Aluminum Vacuum Chamber Research Articles

Aluminum Vacuum Chamber for the Sirius Commissioning Undulators

Aluminum Vacuum Chamber for the Sirius Commissioning Undulators

The Role of DC Biased Plasma Treatment of Polystyrene on the Formation of the C≡N Functional Group Controlling Its Hydrophobicity

Nitrogen plasma treatment was carried out to modify the surface of polystyrene film deposited on a quartz crystal microbalance (QCM) sensor. The modification was intended to enhance the wettability of the film by inducing the formation of CN functional group on its surface. This work investigated the effect of DC bias controlling N* in the plasma on the effectiveness of the nitrogen plasma treatment. The polystyrene was deposited by a spin coating method on the surface of a quartz crystal normally used in an electronic resonator. The nitrogen plasma was generated in an aluminium vacuum chamber using a 2 MHz radio frequency (RF) generator. The vacuum pressure and the gas flow rate were kept constant during the experiments. The plasma character in the chamber was controlled by applying a DC bias between the RF electrodes and the sample stage. The DC voltage was varied from 100 to 500 volts at 100 volts’ step, while maintaining the RF voltage constant. During the process, the species in the plasma was characterized using an optical emission spectroscopy (OES). The wettability of the treated samples was tested using a contact angle measurement system. FTIR measurement was utilized to study the polar functional groups on the surface of the polystyrene before and after the treatment. The OES identified the existence of N radical (N*). The reduced intensity of emission line of the N* increased with the increase of the DC voltage. However, a small decrease was also evidence at DC voltage higher than 400 volts. The decrease of the line intensity was directly related to the decrease of the contact angle (CA < 40°). The relation of the N* and the resulted wettability is related to the polar functional group of the C≡N bond found in the treated polystyrene’s surface.

Vacuum systems for the TPS accelerator

The Taiwan Photon Source (TPS) is a 3 GeV third generation accelerator light source. The vacuum systems contain an electron storage ring (SR) of 518.4 m in circumference and a concentric booster (BR) of 496.8 m in circumference, linked with the transport lines one from the booster to storage ring (BTS) and the other from the linear accelerator to the booster (LTB). To ensure the highest stability of the electron beam in the storage ring, all the vacuum systems for the SR, BTS, and BR, have been baked to the ultrahigh vacuum (UHV). The aluminum vacuum chambers with the completely oil-free precise manufacturing process provide a lowest surface outgassing rate and lowest broadband impedance for accommodating the beam in stable. The combination of the triode ion pumps and the non-evaporable getter (NEG) pumps provides a superior pumping efficiency and the ultimate pressure < 5 nPa. The 24 arc-cell vacuum systems, each about 14 m in length, have been baked to the UHV and sealed in the laboratory prior to transport to the TPS tunnel for the installation. Other vacuum systems were installed and baked on site in parallel. After completing the installations, commissioning of TPS was started in August 2014.

Study of the ultra-high-vacuum system of the 14-m-long vacuum chamber of the Taiwan Photon Source using the pressure build-up method

The pressure build-up method was suitable for diagnosing and qualifying the vacuum status in the chamber and thus can be applied to determine the maintenance and recovery of a large vacuum system. The thermal outgassing rate and the pumping speed can be estimated using this method. In its electron storage ring, the Taiwan Photon Source (TPS) contains 24 aluminum arc-cells that are 14 m in length. Each cell was baked ex situ to 150 °C for 24 h in the laboratory to achieve ultra-high-vacuum. The cells reached 6.4 × 10−9 Pa on average, under pumping with primarily ion pumps and non-evaporable getter (NEG) pumps. The thermal outgassing rate, the pumping speed, and the residual gas compositions of a typical cell were analyzed. With all ion pumps turned off for more than 80 h, the vacuum pressure rose to approximately 8 × 10−7 Pa. The measured pumping speed was 6.9 × 10−4 m3∙s−1 on average for most of the cells extractor gauges associated with major inert gases in the 14 m-long cells. An experimental analysis of the emitted residual gases indicated that the gas in the aluminum vacuum chamber was primarily CH4 after the ion pumps were deactivated. Moreover, the one-cell vacuum chamber recovered to UHV status on using the pressure build-up method, including calculation of the outgassing rate and the pumping speed.

