Ion optical design of a collinear laser-negative ion beam apparatus

An apparatus for photodetachment studies on atomic and molecular negative ions of medium up to heavy mass (M ? 500) has been designed and constructed. Laser and ion beams are merged in the apparatus in a collinear geometry and atoms, neutral molecules and negative ions are detected in the forward direction. The ion optical design and the components used to optimize the mass resolution and the transmission through the extended field-free interaction region are described. A 90° sector field magnet with 50 cm bending radius in combination with two slits is used for mass dispersion providing a resolution of M∕ΔM?800 for molecular ions and M∕ΔM?400 for atomic ions. The difference in mass resolution for atomic and molecular ions is attributed to different energy distributions of the sputtered ions. With 1 mm slits, transmission from the source through the interaction region to the final ion detector was determined to be about 0.14%.     

Laser measurement of H- ions in a field-effect-transistor based radio frequency ion source

Hydrogen negative ion density measurements are required to clarify the characteristics of negative ion production and ion source performance. Both of laser photodetachment and cavity ring down (CRD) measurements have been implemented to a field-effect-transistor based radio-frequency ion source. The density ratio of negative hydrogen ions to electrons was successfully measured by laser photodetachment and effect of magnetic filter field on negative ion density was confirmed. The calculated CRD signal showed that CRD mirrors with >99.990% reflectivity are required and loss of reflectivity due to cesium contamination should be minimized.     

Measurement of H- density in plasma by photodetachment

Techniques have been developed for measurement of the density of H- in a plasma by photodetachment. Photodetachment is detected by the increase in electron density with no change in positive ion density after a light pulse from a ruby laser. The authenticity of photodetachment signals can be assured by their comparison with known cross sections for photodetachment of H-. Interpretations of photodetachment data are less ambiguous than probe interpretations because photodetachment is not affected by the mass of positive ions and is not limited in usefulness by the Debye distance. Photodetachment measurements with time resolution and spatial resolution are straightforward.     

Molecular and negative ion production by a standard electron cyclotron resonance ion source

Molecular and negative ion beams, usually produced in special ion sources, play an increasingly important role in fundamental and applied atomic physics. The ATOMKI-ECRIS is a standard ECR ion source, designed to provide highly charged ion (HCI) plasmas and beams. In the present work, H(-), O(-), OH(-), O(2)(-), C(-), C(60)(-) negative ions and H(2)(+), H(3)(+), OH(+), H(2)O(+), H(3)O(+), O(2)(+) positive molecular ions were generated in this HCI-ECRIS. Without any major modification in the source and without any commonly applied tricks (such as usage of cesium or magnetic filter), negative ion beams of several μA and positive molecular ion beams in the mA range were successfully obtained.     

The development of the radio frequency driven negative ion source for neutral beam injectors (invited)

Large and powerful negative hydrogen ion sources are required for the neutral beam injection (NBI) systems of future fusion devices. Simplicity and maintenance-free operation favors RF sources, which are developed intensively at the Max-Planck-Institut fu?r Plasmaphysik (IPP) since many years. The negative hydrogen ions are generated by caesium-enhanced surface conversion of atoms and positive ions on the plasma grid surface. With a small scale prototype the required high ion current density and the low fraction of co-extracted electrons at low pressure as well as stable pulses up to 1 h could be demonstrated. The modular design allows extension to large source dimensions. This has led to the decision to choose RF sources for the NBI of the international fusion reactor, ITER. As an intermediate step towards the full size ITER source at IPP, the development will be continued with a half-size source on the new ELISE testbed. This will enable to gain experience for the first time with negative hydrogen ion beams from RF sources of these dimensions.     

