Source Chamber Research Articles

Effect of reverberation chamber volume on result of qualification procedure for loudspeaker and loudspeaker positions for airborne sound insulation measurements

Measurement of sound insulation from airborne sound is carried out by determining the level of sound power radiated by the test item. In laboratory practice, this translates into measuring the sound level in the transmitting and receiving chambers and measuring the reverberation time in the receiving chamber. When performing these measurements, significant fluctuations in the sound level for low frequencies can be observed, which is related to the occurrence of standing waves inside the chambers. To ensure proper level averaging, as well as repeatability and reproducibility of measurements ISO 10140-5 describes a qualification procedure for sources and source positions. This article presents the effect of increasing the volume of the source chamber on the results of the qualification procedure for sources and source positions for floor airborne sound insulation measurements.

Compact Ion Beam System for Fusion Demonstration

We demonstrate a compact ion beam device capable of accelerating H+ and D+ ions up to 75 keV energy, onto a solid target, with sufficient beam current to study fusion reactions. The ion beam system uses a microwave driven plasma source to generate ions that are accelerated to high energy with a direct current (DC) acceleration structure. The plasma source is driven by pulsed microwaves from a solid-state radiofrequency (RF) amplifier, which is impedance matched to the plasma source chamber at the S-band frequency in the range of 2.4–2.5 GHz. The plasma chamber is held at high positive DC potential and is isolated from the impedance matching structure (at ground potential) by a dielectric-filled gap. To facilitate the use of high-energy-particle detectors near the target, the plasma chamber is biased to a high positive voltage, while the target remains grounded. A target loaded with deuterium is used to study D-D fusion and a B4C or LaB6 target is used to study p-11B fusion. Detectors include solid-state charged particle detector and a scintillation fast neutron detector. The complete ion beam system can fit on a laboratory table and is a useful tool for teaching undergraduate and graduate students about the physics of fusion.

Development of a new magnetic mirror device at the Korea Advanced Institute of Science and Technology

A new magnetic mirror machine named KAIMIR (KAIST mirror) has been designed and constructed at the Korea Advanced Institute of Science and Technology (KAIST) to study mirror plasma physics and simulate the boundary regions of magnetic fusion plasmas such as in a tokamak. The purpose of this paper is to introduce the characteristics and initial experimental results of KAIMIR. The cylindrical vacuum chamber has a length of 2.48 m and a diameter of 0.5 m and consists of three sub-chambers, namely the source, centre and expander chambers. A magnetic mirror configuration is achieved by electromagnetic coils with a maximum magnetic field strength of 0.4 T at the mirror nozzles and 0.1 T at the centre. The source plasma is generated by a plasma washer gun installed in the source chamber with a pulse forming network system. The typical discharge time is ~12 ms with a ~6 ms (1–7 ms) steady period. Initial results show that the on-axis electron density at the centre is 1019–20 m−3 and the electron temperature is 4–7 eV. Two parameters were varied in this initial phase, the source power and the mirror ratio, which is the ratio of highest to lowest magnetic field strength in the mirror-confined region. We observed that the increase of the electron density was mitigated for a source power above 0.2 MW. It was also found that the electron density increases almost linearly with the mirror ratio. Accordingly, the stored electron energy was also linearly proportional to the mirror ratio, similar to the scaling of the gas dynamic trap.

Targeting the NF-κB p65/Bcl-2 signaling pathway in hepatic cellular carcinoma using radiation assisted synthesis of zinc nanoparticles coated with naturally isolated gallic acid