Design and fabrication of the vacuum systems for TPS pulsed septum magnets

Three in-air pulsed septum magnets were developed to inject and extract electron beams for the 3GeV synchrotron facility, the Taiwan Photon Source (TPS). The vacuum chamber is a novel combined aluminium-stainless steel design, using a bimetallic flange to connect the two material types. To evaluate the vacuum performances of these vacuum chambers, we set up a test bench at which we simultaneously measure the rates of thermal outgassing of the aluminium chamber and the septum tube with a throughput method. The test result indicates that the rate q72 of thermal outgassing measured after 1 day from baking at 150°C was 1×10−13mbarLs−1cm−2. The magnetic leakage measurements show the combination of conductor slitting, magnetic shielding and the aluminium vacuum chamber reduce the peak value of the leakage field integral to ~10Gcm along the trajectory of the stored beam.

Design, implementation, and testing of a cryogenic loading capability on an engineering neutron diffractometer

A novel capability was designed, implemented, and tested for in situ neutron diffraction measurements during loading at cryogenic temperatures on the spectrometer for materials research at temperature and stress at Los Alamos National Laboratory. This capability allowed for the application of dynamic compressive forces of up to 250 kN on standard samples controlled at temperatures between 300 and 90 K. The approach comprised of cooling thermally isolated compression platens that in turn conductively cooled the sample in an aluminum vacuum chamber which was nominally transparent to the incident and diffracted neutrons. The cooling/heat rate and final temperature were controlled by regulating the flow of liquid nitrogen in channels inside the platens that were connected through bellows to the mechanical actuator of the load frame and by heaters placed on the platens. Various performance parameters of this system are reported here. The system was used to investigate deformation in Ni-Ti-Fe shape memory alloys at cryogenic temperatures and preliminary results are presented.

An installation for magnetron deposition of getter coatings in narrow-aperture chambers

An installation for magnetron sputtering of thin-film coatings has been designed to deposit getter films in extended vacuum structures with a complex aperture. A solenoid used in the installation (diameter, 600 mm; length, 6000 mm; and maximum field, 800 G) makes it possible to deposit materials by sputtering onto internal walls in any type of vacuum chambers employed in modern accelerators. Results of deposition of a TiZrV getter coating in narrow-aperture aluminum vacuum chambers that will be mounted in the damping sections of a PETRA III synchrotron radiation source by DESY (Hamburg, Germany) are presented. The atomic composition and the homogeneity of the film along its length have been investigated on a channel for SR-XRF analysis at the Budker Institute of Nuclear Physics.

Optimization of an IEC Fusion Device to Increase Steady-State D-D Neutron Generation Rates

The University of Wisconsin-Madison Inertial Electrostatic Confinement (IEC) Fusion Research Group has been performing experiments on an IEC device known as HOMER. This device is a 65cm high, 91cm diameter cylindrical aluminum vacuum chamber that contains two concentric spherical wire grids, the outer grid acting as the anode and the inner grid as the cathode. The potential difference between the anode and cathode drives ions towards the center of the grids. Using this device, steady-state D-D fusion reactions are created in order to produce 2.45 MeV neutrons. With the goal of achieving maximum neutron production rates, the following parameters have been varied: cathode voltage, ion current, operating pressure, and the separation distance between the anode and cathode. The studies on pressure, voltage, and current have led to the discovery of trends that allow for the extrapolation of neutron rates at various conditions. The cathode/anode separation studies have offered valuable insight into how the distance between the electrodes effects the concentration of deuterium molecular ions and the ion energy spectra, and has led to the implementation of a configuration that better maximizes neutron production rates.

