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Fusion Engineering and Design 84 (2009) 1038–1042

Contents lists available at ScienceDirect

Fusion Engineering and Design

journa l homepage: www.e lsev ier .com/ locate / fusengdes

verview of the KSTAR vacuum pumping system

.P. Kim ∗, K.S. Lee, H.L. Yang, M.K. Kim, H.K. Kim, G.H. Kim, K.M. Kim, H.T. Kim, K.H. Kim,.K. Park, Y.K. Oh, J.S. Bak

ational Fusion Research Institute (NFRI), 52 Yeoeun-dong, Yusung-ku, Daejeon 305-333, Republic of Korea

r t i c l e i n f o

rticle history:vailable online 25 January 2009

eywords:STAR

a b s t r a c t

The installation of the Korea Superconducting Tokamak Advanced Research (KSTAR) device vacuumpumping system for both the vacuum vessel and the cryostat was finished in the middle of 2007. After thesuccessful self-commissioning of the main vacuum pumping system by August 2007, the system success-fully operated in the integrated system commissioning and 1st plasma experiments of the KSTAR device.

acuum pumping systemacuum vesselryostatacuum commissioning

The vacuum pumping system has successfully operated and achieved the target vacuum pressure for thevacuum vessel and the cryostat during the machine commissioning and 1st plasma experiments with nosevere troubles and problems, which is one of the main factors that led the KSTAR project to achieve suc-cessful 1st plasma. Furthermore, the vacuum pumping system has been satisfactorily operated by remotecontrol and synchronization in gas puffing experiments. This paper describes the final configuration ofthe KSTAR vacuum pumping system, the results of vacuum commissioning, and the other results of the

elate

vacuum conditions that r

. Introduction

The vacuum pumping systems for the vacuum vessel and theryostat are the most important and basic systems of the Koreauperconducting Tokamak Advanced Research (KSTAR) device1] to achieve success in the machine commissioning includingool-down, superconducting (SC) magnet commissioning, and 1stlasma generation. Therefore, both the design and configuration ofhe vacuum pumping system have been changed several times toptimize vacuum conditions for the vacuum vessel and the cryo-tat since the basic conceptual design was launched in the earlytages of the KSTAR project. The final configuration of the vac-um pumping system and its control system was fixed in early007 following several changes from the configuration which waseported in detail in Ref. [2]. Fig. 1 is a schematic drawing of thenal vacuum pumping system of KSTAR. The commissioning ofhe vacuum pumping system was successfully finished by Aprilf 2007. This was followed by the 1st vacuum test for the vac-um vessel and the cryostat by August 2007. In this commissioningeriod, the target vacuum pressure for the 1st plasma campaign

as successfully achieved in both the vacuum vessel and the cryo-

tat.In addition to achieving good vacuum conditions for the KSTAR

evice, the vacuum pumping system was satisfactorily operated

∗ Corresponding author. Tel.: +82 42 870 1732; fax: +82 42 870 1709.E-mail address: kpkim@nfri.re.kr (K.P. Kim).

920-3796/$ – see front matter © 2008 Elsevier B.V. All rights reserved.oi:10.1016/j.fusengdes.2008.12.064

to wall conditioning.© 2008 Elsevier B.V. All rights reserved.

during the machine cool down and 1st plasma experiments. In themachine cool down period, the vacuum system monitored the vac-uum pressure, partial gas pressures, and pressure changes due tothe temperature change of the SC magnet, thermal shields, and allthe other cryogenic components contained in the cryostat. The vac-uum pumping system also cooperated with the wall conditioningsystem and gas fueling system in the vacuum vessel during the 1stplasma experiments. As a result, the vacuum pumping system pro-vided fundamental conditions for the successful achievement of theKSTAR 1st plasma in June 2008.