PurposeOral diethylnitrosamine (DEN) is a known hepatocarcinogen that damages the liver and causes cancer. DEN damages the liver through reactive oxygen species-mediated inflammation and biological process regulation. Materials and methodsGallic acid-coated zinc oxide nanoparticles (Zn-GANPs) were made from zinc oxide (ZnO) synthesized by irradiation dose of 50 kGy utilizing a Co-60 γ-ray source chamber with a dose rate of 0.83 kGy/h and gallic acid from pomegranate peel. UV–visible (UV) spectrophotometry verified Zn-GANP synthesis. TEM, DLS, and FTIR were utilized to investigate ZnO-NPs' characteristics.Rats were orally exposed to DEN for 8 weeks at 20 mg/kg five times per week, followed by intraperitoneal injection of Zn-GANPs at 20 mg/kg for 5 weeks. Using oxidative stress, anti-inflammatory, liver function, histologic, apoptotic, and cell cycle parameters for evaluating Zn-GANPs treatment. ResultsDEN exposure elevated inflammatory markers (AFP and NF-κB p65), transaminases (AST, ALT), γ-GT, globulin, and total bilirubin, with reduced protein and albumin levels. It also increased MDA levels, oxidative liver cell damage, and Bcl-2, while decreasing caspase-3 and antioxidants like GSH, and CAT. Zn-GANPs significantly mitigated these effects and lowered lipid peroxidation, AST, ALT, and γ-GT levels, significantly increased CAT and GSH levels (p<0.05). Zn-GANPs caused S and G2/M cell cycle arrest and G0/G1 apoptosis. These results were associated with higher caspase-3 levels and lower Bcl-2 and TGF-β1 levels. Zn-GANPs enhance and restore the histology and ultrastructure of the liver in DEN-induced rats. ConclusionThe data imply that Zn-GANPs may prevent and treat DEN-induced liver damage and carcinogenesis.

Methodology for assessment of radon diffusion coefficients in membranes, used as radon barriers in construction and refurbishment

In the near future, research on new materials for radon barriers can be expected to rise in order to meet a greater demand of radon mitigation solutions because of the increasingly lower radon levels that the EU legislation aims to. Such research would need a method for the determination of the radon diffusion coefficient and this paper presents an inexpensive method for that purpose, using affordable radon detectors and a simple experimental setup that does not require any tubing or any pumping. Besides the use of two Electronic Integration Devices as radon detectors, the experimental setup used in our method consists only in a two-chamber container made of steel and a small-sized radon source, which was produced in our lab using a 226Ra solution. The radon diffusion coefficient is determined by measuring radon levels in both chambers of the container, which are separated by a membrane made of the material whose radon diffusion coefficient is to be determined. Radon diffuses from a source chamber to a receiver chamber trough the membrane, being the amount of radon that has passed through and the rate at which it has done so the key parameters in the calculation of the radon diffusion coefficient. Our method can handily measure materials with a radon diffusion coefficient above or equal to 10-11 m2 s-1 or, provided that the sample is thin enough, verify that the coefficient is lower than 10-12 m2 s-1. Its precision is good enough to provide radon coefficient diffusion values with a good repeatability as the RSD is as low as a 35% for materials in which the coefficient is in the order of 10-11 m2 s-1. This means that our method is valid for screening materials for radon barriers and checking their compliance with technical specifications.

Gamma irradiation system's performance tests.

This study reviews the performance analysis of a 137Cs irradiation system that has recently been installed in the laboratory of Uzbek National Institute of Metrology. The laboratory is responsible for calibrating calibration facilities and for calibrating most protection level radiation monitoring instruments used in medical, nuclear, industrial and academic settings in Uzbekistan. This system employs the most advanced radiation safety standards, along with 21st century source automation methods. In this work, we review the system's performance according to ISO 4037 and present measurement uncertainty budget. Our analysis shows excellent results in terms of scattered radiation, beam uniformity and field size, change in source position, test for source impurities, chamber stability and source calibration, and all these parameters fully comply with the requirements of ISO 4037.

A multiscale magma system beneath the Tengchong volcano in western Yunnan revealed by ambient noise tomography

SUMMARY The western Yunnan is located in the SE Tibetan Plateau, and is characterized by the active Tengchong volcano (TCV), complex crust–mantle coupling and intense earthquakes. To elucidate tectonism in the western Yunnan, we construct a 3-D S-wave velocity model to 80 km depth via ambient noise tomography using dense seismic stations. Our model shows significant low-velocity anomalies at different depths in the crust and uppermost mantle. Compared with the results of previous regional tomography, we image low-velocity anomalies consistent with a large-scale source of partial melts in the uppermost mantle beneath the Tengchong and Baoshan blocks, rather than just below the Tengchong block. Our results also reveal a magma chamber extending from the shallow subsurface to the lower crust beneath the TCV, which is fed by the mantle source. Based on these findings, we propose that the mantle source and crustal magma chamber form a multiscale magma system. Moreover, the mantle source is potentially resulted from asthenospheric upwelling, which is related to the subduction of the Indian slab. In addition, our model shows that the 1976 M7.4 and M7.3 Longling earthquakes occurred near a magma chamber. Thus, fluids from the magma chamber likely reduced the frictional coefficient on the seismogenic fault and caused the Longling earthquakes.