A comparison of the measured responses of a tissue-equivalent proportional counter to high energy heavy (HZE) particles and those simulated using the Geant4 Monte Carlo code

Monte Carlo simulations of heavy ion interactions using the Geant4 toolkit were compared with measurements of energy deposition in a spherical tissue-equivalent proportional counter (TEPC). A spherical cavity with a physical diameter of 12.7 mm was filled with propane-based tissue-equivalent gas surrounded by a wall of A-150 tissue-equivalent plastic that was 2.54 mm to thick. Measurements and Monte Carlo simulations were used to record the energy deposition and the trajectory of the incident particle on an event-by-event basis for ions ranging in atomic number from 2 ( 4He) to 26 ( 56Fe) and in energy from 200 MeV/nucleon to 1000 MeV/nucleon. In the simulations, tracking of secondary electrons was terminated when the range of an electron was below a specified threshold. The effects of range cuts for electrons at 0.5 μm, 1 μm, 10 μm, and 100 μm were evaluated. To simulate an energy deposition influenced by large numbers of low energy electrons with large transverse momentum, it was necessary to track electrons down to range cuts of 10 μm or less. The Geant4 simulated data closely matched the measured data acquired using a TEPC for incident particles traversing the center of the detector as well as near the gas-wall interface. Values of frequency mean lineal energy and dose mean lineal energy were within 8% of the measured data. The production of secondary particles in the aluminum vacuum chamber had no effect on the response of the TEPC for 56Fe at 1000 MeV/nucleon. The results of this study confirm that Geant4 can simulate patterns of energy deposition for existing microdosimeters and is valuable for improving the design of a new generation of detectors used for space dosimetry and for characterizing particle beams used in hadron radiotherapy.

Development of UHV compatible machined diamond profile gaskets for INDUS-2

Ultra High Vacuum (UHV) compatible demountable joints are needed in Indus-2 (2.5 GeV, 300mA) electron storage ring for connecting Al-alloy vacuum chambers (homogeneous joints) as well as Al-alloy vacuum chambers to well proven stainless steel components like beam diagnostic components and RF-shielded bellow assemblies (heterogeneous joints). Bakeable & reliable diamond profile Al-alloy gaskets have been developed for Helium leak rate less than 2×10−10 Std. CC/sec, which eliminated the need of any Al to SS transition pieces onto the Aluminium vacuum chambers. Salient features of these gaskets are: high reliability, low cost, reduced flange thickness, self alignment, ease in installation, less torque requirement, formability to non-circular shape & ultra cleanliness. These diamond profile gaskets were machined from extruded Al-alloy 6061-T5 pipes using specially developed high-speed steel formed cutting tools. Thermal cyclic tests were carried to check the reliability of these gaskets. No leaks were found even after several bakeouts at 150°C. Non-circular metallic gaskets like the one used in UHV gate valve bonnet seal can also be manufactured using specially developed formed toolings. This paper describes basic design philosophy, manufacturing process and testing details of these gaskets.

Cleaning of aluminium alloy chambers with ozonized water

In the fabrication of aluminium vacuum chambers of the Taiwan Photon Source (TPS), a cleaning treatment with ozonized water followed machining in an ethanol environment. After cleaning with ozonized water, aluminium samples were analyzed according to Auger electron spectroscopy (AES) and measurement of the thermal outgassing rate and photon-stimulated desorption (PSD). The results showed that cleaning with ozonized water has a superior performance. A thermal outgassing rate q72 ~ 6.4 × 10−12 Pa · m/s after baking and a photon-desorption yield η ~ 2 × 10−5 molecules/photon at an accumulated beam dose 3 × 1021 photons/cm2 were obtained.