离子阀技术在垂直引入式飞行时间质谱仪中的应用

垂直引入式飞行时间质谱仪（O-TOF MS）是以脉冲的工作方式对样品进行检测,对于离子源产生的连续离子流利用率极低。为了使O-TOF MS更好地匹配离子源,在自制的大气压接口垂直引入式飞行时间质谱仪（API-O-TOF MS）的基础上开发了离子阀技术,将原本连续进入推斥区的离子流调制为与推斥脉冲同步的离子团,提高推斥占空比,进而提高离子利用率。通过进一步研究富集原理以及分析富集参数的影响,确定了离子富集的最佳参数。以PPG-1000为实验对象,在同等条件下,离子信号强度普遍提升1个数量级以上。该结果表明,离子阀技术在O-TOF MS中的应用可有效提高仪器的离子利用率。     

Electron ionization time-of-flight mass spectrometry: historical review and current applications

This review presents an overview of electron ionization time-of-flight mass spectroscopy (EITOFMS), beginning with its early development to the employment of modern high-resolution electron ionization sources. The EITOFMS is demonstrated to be ideally suited for analytical and basic chemical physics studies. Studies of the formation of positive ions by electron ionization time-of-flight mass spectroscopy have been responsible for many of the known ionization potentials of molecules and radicals, as well as accepted bond dissociation energies for ions and neutral molecules. The application of TOFMS has been particularly important in the area of negative ion physics and chemistry. A wide variety of negative ion properties have been discovered and studied by using these methods including: autodetachment lifetimes, metastable dissociation, Rydberg electron transfer reactions and field detachment, SF(6) Scavenger method for detecting temporary negative ion states, and many others.     

A review of ion sources for medical accelerators (invited)

There are two major medical applications of ion accelerators. One is a production of short-lived isotopes for radionuclide imaging with positron emission tomography and single photon emission computer tomography. Generally, a combination of a source for negative ions (usually H- and/or D-) and a cyclotron is used; this system is well established and distributed over the world. Other important medical application is charged-particle radiotherapy, where the accelerated ion beam itself is being used for patient treatment. Two distinctly different methods are being applied: either with protons or with heavy-ions (mostly carbon ions). Proton radiotherapy for deep-seated tumors has become widespread since the 1990s. The energy and intensity are typically over 200 MeV and several 10(10) pps, respectively. Cyclotrons as well as synchrotrons are utilized. The ion source for the cyclotron is generally similar to the type for production of radioisotopes. For a synchrotron, one applies a positive ion source in combination with an injector linac. Carbon ion radiotherapy awakens a worldwide interest. About 6000 cancer patients have already been treated with carbon beams from the Heavy Ion Medical Accelerator in Chiba at the National Institute of Radiological Sciences in Japan. These clinical results have clearly verified the advantages of carbon ions. Heidelberg Ion Therapy Center and Gunma University Heavy Ion Medical Center have been successfully launched. Several new facilities are under commissioning or construction. The beam energy is adjusted to the depth of tumors. It is usually between 140 and 430 MeV∕u. Although the beam intensity depends on the irradiation method, it is typically several 10(8) or 10(9) pps. Synchrotrons are only utilized for carbon ion radiotherapy. An ECR ion source supplies multi-charged carbon ions for this requirement. Some other medical applications with ion beams attract developer's interests. For example, the several types of accelerators are under development for the boron neutron capture therapy. This treatment is conventionally demonstrated by a nuclear reactor, but it is strongly expected to replace the reactor by the accelerator. We report status of ion source for medical application and such scope for further developments.     

A procedure for determining the absorbed dose in a substance exposed to pulsed heavy ion beams

An experimental setup based on the TWAC-ITEP accelerating complex for performing radiobiological studies on heavy ion beams is described. Using magnetic elements of transportation lines and collimator systems, the procedure for forming a parallel beam with required transverse sizes is adjusted. A dosimetric system intended to measure spatial distributions of absorbed doses in a substance exposed to pulsed beams of heavy ions has been designed and implemented in the performed studies. Using this system, the distribution of the absorbed dose in water was studied for a monoenergetic beam of carbon ions with an initial energy of 215 MeV/amu. Based on this information, the absorbed dose was estimated in a thin water layer for the given depth and beam intensity. The use of this procedure ensures the accuracy in determining the absorbed dose of no worse than 5%.     