Ultralow H2O content analysis with a large-geometry secondary ion mass spectrometer

An improved LG-SIMS (CAMECA IMS 1280-HR) procedure for achieving sub-ppm LOD for water analysis by updating the cooling trap.

Extended X-ray absorption fine structure (EXAFS) measurement of Cu metal foil using thermal wave detector: A comparative study

In this study, we compared two methods for measuring EXAFS spectra, which provide insights into material local structures. The conventional transmission mode used a synchrotron beam as a source and ionization chambers as detectors. Alternatively, we employed thermal wave detectors, specifically a pyroelectric crystal, for a simpler approach. The experiment was conducted using a LiNbO3 crystal at a synchrotron facility operating in the hard X-ray energy range. The chopping frequency of the X-ray beam was set at 1.8 Hz to optimize data collection. We discussed the challenges of selecting the appropriate chopping frequency for EXAFS measurements and the importance of detector sensitivity. We shared results from experiments at various chopping frequencies, highlighting the suitability of pyroelectric detectors. The study demonstrated the feasibility of using pyroelectric detectors for EXAFS measurements, providing valuable data with minimal artifact effects. The findings contribute to the understanding of material local structures and open possibilities for further exploration of thermal wave detectors in continuous theta scan applications.

Origin and mineralization processes of REE during magmatic-hydrothermal evolution: Insights from in-situ geochemistry of calcite from the Weishan REE deposit, eastern North China Craton

The Weishan REE deposit, hosting more than one million tons of light REE oxides (LREE2O3), is one of the largest LREE deposits in China. It has been considered to be a carbonatite-related REE deposit, but whether carbonatites occurred or not is still controversial, leading to the confusions of how the LREE originated and mineralized. Here, we conducted in-situ elemental and Sr-Nd isotopic analyses on different stages of calcite from the Weishan REE deposit, combined with petrographic and bulk C-O isotopic studies, with the aim to unravel the origin and mineralization processes of REE. Four stages of calcite (Cal-1, Cal-2, Cal-3 and Cal-4) were identified, of which the Cal-1 typically coexists with K-feldspar and quartz while the Cal-2 and Cal-3 coexist with sulfates and REE minerals (e.g., bastnäsite and parisite), respectively. The Cal-4 occurs in the post-ore veinlets and coexists with sulfides. The Cal-1 is characterized by exsolution of carbocernaite along its cleavage planes with highest Na, K, Sr, Ba and LREE contents. The other stages of calcite show continuous decrease of the above elements. Combined with petrographic features and elemental discrimination diagrams, it is concluded that the Cal-1 is magmatic while the others are hydrothermal. These calcites thus indicate a continuous magmatic-hydrothermal evolution. The four stages of calcite show similar isotopic compositions, which are consistent with those of the alkaline silicate rocks in the ore district, suggesting an uniform source or magma chamber for their derivation. Considering the magmatic features of Cal-1, it is inferred that carbonate melts coupled with abundant alkaline fluids were exsolved from the alkaline magmas. Alkalis (e. g., K and Na) were enriched in the magmatic-hydrothermal system with potassic metasomatism being more prevalent, which might play an important role in REE exsolution and transportation. Focused REE deposition occurred shortly after massive deposition of sulfates, indicating that REE-sulfate complexes might be the dominant transporting ligands of REE. The deposition of REE was mainly induced by fluid boiling, as indicated by the boiling/unmixing features of fluid inclusions. The Sr-Nd isotopic compositions of ores and associated alkaline rocks show affinities to the enriched lithospheric mantle (EM) beneath the study region, but are more depleted. Because subduction of the Paleo-Pacific oceanic plate beneath the eastern Asian occurred since the Jurassic, it is inferred that CO2- and REE-rich melts/fluids released from the subducted oceanic slab metasomatized the EM, leading to a REE-rich carbonated mantle. Rollback of the subducted slab occurred during the early Cretaceous, resulting in partial melting of the EM and thus generating the CO2- and REE-rich alkaline magmas. This deposit shows significant hydrothermal features with poorly-developed carbonatites, distinct from the typical carbonatite-related REE deposits in the other places. The REE mineralization is thus considered to be basically controlled by the alkaline magmas rather than the carbonatites.