Langmuir probe diagnostics of a microfabricated inductively coupled plasma on a chip

The experimental values for electron temperature and plasma density are measured in a microfabricated, inductively coupled plasma on a chip (ICP). The miniature ICP system consists of a planar plasma source that is microfabricated on a glass wafer and a miniature aluminum vacuum chamber (φ=6 mm). A reliable Langmuir probe diagnostic for microplasma reactors was developed because classic probe measurements would be hindered by the small plasma volume, the small surface area of grounded reactor walls, collisional ion sheathes, and the radio-frequency (rf) interference from the high-frequency power supply. Once the ion density and electron temperature are determined, the neutral gas temperature was estimated to be nearly equal to room temperature. At low pressures, one finds that the plasma sheath width limits the dimensional scaling of the reactor, since the sheath is, typically, ∼0.6 mm. The plasma operates from 0.1 to 10 Torr, and requires less than 3 W of transmitted power at a frequency of 493 MHz. Direct measurement of the power absorbed by the gas discharge, however, shows that between 2% and 18% of the power supplied to the microstructure is absorbed by the discharge. The transfer of power to the discharge is most inefficient at low pressures where the electron neutral collision frequency is less than that of the rf power supply.

Microfabricated inductively coupled plasma-on-a-chip for molecular SO2 detection: a comparison between global model and optical emission spectrometry

In this work the molecular SO2 detection limit obtained using a microfabricated inductively coupled plasma-on-a-chip (mICP) system is compared with a volume-averaged plasma model. The miniature ICP system consists of a planar plasma source that is microfabricated on a glass wafer and a miniature aluminium vacuum chamber. The plasma operates from 0.1 to 10 Torr, and requires less than 4 W of power at a frequency of 493 MHz. Molecular detection limits were measured using the SO2 MUV2 band (A(1B1), a(3B1) → X(1A1)). Detection limits improve with increase of both the operating power and pressure due to increases in electron and metastable state Ar densities, with the best DL value being 45 ppb. A global plasma model is developed to calculate the metastable Ar density, electron temperature, and SO2 excitation rates in the mICP. Excitation rates for electron-impact collisions and the quenching reaction with Ar metastables, together with the known sensitivity of the optical system, allow one to calculate detection limits for molecular SO2 excitation. Calculated DLs are in reasonable agreement with experimental OES results.

Emission spectroscopy using a microfabricated inductively coupled plasma-on-a-chip : Invited Lecture

In this work a novel, microfabricated inductively coupled plasma (mICP) generator for emission spectroscopy is described. The spatial distribution of light emitted from the mICP, the electron temperature and ion density of the plasma, and the detection of trace amounts of SO2 excited by the mICP are presented. The miniature ICP system consists of a planar, spiral-shaped inductor and an impedance matching network that are microfabricated on a glass wafer and subsequently bonded to a miniature aluminum vacuum chamber. The plasma operates from 0.1 to 10 Torr, and requires less than 4 W of power at a frequency of 490 MHz. The chamber was designed to maximize the excitation and emission from SO2 molecules. An SO2 fraction as low as 3 ppm is directly measured using the intensity of atomic sulfur emission at 469.5 nm. The detection limit, however, is found to improve with both increasing plasma power and argon pressure, and is as low as 190 ppb. It is also clear from the optical emission spectra that this mICP has the ability to excite the entire SO2 molecule, which suggests that it is also a promising molecular detection tool.

Secondary electron emission yields from PEP-II accelerator materials

The PEP-II B-Factory at SLAC operates with aluminum alloy and copper vacuum chambers, having design positron and electron beam currents of 2 and 1 A, respectively. Titanium nitride coating of the aluminum vacuum chamber in the arcs of the positron ring is needed in order to reduce undesirable electron-cloud effects. The total secondary electron emission yield of TiN-coated aluminum alloy has been measured after samples of beam chamber material were exposed to air and again after electron-beam bombardment, as a function of incident electron beam angle and energy. The results may be used to simulate and better understand electron-cloud effects under actual operating conditions. We also present yield measurements for other accelerator materials because new surface effects are expected to arise as beam currents increase. Copper, in particular, is growing in popularity for its good thermal conductivity and self-radiation-shielding properties. The effect of electron bombardment, “conditioning”, on the yield of TiN and copper is shown.

