Differential Pumping System Research Articles

Nuclear physics experiments with a windowless supersonic gas jet target

A new windowless gas target has been developed in Mexico. It is a supersonic gas jet flow produced inside a vacuum chamber which can be coupled to a regular beam line in an accelerator laboratory as a differential pumping system brings the pressure of the gas target system down to a microTorr, or better, at the connecting stage.In this work, we present the system as it was designed and constructed as well as the first results using air, Nitrogen and Argon.

Pillow seal system at the BigRIPS separator

We have designed and installed a pillow seal system for the BigRIPS fragment separator at the RIKEN Radioactive Isotope Beam Factory (RIBF) to facilitate remote maintenance in a radioactive environment. The pillow seal system is a device to connect a vacuum chamber and a beam tube. It allows quick attachment and detachment of vacuum connections in the BigRIPS separator and consists of a double diaphragm with a differential pumping system. The leakage rate achieved with this system is as low as 10–9Pam3/s. We have also designed and installed a local radiation-shielding system, integrated with the pillow seal system, to protect the superconducting magnets and to reduce the heat load on the cryogenic system. We present an overview of the pillow seal and the local shielding systems.

Vacuum Ultraviolet and Soft X‐ray Photoelectron Spectroscopy of Liquid Beams Using a Hemispherical Photoelectron Spectrometer with a Multistage Differential Pumping System

AbstractWe present photoelectron spectroscopy of liquid beams using a high‐resolution hemispherical photoelectron spectrometer with a multistage differential pumping system developed in our laboratory. Intense soft X‐ray synchrotron radiation (500‐1200 eV) at SPring‐8 and a relatively large detection solid angle (1.5 × 10−2 π sr) of the spectrometer enable highly efficient measurements of X‐ray photoelectron spectra of liquids. Vacuum ultraviolet photoelectron spectroscopy using the same spectrometer provides sufficiently high spectral resolution to resolve rotational isomers of gas‐phase molecules.

Development of Plasma Window for gas charge stripper at RIKEN RIBF

A differential pumping system with a Plasma Window (PW) has been developed for an application to a window-less He gas charge stripper. A PW with Southern Methodist University design was newly fabricated and tested off-line for evaluation of differential pumping efficiency. Switching gases for plasma seed from Ar to He was tested. It was found that the PW reduced the pressure at the first differential pumping section to 1/13 for Ar and to 1/17 for He, comparing with differential pumping without PW. At the second pumping section, the pressures were drastically reduced to 1/160 and to 1/4,520 for Ar and He, respectively. These pressure reduction factors indicate that one differentially pumped stage could be removed from a conventional differential pumping system.

Electrospray ion source with a dynamic liquid flow splitter

Although the electrospray method is widely used in biomedical mass spectrometry and ion-drift spectrometry, the electrospray system can generate large drops that are the cause of electrical breakdowns, and of the fast clogging of the inlet diaphragm of the differential pumping first stage and system of ion transportation to the analyzer. Thus, a system free of such problems would be of benefit. To drain the condensate away from the electrospraying zone and to maintain stability of spraying, a source was designed where the excessive non-sprayed solution flowing down over the metal capillary outer wall is pumped away by an air micropump. An anti-electrode is mounted opposite the metal capillary and is slightly tilted with respect to the horizon to make the condensed liquid flow down. An electrospray ion source allowing work with chromatographic flows of the solution under normal conditions was tested. The applicability of the operating modes of the electrospray ion source with dynamic liquid flow splitting for both ion-drift and mass spectrometers was demonstrated. The flow rate range of liquid fed to the electrospray ion source with dynamic liquid flow splitting is such that it can be used in high performance liquid chromatography/Ion Mobility Spectrometry (HPLC/IMS) and HPLC/MS in the online mode. An electrospray ion source with a dynamic liquid flow splitter was developed and tested. Optimal operating modes of the electrospray ion source with dynamic liquid flow splitting were determined.

