WAO 2021

A Fire at KEK LINAC
and Its Recovery
Kazuro Furukawa<kazuro.furukawa@kek.jp>

for KEK e–/e+ Injector LINAC

Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

1 / 25

WAO 2021

Injector Linac Building and Assembly HallSouthern 1/3 of 40-year-old Injector Linac

Assembly Hall

(Left-side is Southward)(250m2)

Sector B

Ａセクター

Ｂセクター

(80m)
機械、電気室

機械室

A1_A
B7

B8

B5

B6

B3

B4

B1

B2

SB_B AC

A4AB

A3AD AA

A2

A1_B

機械室

副制御室

加速管組立室MB
SB_C
C1

C2C3C4C5C6加速管準備室

C7C8SB_1

1112FC_13
1A

15 FC_15

1E161718

1B 1C

電気室 空調機械室(150m2) Sector R

J-ARC

SouthSector C
Cセクター

(80m)

１セクター

v The fire at the assembly hall affected
B,R,C sectors of the injector linac building³ About 25% of the 700-m injector linac building
Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

2 / 25

WAO 2021

Accelerating Structure Test Facility
in the Assembly Hall
u Adjacent to the south of the injector building(Apr.2.2019.)

v X-band, C-band, S-band developmentsv Nextef : research collaboration
with CERN and US labs. (for 13 years)

Shield door to linac�Shielded caves forstructure tests�

v On the 2nd day of a planned 3-month workv Planned to be used for S-band from FY2020

Staircase�³ 150 MW high-power pulsed power modulator

SouthPulsed power
modulator�

Klystron�
SouthAccelerating structure assembly room�
Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

3 / 25

WAO 2021

Fire at Injector Linac Buildingu A fire broke out at the assembly hall adjacent to the injector buildingv The hall was used for R&D of S-band, C-band, X-band structuresv On the day, a collaboration research program with CERN/SLAC for X-bandu A fire started in a microwave high-power modulator³ X-band microwave: 11.424 GHz、10 - 100 MW、1 μs、50 Hz

v An aged capacitor in the pulse-forming network (PFN) burst, discharged, ignitedu High-power interlocked, fire-alarm triggered, much smoke
v Fortunately, no injury
v Most of equipment was damaged³ S-band development at the test-stand was important, and recovered at early 2020
³ X-band devices were much more damaged, and approved to restart in this month, Sep.2021

u Fire stopped when firemen entered (1.5 hour later)v No media/press investigation（on site）³ “No environmental hazards found” on TV and papers³ While “no environmental hazards” was surely true, the reality was so disruptive

Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

4 / 25

WAO 2021

Finding Overview
u No injury (could not enter the hall because of smoke)u Self-extinguished when firemen entered with oxygenu No direct fire damage to the main injector linac…
u Large amount of carbon soot sneaked into the injector
v Discharge might prevent high-voltage operation of high-power pulsed
modulators
v Short-circuit might prevent high-precision operation of the instrumentation

u Chemical material (Dioctyl Phthalate: cancer causing)accompanied with carbon sootv Required full Tyvek protective clothing³ Later, it turned out that the density was rather low, and the clothing was relaxedu Quick recovery required for SuperKEKB commissioningv Large discrepancy in understanding between the institute and the divisionv Investigated technical aspects, resources, and mental health, etc³ Finally, succeeded in tentative recovery
Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

5 / 25

WAO 2021

Early Difficulties
u We entered into buildings just after the extinguishing,
however, firemen evacuated us as the level of carbon
mono-oxide was highu The damage in the assembly hall was obvious, however,
the impact of carbon soot was significant to the main
injector LINAC, that was not recognized by the institutev We were told to restart within 3 days
v However, we estimated that it may take 1-3 months

u Limited material availability
v Only about 8 sets of protective clothing and masks were available innearby cities. During the weekend, group leaders started toinvestigate the damage and to plan the recovery works
v Later, purchased hundreds of material sets of Tyvek clothing, gasmasks with active charcoal, gloves, shoe covers, etc.
Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

