Ph. D. Thesis Defence
Department of Instrumentation and Applied Physics
Ph. D. Thesis Defence
NAME OF THE CANDIDATE : Mr. Ravi Verma
DEGREE : Ph.D.
TITLE OF THE THESIS : Development of Cryocooler Based High Performance
SUPERVISORS : Dr. Upendra Behera, CCT &
Dr. N C Shivaprakash, IAP
DATE AND TIME : Thursday, 13th December 2018 at 09.30 A.M.
VENUE : Lecture Hall-1, Dept. of Instrumentation
And Applied Physics.
The cryosorption (also known as cryoadsorpion) pumps belong to the class of vacuum pumps which comes under the category of gas binding pumps. In a cryosorption pump, the vacuum is created by the adsorption of the gas molecules on a cryopanel which is bonded with adsorbent materials using suitable adhesives. The adsorbent has porous structures and enables the entry of gas molecules into the pores. This is one of the important inventions for the production of clean, ultra high vacuum with high pumping speeds. Cryosorption pumps produce very clean vacuum and hence are being used for number of applications in areas such as metallurgy, chemical industries, semiconductor industries, fusion systems etc. Due to the absence of moving components, these pumps can work in high electric and magnetic field environments. In fact, they are the only suitable solution (as on date) for fusion applications (such as in a tokamak) wherein the deuterium and tritium atoms are combined to produce helium, neutron and energy.
The aim of this work is to develop a cryocooler based high performance cryosorption (or cryoadsorption) pump specifically for fusion applications. We discuss the works carried out for the development of the best performing cryosorption pump based on GM cryocooler.
- A specially prepared indigenously developed Knitted Carbon Cloth (KCC/IIS01) is found to have a larger surface area for adsorption compared to the others. This adsorbent has a surface area of ~ 3000 m2/g for helium adsorption at 4.5 K, which is significantly higher than those of granular charcoals which are in the range of ~ 1600 m2/g for similar experimental conditions.
- A special epoxy based adhesive (SEBA/IIS01) with higher thermal conductivity in the temperature range from 4.5 K to 7 K (which is generally the operating temperature range of cryosorption pump for efficiently pumping of helium gas) compared to the commercially available epoxy adhesives such as STYCAST 2850 FT and G10 Cryocomp has been developed indigenously and used for the development of the cryosorption pump.
- Using the above epoxy adhesive SEBA/IIS01 and the Knitted Carbon Cloth KCC/IIS01, cryopanel has been prepared and studied for its performance. The pumping speeds of the developed cryopanel are improved on an average by factors of 1.55 and 1.54 (when compared with those of commercial panel) for gases such as hydrogen and helium respectively in the required pressure range.
- The thermal conductivity of the epoxy adhesive has been further enhanced by addition of fine aluminium powder as filler in the base epoxy without hampering the bonding strength of the adsorbents on the metallic cryopanel. Based on the experimental studies both on the increased thermal conductivity and the reduced bonding strength by addition of aluminium filler particles, an optimum composition of the aluminium powder filler in the epoxy adhesive has been estimated as ~ 35 % by volume fraction.
- A new cryopanel has been fabricated wherein the knitted carbon cloth KCC/IIS01 is bonded using the epoxy-aluminium adhesive with 35% aluminium powder. The pumping speeds of the newly developed cryopanel are improved on an average by factors of 3.63 and 3.62 (when compared with those of commercial panel) for gases such as hydrogen and helium respectively in the pressure range from 5E-6 to 4E-5 mbar. The studies have led to the development of a cryocooler based cryosorption pump with substantial higher pumping speeds for gases such as hydrogen and helium compared to the commercial cryosorption pumps. Hence the developed cryosorption pump can become quite useful for the tokamak related applications.
ALL ARE WELCOME
Date(s) - 13/12/2018
9:30 am - 10:30 am
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