Injector for scattering measurements on fully solvated biospecies

We describe a liquid jet injector system developed to deliver fully solvated microscopic target species into a probe beam under either vacuum or ambient conditions. The injector was designed specifically for x-ray scattering studies of biological nanospecies using x-ray free electron lasers and third generation synchrotrons, but is of interest to any application in which microscopic samples must be delivered in a fully solvated state and with microscopic precision. By utilizing a gas dynamic virtual nozzle (GDVN) to generate a sample-containing liquid jet of diameter ranging from 300 nm to 20 μm, the injector avoids the clogging problems associated in this size range with conventional Rayleigh jets. A differential pumping system incorporated into the injector shields the experimental chamber from the gas load of the GDVN, making the injector compatible with high vacuum systems. The injector houses a fiber-optically coupled pump laser to illuminate the jet for pump-probe experiments and a hermetically sealed microscope to observe the liquid jet for diagnostics and alignment during operation. This injector system has now been used during several experimental runs at the Linac Coherent Light Source. Recent refinements in GDVN design are also presented.

Tracer-encapsulated solid pellet injection system

The method of tracer-encapsulated solid pellet (TESPEL) is now flourishing in various fields. The original purpose to study impurity transport without giving substantial perturbation on the plasma is implemented successfully for years. In addition to this, TESPEL is being intensively applied to study thermal (especially non-local) transport, high energy particles with the use of TESPEL ablation cloud, and spectroscopy from the viewpoint of atomic data. It is now further growing up to the utilization of multiple tracer methods which was not planned at the initial phase of the project. The proof-of-principle experiment using triple tracers has been successfully implemented. This opens a way to compare the Z dependence or mass dependence of impurity transport. In this article, as TESPEL is used in a variety of fields, the TESPEL injection system is summarized together with the method of TESPEL production, TESPEL storage disk, TESPEL guide system, and the differential pumping system. Also, the observation system for TESPEL flight and TESPEL ablation is explained.

Steady-State Recombining Plasma in a Radio-Frequency Plasma Device for Divertor-Detachment Study

Stable plasma production in a radio-frequency plasma source and steady-state high-neutral-pressure environment in a test region has been achieved simultaneously with backflow suppression components such as orifices and a differential pumping system. Neutral pressure in the test region is changed by two orders, resulting in changes in the electron temperature and density in the test region. Conversely, neutral pressure, electron temperature, and electron density near a plasma production region showed little change. The result indicates that the experimental device provides us independent control knobs of source plasma and neutral pressure in the test region.

Deposition of novel nanocomposite films by a newly developed differential pumping co-sputtering system

A differential pumping co-sputtering system was developed to facilitate a controlled, but flexible fabrication of multifunctional nanocomposite films with compositions not limited by thermodynamic restrictions. This system features a multichamber design with a differential pumping system. Dividing atmospheres with this set up greatly reduced the cross-contamination between chambers, and each material could be co-deposited by rapid rotation of the substrate. The clearance between the substrate holder and the chamber was set at 1–2 mm, and the conductance of the clearance was examined roughly using conductance equations for typical types of orifices. It was found that the potential difference (PD) value of the clearance between the two chambers was less than 0.01; the gas flow between the two chambers through the clearance thus appears to be a practical molecular flow. The PD value, where P is a pressure (Pa) and D is a diameter of an orifice or a pipe (m), is a gas flow indicator or parameter obtained from an equation of Knudsen number. The changes in the oxygen partial pressure and glow discharge plasma in the left chamber were investigated using a process gas monitor (PGM) and optical emission spectroscope (OES) by introducing different gases to each chamber. The PGM results revealed that the cross-contamination of oxygen from the other chamber was suppressed to 10 ± 3% of the original. In addition, the OES measurement for glow discharge plasma did not detect substantial oxygen contamination from the other chamber. Using the newly developed system, an AlN/SiOx nanocomposite film consisting of B4-type AlN and amorphous SiOx was obtained successfully.

