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       HT-7 Vacuum System


                Peng Xuebing
         Tokamak Design Division
                  July 2008


         References: Yang Yu, ASIPP(2006)
             Gu Xuemao,ASIPP(2005)
              HT-7 Vacuum System

                              Questions


                1. what’s the primary purpose of HT-7
                   Vacuum System?


                2. What types of pumps are used?




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               HT-7 Vacuum System



                        1、Introduction

                          2、Pumping systems


CONTENTS                  3、Vacuum Operation

                         4、Other issues

                        5、Summary


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               1、Introduction

           The HT-7 vacuum system consists of two groups: PVV(Plasma
           Vacuum Vessel), CVV(Cryostat Vacuum Vessel)


PVV                               CVV
Purpose: provide a cleanliness    Purpose: provide a lower ultimate pressure
ultrahigh or high vacuum for      for good thermal isolation
plasma discharge
                                  Volume & surface area: 5m3, 198m2(total)
Volume & surface area:
                                  Wall temperature: <250℃(18m2), 20℃
4.5m3, 82m2(including tiles)
                                  (36m2), about 5K(100m2)
Wall temperature: <250℃           Ultimate pressure: 5×10-2Pa (at room
Ultimate pressure: <5×10-5Pa      temperature), 5×10-4Pa (during cryogenic
                                  operation)



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              2、Pumping Systems

                       Three pumping systems




    Rough vacuum             Plasma vacuum              Cryostat vacuum
    pumping system           vessel pumping             vessel pumping
                             system                     system



       Three independent systems have diferent fuctions and are divided
       into 6 Pumping Groups (PGs) or 7 Pumping Stations.



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                  HT-7 Vacuum System




                                       PG 3 (for CVV)
  Pumping Group
  (PG) 1 (for PVV)


                                         PG 2 (for PVV)

PG 4&6 (for CVV)




PG 5 (Rough Vacuum
Pumping System)

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              Rough Vacuum Pumping System




PG 5: Two roots
pumping stations                      Liquid nitrogen
(300 l/s each with a                  cooled traps
back pump of 70
l/s) are used to
pump the CVV                           Roots pumps
from the
atmosphere to about
10 Pa                                   Rotary pumps


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                  PVV Pumping System



                                       PG 2: A TMP (speed
                                       of 1500L/s) with a
                                       back rotary pump with
PG 1: A TMP(Turb-                      speed of 15L/s,
moleculor pump) with
speed of 450L/s plus a
back rotary pump with
speed of 8L/s, and
another same TMP is
placed on the by-pass
tube.




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                 CVV Pumping System

                          PG 3: A TMP (speed
                          of 450L/s) with a back
                          rotary pump with
                          speed of 8L/s,



PG 4: A TMP
(speed of 1500L/s)
with a back rotary
pump with speed of                                 PG 6: A TMP (speed of
15L/s,                                             450L/s) with a back rotary
                                                   pump with speed of 8L/s,
                                                   connecting with the current
                                                   lead tank,




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              3、Vacuum Operation

                                Three Stages

    •Rough Pumping Stage: The PVV is connected with the CVV, and a
    rough pumping station pumps two vessels from the atmosphere to about 10
    Pa in 2–4 h.

    •High Vacuum Pumping Stage: Two vessels are pumped separately
    by two pumping groups. The CVV is kept at 10−2Pa, and leak detecting and
    wall conditioning is carried out in the PVV. This stage lasts 5–7 days
    typically.

    •Cooling Down and Wall Conditioning Stage: The cryostat is
    cooled in 4–5 days, and further wall conditioning is carried out at the same
    time. At the end of this stage, the device is ready for plasma experiments.




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              4、Other issues


              Flange sealing techniques:
              metal sealing because of baking temperature on plasma vacuum
              chamber, except some rubber O-ring sealing at particular places
              Cold trap:
              prevent contamination such as oil diffuse up into the vacuum
              chamber
              Baking:
              desorbs physical adsorbtion melecules
              RF & GDC discharge cleaning:
              desorbs chemical adsorbtion melecules




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              5、Summary


            1. The HT-7 vacuum system has two chambers with different
               requirements and 7 pumping stations.
            2. A rough pumping system: two pumping stations, roots
               pump plus rotary pump.
            3. There are 5 analogical TM pumping stations with a back
               rotary pump, two stations for PVV and three stations for
               CVV.
            4. Combined with other vacuum technology such as flang
               sealing, baking, discharge clearing, etc.
            5. The ultimate pressure in two chambers can meet the
               vacuum requirements for plasma discharge in PVV and
               superconducting coils operation in CVV.


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       Thank You for Your Attention!




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