Cryogenic system for the MYRRHA linac

Nicolas ChevalierTomas Junquera

20.10.2012

Part 1

Heat load budget and operating temperature

Static heat load

For MYRRHA, short cryomodules : • 5 W/m at 2K• 40 W/m at 40 K

SNS [10] XFEL [11] CEBAF [12], [13] Project X [14]

Cryomodule content 3 med-β elliptical

4 high-β elliptical 8 β=1 elliptical 8 β=1 elliptical 18 single spoke

Focusing magnets outside cryomod

outside cryomod 1 inside outside

cryomod18 solenoids

inside cryomod

Cryomodule Length (m) 4.24 6.29 12.2 8.25 11.2

Static Loss into 2 K (W/m) 4.64 3.55 0.11 1.8 1.73

Static Loss into 5-8 K (W/m) - - 0.9 - -

Static Loss into 40-K (W/m) 36.55 30.36 5.82 17 8.24

CHβ=0.1

352 MHz

Spoke β=0.36

352 MHz

Elliptic β=0.47

704 MHz

Elliptic β=0.65

704 MHzRres (nΩ) 43 10.0RBCS (nΩ) 0.8 0.8 3.2 3.2

Q0 theoretical 1.3E+09 9.4E+09 1.0E+10 1.3E+10Eаcc (MV) 4 6.2 8.2 12

Q0 exp @ Eacc* 2.0E+08 2.0E+09 1.0E+10 3E+10

Pcav (W) from lowest Q0 including +1 W coupler

conduction 11 8.9 11.3 15.5

Cavity dynamic heat load at 2K

* Values from prototype cavities : Podlech et al., Bosotti et al. , Visentin et al., Olry et al.

Spoke 350 MHz Elliptic 700 MHz β=0.47

Elliptic 700 MHz β=0.65

Number of cavities 48 34 60

Coupler type Prototype Eurotrans (20 KW) Prototype Eurotrans (100 KW)

Max RF power per cavity (kW) 8 17 32

Cooling Thermal sinks at 40 K and 5K

Cooling loop between 5 and 300

K

Cooling loop between 5 and 300

K

Dynamic RF power dissipated in

external conductor of coupler (W)

2.6 9.3 17.5

Static + Dynamic Load (W)

8 W @ 40 K1.15 W @ 5K 10 W @5K-300K 10 W @ 5K-300K

Coupler heat loads

Coefficient of performance of cryoplant

Accelerator LHC (one sector) SNS Project X XFEL

Type of data measured specifications

Operating Temperature (K) 1.8 2 2 2Cryo Power (kW) @ 4.5 K 18 10 41 12

Cryo Power (kW) at op. temp. 2.4 2.4 4.3 2.8

COP (W/W) of 2K | 4.5 K 950 240 1150 386 588 240 870 -

COP(T2)/COP(T1) 3.96 2.97 2.45 -

),(1

TpowerTT

T

COP r

For MYRRHA, cryo power at 2K : ~14.2 kW Close to XFEL or one LHC unit

Realistic goal : COP(2K) = 720 ; COP(4K)= 220 COP(2K)/COP(4K) = 3.3

Overcapacity. Total heat load budget

Power @ 4.5 K Temperature (K) Heat Load (kW) COP (W/W) Function

2.1 5.4 720 Cavities

14.2 kW5 0.45 220 Coupler

cooling

40 15.2 20 Shield

Overcapacity factor : 1.5 speed cool-down, use machine < 100 % performanceUncertainty factor : 1.25 imperfect Nb, electron loading, imperfect MLI wrapping etc.

Overall power similar to :LHC (18 kW), JLAB (11 kW),

XFEL (12 kW), 2 x SNS (2 x 6.4 kW)

Overall margin : 1.875

LHC « recipe » is applied for safety factor :

Heat load breakdown

• heat load is roughly 25 % | 20 % | 50 % across the three sections

• static losses ~ ½ dynamics losses small cryomodule, low field

SPOKE HIGH β ELL.LOW β ELL.

735 W~27 %

635 W~22 %

1360 W~46%

Total Static (W) Total Dynamic (W)

1015 1860

• Dynamic range at 2K: Load beam on/beam off = (dynamic + static)/static

Dynamic range = 2.8LHC : 3

Important parameter for choice ofrefrigeration scheme (full cold compression

or mixed compression)

• Heat load distribution along linac :

CH

150 W~5.2 %

Temperature optimization of the MYRRHA linac

Optimal temperature:

Broad minimum around 1.9-2 K

COP decreases with T, RBCS increases with T optimum of power consumption

1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 30.0

1,000,000.0

2,000,000.0

3,000,000.0

4,000,000.0

5,000,000.0

6,000,000.0

7,000,000.0

8,000,000.0

dynamic

static

total

Temperature (K)

Wel

(MW

)

Possible 4K operation of Spoke cavities

4K operation 2K operation

Easier to implement (no JT, subcooling heat exchanger, etc.)