6 / 25

WAO 2021

Chemical Hazard
u Carbon soot was collected immediately for chemical analysis
v It takes a month for quantitative analysis normallyu Partial analysis on sitev Only for soluble in organic solvent³ Dioctyl Phthalate (softener for vinyl chloride)³ Cancer causing, reproductive toxicity, etc³ (A month later, found to be safe as the density was too low)u Full protective clothing (Tyvek) (needed also for soot)³ Detailed explanation was made to contractors as well
³ Youth and women were excluded from the workers

v Gas masks, Tyvek, goggles, gloves, entrance management³ Gas masks were ordered directly to the factory in hundredsv Conversation, face-recognition, …
³ Names on front/back of Tyvek

v Air temperature rise
³ Water and food at the entrance³ Daily health suggestions from doctor
Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

7 / 25

WAO 2021

Fireman in the smoke and carbon sootFire and Recovery at Injector Linac

Modulator burnt

K.Furukawa, KEK, Oct.2021.

8 / 25

WAO 2021v Carbon soot sneaked through holes between rooms

Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

9 / 25

WAO 2021v Carbon soot in the equipment

Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

10 / 25

WAO 2021v Cleanup one by one

Fire and Recovery at Injector Linacv Low-power & high-power tests

K.Furukawa, KEK, Oct.2021.

11 / 25

WAO 2021
入射器火災復旧について (Linac Fire Recovery, April 2019)u Information Sharing
via Meeting,Mail and Web

2019/11/20 2'56

入射器火災復旧について (Linac Fire Recovery, April - November 2019)
ストレスイベント後の反応について (安全衛生推進室、大井雄一産業医)(Response after stress event, May.10) [pdf]電子陽電子入射器の作業者のみなさまへ (環境安全管理室, 安全衛生推進室)(Linac safety reminder, Oct.30, NEW) [pdf]こころのケアについて (安全衛生推進室, 健康相談室) (Mental care, Apr.19)[pdf]揮発性有機化合物調査結果と作業管理 (環境安全管理室, 安全衛生推進室) (Gas analysis and healthcare, May.27) [pdf] : [word]
保護具に関する作業管理の質問と回答 (安全衛生推進室) (Gas mask and healthcare Q&A, Apr.22) [pdf]
保護具に関する作業管理と健康管理 (安全衛生推進室) (Gas mask and healthcare, Apr.19) [pdf]
入射器棟粉塵濃度測定結果と今後の作業における注意 (Dust assessment and recovery, Apr.17) [pdf]化学物質情報概要 (Chemical overview, Apr.6) [pdf]v Meeting in every morning³ Some from other divisionsv Group leader meetingin every eveningv Daily updatev Mental healthv Physical healthv Environmental analysis
v Recovering strategy
v Utility recovery
v Equipment recovery
v Testing progress
v Beam schedule

化学物質情報 (SDS) [pdf] : [Original link]
入射器入域安全確保 (Linac safety, Apr.5, OBSOLETE) [pdf]安衛室分析 (Chemical analysis, Apr.5, OBSOLETE) [pdf]
安全衛生推進室巡視点検報告 (衛生管理者, 安全衛生管理者) (Safety health inspection, May.9) [pdf] : [word]
安全衛生推進室巡視点検報告 (産業医, 産業看護師) (Safety health inspection, May.9)[pdf] : [word]
安全衛生推進室巡視点検報告 (Safety inspection, Apr.11) [mail] : [word]

入射器 Beam 立ち上げ進捗 (Linac restart progress, Apr.25) [pdf] : [excel]
入射器復旧作業進捗 (Linac recovery progress, Apr.19) [pdf] : [excel]
入射器 Beam 立ち上げ進捗概要 (Linac restart progress overview, Apr.24) [pdf]
火災報知設備と加速器運転 (Fire alarm and operation, Apr.19) [pdf]
施設部復旧情報 (Utility recovery daily progress, Apr.26) [pdf]
施設部復旧情報 (Utility recovery daily progress, Apr.24) [pdf]
サブ変電室回復情報 (Substation recovery progress, Apr.16) [pdf]
対策会議報告と立上げ打合せ (Recovery daily progress report, Apr.22) [mail] : [powerpoint]
対策会議報告 (Recovery daily progress report, Apr.19) [mail] : [powerpoint]

