Archimedes (Parker) spiral predicted on the basis of radial fields close to the Sun combined with the effects of solar rotation. The fluctuations about the average direction were so large, however, that there was little latitudinal variation of the average value of |BR|B, where BR is the radial component of the field with magnitude B. Latitudinal transport of field lines and nonradial field directions near the Sun appear to be other necessary additions to the simple Parker model. Some unexpected differences were found between the low‐ and the high‐latitude properties of the plasma from transient events called coronal mass ejections (CMEs). At high latitudes, the speeds of the CME plasma clouds were close to the speed of the ambient fast wind, shocks were observed both ahead of and behind the CMEs, and enhancements of the helium abundance and of high charge states of heavy ions were not observed, as they often are at low latitudes. The review closes with a summary of arguments in support of the view that the fast solar wind observed by Ulysses at intermediate latitudes has its origin at higher latitudes in the polar coronal holes.

Unusual composition of the solar wind in the 2–3 May 1998 CME observed with SWICS on ACE

Elemental, isotopic and charge state abundances provide valuable information about the source and acceleration mechanism of Coronal Mass Ejections (CMEs). Even though the kinetic properties of the plasma might be subject to changes because of dynamic effects occurring during the expansion of the CME, the composition of the solar wind remains unchanged after it leaves the low corona. Data from the Solar Wind Ion Composition Spectrometer (SWICS) on ACE are used to study the elemental and charge state composition of He, O, C, N, and Fe as well as the isotopic ratio of He during the very large CME of May 2–3, 1998. We find in this CME anomalously large enrichment of ³He++/4He++, He/O and Fe/O. During the 28 hour long cloud portion of the CME unusually cold material (4He+ and very low charge state heavy ions) was observed together with hot (high charge state ions) and normal solar wind plasma.

Report on the workshop on ion sources for hadron colliders (invited)

A workshop on Ion Sources for Hadron Colliders was held September 4–5, 1997 in Gelnhausen, Germany. This workshop, organized by the WE-Heraeus-Stiftung Foundation, the University of Frankfurt, Brookhaven National Laboratory, and CERN, directly followed the 7th Symposium on Electron Beam Ion Sources and Traps. Various options were reviewed for the development of a high current, intermediate charge state heavy ion source for use on colliders such as RHIC and LHC. In addition to status reports on electron cyclotron resonance, electron beam ion source, and laser sources, there was also discussion of issues relevant to the scaling of these sources to intensities as required by RHIC and LHC. The presentations and discussions from this workshop are summarized.

A high charge state heavy ion beam source for heavy ion fusion

A high current, low emittance, high charge state heavy ion beam source is being developed. This is designed to deliver a heavy ion fusion (HIF) driver accelerator scale beam. Using a high charge state beam in a driver accelerator for HIF may increase the acceleration efficiency, leading to a reduction in the driver accelerator size and cost. The proposed source system, which consists of a gas beam electron stripper followed by a high charge state beam separator, can be added to existing single charge state, low emittance, high brightness ion sources and injectors. We shall report on the source physics design using 3D beam simulations and experimental feasibility study results using a neutral gas stripper and a beam separator at the exit of the LBL 2 MV injector.

Numerical solution of the heavy ion radial diffusion problem in the earth's magnetosphere

The results of the numerical solution of the Fokker-Planck equation, describing radial diffusion of protons and heavy ions in the Earth's magnetosphere, are presented. Radial transport driven by fluctuations of the geomagnetic or the electric field, or a combination of both, was included in the solution. Coulomb interaction and charge exchange processes were also taken into account. Resulting energy and radial dependencies of ion fluxes and pitch-angle distributions for protons and various charge states of heavy ions are discussed.