Highlights of recent SPIDER results and improvements

Three years of experiments on SPIDER allowed characterization of the main features of the source plasma and of the negative ion beam, in the original design configuration. For the large dimensions of the source chamber, and of the extraction area, the investigation of the single-beamlet currents and of the source plasma uniformity had to be carried out to extend the knowledge gained in smaller prototype sources. The configuration of the multiple RF drivers and filter field topologies were found to cause a peculiar behavior in the plasma confinement in the drivers, creating left-right asymmetries which were also visible in the extracted negative ion currents, even after the early implementation of a new scheme of plasma-grid current send and return busbars that greatly improved performance at high filter fields. The plasma properties in the driver and expansion region as well as the positive ion energy at the extraction region were studied in different experimental conditions, and interpreted also with the support of numerical models, suggesting that an improved plasma confinement could contribute to the increase of the plasma density, and to a certain extent to a lowering of the plasma potential profile; both effects shall contribute to increase the presence of cold negative ions for the formation of low-divergence beamlets. Early results related to unwanted RF discharges on the back of the plasma source and the gas conductance of the beam source suggested the reduction of the vessel pressure as mitigation, leading to the definition of a new pumping system. The difficulties related to the simultaneous operation, stable control and high-power operation of multiple RF self-oscillating vacuum tube based RF generators were an unambiguous obstruction to the experimentation, calling for the implementation of RF solid-state amplifiers. The initial tests related to caesium management, the non-uniform plasma properties at different locations across the plasma grid, and the challenges in the measurement of the current and divergence of the accelerated beamlet, unambiguously resulted in the need of new diagnostic systems to investigate with better resolution the spatial uniformities. This contribution summarises how the main experimental findings in the previous experimental campaigns are driving modifications to the SPIDER experiment, during the present shut down, in view of future operations.

Sustainable and smart HPTLC determination of silodosin and solifenacin using a constructed two illumination source chamber with a smartphone camera as a detector: Comparative study with conventional densitometric scanner

The tremendous revolution in the built-in digital camera of smartphones has opened new horizons for its applicability as a portable, easily accessible, and user-friendly detector in different analytical techniques. In this article, we proposed and developed a new and inexpensive detector for simultaneous analysis of silodosin and solifenacin. The innovation makes use of a smartphone camera coupled with high-performance thin layer chromatographic (HPTLC) approach. Firstly, chromatographic separation was attained using HPTLC plates with an ecofriendly mobile phase composed of ethyl acetate, ethanol & 25% w/w ammonia (3.0: 7.0: 0.3, by volume). The developed plates were then visualized using Dragendorff's reagent and then photographed via smartphone's rear-facing camera fixed on a fabricated two-illumination source chamber. The intensities of drug spots were quantified using an open-source image analysis software, ImageJ, over concentration ranges of 2.0–30.0 μg/band. Moreover, the study was extended to compare the obtained results with a benchtop densitometric method at 215.0 nm where the densitometric one gave linear response ranging from 0.1 to 7.0 μg/band for silodosin and 0.1–6.0 μg/band for solifenacin. The fast, simple, reliable and green merits of the proposed HPTLC/smartphone method promted it as an excellent platform for assaying marketed combined tablets and assuring their content uniformity. Moreover, the high sensitivity of the densitometric method was exploited, for the first time, for determining the residual content of the cited drugs on manufacturing equipment surfaces during cleaning validation. Finally, the environmental impact of the methods was appraised via three state-of-the-art greenness metrics.

Microfluidic Bi-Layer Platform to Study Functional Interaction between Co-Cultured Neural Networks with Unidirectional Synaptic Connectivity

The complex synaptic connectivity architecture of neuronal networks underlies cognition and brain function. However, studying the spiking activity propagation and processing in heterogeneous networks in vivo poses significant challenges. In this study, we present a novel two-layer PDMS chip that facilitates the culturing and examination of the functional interaction of two interconnected neural networks. We utilized cultures of hippocampal neurons grown in a two-chamber microfluidic chip combined with a microelectrode array. The asymmetric configuration of the microchannels between the chambers ensured the growth of axons predominantly in one direction from the Source chamber to the Target chamber, forming two neuronal networks with unidirectional synaptic connectivity. We showed that the local application of tetrodotoxin (TTX) to the Source network did not alter the spiking rate in the Target network. The results indicate that stable network activity in the Target network was maintained for at least 1–3 h after TTX application, demonstrating the feasibility of local chemical activity modulation and the influence of electrical activity from one network on the other. Additionally, suppression of synaptic activity in the Source network by the application of CPP and CNQX reorganized spatio-temporal characteristics of spontaneous and stimulus-evoked spiking activity in the Target network. The proposed methodology and results provide a more in-depth examination of the network-level functional interaction between neural circuits with heterogeneous synaptic connectivity.