火災について（共同利用者の方へ）[KEK News] : To KEK Users: On the fire, Apr.25 [English]
火災について（共同利用者の方へ）[ KEK News]: To KEK Users: On the fire, Apr.11 [English]

火災について [KEK Press release] : Fire at linac, Apr.4 [English]
入射器入域手順 (Linac entrance procedure, Apr.8) [pdf]
入射器概略図面 (Linac floor plan) [pdf]Gallery 概略図面 (Gallery floor plan) [pdf] : Tunnel 概略図面 (Tunnel floor plan) [pdf] : 空調範囲図面 (Airconditioner floor plan)

詳細 Mail 共有情報 (Linac-Update mail archive)
入射器復旧写真 (Linac recovery photo archive)
加速器学会報告 (Report at particle accelerator society, Aug.2) [pdf]
火災報告 (Analysis report, Jun.28) [pdf]暫定報告 (Tentative report, May.10) [pdf]
火災概要 (Incident overview slide, Apr.8) [pdf]
火災概要 (Incident overview slide, Apr.5) [pdf]
火災概要報告 (Incident overview 3-page report, Apr.4) [pdf]

時系列記録 (Timeline) [html]
NHK 首都圏 (Apr.4) : つくば市 (Apr.4)
Kazuro Furukawa <linac-request@mail-linac.kek.jp> , Apr.7-Oct.30.2019.
[ Linac ] [ Linac-update ] [ SuperKEKB ] [ Accelerator ] [ KEK Staff ] [ KEK ]Page 1 of 1

http://www-linac2.kek.jp/ope/apr2019/

Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

12 / 25

WAO 2021

Exploration of the Landing Positionu Negotiation between early recovery and limitationsu Might take several months to recover all devices
u Abandoned redundancies in certain devices
u Important devices that might need long recovery periodv Several of 60 high-power microwave modulators³ Some of them act as redundancies

v Two magnet power-supplies for 180-degree bending section (J-ARC)³ One backup existed, fortunately stored in a distant roomu Investigated the beam energy profile around J-ARC
u If it took more than 3 weeks, limited mon-power inside/outside
because of consecutive national holidays in May (Golden week)

Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

13 / 25

WAO 2021

Recovery progress
Apr.3: Fire. Carbon soot was anticipated for high-power and high-precision operation.
Apr.4: During the investigation, hazardous chemical material was found as well as carbonsoot.
Apr.5, 6: Partial clean-up was performed as a test, and also for devices to be sent out tomaker companies, with limited pieces of protective clothing.
Apr.8: As protective clothing arrived, full clean-up started. Several devices were found to
be difficult to fix in a short term, and an operation plan was developed.
Apr.18: Low power test started.
Apr.22, 23: High power test was performed successfully.
Apr.23: Beam test began.
Apr.25: Limited SuperKEKB HER injection restarted.
Apr.26: SuperKEKB HER and LER injections, and then the collision restarted.
May.7: PF light source injection started as originally scheduled.
Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

14 / 25

WAO 2021

Impact on Injector Recovery
u Recovered with much help from everyone
v All divisions in KEK and outside companies joinedu Certain equipment recovery was postponedv Energy lowered from 1.5 GeV to 1.35 GeV³ at J-ARC, 180 degree bending sectionv Until summer shutdown³ 2 of 60 RF sources were off³ 1 of 2 bending magnet power supplies was off

v Found not to impact much on the injection³ with the required beam specifications at the time (just after the commissioning)v Mostly recovered before autumn operationu Most of backup devices were consumed
v Many damaged devices were abandonedv Might mean acceleration of renewal for aging devices, actuallyv Budget depended on insurance refund

Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

15 / 25

WAO 2021

Investigations and Countermeasuresv A review meeting was organized in the accelerator department, and later wasendorsed by the institute as wellu Factv A capacitor with plastic container in the pulse forming network of high-power
modulator punctured, discharged, and fired
v The modulator was restarted after the initial interlock without detailed
investigations

u Recommendations
v Usage of metal (or ceramic) container capacitors
v Conservative (long-life) capacitor design with lower gradientv Routine inspection of characteristics of capacitors
v Rigid interlock handlingv Improve the sensors and video cameras
v Documentations especially with power board connections
v Tight communication between main injector operation and test-standexperiments
Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

