Transients scenarios for the cryogenic operation of superconducting magnets of LHC experiments

R. Pengo June 1st, 2007

Transients scenarios for the Transients scenarios for the cryogenic operation of cryogenic operation of

superconducting magnets of LHC superconducting magnets of LHC experiments experiments

Experience at CERNExperience at CERNR.Pengo R.Pengo

CERN, AT-ECRCERN, AT-ECR

Content of the presentationContent of the presentation

Details for CMS and ATLAS of:• cooling down process• static heat load• dynamic heat load• fast discharge of the magnets• recovery after a fast dump

Structure of the s/c magnetsStructure of the s/c magnets

CMS is composed of• a s/c solenoid, divided in 5 sectors

ATLAS is composed of• a s/c Central Solenoid (CS)• a Barrel Toroid (BT), formed by 8 s/c

race-track coils• 2 End Cap Toroids (ECT), each formed

by 8 s/c squared coils

Cooling methods for CMS & ATLASCooling methods for CMS & ATLAS

CMS • The solenoid is indirectly cooled by LHe,

driven by thermosyphon movement (i.e. gravity driven)

ATLAS• The CS is indirectly cooled either by the

JT circuit of the Main Refrigerator (MR) or by thermosyphon movement

• Both BT and ECT’s coils are indirectly cooled by forced LHe flow produced by a 1.2 kg/s centrifugal pump

Cold Mass InventoryCold Mass Inventory

CMS total cold mass is 220 Tons (cylinder 6.6 m x 12.5 m)

ATLAS total cold mass is ca. 700 Tons• CS ca. 6 Tons (cylinder 2.5m x 5.3m)• BT (340 +20) Tons (8: 25 m x 5 m)• ECT’s (2 x 160) Tons (8: 5m x 5m)

Where we are with the commissioningWhere we are with the commissioning

Actual status:• CMS fully tested on the surface• ATLAS

– CS fully tested (surface and cavern)– BT fully tested (surface and cavern)– ECT-A tested at LN2 temperature on surface– ECT-C under test on the surface

Cooling down of the MagnetsCooling down of the Magnets

Cooling CMS

2-Feb-06 7-Feb-06 12-Feb-06 17-Feb-06 22-Feb-06 27-Feb-06

QUR1H_C_TTMAGMIN.POSST QUU1H_C_TTMAGMAX.POSST Delta T

10 days

DT< 22K

1.2 kW @ 4.5 K Refrigerator used

Cooling Time ca. 22 days

ATLAS :CS• Shield Refrigerator (SR) & Main Refrigerator (MR) used

Central Solenoid Cooldown

16-May-06 18-May-06 20-May-06 22-May-06 24-May-06

Control Dewar Bottom Solenoid coil

4 days

SR: Cold Mass and shield in

series

-SR for shield

- MR for CM75 K

ATLAS :BT• Shield Refrigerator (SR) & Main Refrigerator (MR) used

BT cooling curve

7/2/0612:00 AM

7/12/0612:00 AM

7/22/0612:00 AM

8/1/0612:00 AM

8/11/0612:00 AM

8/21/0612:00 AM

8/31/0612:00 AM

9/10/0612:00 AM

9/20/0612:00 AM

9/30/0612:00 AM

SR: cold mass and shield in

parallel

-SR for the shields

-MR for Cold mass

Start of the 1.2 kg/s LHe pump

10 days

ATLAS :BT• Shield Refrigerator (SR) & Main Refrigerator (MR) used

BT cooling curve

04-Jul-06 24-Jul-06 13-Aug-06 02-Sep-06 22-Sep-06

DT< 40 K

ATLAS : ECT-A

Cooling of ECT-A

2/16/07 0:00 2/26/07 0:00 3/8/07 0:00 3/18/07 0:00 3/28/07 0:00 4/7/07 0:00

Calculation Coil Shield

Only LN2 precooler used

10 Days

ATLAS : ECT-C (in progress)

Cooling of ECT-C

May 15, 2007 May 20, 2007 May 25, 2007 May 30, 2007 June 4, 2007 June 9, 2007 June 14, 2007

Shield out Aveage Shield Average Total

10 days

STATIC HEAT LOADSTATIC HEAT LOAD

CMS• Measured by LHe level decreasing in

Phase Separator• Natural Temperature increasing on the

cold mass

CMS: Measured by LHe level decreasing in Phase Separator (178 W)

Débit AdI 2 x 0,4 g/sDniv(A-B) = 6,75% en 10’=Soit 277 l/h

Bilan = 254 l/h = 178 W

From Ph. Bredy, CEA

Saclay

LHe level in Phase

Separator

CMS: Natural Temperature increasing of the cold mass (174 W)

2 K/ 21 ½ min = 154 W on Cold mass alone

(SdP heat loads to be added 20 W)

Total = 174 W

Cold mass bilan :NbTi 4.9 tCu 8.6 tAl pur 73.9 tAl renf 6082 90.4 tG10 9.9 tAl cyl 5083 34.8 t

From Ph. Bredy, CEA

Saclay

CDS synchronization !

ATLAS: CS

Measurement of total loss was done during thermosyphon operation mode with disconnected refrigerator and looking at the level/time change in the control dewar

Results: - 17 Watts for the solenoid and

the chimney;- below 10 Watts for the dewar.