Wave frequency dependence of H- ion production and extraction in a transformer coupled plasma H- ion source at SNU

The effect of rf wave frequencies on the production of H(-) ion is investigated in a transformer coupled plasma H(-) ion source at Seoul National University. A Langmuir probe is installed to measure the plasma density and temperature, and these plasma parameters are correlated to the extracted H(-) beam currents at various frequencies. The Langmuir probe is also used to measure the density of H(-) ions at the ion source by generating photodetachment with an Nd:YAG laser. The extracted H(-) currents decrease to a minimum value until 13 MHz and then, increase as the driving frequency increases from 13 MHz while the relative H(-) population measured by photodetachment monotonically decreases as the driving rf frequency increases from 11 MHz to 15 MHz. A potential well formed at the extraction region at high frequencies of more than 13 MHz is considered responsible for the increased H(-) beam extraction even with a lower photodetachment signal. The variation in the driving rf frequency not only affects the density and temperature of the plasma but also modifies the plasma potential with the existence of a filtering magnetic field and consequently, influences the extracted H(-) current through the extraction as well as formation of H(-) ions.     

Development of a new photoelectron spectroscopy instrument combining an electrospray ion source and photoelectron imaging

A new apparatus has been constructed that combines electrospray ionization with a quadrupole mass filter, hexapole ion trap, and velocity-map imaging. The purpose is to record photoelectron images of isolated chromophore anions. To demonstrate the capability of our instrument we have recorded the photodetachment spectra of isolated deprotonated phenol and indole anions. To our knowledge, this is the first time that the photodetachment energy of the deprotonated indole anion has been recorded.     

Lifetime measurements in an electrostatic ion beam trap using image charge monitoring

A technique for mass-selective lifetime measurements of keV ions in a linear electrostatic ion beam trap is presented. The technique is based on bunching the ions using a weak RF potential and non-destructive ion detection by a pick-up electrode. This method has no mass-limitation, possesses the advantage of inherent mass-selectivity, and offers a possibility of measuring simultaneously the lifetimes of different ion species with no need for prior mass-selection.     

Design of a cavity ring-down spectroscopy diagnostic for negative ion rf source SPIDER

The rf source test facility SPIDER will test and optimize the source of the 1 MV neutral beam injection systems for ITER. Cavity ring-down spectroscopy (CRDS) will measure the absolute line-of-sight integrated density of negative (H(-) and D(-)) ions, produced in the extraction region of the source. CRDS takes advantage of the photodetachment process: negative ions are converted to neutral hydrogen atoms by electron stripping through absorption of a photon from a laser. The design of this diagnostic is presented with the corresponding simulation of the expected performance. A prototype operated without plasma has provided CRDS reference signals, design validation, and results concerning the signal-to-noise ratio.     

Studies for aluminum photoionization in hot cavity for the selective production of exotic species project

Selective production of exotic species (SPES) is an ISOL-based accelerator facility that will be built in the Legnaro INFN Laboratory (Italy), intended to provide an intense neutron-rich radioactive ion beams obtained by proton induced fission of an uranium carbide target. Beside this main target, a silicon carbide (SiC) target will the first to be used to deliver some p-rich beams. This target will validate also the functionality of the SPES facility with aluminum beam as result of hitting SiC target with protons. In the past off-line studies on laser photoionization of aluminum have performed in Pavia Spectroscopy Laboratory and in Laboratori Nazionali di Legnaro where, recently, a XeCl excimer laser was installed in order to test the laser ionization in the SPES hot cavity. Results are promising to justify further studies with this technique, aiming a better characterization of the SPES ion extraction capability under laser photoionization.     

A system of distributed cesium feeding for increasing the efficiency of powerful sources of negative hydrogen ions

Injection of high-power flows of high-energy neutral atoms is often required in modern facilities designed for fusion research. At energies of several hundreds keV, obtaining neutral atom flows is ineffective and converting them from negative ion beams is expedient. The efficiency of negative-ion production increases by many times if a cesium film is applied to the surface on which negative ions are produced. An optimized system of distributed cesium feeding is described. Using this system, it is possible to transport cesium vapor through large distances and its uniform application to large-area emitting surfaces in high-power sources of negative hydrogen ions.     