16 / 25

WAO 2021

Auto-extinguisher and Cameras
u We experienced punctures before
u We learnt that several other instituteexperience such fire incidentsv At least we got information from SLAC and CERN

u An automatic extinguisher was installed in
the new Nextef modulatorv A smoke sensor triggers non-combustible gas into PFNbox

u Hundred of video cameras wereinstalled to observe interlocked
devices in main LINAC

Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

17 / 25

WAO 2021

Operation Considerationsu Capacitors at injector are different from Nextef's
v Has ceramic container instead of plastic containerv Has lower designed potential gradient (longer lifetime)v Has puncture protectionv Performed degradation check every other summer (tangent delta)u Tentative operation procedure in injector linac
v Local operator investigation is enforced on modulator HV interlock³ Observation for any anomalous behavior or capacitor puncturev More frequent observation of southern part of injectoru More surveillance devices would be installedu Important to start S-band structure assembly in 2020v As originally planned to fight against aging structuresv Structure assembly room should be recovered earlyu Careful knowledge transfer from the original designer to the nextgeneration
Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

18 / 25

WAO 2021

Impact on SuperKEKB Operationu Beam suspension for 3 weeks³ at the first stage of phase 3 operation³ at the middle of luminosity development
HER e– beam current

Fire Recovery

LER e+ beam current

Collision luminosity

Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

19 / 25WAO 2021

Pulse-to-pulse modulationu Four PPM virtual accelerators
for SuperKEKB andphoton science projects
u As initially plannedin May.2019
Based onDual-tier controls withEPICS and event-system
Independent parameter setsfor each VA (20ms)

Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

20 / 25

WAO 2021

Simultaneous 4 + 1 Ring Top-up Injection
u Realized for the first time
³ SuperKEKB HER 7 GeV e–³ SuperKEKB DR and LER 4 GeV e+³ Photon Factory 2.5 GeV e–³ PF-AR 5.0 / 6.5 GeV e–v4 beams are modulated at 20ms PPM
vMore than 200 pulsed devices
were constructed forSuperKEKB, as well as beam
and RF monitors
vInjection noise (background)
were well studied from the 2nd
week of May
Fire and Recovery at Injector Linac

HER

337.5 ± 1.6 mA (0.48%)

LER

348.2 ± 1.2 mA (0.34%)

PF

449.9 ± 0.1 mA (0.02%)

PF-AR

55.1 ± 0.2 mA (0.38%)

K.Furukawa, KEK, Oct.2021.

21 / 25

WAO 2021

Simultaneous Top-up Injections
uIntegrated luminosity improvement (example)
17.54 /pb in 5.15 hr(5 fills)
on May.6

41.64 /pb in 5.15 hr(top-up)
on May.16

237%
improvement
Heavy work in April
was rewarded
Fire and Recovery at Injector LinacK.Furukawa, KEK, Oct.2021.

22 / 25

WAO 2021

Trans-scienceu I was much astonished to see such a big disaster in our facility
u That reminded a word “Trans-science” by Alvin Weinberg
v He invented the light-water reactor in Navy for submarine, but insisted that it is too
dangerous for civilian applications. Later, he as the director general of ORNL

invented Thorium molten-salt reactor. But the world didn’t appreciate him
until recently.
v If the probability of an incident is very low, we make mistakes in the evaluation,and tend to or try to forget that.

u We need to keep balance between many conditions with pursuing
scientific evaluations.

Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

23 / 25

Summary WAO 2021

Summaryu We should not have the same disaster, with better preparationu We could have learnt from other institutes
u We could be very nervous in unusual situation, be preparedu We’ve mostly recovered from the disasteru Active safety measures are necessary instead of reacting onlyu We are improving with the experiencesu With some Phronesis we can enjoy accelerators
v Phronesis [Greek]: Practical wisdom, Ability to understand the Universal Truth

Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

24 / 25

WAO 2021

Mt. Tsukuba

Thank you
PF-ARPFSuperKEKB
dual rings

700m Injector
Linac

Conference papers at <http://www-linac.kek.jp/linac/>Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

25 / 25

WAO 2021

Fire and Recovery at Injector Linac

K.Furukawa, KEK, Oct.2021.

26 / 25