2. Vacuum pumping system for the vacuum vessel

The vacuum pumping system for the vacuum vessel is comprisedof a pumping duct, a main pumps unit, a backing and roughingpump system, and its control system to maintain the vacuum pres-sure under the target value (<5 × 10−7 mbar) in the vacuum vessel,which has 80 m2 of total surface area and an inner volume of 100 m3.The main pumping system is composed of eight turbo molecularpumps (TMP) and two cryo-pumps. The pumping capacities of eachTMP and the cryo-pumps are 2800 l/s and 10,000 l/s, respectively.Due to a restriction on the TMP operation that requires less than100 Gauss of vertical stray magnetic field; the TMP unit needed

to be located at a distance of 10 m from the machine center. Thisrestriction requires an 8.0 m long pumping duct with a of diame-ter 1.38 m, which was determined by consideration of the requiredpumping speed as is described in Ref. [2]. The pumping duct isconnected to the tokamak by means of a 30 mm-thick epoxy glass

K.P. Kim et al. / Fusion Engineering and Design 84 (2009) 1038–1042 1039

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Fig. 1. Schematic drawing of th

late to electrically isolate the pumping system from the tokamakystem.

The roughing pumps and backing pumps for the TMP system uti-ize various combinations of the mechanical booster pumps and dryumps that are connected to the main pump unit through roughingnd backing pump lines of length 40 m and diameter 200–250 mm.

very TMP and cryo-pump unit has a main gate valve to isolate theump from the pumping duct in the case of a vacuum break of theacuum vessel or the pumping duct. Various kinds of the vacuumauges are installed on the several positions of the vacuum vesselorts and pumping ducts to measure the vacuum pressure as

able 1ajor components of the vacuum vessel and the cryostat pumping system.

Vacuum vesselpumping system

Cryostat pumping system

ain pump

4 × 2800 l/s TMP8 × 2,800 l/s OSAKA TG2810 TMPOSAKA TG2810 TMP 3 × 1900 l/s TMP

PFEIFFER TPH2301 TMP

ubsidiary pump2 × 10,000 l/s 2 × 10,000 l/sULVAC U20HLKcryo-pump

ULVAC U20HLK cryo-pump

MP backing pump1 × 1800 m3/h 1 × 1800 m3/hEDWARDS iF1800 Dry EDWARDS iF1800 Dry

oughing pump1 × 1800 m3/h 2 × 1800 m3/hEDWARDS iF1800 Dry EDWARDS iF1800 Dry

esidual gas analyzer1 unit 1 unitSRS 100 SRS 100

lectrical isolation 30 t epoxy glass plate 30 t epoxy glass plate

acuum gauge 10 units 8 units

acuum gate valve 23 units 21 units

AR vacuum pumping systems.

accurately as possible. At the end of the pumping duct is a residualgas analyzer (RGA) for measurement of the gas partial pressuresduring the helium leak tests and wall conditioning. The vacuumcomponents for the vacuum vessel are summarized in Table 1.

3. The vacuum pumping system for the cryostat

The vacuum pumping system for the cryostat was preparedto achieve the vacuum condition in of the cryostat with a pres-sure less than 1 × 10−4 mbar at room temperature, which is a basicrequirement for the start of the cool down of the KSTAR devicewith the normal operation mode of the helium refrigeration sys-tem [3]. The configuration of the vacuum pumping system is verysimilar to that of the vacuum vessel except that the inside of thecryostat is much more complicated. It has 38,000 m2 of total sur-face area including that of the multi-layer insulation (MLI) forthe cryostat thermal shields, a volume of 480 m3, 5000 weldingpoints, 72 welded bellows, and helium lines of almost 2 km length.Table 1 also shows a list of the main vacuum components for thecryostat.

4. Control system

The KSTAR vacuum control system has two main parts which arethe cryostat vacuum control system and the vacuum vessel vacuumcontrol system. These are independently operated not only from alocal control panel but also in the main control room. The systemcontrols all the vacuum components including TMPs, cryo-pumps

for high vacuum, dry and mechanical booster pumps for roughvacuum, vacuum gate valves, vacuum gauges, and a residual gasanalyzer (RGA) system to measure gas partial pressures in both thevacuum vessel and the cryostat. It requires functional cooperationwith the KSTAR machine control system including data visualiza-

1040 K.P. Kim et al. / Fusion Engineering and Design 84 (2009) 1038–1042

STAR

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Fig. 2. Control logic of the K

ion, data archiving, data analysis, machine interlocks, and humanafety.

