Vacuum System of the Large Cyclotrons at VECC

Yadav

Akhter

et al. 2012

J. Phys.: Conf. Ser.

Self Cite

The water vapour contained in the atmosphere contaminates a vacuum systems, when it is exposed to air. The degree of contamination will depend on the surface characteristics, treatment of the system walls, the relative humidity and the turbulence of air, the amount of time the system is opened to the atmosphere, etc. If the temperature of the exposed surface is low, possibility of water condensing on the surface exists. In order to study the effect and optimise procedure for achieving high vacuum in a vacuum chamber initially containing water, a vacuum chamber has been fabricated. Pump down time has been measured for different amount of water placed in the vacuum chamber with varying pumping speeds. The paper presents a review of similar activities and results of the experimental study. Introduction:The beam chamber of VEC superconducting cyclotron [1] has a number of penetrations in the median plane in between the upper and lower superconducting coils to accommodate extraction components and beam diagnostic components. Because of the compact structure, adequate space was not available at the penetrations for placing a thermal shield. The temperature at these penetrations is quite low. It is observed that moisture from air condenses there and considerable time is taken to achieve good vacuum, specially, in monsoon. In the case of water leakage in the system, considerable amount of water gets accumulated in the beam chamber. Because of the complex geometry of the cyclotron, it is quite difficult to remove water from the restricted areas. It is also not possible to bake the acceleration chamber to enhance the rate of moisture removal.An experimental set-up has been fabricated to study the pump down characteristics in the presence of water in a vacuum enclosure. The paper presents a literature survey on work carried out on similar lines and results of experiments carried out. Review of similar activitiesChan 2010 [2] examined the effect of environment humidity on the rate of thermal outgassing from an aluminium chamber. An aluminium glove box and an air shower, which provided dehumidified environments with water vapor concentrations of 0.1 ppm and 5 ppm respectively, were utilized to assess the effect of environmental humidity on the rate of thermal outgassing. Chan observed that only 4 h of evacuation was required to yield a small rate of the order of 1 x 10 -13 mbar L s -1 cm 2 of thermal outgassing upon filling with super-dry nitrogen without baking. A smaller rate of thermal outgassing was obtained using a drier venting gas, or by exposure to a drier environment. A thermal outgassing rate of the order of 1 x 10 -11 mbar L s -1 cm 2 was achieved by venting the glove box with super-dry nitrogen inside and controlling of environmental humidity at 0.1 ppm.Yamazaki 2010 [3] carried out control of water vapor in a nitrogen gas purge line in addition to surface treatments of chambers using buff polishing and electrolytic polishing, followed by

Section: Discussionmentioning

confidence: 99%

Removal of water from unbaked vacuum system

Yadav

Akhter

et al. 2012

J. Phys.: Conf. Ser.

Self Cite

“…Due to conductance limitations, high vacuum pumping is done by three cryopanels. 6 The liquid helium cooled cryopanels are placed inside the lower dees in the valley gap of the superconducting magnet. The chevron baffle and radiation shield of the cryopanel is cooled by liquid nitrogen.…”

Section: B Cryopanels For Cyclotron Beam Chambermentioning

confidence: 99%

Performance of Variable Energy Cyclotron Centre superconducting cyclotron liquid nitrogen distribution system

Review of Scientific Instruments

Nandi

Bhattacharyya

2014

The liquid nitrogen distribution at Variable Energy Cyclotron Centre, Kolkata, India K500 superconducting cyclotron uses parallel branches to cool the thermal shield of helium vessel housing the superconducting coil and the cryopanels. Liquid nitrogen is supplied to the thermal shields from a pressurised liquid nitrogen dewar. Direct measurement of flow is quite difficult and seldom used in an operational cryogenic system. The total flow and heat load of the liquid nitrogen system was estimated indirectly by continuous measurement of level in the liquid nitrogen tanks. A mathematical model was developed to evaluate liquid nitrogen flow in the parallel branches. The model was used to generate flow distribution for different settings and the total flow was compared with measured data.

“…Due to conductance limitations, cryopumping is preferred in cyclotrons. 13,14 In VECC SCC, three cryopanels are placed inside the Dees (Fig. 2).…”

Section: K = 500 Cyclotron Beam Chamber Vacuum Systemmentioning

confidence: 99%

Performance of the beam chamber vacuum system of K = 500 cyclotron at Variable Energy Cyclotron Centre Kolkata

Review of Scientific Instruments

Duttagupta

2014

The beam chamber of Variable Energy Cyclotron Centre, Kolkata's K = 500 superconducting cyclotron is pumped by liquid helium cooled cryopanel with liquid nitrogen cooled radiation shield. Performance of the vacuum system was evaluated by cooling the cryopanel assembly with liquid nitrogen and liquid helium. Direct measurement of beam chamber pressure is quite difficult because of space restrictions and the presence of high magnetic field. Pressure gauges were placed away from the beam chamber. The beam chamber pressure was evaluated using a Monte Carlo simulation software for vacuum system and compared with measurements. The details of the vacuum system, measurements, and estimation of pressure of the beam chamber are described in this paper.