ATLAS: Barrel Toroid CM• For each of the 8 race-track coils the

heat load has been measured – in the surface test hall (Mass-flow meter)– in the UX15 cavern after assembling into BT

(natural temperature increase)

• The total heat load of the BT has been also measured in the cavern

ATLAS: Barrel ToroidNatural Warm Up

28-Nov 8-Dec 18-Dec 28-Dec 7-Jan

S1_OUT

S2_OUT

S3_OUT

S4_OUT

S5_OUT

S6_OUT

S7_OUT

S8_OUT

Natural Warm Up Jan 9th, 2007

29-Nov-06 09-Dec-06 19-Dec-06 29-Dec-06 08-Jan-07

Tin-Tout on the pipes

Tmax, Tmin on coils

Pt1000

Carbon resistors

ATLAS: Barrel ToroidAverage BT heat load in Cryoring (14 Dec 2006)

1 2 3 4 5 6 7 8

BT coils

Values measured in test station

TOTAL MEASURED IN TEST STATION 571 W TOTAL IN UX15 IS 586 W

ATLAS: Barrel Toroid

LHe Pumps: 660 W

PCS+TL11+Cryoring: 250 W

BT: 620 W (or 1530-660-250)W

ATLAS: Barrel Toroid Shields• For each of the 8 cryostats

– in the surface test hall (Mass-flow meter)– Average 800 W

– the total heat load of the BT shield has been also measured in the cavern (Mass-flow meter)

– Total 6000 W

DYNAMIC HEAT LOADDYNAMIC HEAT LOAD

Flux is proportional to Current:• Φ = L x I , V = -dΦ /dt = - L x dI/dt

– Voltage is induced when changing current– And energy is dissipated by the induced current on the

casing (~ autotransformer)

Al Coil casing

2 x 60 = 120 turns

ATLAS:

gcaRdt

Calculated: No Fit!

Dynamic heat load

0 1 2 3 4 5 6 7 8 9

dI/dt [A/s]

P,th (12.63 micro ohm) P,th (13.33 micro ohm) B2 B3 B4 B5 B6 B8

Slow dump equivalent

One coil: L = 0.5667 H, Total BT: L= 5.5 H => expected value 350 W

ATLAS: BTSlow dump on Nov. 18th, 2006

Return Buckets Levels

14:24 15:36 16:48 18:00 19:12 20:24

Time [hh:mm]

Level of LHe is reduced due to the

higher vaporization during slow discharge

ATLAS: BTSlow Dump 20.5 kA on Nov. 18, 2006

7:12 9:36 12:00 14:24 16:48 19:12 21:36 0:00

Time [hours]

LHe vapor mass flow on the

phase separator is increased due

to the higher heat load

~380 W

ATLAS: CS• Eddy current loss are around 25 Watts.

Measurement principle: compare consumption during ramp up at 6 A/s with previously measured

static losses by looking at the heater power in the control dewar which is reduced by 25 watts.

Furthermore “gas counting”.

CMS slow dump (~4 hours)

12:00 14:24 16:48 19:12 21:36 0:00

Current Level Buffer Dewar

Thermosyphon Mass flow is

naturally increased due to the higher heat

Current decreasing during slow discharge

Temperature increase ~ 0.28 K

CMSSlow discharge

20/10/200617:02:24

20/10/200618:14:24

20/10/200619:26:24

20/10/200620:38:24

20/10/200621:50:24

Fast discharge at 5000 A

Slow discharge

Temperature increase ~ 0.28 K

FAST CURRENT DISCHARGEFAST CURRENT DISCHARGE

CMS: stored EM energy is 2.5 GJ (about 220 Tons)

Fast dump on August 22nd, 2006

22/08/200613:12:00

22/08/200613:40:48

22/08/200614:09:36

22/08/200614:38:24

22/08/200615:07:12

22/08/200615:36:00

22/08/200616:04:48

Current Pressure Temperature

Temperature rise up to 70 K

Pressure rise in PS

1 hour

ATLAS-CS: Stored EM energy is 40 MJ

Solenoid Fast Dump

100.00

120.00

10:27:33 10:28:16 10:29:00 10:29:43 10:30:26

Chimney Coil Tmax Coil Tmin Current

ATLAS-CS: pressure rise

From F.Haug

Coil return: max 7.11 bar

Coil inlet: max 4.32 bar

Current: 7800 A

ATLAS-BT: Stored EM vs. EnthalpyFast Dump Temperature

0102030405060708090

0 200 400 600 800 1000 1200

Energy (MJoule)

0200040006000800010000120001400016000180002000022000

EM Energy at Current [A]

BT Enthalpy

ATLAS-BT:Fast Dump 20.5 kA

9th Nov., 2006

11:24 PM 11:31 PM 11:38 PM 11:45 PM 11:52 PM 12:00 AM

Pressure PS Pressure return Current

Pressure in Phase Separator

Pressure on the return to the Shield

Refrigerator

15 min

ATLAS-BT:Fast Dump Pressures

10/25/2006 10/30/2006 11/4/2006 11/9/2006 11/14/2006

BT: Recovery after a full current fast dump

Recovery from 20.5 kA fast dump

11/9/0612:00

11/10/060:00

11/10/0612:00

11/11/060:00

11/11/0612:00

11/12/060:00

11/12/0612:00

One day58 K

SummarySummary

Data on transient modes of operation have been Data on transient modes of operation have been displayed and discussed, namely:displayed and discussed, namely:

-- cooling down process cooling down process- static heat loadstatic heat loaddynamic heat loaddynamic heat load- fast discharge of the magnets- fast discharge of the magnets- recovery after a fast dump.- recovery after a fast dump.

The results are in good agreement with the design The results are in good agreement with the design

I would like to thank for their collaboration all I would like to thank for their collaboration all colleagues from CERN and from the external colleagues from CERN and from the external

Institutes involved (CEA-SACLAY,INFN,KEK,RAL)Institutes involved (CEA-SACLAY,INFN,KEK,RAL)

Transients scenarios for the cryogenic operation of superconducting magnets of LHC experiments

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