Application of a double-sided silicon-strip detector as a differential pumping barrier for NESR experiments at FAIR

Abstract The presented work focuses on the development of a differential pumping system using double-sided silicon-strip detectors to separate the ultra-high vacuum of a storage ring from subsequent detectors and outgassing components placed in an auxiliary vacuum. Such a technical concept will give the opportunity to use telescope-like detector systems in an ultra-high vacuum environment, such as a storage ring, without enclosing the entire system in a pocket. Therefore, it will enable the detection of recoil particles with the smallest possible energy due to the use of the innermost strip detector as an active window. Our results prove that such an assembly is feasible without having an effect, within experimental errors, on the performance of the strip detector. Vacuum separation better than six orders of magnitude was achieved with the ultra-high vacuum side reaching down to the 10 − 10 mbar pressure region.

Charge-state distribution measurements using gas charge stripper toward 238U and 136Xe acceleration at RIKEN RIBF

The charge-state distributions of 238U and 136Xe ions at 11MeV/nucleon were measured using a gas charge stripper to test whether the charge states in gaseous media were acceptable for acceleration at the RIKEN RI-Beam Factory (RIBF). A differential pumping system facilitated the increase of the N2 gas thickness to 1.3mg/cm2; this is sufficient for the most probable charge state to attain equilibrium. The charge states of 238U attain equilibrium at 56.0, 56.6, and 55.7 in N2, Ar, and CO2 media with thicknesses of 125, 79, and 126μg/cm2, respectively, whereas those of 136Xe attain equilibrium at 40.5, 40.1, and 40.3 in N2, Ar, CO2 media with thicknesses of 163, 95, and 139μg/cm2, respectively. The equilibrium charge states of 136Xe are acceptable for acceleration by the subsequent cyclotron, whereas those of 238U are not acceptable for acceleration without a major remodeling of the accelerator.

Laser-plasma EUV source dedicated for surface processing of polymers

In this work, a 10 Hz laser-plasma extreme ultraviolet (EUV) source built for surface processing of polymers is presented. The source is based on a double-stream gas puff target created in a vacuum chamber synchronously with the pumping laser pulse. The target is formed by pulsed injection of Kr, Xe or a KrXe gas mixture into a hollow stream of helium. The EUV radiation is focused using a grazing incidence gold-plated ellipsoidal collector. Spectrum of the reflected radiation consists of a narrow feature with intensity maximum at 10–11 nm wavelength and a long-wavelength spectral tail up to 70 nm. The exact spectral distribution depends on a gas applied for plasma creation. To avoid strong absorption of the EUV radiation in a residual gas present in the chamber during the source operation a two step differential pumping system was employed. The system allows for polymer processing under relatively high vacuum conditions (10 −5 mbar) or in a reactive gas atmosphere. Polymer samples can be irradiated in a focal plane of the EUV collector or at some distance downstream the focal plane. This way fluence of the EUV beam at the polymer surface can be regulated.

A differential pumping system to deliver windowless VUV photons at atmospheric pressure

In order to deliver VUV (vacuum ultraviolet) photons under atmospheric pressure conditions, a differential pumping system has been built on the DISCO beamline at the SOLEIL synchrotron radiation facility. The system is made of four stages and is 840 mm long. The conductance-limiting body has been designed to allow practicable optical alignment. VUV transmission of the system was tested under air, nitrogen, argon and neon, and photons could be delivered down to 60 nm (20 eV).

Note: Design of transverse electron gun for electron beam based reactive evaporation system

In this paper design of a 10 kV, 10 kW transverse electron gun, suitable for reactive evaporation, supported by simulation and modeling, is presented. Simulation of the electron beam trajectory helps in locating the emergence aperture after 90° bend and also in designing the crucible on which the beam is finally incident after 270° bend. The dimension of emergence aperture plays a vital role in designing the differential pumping system between the gun chamber and the substrate chamber. Experimental validation is done for beam trajectory by piercing a stainless steel plate at 90° position which is kept above the crucible.