More stable against microphonics

More reliable A 2K pumping line will anyway be installed for elliptical cavities

Cavities are cooled to 4K before pumping to 2K

Overall consumption is the same for 2K and 4K : 2.1 MW electric

2K operation of Spoke cavities is the reference design for now4K operation should be tested on prototype Spoke cryomoduleIn the design phase, pipes should be sized to allow 4K and 2K operation

Part 2

Cryofluid distribution : valve box, transfer line and cool down characteristics

Distributed scheme Centralized scheme

Pros

Better control of individual cryomodules (ncecessary for commisioning, test and cooldown)

no additional supply line necessary : more economical and reliable TL

less heat flux on the 2K level

only one HX: more economical, compact, and reliable HX

return line load losses are reduced at 2K, smaller LP pipe diameter (190 mm rather than 236 mm)

simplified VB design

Adopted by … SNS, LHC, XFEL JLAB (CEBAF)

Distributed or central subcooling heat exchanger

Distributed : • 2K subcooling is achieved in each valve box via heat exchanger• Low pressure vapor is returned at 5K

Central :• 2K subcooling is achieved in a single central heat exchanger; • Subcooled supercriticalhelium is distributed in a separate transfer line• Low pressure vapor is returned at 2K

SNS LHC MYRRHASHX

arrangement 1 SHX per CM 1 SHX for 107 m magnet section 1 SHX per CM

Mass flow (g/sec)

6 max

1.95 low β

2.4 high β

4.5 nominal

4.35 nom CH

1.8 nom Spoke

2.2 nom low β

5.3 nom high βFluid inlet pressure

2.98 bar 40 mbar 2.4-3.6 bar 16.4 mbar 3bar 30 mbar

Max pressure drop 20 mbar 1 mbar 200 mbar 1 mbar 1 mbar

Fluid inlet temperature (K) 5 2.2 4.9 1.8 5 2

Fluid outlet temperature (K) 2.1 3.96 <2.2 >3.38 2 4.5

Capacity (W) 60 31 30

Subcooling heat exchanger (SHX) specifications

• LHC SHX can be used if 1 SHX is used for 1 cryomodule• If 1 SHX feeds more than 1 cryomodule, SHX has to be modified (up to 10 g/sec)

40K 4 bar

5K 3bar

4.5K 30 mbar

6K 1.2 bar

80K 3bar

TI

TI

TI

TI

TI

TI

LI

TI

TI

SHX

POTJT

bypass EV

EV

shield

2K header

cavity

beamline

vacuumbarrier

couplerCC loop

CV

SV RD

LI

4K FUVto

con

ditio

ning

CD

TI

TI

TI

TI

TI P

P

Valve box :Spoke prototypeCryomodule

CV : conditioning valveEV : expansion valveCD : cooldown4K FUV : JT : Joule-Thomson valveSHX : sucooling heat exchangerSV : safety valveRD : rupture diskTI : temperature gaugeLI : level gauge

40K 4 bar

5K 3bar

4.5K 30 mbar

6K 1.2 bar

80K 3bar

TI

TI

TI

TI

TI

TI

LT

TI

TI

P

P

Valve box :Spoke seriesCryomodule ?

All valves that can be removed without compromising control should be removed

40K 4 bar

5K 3bar

4.5K 30 mbar

6K 1.2 bar

80K 3bar

TI

TI

TI

TI

TI

TI

LT

TI

TI

EV

JT

P

P

Valve box :Low β elliptic Cryomodule

Similar scheme for high β elliptical is available

Spoke Elliptical low β Elliptical high β

NECESSARY

3 conditioning valves3 coupler cooling valves2 shield valves2 cool down valves1 JT valve1 2K-return valve1 HX bypass valve1 subcooling heat exchanger1 rupture disk1 safety valve2-8 thermometer probes1-2 level probes2 pressure gauges

3 conditioning valves3 coupler cooling valves2 shield valves2 cool down valves1 JT valve1 2K-return valve1 HX bypass valve1 subcooling heat exchanger1 rupture disk1 safety valve2-8 thermometer probes1 level probe2 pressure gauges

3 conditioning valves5 coupler cooling valves2 shield valves4 cool down valves1 JT valve1 2K-return valve1 HX bypass valve1 subcooling heat exchanger1 rupture disk1 safety valve4-12 thermometer probes1 level probe2 pressure gauges

OPTIONAL

1 supercritical 4K liquid Helium expansion valve1 4K fill-up valve1 4K liquid Helium phase separator (PS)3 warm-up valves

