Very Large Hadron Collider - phase 2 Optimization of the beam screen cooling & Impact of the photon stop on the cryogenic system

Transcription

1 Very Large Hadron Collider - phase 2 Optimization of the beam screen cooling & Impact of the photon stop on the cryogenic system VLHC workshop on the beam tube vacuum Saturday June 23, 21 - Christine Darve & Pierre Bauer

2 Headlines Specification and Model for the beam screen cooling Influence of the synchrotron radiation Heat flux equations Cooling loop optimization RT Design of the beam screen Impact of the photon-stop on the cryogenic system CD - June 23, 21 VLHC workshop on the beam tube vacuum 2

3 Specification Extract the beam-induced heating: Synchrotron radiation, resistive wall and multipacting heat loads Tolerant of vacuum, irradiation and cryogenic environments, Allow the gas-load to be cryopumped by the cold bore, Limit the photodesorption, The design must be cost effective (minimize the total refrigeration cost). CD - June 23, 21 VLHC workshop on the beam tube vacuum 3

4 Space requirement CD - June 23, 21 VLHC workshop on the beam tube vacuum 4

5 Space requirement Cold bore Cooling surface < 28% x Cold bore X-sectional area D 32.5 mm D 2 mm D2< Available cooling space <D32.5 CD - June 23, 21 VLHC workshop on the beam tube vacuum 5

6 Cooling System - Schematic S by Tom Peterson Tom Peterson 19 March 21 High Field VLHC cell flow concept with S. Zlobin electrical scheme Dipole bus and coil leads Focussing quad bus and coil leads Defocussing quad bus and coil leads 6 IPS (17 cm) pipe 3 K, 1.2 bar helium gas return 4.5 K, 4 bar magnet helium flow One 27 meter cell Relief and cooldown valve D D C C C D dq Spool D D D D D D D fq Large D D D D D D D dq Spool Spool Magnet cryostat Transfer line 9 K to 11 K beam screens 8 K to 9 K thermal shield Jumper connections (Include vacuum breaks) 1.5 inch (3.8 cm) tube 36 inch (92 cm) magnet cryostat vacuum shell 26 inch (66 cm) OD transfer line vacuum shell Pipe includes 4.5 K, 4 bar helium flow parallel to magnet flow Four 25 ka bus in 4 IPS (11 cm) helium pipe Shield and beam screen flow valve 4 IPS (11 cm) pipe 5.5 K, 1.8 bar helium return and quench header 5 IPS (14 cm) pipe 8 K, 2 bar helium thermal shield supply and beam screen supply 6 IPS (17 cm) pipe 11 K, 17 bar helium shield return flow and transfer line shield Quench and cooldown valve CD - June 23, 21 VLHC workshop on the beam tube vacuum 6

7 Cooling System Parameters that influence the refrigeration cost: Limits: Luminosity Synchrotron radiation Cell length Inlet temperature of the beam screen Cooling X-section area Mass flow: Pressure drop Cross-sectional area of the cooling channel < 28 % of the cold bore one Temperature gradients Output: Optimal temperature of the thermal shield Optimal temperature of the beam screen Different wall plug powers CD - June 23, 21 VLHC workshop on the beam tube vacuum 7

8 Definition of parameters Symb Definition Unit Value ol T bs Beam screen average temperature K T ts +DT bs /2+DT ts /2 T cb Cold bore temperature K 5 d cb Cold bore inner diameter mm 34 d bs Beam screen outer diameter mm 32.5 g Thermal conductance coefficients (*) W/m/K h Efficiency.3 ess Emissivity of stainless steel 4 3 K eal Emissivity of aluminum 4 3 K s Stefan-Boltzmann constant Watt/m 2 /K DT BS Allowable temperature gradient in the K 2 beam screen cooling pipe DT TS Allowable temperature gradient in the K 5 thermal shield cooling pipe m Cryogen mass-flow g/s TBD L Cell length m TBD (135) N Number of cooling tube TBD CD - June 23, 21 VLHC workshop on the beam tube vacuum 8

9 Model for the beam screen cooling L is the beam screen cooling loop length (equal to n x 135 meters by default ) Cooling tube th=.5 mm L Beam screen th=1 mm Qs Qc ( T ) = Po P ( T T ) P, bs bs cb bs cb P bs R SS R He T bs T ct T P He CD - June 23, 21 VLHC workshop on the beam tube vacuum 9