Development of an electron-beam ion source for a relativistic heavy-ion collider preinjector

At Brookhaven National Laboratory (BNL), an electron-beam ion source (EBIS) is operational as a test bed for development of a high current EBIS for relativistic heavy-ion collider (RHIC). Previously, the goal of most EBIS research has been to produce bare or nearly bare nuclei. At BNL, the EBIS is required to produce only medium charge states of heavy ions, e.g., Au35+, since there is further stripping at higher energies. The BNL effort is directed at reaching intensities of interest to RHIC, approximately 3×109 particles/pulse, which will require an EBIS electron beam on the order of 10 A. Initial tests using a 1 mm LaB6 cathode have produced electron beam currents up to the design value of 110 mA. A 2 mm LaB6 cathode has been installed and in a first run has produced currents up to 350 mA. This source has so far produced charge states up to Ar16+ using neutral gas injection, and up to Tl50+ using external ion injection. Results of these studies and ion injection trials are presented.

Hot and warm electron energy distribution at different electron cyclotron resonance ion source operation regimes

High charge states of heavy ions inside the electron cyclotron resonance plasma are produced by hot and warm electrons with energies above 3 keV. The slope of the electron energy distribution function and the density of these populations were obtained from bremsstrahlung spectra emitted by the 7.5 GHz Electron Cyclotron Resonance Ion Source of the Forschungszentrum Rossendorf measured with a HP Ge solid state detector. For this a new deconvolution method has been used. The operating condition of the ion source influences the behavior of the electrons. Mixing in of light gases to the discharge strongly increases the electron density.

Experimental investigation of the afterglow of the pulsed electron cyclotron resonance discharge

During the afterglow of the pulsed electron cyclotron resonance discharge, currents can be extracted, which are substantially higher than the ion current during the heating phase of the plasma. This is especially the case for the high charge states of heavy ions. An operating regime was found, which gives an extremely stable and reproducible afterglow. The variation from pulse to pulse is hardly visible and the long-term stability is also very good. This mode, which made the setting up and operation of the accelerators much easier than is normally the case, can also give an insight into the processes responsible for the afterglow. An investigation of the shape and duration of the afterglow for the different charge states of lead is presented. A 1/ζ2 dependence for the decay time of the afterglow was found for operation with oxygen, while no such dependence appears for operation with neon as the auxiliary gas.

Production of high charge state ions with the Advanced Electron Cyclotron Resonance Ion Source at LBNL

Production of high charge state ions with the Advanced Electron Cyclotron Resonance ion source (AECR) at Lawrence Berkeley National Laboratory (LBNL) has been significantly improved by application of various new techniques. Heating the plasma simultaneously with microwaves of two frequencies (10 and 14 GHz) has increased the production of very high charge state heavy ions. The two-frequency technique provides extra electron cyclotron resonance heating zone as compared to the single-frequency heating and improves the heating of the plasma electrons. Aluminum oxide on the plasma chamber surface improves the production of cold electrons at the chamber surfaces and increases the performance of the AECR. Fully stripped argon ions, ≥5 enA, were produced and directly identified by the source charge state analyzing system. High charge state ion beams of bismuth and uranium, such as 209Bi51+ and 238U53+, were produced by the source and accelerated by the 88-in. cyclotron to energies above 6 MeV/nucleon for the first time.

The SERSE project

The project for a superconducting electron cyclotron resonance (ECR) ion source has been funded by INFN in 1992 as a joint venture between INFN and CEA/DRFMC. The source is devoted to the production of high charge state heavy ions to be injected into the K-800 superconducting cyclotron. The magnetic system consists of three solenoids and of an hexapole which will allow one to attain a strong plasma confinement by means of a B-min field configuration with a very high magnetic field (1.4 T on the plasma chamber wall). At the intermediate frequency of 14.5 GHz, it will be possible to study the scaling of ECR ion sources at different magnetic fields far beyond the existing levels. The source will eventually work at a higher frequency, in the range 28–35 GHz of gyrotron tubes. The design of the superconducting magnets and of the cryostat has been carefully carried out, taking into account this goal, and the construction is now under course. The mechanical design of the plasma chamber is also outlined.