Valve box premiminary inventory

40K 4 bar

5K 3bar

4.5K 30

mbar

6K 1.2 bar

80K 3barAlternative distributionscheme : 1 VB for 2 CM

Advantages of 1VB-1CM and 1VB-2CM solutions

1 VB – 1 CM 1 VB – 2 CM

Control Same number of valves1 CM could be warm and the other cold in both schemes

Cost ½ the number of VB shell, SHX and tanks

Space No VB-CM connecting arms Could be placed between CMs

Heat loads No VB-CM connecting arms Less hot-cold interface

Engineering complexity Less crowded valve boxNo VB-CM connecting arms

Reliability Needs to be checked (EA)

Reference solution will be 1 VB – 1 CM as it seems more straightforward.But 1 VB – 2CM could be more economical in terms of cost and space (e.g. ceiling)

Nominal Full 2K

Installed Standby Full 2K

Standby4K-2K

Nominal 4K-2K

Cool Down

Description of mode

Dynamic + static at 2K

Nominal x 1.875(overcapacity

and uncertainty factor)

Only static at 2K Only static at 4K (CH, Spoke) and

2K (elliptic)

Dynamic + static 4K (CH, Spoke) and 2K (elliptic)

Only static at 2K x 1.5

(overcapacity factor)

Low Pressure Return 4.5 K

30mbar

163.2 306.0 58.5 40.0 117.3 87.8

Supply and Return

40-80 K 4-3 bar

40.4 75.8 40.4 40.4 40.4 60.7

Gaz return10 K 1.2 Bar

5.5 10.4 1.9 17.6 135.0 2.8

Supply Supercritical4.5 K 3 Bar

168.7 316.3 60.4 57.6 252.3 90.6

CH Spoke Elliptic 1 Elliptic 2Low Pressure Return

4.5K 30 mbar 4.03 1.63 2.15 5.21

Supply and Return40-80 K 4-3 bar 1.22 0.43 0.60 1.16

Gaz return10 K 1.2 Bar 0.28 0.14 0.03 0.08

Supply Supercritical4.5 K 3 Bar 4.31 1.77 2.18 5.29

Operational modes, helium mass flows

Whole linac

Per cryomodule

Short name Max mass flow (g/sec) Max load loss Pipe diameter

Low Pressure Return4.5K 30 mbar LP 153 100 Pa 238 mm

Supply and Return40-80 K 4-3 bar Shield 37.9 100 kPa 2 x 45 mm

Gaz return10 K 1.2 Bar Coupler Return 67.5 10 kPa 29 mm

Supply Supercritical4.5 K 3 Bar Supercritical 158.2 10 kPa 40 mm

Transfer line

• Transfer line is assumed to split in two parts at middle of linac

• Shielding is provided by thermalization with 80 K return (LHC design)

Length (m)

Diameter (mm)

Thickness (mm) Mass (kg)

Supply 40 K 2x120 45 1 271Return 80 K 2x120 45 1 271

Supply Supercritical 2x120 40 1 241Return Coupler &

Cooldown 2x120 29 1 175

Return Low Pressure 2x120 238 3 4306Total 5266

CH Spoke Elliptical low beta

Elliptic high beta Total

Number of cavity per CM 4 2 2 4Number of CMs 2 24 17 15 58

Cryomodule length (m) 6 2.12 2.96 5.76 199Weight of one cavity + tuner + tank + magnetic shield (kg) 80 80 80 80

Weight of valve box interior(kg) 100 100 100 100

Linear Mass/ thermal shield + support post (kg/m) 160 160 100 100

Cold mass per CM (kg) 1380 599.2 556 992Cold Mass of n CMs (kg) 2760 14380.8 9452 14880 41473

Cold Mass Estimate

Transfer line

CM + VB

Cold mass (tons) Enthalpy (GJ) Max mass

flow (g/sec)

Mass of Helium

required to cool (tons)

Minimal time for cooldown

(hours)

40K 36.3 3.15 75.8 3.13 11.42 K 33.75 3 316.3 3.37 3

total 70.05 6.15 0 0 0

Mass Temperature Mass Flow Reynolds Exchange

Coeff

Cool Down Time

kg [K] g/sec [-] W/m²/K MinSupply 40 K 254.0 40 51.8 2.5E+05 292.1 15.8Return 80 K 254.0 40 51.8 2.5E+05 348.8 15.8