The hardware of the vacuum control system is based on Pro-rammable Logic Controllers (PLC). The basic function of theacuum control system that is based on the PLC system is to provideachine operational safety in reference to the entire vacuum con-

ition. In the integrated commissioning period, the vacuum controlystem has set the emergency vacuum pressure level of the vacuumessel and the cryostat as 5 × 10−2 mbar and 1 × 10−5 mbar at cryo-enic temperature, respectively. The software of the vacuum controlystem is based on experimental physics and industrial controlystem (EPICS) under the Linux platform [4]. The EPICS IOC commu-icates with the PLC through Ethernet. The operator interface (OPI)as also developed to monitor the KSTAR vacuum control system in

he KSTAR main control room for 24 h 365 days per year operation.ig. 2 shows the configuration of the KSTAR vacuum control systemhich is based on PLC and EPICS.

. 1st Vacuum commissioning for the vacuum vessel andhe cryostat

The first vacuum commissioning for both the vacuum vesselnd the cryostat was performed after the assembly was finished

Fig. 3. Helium partial pressure in the cryostat for the helium leak test.

vacuum pumping systems.

in June 2007. In this commissioning period, the vacuum pressure ofthe vacuum vessel and the cryostat reached about 4.5 × 10−8 mbarand 2.5 × 10−5 mbar, respectively. These results showed that thebasic requirement for achieving the target vacuum pressure in thefirst trial had been achieved. The helium leak test result showedthat there was no detectable leak point when the sensitivity ofthe helium leak detector was less than 5 × 10−10 mbar l/s and5 × 10−9 mbar l/s for the vacuum vessel and the cryostat, respec-tively. However, a minor leak in the cryostat thermal shield wasfound in the final leak test with gaseous helium pressurizing tooperational pressure when the cryostat was under vacuum [5]. Fig. 3shows the helium partial pressure change in the leak test, which isclear evidence of a helium leak in the helium circuit of the cryo-stat thermal shield. The leak point was found to be one of the smallbellows connecting the cryostat base thermal shield to the bodythermal shield. It took almost three months to find the exact leakpoint and it took a day for the repair.

6. Final vacuum commissioning for the vacuum vessel

After all the helium distribution systems were installed and con-nected to the tokamak, final vacuum commissioning was startedin early March, 2008. The final vacuum commissioning includedvacuum pumping, leak tests, and vacuum monitoring during thewall conditioning period of the vacuum vessel. The commissioningalso covered the vacuum pumping and monitoring for the cryostatbefore and after the machine cool down period. The vacuum pres-sure of the vacuum vessel reached below 5.0 × 10−7 mbar within12 h from the start of the vacuum pumping, and the pressure wasmaintained in the range of 2.5–3 × 10−8 mbar before the vacuumvessel baking started. While the vacuum vessel is baked up to 100 ◦Cwith hot pressurized water, the vacuum pressure continuouslyincreased to 10−7 mbar range. This process was followed by glowdischarge cleaning (GDC) that is described in detail in Ref. [6]. Inthe final vacuum commissioning of the vacuum vessel, all the basicdiagnostics and ECH and ICRH heating system for were installed forthe KSTAR 1st plasma experimental campaign. The helium leak testresult showed that there was no detectable leak point for a detector

sensitivity less than 5.0 × 10−10 mbar l/s in all the sub-componentsthat were installed in the vacuum vessel and on the vacuum vesselports. Fig. 4 shows the vacuum pressure history of the vacuum ves-sel from the start of the vacuum commissioning to the end of themachine cool down period.

K.P. Kim et al. / Fusion Engineering and Design 84 (2009) 1038–1042 1041

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Fig. 4. Vacuum pressure of the vacuum vessel vs. operation time.

. Final vacuum commissioning for the cryostat

The final vacuum commissioning for the cryostat was simultane-usly performed with that of the vacuum vessel. The base pressuren the cryostat reached 2.7 × 10−6 mbar at room temperature withinday from the start of the vacuum pumping. In the cryostat vacuumumping phase, all of the cryogenic temperature systems contained

n the cryostat including SC magnets, SC bus-lines, the helium pip-ng system and thermal shields were pressurized with gaseouselium to the operational pressure for a final confirmation of theelium tightness at room temperature. The final leak test verifiedhat there was no evidence or symptom of a helium leak.