Friction and wear characteristics of ion-beam modified graphite coatings

Solid lubricated surfaces are now widely used in the tool industry, and the new concept of ‘soft tools’ recently introduced has emphasized low-friction surfaces. The present paper deals with a novel ‘burnishing’ process based on ionic bombardment of powder graphite coating/substrate systems. This process may influence both the coating and the coating/substrate interface, and it is effective for improving lubrication even at low doses of bombarding ions. The present study will discuss the friction and wear properties of graphite-powder coatings on a silicon wafer bombarded with 200 keV ion beams of argon, nitrogen and hydrogen ions, the last two as molecular ions. The coefficients of friction and wear rates of the coatings were found to be strongly dependent on the ion-bombarding species and ion dose. The argon ion bombardment increased the coefficient of friction and wear rate of the powder coating. However, at the interface of the silicon substrate, the ion-induced burnishing improved the tribological behaviour of the silicon material. Bombardment with nitrogen and hydrogen ions showed a marked improvement in the tribological properties of the graphite powder coating. Thus a reduction in wear rate by three orders of magnitude was observed in the case of nitrogen, and for both ions it was noted that ion-beam burnished graphite was lubricating in a dry environment, which has not been reported previously. The perspectives of ion bombardment as a burnishing process will be discussed and the observed effects will be qualitatively explained in the context of the theory for ionic penetration into solids.     

An ultra-low energy (30-200 eV) ion-atomic beam source for ion-beam-assisted deposition in ultrahigh vacuum

The paper describes the design and construction of an ion-atomic beam source with an optimized generation of ions for ion-beam-assisted deposition under ultrahigh vacuum (UHV) conditions. The source combines an effusion cell and an electron impact ion source and produces ion beams with ultra-low energies in the range from 30 eV to 200 eV. Decreasing ion beam energy to hyperthermal values (≈10(1) eV) without loosing optimum ionization conditions has been mainly achieved by the incorporation of an ionization chamber with a grid transparent enough for electron and ion beams. In this way the energy and current density of nitrogen ion beams in the order of 10(1) eV and 10(1) nA/cm(2), respectively, have been achieved. The source is capable of growing ultrathin layers or nanostructures at ultra-low energies with a growth rate of several MLs/h. The ion-atomic beam source will be preferentially applied for the synthesis of GaN under UHV conditions.     

MeV negative ion source from ultra-intense laser-matter interaction

Experimental demonstration of negative ion acceleration to MeV energies from sub-micron size droplets of water spray irradiated by ultra-intense laser pulses is presented. Thanks to the specific target configuration and laser parameters, more than 10(9) negative ions per steradian solid angle in 5% energy bandwidth are accelerated in a stable and reliable manner. To our knowledge, by virtue of the ultra-short duration of the emission, this is by far the brightest negative ion source reported. The data also indicate the existence of beams of neutrals with at least similar numbers and energies.     

Ion source with longitudinal ionization of a molecular beam by an electron beam in a magnetic field

A high-efficiency ion source for a mass-spectrometer’s detector of molecular beams and their scattering products is described. The ion source is designed according to a scheme of impact ionization of a beam particle by a longitudinal electron beam in a magnetic field with a strength of up to 130 mT. The design of the source developed is very flexible and has no limitations for use in any experiments with molecular beams. An ionization efficiency of particles of an atomic helium beam of 10^?3 ions/atom has been achieved. The useful signal-to-background ratio in the detector’s chamber is 3 × 10⁴ during detection of ions with mass-to-charge ratio m/q = 4 amu.     

Transport and emittance study for 18 GHz superconducting-ECR ion source at RCNP

As the upgrade program of the azimuthally varying field (AVF) cyclotron is at the cyclotron facility of the RCNP, Osaka University for the improvement of the quality, stability, and intensity of accelerated beams, an 18 GHz superconducting (SC) ECR ion source has been installed to increase beam currents and to extend the variety of ions, especially for highly charged heavy ions which can be accelerated by RCNP AVF cyclotron. The production development of several ions such as B, O, N, Ne, Ar, Ni, Kr, and Xe has been performed by Yorita et al. [Rev. Sci. Instrum. 79, 02A311(2008); 81, 02A332 (2010)]. Further studies for the beam transport have been done in order to improve the beam current more for injection of cyclotron. The effect of field leakage of AVF main coil is not negligible and additional steering magnet has been installed and then beam transmission has been improved. The emittance monitor has also been developed for the purpose of investigating correlation between emittance of beam from ECR ion sources and injection efficiency. The monitor consists with BPM82 with rotating wire for fast measurement for efficient study.