Elettra vacuum system: status and experience with the new Al vacuum chambers

The status and recent developments of the Elettra vacuum system are reported. Due to the fact that in our facility no in-situ bake out is applied, we focused our work to contribute to the theoretical explanation of the beam cleaning efficiency. Gas injection experiments have been performed introducing various gases into the vacuum chamber of the storage ring. These experiments are very useful and help us to analyse better behaviour of vacuum chambers having a higher pressure profile. New aluminium vacuum chambers have been recently installed into the storage ring. Operational experience is also reported.

Induced Activity Calculations in View of the Large Electron Positron Collider Decommissioning

The future installation of the Large Hadron Collider (LHC) in the tunnel presently housing the Large Electron Positron collider (LEP) requires the dismantling of the latter after more than 10 years of operation. The decommissioning of an accelerator facility leads to the production of large amounts of waste, which in the case of an electron accelerator mostly is of very low level of radioactivity. LEP is classified as Nuclear Basic Installation (Installation Nucléaire de Base, INB) in France, where no unconditional clearance levels are fixed for the specific activity in materials to be released into the public domain. In the case of LEP, the possible sources of induced activity taken here into account are: localised beam losses, distributed beam losses and synchrotron radiation. Reference values of induced specific activity at saturation, normalised to lost beam power, were determined by comparing Monte-Carlo calculations carried out with the FLUKA code and experimental results. These figures are directly employed to estimate the expected amount of low level radioactivity around localised beam loss points in LEP. Regarding the synchrotron radiation, calculations of the total production of radionuclides from photon, thermal neutron and fast neutron activation in the aluminium vacuum chamber, the lead shielding and the magnet pole-faces of a dipole, showed that at beam energies less than 105 GeV, none of the components will be considered as radioactive for decay periods of longer than ten days.

Plasma-based Ion Implantation Facility and Research at the National Accelerator Centre, Faure

A new plasma-based ion implantation (PBII) facility consisting of a dedicated PBII chamber plus characterization equipment has been established at the Van de Graaff Group, National Accelerator Centre, Faure. The implantation unit has an aluminum vacuum chamber with a volume of 1 m3, and it incorporates conventional plasma generation capability for gas plasmas, such as a set of multifilaments. The implantation power supply is capable of delivering 30 kV, with a pulse duration of up to 1000 μs, and a repetition rate of 1 kHz. This allows a maximum average load of 12 J to the target. The facility is being used at the outset for the fundamental study of plasmas, time-dependent x-ray generation during the implantation pulse, and plasma immersion implantation. The facility is supported by a 6 MV Van de Graaff accelerator equipped with the ion-beam analytical tools necessary for characterization of modified surfaces.

Vacuum assisted drying of hydrophilic plates: static drying experiments

This investigation seeks to identify the effects of partial vacuums on the steady-state drying rate of cotton plates. Five pressure levels between atmospheric pressure and 33.6 kPa (20″ Hg vacuum) were tested in an aluminum vacuum chamber. Improvements in steady state drying rates on the order of 62% were observed at the lowest pressure level. The hoped-for design points were not discovered. Both theoretical and experimental values of the mass transfer rate are developed.

Vacuum chamber for the wiggler of the Taiwan Light Source at the Synchrotron Radiation Research Center

An aluminum vacuum chamber 3 m long and 21.5 mm high was fabricated, tested and installed in the wiggler section of the Taiwan Light Source at the Synchrotron Radiation Research Center. The chamber was made by the extrusion method and machined to a flatness of &amp;lt;±0.1 mm/3 m. The inner aperture included an elliptical channel (17 mm×80 mm) for electron beam and a pumping channel for a nonevaporable getter (NEG) strip. Two heat-treated Be–Cu springs were used to absorb the thermal expansion of the NEG strip during activation. After installation of the wiggler chamber in the storage ring, a pressure of 0.45 nTorr was reached after an in situ bakeout with NEG activated. The high temperature properties of the Be–Cu spring and the vacuum performance of the complete chamber have been tested. No obvious influence, due to the narrow beam aperture or limited gas conductance to the beam life time was found.