Supply Supercritical 281.0 4.5 223.4 1.6E+06 565.6 2.4Return Coupler &

Cooldown 248.6 4.5 223.4 1.8E+06 694.1 2.1

Return Low Pressure

4814.6 4.5 223.4 2.8E+05 30.6 41.5

Mass Temperature Mass Flow Reynolds Exchange

CoeffCool Down

Timekg K g/sec [-] W/m²/K hours

Thermal Shield 40-80 K + Support

Post Cavity300.0 40 2 4.5E+04 411.4 7.7

Cavity + Tank + Magnetic Shield +

Tuning System80.0 4.5 1.5 5.5E+04 225.9 2.1

Valve Box inside 100.0 4.5 1.5 4.0E+03 0.3 1.1

Cool down time

Whole linac at once (will not happen)

Transfer line

Cryomodule

Part 3

Cryogenic plant main components

Implantation

Reliability

Preliminary cost analysis

Conclusions

Cryogenic system functional scheme and components

Placement of cryogenic plantand dimensions

Heat load center ofmass is close to geometrical center

Hypothesis : - Building surfacelinearly scales with power. - Scaling from LHC dimensions

In agreement with XFEL (12 kW) dimensions.

Low-Stage 1 Low-Stage 2 High-StageNumber of elements 2 1 2

Dimensions (l x P x H , m) 5 x 2.5 x 2.5* 5 x 2.5 x 2.5*

Mass (tons) 10* 10*

Inlet pressure (bar) 1 1 4Outlet pressure (bar) 4 4 21.6

Mass flow (g/sec) 300 230 820Isothermal Compression

Power (kW) 259 198 861

Electrical Power (kW) 440 370 1640Isothermal efficiency 58.8 % 53.6 % 52.5 %

Compressor Building : compressors

B Bradu. Modelisation, simulation et contrôle des installations cryogeniques du cern. PhD Thesis, 2010.

Liquefier building 4.5 K cold box of the LHC

2.4 kW@ 1.8K cold box of the LHC :

In MYRRHA (unlike LHC),4.5 K and 1.8 K cold boxcan be fused in one cold box:

• better COP, goal : 720 W/W @ 2K• how to handle large 5.4 kW @ 2K load ?

LHC, at point 1.8 SNS

StorageArea

66m x 25m1 x 120000 L liquid

Helium12 x 250 m3 gaseous 20

bar Helium100 000 L liquid

nitrogen

40m x 20 m8 x 114 m3 L gaseous helium

1 x 37800 L liquid helium1 x 75600 L liquid nitrogen

Liquid He Volume per

(L)

Number of elements

Total liquid He Volume

(L)

Cavity 40 154 6160

Phase separator 10 58 580

Piping 114 1 193

Total 6933

Storage, helium inventory

MYRRHA need corresponds toone 250 m3 20 bar bottle

LHC 20 bar gas storage at point 1.8

Reliability

High levels of availability of cryogenic systems (99 %) can be achieved if:

• Mean Time Between Maintenance > 8000 hrs

• Impurities : dryers to remove water , 80K adsorbers (air), 20 K absorbers (hydrogen), helium guard (2 joints) on 2K circuit

• Elements containing moving/vibrating parts : turbines, compressors, etc.• At least two identical machines per stage• Double all oil filters and oil pumps • Periodic maintenance, oil checks, vibration surveillance program

• Utilities : common cause of cryogenic system malfunction

• Periodic insulation vacuum control (thermal cycling leaks)

• Easily exchangeable cold compressors

• Claudet, “Lhc cryogenics, the approach towards availability,” 2011• Commeaux, “Reliability of cryogenic facilities: a preliminary approach,” 2002

Preliminary cost estimate of cryogenic system

Project Material (M€) Manpower (M€) Detail

LHC 15 (in 2001)21 (today)

Compressor : 4 M€Liquefier : 8 M€2K part : 3 M€

SNS 16 4.8

JLAB Upgrade 21

MYRRHAEstimate

21(like LHC or JLAB

upgrade)

7(1/3 of material cost)

EUROTRANS report estimatefor 8.5 kW @ 4.2 K plant : 24.5 M€ without manpower So :

Material 21-25 M€ + Manpower 7-8 M€ = Total 28-33 M€

Conclusions and perspectives

• Location of compressor station : too close to linac ? Max achievable

dampening of vibrations ?

• Linac-refrigerator connection : over linac or under the linac ?

• Valve box distribution scheme : 1 VB-1 CM or 1VB -2CM ?

• Transfer line design, other possibilities (SNS, 2 concentric transfer line ?)

• Location of transfer line « T »junction : in cold box or in tunnel ?

• How can the refrigerator be made more reliable ? rotating parts

• How to integrate the 2K and 4K cold box ? Can the 720 W/W be achieved ?

• How to handle the 5.4 kW 2K load of MYRHHA (twice that of the LHC) ?

Upgraded cold compressors ? Cold compressors in parallel ?

• Detailed cost analysis THANK YOU FOR YOUR ATTENTION. QUESTIONS ?