A newly constructed Linear Experimental Advanced Device LEAD

The Linear Experimental Advanced Device (LEAD) has been constructed for comprehensive studies on plasma turbulence, plasma-material interaction and new techniques for tokamaks at Southwestern Institute of Physics (SWIP). The vacuum vessel of this linear device is 3055 mm long. It consists of three parts, i.e. the source chamber, the linear magnetized confinement chamber and the plasma-material interaction (PMI) chamber. Kinds of plasma sources, including radio-frequency (RF) sources and a hot cathode source, have been developed to produce steady-state plasma. Wave-mode helicon plasmas can be excited by a large-size four-ring-antenna RF source when the input power is higher than 180 W. The typical electron density is higher than 1019/m3. Transfer from distinct narrowband drift waves to broadband turbulence is observed by means of adjusting the axial magnetic field, which makes LEAD a suitable device to investigate plasma turbulence. Auxiliary heating systems, including a 2.45 GHz Electron Cyclotron Resonance and an ion heating source, and a 1.5 MV ion accelerator are to be installed on LEAD. It promises a particle flow of over 1023/m2s and a heat load of several MW/m2, which makes LEAD a suitable platform for not only fundamental plasma physics but also PMI research.

Translation of the function of hydrothermal mineralization-related focused fluid flux into a mappable exploration criterion for mineral exploration targeting

Formation of hydrothermal mineralization is related to the late stages of, or immediate following, orogenic compressional regimes that have been superimposed on arc magmatism. For instance, mineralization-related fluid flux mechanisms of porphyry Cu formation deal with how magmatic fluids are transferred from the corresponding source chambers to the environment of stock emplacement related to porphyry systems. In this paper, firstly, we review the imperative physicochemical processes of mineralizing fluid flux mechanisms, e.g., the function of intrusive, metalliferous compounds, and permeable structures, and then assemble them to translate the mechanism of forming focused fluid flux into 2D mappable criteria for mineral exploration targeting. According to the review and the ensuing knowledge and idea, we propose a simplifying approach by focusing on a geological point feature - inferred sites of strongly concentrated ore fluid flux - that represents a critical, if not the most critical, geological element in mineral exploration targeting. We demonstrate that this point feature can be derived as a mappable criterion and that there are stronger spatial and thermal relationships between the location of hydrothermal mineral deposits and this proposed point feature relative to the existing point and line features (e.g., intrusive contacts, fault density, fault intersections, and proximity to faults), which have been widely used in the procedure of prospectivity analysis for mineral exploration targeting. We illustrate the procedures of generating mineral exploration targets, proposed in this paper, using geochemical and geological data sets of porphyry Cu deposits of Iran.

Development of UCN sources at PNPI

This article reviews the development of various sources for ultracold neutrons (UCNs) at the Petersburg Nuclear Physics Institute (PNPI). For 45 years, PNPI has proposed and manufactured cryogenic devices for neutron conversion to low energies. Based on beryllium, hydrogen and deuterium, they can be operated in the intense radiation fields near the core of a nuclear reactor. A more recently launched UCN source development utilizes superfluid helium (He-II) as conversion medium. Initially proposed and designed for PNPI’s old WWR-M reactor, the project has been reshaped to equip the institute’s PIK reactor with a modern UCN source of this type. The projected UCN density in the closed source chamber is 2.2 × 103 cm−3, which, as calculations of neutron transport show, will provide 200 cm−3 in the chambers of a neutron EDM spectrometer connected to the source by a UCN guide. Experiments at PNPI with a full-scale UCN source model have demonstrated that a heat load of 60 W can be removed from the He-II in the converter at a temperature of 1.37 K. This fact confirms the practical possibility to implement low-temperature converters under “in-pile” conditions with large heat inflows. The review concludes with a presentation of various proposed options for a He-II based UCN source at the European Spallation Source.

