KATRIN NEG pumping concept investigation

The Karlsruhe Tritium Neutrino experiment (KATRIN) is going to use a very large electro-static tandem spectrometer to measure the electron spectrum from the tritium beta decay, where several kilometers of non-evaporable getter (NEG) strips (type ST707) are to be used to achieve the UHV requirements. Different geometrical configurations of the NEG strips have been studied by Monte Carlo simulations. It is shown that the resulting pumping speed of the getter pumps will allow to get a pressure below 10⁻¹¹ mbar in the huge vessel with a volume of 1400 m³. By systematic assessment of the statistics of the pumping surfaces, it could be demonstrated that the design is sound.     

非蒸散型吸气剂对混合气体的抽气行为研究

NEG抽除混合气体的行为不同于抽单纯气体.测试了SEAS公司的NEG组件ST707WP 1250对由80%H2和20%CO组成的混合气体的抽气性能,并和抽纯气性能进行了比较.混合气体中的NEG对H2的抽速受CO影响,随H2吸气量的增加而明显下降.混合气体中的NEG对CO的抽速不受H2影响.研究结果为SSRF储存环真空系统设计提供了重要依据.     

Effect of coating morphology on the electron stimulated desorption from Ti-Zr-Hf-V nonevaporable-getter-coated stainless steel

The electron stimulated desorption (ESD) was studied for quaternary Ti-Zr-Hf-V alloy coated stainless steel samples with different surface structures: dense on one sample and columnar on another. The ESD yields were measured as a function of electron accumulated dose up to ∼10²³ e⁻/m² or greater and three different NEG coating activation temperatures: 150, 180 and 250 °C. After each ESD experiment the samples were saturated with a mixture of H₂, CO and CO₂. Both samples depicted lower ESD yields for all desorbed species compared to a ternary Ti-Zr-V alloy. It was also shown that although the columnar NEG coating demonstrated better pumping properties and, for NEG activated at 150 °C, lower initial ESD yields, the higher activation temperature may result in a significant H₂ yield increase with dose for the columnar NEG coating. This effect was demonstrated for the first time and should be considered for application in particle accelerators.     

非蒸散型吸气剂泵在真空计量中的应用研究

本文简要阐述了非蒸散型吸气剂(NEG)泵的吸气机理,着重介绍了NEG泵在超高/极高真空标准、静态膨胀法真空标准等真空计量标准中的最新应用结果。结果表明:利用NEG泵在室温下获得了10-10Pa的XHV;利用NEG泵将超高/极高真空标准校准下限延伸到了10-10Pa量级;利用NEG泵将静态膨胀法真空标准的校准下限延伸到了10-7Pa量级。最后还对用NEG泵延伸固定流导法微流量标准测量下限的可行性进行了分析。     

“50 Years of Varian sputter ion pumps and new technologies”

Varian was co-founded by Russel Varian, the inventor of the Klystron, and its original activity was in the field of microwave electron tubes. The Sputter Ion pump (SIP) was invented as the solution for clean pumping of electron tubes.Following the SIP, the Ultra High Vacuum (UHV) technology was developed, mainly driven by High Energy Physics and Surface Science. During the two following decades most of Research & Development activities were focused to improve the operation of SIP towards high pressure. Most of the achievements were then made obsolete by turbomolecular pumps, which became the ideal complement of SIP at relatively high pressure. The range of applications for ion pumps than became more clearly defined as UHV. Therefore R&D focus moved to low pressure performance of SIP (magnetic field, controller, anode structure). A combination of sputter ion pumps with evaporable getters in the Titanium sublimation pump has been implemented since early times. More recently, the combination with non-evaporable getters (NEG) has become very common especially in particle accelerators. Integration of NEG in SIP, by applying inside the pump a NEG film with the technology originally developed at the European Organization for Nuclear Research (CERN) in Geneva, is the most recent development.     