Low-Zgas stripper as an alternative to carbon foils for the acceleration of high-power uranium beams

The RIKEN accelerator complex started feeding the next-generation exotic beam facility radioisotope beam factory (RIBF) with heavy-ion beams from 2007 after the successful commissioning of RIBF at the end of 2006. Many improvements made from 2007 to 2010 were instrumental in increasing the intensity of various heavy-ion beams. However, the available beam intensity of very heavy ion beams, especially uranium beams, is far below our goal of $1\text{ }\text{ }\mathrm{p}\ensuremath{\mu}\mathrm{A}$ ($6\ifmmode\times\else\texttimes\fi{}{10}^{12}\text{ }\text{ }\mathrm{particles}/\mathrm{s}$). In order to achieve this goal, upgrade programs are already in progress; the programs include the construction of a new 28-GHz superconducting electron cyclotron resonance ion source and a new injector linac. However, the most serious problem, that of a charge stripper for high-power uranium beams, still remains unsolved, despite extensive research and development work using large foils mounted on a rotating cylinder and a ${\mathrm{N}}_{2}$ gas stripper. A gas stripper is free from problems related to lifetime, though the equilibrium charge state in this stripper is considerably lower than that in a carbon foil, owing to the absence of the density effect. Nevertheless, the merits of gas strippers motivated us to develop a low-$Z$ gas stripper to achieve a higher equilibrium charge state even in gases. We measured the electron-loss and electron-capture cross sections of uranium ions in He gas as a function of their charge state at 11, 14, and $15\text{ }\text{ }\mathrm{MeV}/\mathrm{nucleon}$. The equilibrium charge states extracted from the intersection of the lines of the two cross sections were promisingly higher than those in ${\mathrm{N}}_{2}$ gas by more than 10. Simple simulations of charge development along the stripper thickness were performed by assuming the measured cross sections. The simulation results show that about $1\text{ }\text{ }\mathrm{mg}/{\mathrm{cm}}^{2}$ of He gas should be accumulated to achieve a charge state higher than that of ${\mathrm{N}}_{2}$ gas, notwithstanding the difficulty in accumulation of this helium amount owing to its fast dispersion. However, we now believe that the following two solutions can overcome this difficulty: a gas cell with a very large differential pumping system and a gas cell with a plasma window. Their merits and demerits are discussed in the paper.

Charge-state distribution measurements ofU238andXe136at11 MeV/nucleonusing gas charge stripper

The charge-state distributions and equilibrium charge states of uranium ($^{238}\mathrm{U}$) and xenon ($^{136}\mathrm{Xe}$) ions at $11\text{ }\text{ }\mathrm{MeV}/\mathrm{nucleon}$ were determined using a gas charge stripper. A differential pumping system facilitated the increase of the nitrogen gas thickness up to $1.3\text{ }\text{ }\mathrm{mg}/{\mathrm{cm}}^{2}$, which is sufficient for the most probable charge state to attain equilibrium. The charge states of $^{238}\mathrm{U}$ attain equilibrium at 56.0, 56.6, and 55.7 in ${\mathrm{N}}_{2}$, Ar, and ${\mathrm{CO}}_{2}$ media with thicknesses of 125, 79, and $126\text{ }\text{ }\ensuremath{\mu}\mathrm{g}/{\mathrm{cm}}^{2}$, respectively, while those of $^{136}\mathrm{Xe}$ attain equilibrium at 40.5, 40.1, and 40.3 in ${\mathrm{N}}_{2}$, Ar, and ${\mathrm{CO}}_{2}$ media with thicknesses of 163, 95, and $139\text{ }\text{ }\ensuremath{\mu}\mathrm{g}/{\mathrm{cm}}^{2}$, respectively. The equilibrium charge states of $^{136}\mathrm{Xe}$ are acceptable for acceleration by the subsequent cyclotron. The measured data of $^{238}\mathrm{U}$ were used to devise an empirical formula for the prediction of the equilibrium charge state in gaseous media over the energy region of $0.01--60\text{ }\text{ }\mathrm{MeV}/\mathrm{nucleon}$. The equilibrium charge state of $^{136}\mathrm{Xe}$ as predicted by the devised formula is in good agreement with the data.