As the machine cooled down towards cryogenic temperature,he vacuum pressure of the cryostat continuously decreased tohe level of 10−7 mbar. Especially, when the temperature of theC magnet and its subsystem reached 40 K, the vacuum pressurerastically decreased and finally was maintained in the range of.0–2.5 × 10−8 mbar when the temperature of the SC magnets, SCus-lines, and helium circuit system reached 4.5 K. The helium par-

ial pressure was monitored through the long cool down phase and

aintained a low level of 10−9 mbar. Fig. 5 shows the vacuum pres-ure history of the cryostat from start of the vacuum commissioningo end of the cool down phase. The total helium leak rate in the

Fig. 5. Vacuum pressure of the cryostat vs. operation time.

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Fig. 6. Changes of the helium partial pressure in the total helium leak measurement.

cryostat was also measured before the start of the machine warmup phase, which was the final step of the 2008 campaign of KSTAR.To measure the total leak rate, all the main gate valves for the TMPsand cryo-pumps were closed and helium partial pressure was mea-sured with the RGA as shown in Fig. 6. The linearly increasing rate ofthe helium partial pressure was multiplied by the effective volumeinside of the cryostat, and the calculated total leak rate was less than8.9 × 10−8 mbar l/s which is much less than allowable total leak rateof 1 × 10−4 mbar l/s.

8. Conclusion

As the first the step of the integrated commissioning state ofthe KSTAR device, the vacuum commissioning for both the vacuumvessel and the cryostat was successfully completed. The success inthe vacuum commissioning provided essential conditions for themachine cool down, SC magnet tests and 1st plasma experiments.The vacuum pressure in the vacuum vessel was maintained below3.0 × 10−8 mbar during the commissioning stage and it is expectedto improve after full installation of the PFC baking system with adesigned maximum temperature of 350 ◦C. There will be a wallboronization system in the future operational phases. The vacuumcommissioning of the cryostat was one of the most important fac-tors for the successful machine cool down in the first trial with nosignificant trouble. The total helium leak rate measurement resultshowed that there was no severe cold leak in the cryostat, although afurther investigation should be made to identify the source of a leakrate of 10−8 mbar l/s. The hardware and software for the vacuumcontrol system were satisfactorily operated through the completecommissioning period. But they need further improvement in theinterlock logic, remote control logic, and data archiving system forthe more complicated environment in the future operation phases.

Acknowledgement

The Korean Ministry of Education, Science and Technology underthe KSTAR Project Contract supported this work.

References

1] G.S. Lee, M. Kwon, C.J. Doh, B.G. Hong, K. Kim, M.H. Cho, et al., Designand construction of the KSTAR tokamak, Nuclear Fusion 41 (10) (2001)1515–1523.

2] In-Keun Yu, Sang-Ryul In, Jong-Yeun Lim, Seungyon Cho, Design and test ofthe KSTAR vacuum pumping system, Fusion Engineering and Design 83 (2008)117–122.

1 ing an

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042 K.P. Kim et al. / Fusion Engineer

3] Chang H.-S., et al., Commissioning results of the KSTAR helium refrigerationsystem, International Cryogenic Engineering Conference, 22 Seoul, Korea, 2008,submitted for publication.

4] Myungkyu Kim, I.K. Yu, Kukhee Kim, M.C. Kyum, M. Kwon, EPICS implementationfor the KSTAR vacuum control system, Fusion Engineering and Design 81 (2006)1823–1827.

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d Design 84 (2009) 1038–1042

5] G.H. Kim, W.C. Kim, H.L. Yang, E.N. Bang, K.P. Kim, K.S. Lee, et al., KSTAR ther-mal shield, 25th Symposium on Fusion Technology, Rostock, Germany, 2008,submitted for publication.

6] K.M. Kim, H.L. Yang, S.T. Kim, H.T. Kim, K.P. Kim, K.S. Lee, et al., Wall conditioningof the KSTAR vacuum vessel, 25th Symposium on Fusion Technology, Rostock,Germany, 2008, submitted for publication.