Thin film getter coatings for the GSI heavy-ion synchrotron upgrade

For the future project the Facility for Antiproton and Ion Research (FAIR) at GSI, an accelerator system with a base pressure of 10⁻¹⁰ Pa is required. The low pressure is needed to reduce the charge exchange rate between the accelerated ions and the residual gas molecules and therefore to increase the ion beam lifetime. Among the different measures undertaken to upgrade the existing UHV system, the installation of non-evaporable getter (NEG)-coated dipole and quadrupole chambers is foreseen. For this purpose a licence agreement for the non-evaporable thin film getters was signed between GSI and CERN in the end of June 2005.A new dedicated magnetron sputtering facility was designed and commissioned at GSI to perform the Ti-Zr-V coating on the dipole chambers of the heavy-ion synchrotron (SIS 18).Those pipes, made from stainless steel, have an elliptical cross section, are 3 m long, and are characterised by a wall thickness of 0.3 mm and a 15° bending angle.The characterisation of the thin films produced has been carried out by Rutherford backscattering spectroscopy (RBS), energy dispersive X-ray spectroscopy (EDX) and elastic recoil detection analysis (ERDA) for the chemical composition, scanning electron microscopy (SEM) for the morphology, and X-ray photoelectron spectroscopy (XPS) for the activation behaviour.The coating facility, its operating mode, and the first results obtained on the NEG characterisation by means of the different techniques will be described.     

Preparation and characterization of non-evaporable porous Ti-Zr-V getter films

Highly porous TiZrV film getters on (100) silicon substrates have been successfully grown by the glancing angle dc magnetron sputtering method. The glancing angle is defined as the angle between the surface normal to the substrate and the surface normal to the target. The main deposition parameters that produce the porous TiZrV films are the pressure of sputtering gas Ar and glancing angle at room temperature. The larger the glancing angle is, the higher the porosity and specific surface area of the TiZrV films are. The specific surface area of the dense and porous TiZrV films is 2 m²/g and 13 m²/g, respectively. The diameter of columnar width and inter-distance between the columnar crystals of the porous film are 200 nm and 50 nm, respectively. The columnar width of dense TiZrV films is about 100 nm. The porous TiZrV films have a larger capability to absorb oxygen than that of the dense TiZrV films.     

Test Particle Monte-Carlo modelling of installations for NEG film pumping properties evaluation

Two installations were built in the ASTeC vacuum science laboratory to investigate the pumping properties of non-evaporable getter (NEG) films. An important parameter to characterise the pumping properties is the film sticking probability (α). Test Particle Monte-Carlo (TPMC) models were used for accurate evaluation of NEG film sticking probability from pressure readings during gas injection. The results of these models were used for interpreting the results of measurements in different experimental configurations: planar, cup and tubular samples. It was shown that there is a difference between simple formulas used in vacuum technique and TPMC results which is significant for α > 0.1 with planar samples, for α > 0.01 with cup samples, and in the full range of α for tubular samples. It was also shown that the gauge positions are very important, the exact position of the gauge or RGA ionisation chamber should be used in the modelling.     

10-10 Pa溅射离子泵和非蒸散型吸气剂的复合泵

不改变商用SIP的基本结构,把NEG组件WP1250装入SIP,构成(SIP NEG)的XHV复合泵.它使SIP和NEG的特点互补,综合性能优越.NEG激活前,SIP单独抽气,极限压强1.1×10-8Pa.NEG激活后,SIP和NEG联合抽气,复合泵的极限压强降到7×10-10Pa,抽速稳定的范围更广,标称抽速约是SIP抽速的2.5倍.     

束流真空管道中放电现象的实验研究

目前正在欧洲核子中心(CERN)建造的LHC(Large Hadron Collider)是世界上最大的加速器,它是一个具有高能量(7 TeV)大流强(0.53 A)的质子加速器.在它的直线节真空系统中,绝大部分的真空盒内表面将被镀上NEG薄膜.这样在又细又长的真空盒里,当有束流通过时,NEG薄膜不仅可以作为分布式吸气剂泵使用,而且NEG薄膜还具有降低二次电子发射系数的作用,因此了解NEG薄膜的性能是很重要的.