The application of ESEM to biological samples

The Environmental Scanning Electron Microscope (ESEM) differs from a conventional SEM in that a differential pumping system maintains a pressure of gas (typically H2O) in thespecimen chamber whilst the gun remains at high vacuum. Ionizing collisions between electrons and these gas molecules create positive ions which drift down onto the sample neutralising specimen charge. It is therefore possible to image insulating samples without the need for metallic coating. The presence of water vapour in the chamber also means that a high relative humidity can be maintained and samples can be imaged in a hydrated state without the need for dehydration and fixation. These features suggest that ESEM could be well suited to imaging biological samples undergoing natural biological processes. We present a proof of principle study on the closure of stomatal pores in Tradescantia andersonia leaf tissue. An imaging protocol is developed and the advantages and limitations of this technique are discussed. Images of Vicia fabaleaf tissue are also presented. Challenges include minimising beam damage and reconciling the need for an adequate physiological temperature and a low gas pressure favourable for imaging, with the thermodynamic constraints on achieving a high relative humidity.

Development of a differential pumping system for soft X-ray beamlines for windowless experiments under normal atmospheric conditions

A novel design for a differential pumping system has been investigated. This system allows windowless experiments in a soft X-ray beamline under normal atmospheric conditions. The new design consists of an aperture-based four-stage differential pumping system, based on a simple model calculation. A prototype system with a total length of 600 mm was constructed to confirm the validity of the design concept. Relatively short conductance-limiting components allow easy installation and alignment of the system on a synchrotron beamline. The fabricated system was installed on a beamline to test the transmission of soft X-rays through atmospheric helium.

Ion Beam Generation from an Electrolyte Solution Containing Polyatomic Cations and Anions for Secondary Ion Mass Spectrometry

A solution-type ion beam source was fabricated to utilize polyatomic anions as well as polyatomic cations that are stable in solutions. The ion source consists of an electrospray section at atmospheric pressure and a vacuum section with a differential pumping system. To demonstrate the beam generation of cations or anions, ethanol solution containing a room-temperature molten salt (i.e., an ionic liquid) was tested. The ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, consists of a polyatomic cation, [C8H20ON]+, and a polyatomic anion, [C2F6NO4S2]-. Ions produced at atmospheric pressure were passed through an aperture into a vacuum chamber and then transported to a target. The effects of the aperture dimensions were investigated in the range from 50 to 200 µm in diameter and 0.25 to 1 mm in thickness. The ratio of current passing through the aperture into the vacuum chamber to the total electrosprayed current was on the order of 10-3 to 10-5. The ratio increased with increasing aperture diameter. A reduction in the aperture thickness also improved the ratio. Beam current increased with applied voltage in both positive-ion and negative-ion modes. It was demonstrated that stable negative-ion beams as well as positive-ion beams on the order of pA were produced.

Tritium gas flow dynamics through the source and transport system of the Karlsruhe tritium neutrino experiment

The source and transport system of the Karlsruhe tritium neutrino experiment (KATRIN) must provide a significant reduction in tritium flow and gas density. It comprises a 10 m long windowless source tube, where the tritium gas is injected, followed by a differential pumping system and a cryogenic pumping system. The primary challenge of the analysis is that the gas flow changes from a viscous flow regime inside the source tube to a transitional flow regime at the first pumping stage, and to a molecular flow regime at the remaining stages of the differential pumping system and further downstream. A strong molecular beaming effect must be considered. This article presents the results of calculations of gas density and flow for the complete source and differential pumping system. It is shown that a total flow-rate reduction factor of 1.4×10−8 can be attained, which is one of the prerequisites to achieve extreme-high vacuum conditions in the spectrometers used in the downstream end of the experiment.