A plasma loss to sidewall model for 1D PIC/MCC simulation for plasma transport estimation

A plasma loss to sidewall model is used for one-dimensional (1D) particle-in-cell (PIC) with Monte Carlo collision (MCC) simulation to calculate plasma transport through a transverse magnetic field in a negative ion source chamber. The presented 1D model includes plasma radial loss treatment when calculating the plasma transport in the axial direction. It does not cost computation effort as much as a 2D or 3D model and can be used to estimate the plasma transport process quickly. The conventional 1D kinetic model calculates particle motion only in the ‘x’-direction. The sidewall loss in the ‘y’ ‘z’ direction is not included, leading to unusual plasma distribution. Especially when applying a transverse magnetic field, the motion and loss of electrons along the magnetic field line to the sidewall are ignored. Thus electrons are completely constrained by the magnetic field, resulting in abnormal plasma density accumulation. The sidewall loss estimation method uses Bohm velocity calculated from plasma parameters as radial loss velocity to obtain the plasma flux to the sidewall. And the sidewall loss rate can be obtained from the flux combined with chamber geometry. This method is integrated into a self-developed 1D PIC–MCC program to examine its effect. Several verification cases are performed separately for the PIC, MCC, and the sidewall loss treatment module, and the results exhibit good reliability. Simulations are then carried out to study plasma transport across the magnetic field under similar conditions to actual experiments. Simulation results agree with the experiment, which indicates that the 1D sidewall loss model is useful when dealing with plasma transport in the source chamber.

Challenges testing high transmission-loss walls in a laboratory

High transmission-loss walls present challenges for laboratory testing. One challenge is the limitation of the test chambers, commonly referred to as the "flanking limit", where the sound that is transmitted through the test specimen begins to compete with interference from other sound transmission paths which flank around the test specimen. Another challenge is where there isn't enough noise in the source chamber for sufficient signal-to-noise in the receiving chamber. Both situations are "flagged" when reporting results according to ASTM E90, which merely means that the specimen offers greater isolation than the laboratory is capable of measuring. To further complicate matters, some wall assemblies seem to exhibit different "flanking limits" which are context-specific to a framing assembly, that is one wall will start to exhibit diminishing returns to transmission loss when adding mass, and another framing assembly will exhibit similar diminishing returns at a different level, as if it's reaching a different flanking limit. This paper explores some of these issues but does not offer specific solutions; these issues require further study.

Remote Plasma Source Chamber Modeling and Generator Design

This paper presents modeling of the plasma load in vacuum chamber of a remote plasma source (RPS) and its generator is designed and implemented correspondingly. Traditionally, equivalent plasma load modeling usually acquired parameters measured by Langmuir probe which is hard to conduct and is basically intrusive. A simple method to model the plasma load into frequency and flow rate related equivalent RLC load without special device is proposed in this study. And two different resonant inverters which are operated around 400 kHz as an igniter and a sustainer of the plasma source generator are designed based on the equivalent load. The igniter generates high voltage 5 kV with argon gas as a trigger to start the plasma progress and the sustainer provides a maximum power of 2.5 kVA to keep plasma generating with nitrogen gas. To avoid interruption of plasma generation under gas flow rate varying from 100 to 600 sccm, a simple PI control with frequency modulation on the sustainer to regulate its output current is adopted. Both system design and equivalent load modeling are verified with simulated and experimental results in the paper.

Metal evaporation study using the GANIL high temperature oven for intense metal ion beams production

A new resistive oven dedicated to the production of metal ion beams using ECR ion sources has been developed at GANIL. It aims to produce beams such as 58Niq+, 50Tiq+, 50Vq+ or 238Uq+ with ECR4 ion source on cyclotrons injectors and with Phoenix V3 ion source on Spiral 2facility. Typical intensity about 1.2 1013 pps is requested for the Super Separator Spectrometer (S3). Evaporated atom fluxes and their angular distributions have been measured on a dedicated test bench thanks to a quartz microbalance. These investigations were carried out using three crucibles with various exit caps geometries for which the fluxes and angular distributions display distinct behaviors. Based on those results, crucible is designed to obtain a high flux of atoms overlapping the ECR plasma while minimizing the atoms losses on the ion source chamber.