10 From Pierre Bauer CHRONOLOGY psr (W/m/beam) electrons protons TEV LEP HERA APS LHC year VLHC1 VLHC2 The VLHC2 would be the first SR dominated cryogenic collider. Accelerator & Technology Seminar Fermilab, June 12, P. Bauer Synchrotron Radiation and Vacuum issues in the VLHC2 CD - June 23, 21 VLHC workshop on the beam tube vacuum 1

11 p P SR peak SR (W/m/beam) Accelerator & Technology Seminar Fermilab, June 12, 21 From Pierre Bauer = SR POWER LAW 4 2 EfN p γ m pc 4πrp fnb N W γ = 2πρ 2 6πρ m ρ r fixed at 29.9 km VLHC2* g P. Bauer Synchrotron Radiation and Vacuum issues in the VLHC2 CD - June 23, 21 VLHC workshop on the beam tube vacuum 11 * 5 times more than in LHC! ini pb 6 4 Ib W/m/beam I b (ma)

12 Influence of the synchrotron radiation New parameters Previous parameters Energy per proton E b (TeV) Peak Luminosity L (cm -2 s -1 ) Total Circumference C (km) Bending radius r (km) Dipole Field B (T) Circumference Arc l arc (km) Magnet packing factor (%) Number of Bunches N b 37,152 81,16 Initial Nr. of Protons per Bunch N p/b Bunch Spacing (ns) Revolution frequency f (Hz) 1,286 1,242 Rms bunch length (cm) Number of IP s 2 2 Beta* (cm) Luminosity life-time (collision loss only) t L (hours) Gamma g 93,284 93,284 Beam Current I b (ma) Radiation damping time t R (hours) SR heat load vs. Luminosity for one beam p peak SR = 4 2 ini pb EfN p γ m pc 4πrp fnbn W γ = 2πρ 2 6πρ m ρ 4 Ib 2 1E+34 3E+34 5E+34 7E+34 9E+34 Luminosity (cm -2 s -1 ) CD - June 23, 21 VLHC workshop on the beam tube vacuum 12

13 Heat flux equations f (T ) = 1 T η TR T η =.3 ptot = pbs (Tbs ) f (T ) + pcb (Tbs ) f (Tcb ) CARNOT EFFICIENCY dptot (Tbs ) = dt 1 5 K 1 97 K TEMPERATURE (K) CD - June 23, 21 VLHC workshop on the beam tube vacuum 13

14 Heat flux equations Heat load to the cold bore (Pcb( Pcb) p cb ( ) ( ) ( 4 4 T = C T T + C σ T T ) bs 1 bs cb 2 bs cb C1 = watt m K 2.32 Ref: LHC-PROJECT-NOTE-2 - Heat Flow Measurements on Beam Screens with and without Supports.125 W/m for Tbs=97 K C2 = σ 4 4 ( T bs T cb ) π d bs 1 εst( T bs d + ) d P cb (T bs )<.15 W/m bs cb 1 1 εst( T cb 1 ) heat transfer (W/m) W/m for Tbs=97 K 1 Radiation Conduction Total beam-screen temp (K) CD - June 23, 21 VLHC workshop on the beam tube vacuum 14

15 Calculation of beam screen parameters Q s = S ll T bs T m=6.6 g/s ct k SS ( T ) Cooling surf=9% Tct=96.45 K Tbsout=15.97K dt QsT ( ) QcTfT (, ) Pbs phemdottout (,, Tin) Q c = N A L ct h ( T )( T ) ct T ( T ) k ( T ) h = Nu d ct Nu =.23Re Pr = µ Re = ρ v ( T ) = ( T ) A ct c ( T ) k m& ρ.8 ( T ) ( T ) p d v µ ct Pr ( T ) ( T ) N T bs ( T ) = Po P ( T T ) P, bs cb bs cb p He = dm dt c p 1 ( T )( Tout Tin ) L CD - June 23, 21 VLHC workshop on the beam tube vacuum 15

16 Ptsrad ( Tts) = Heat flux to the thermal shield α P ts ( Tts) = Ptsrad ( Tts) + Ptscond ( Tts) 2 ( Tvv Tts 2 N 2 ) + β ( Tvv 4 Tts N 4 ) Per ts Perimeter of the thermal shield a,b are coefficients taking into account the thermal conductivity of the superinsulation system and the emissivity factor of superinsulation, respectively. Both coefficients are deduced from the type of superinsulation and the residual gas pressure in the vacuum vessel. Ptscond ( Tts) = 5 2 ( Tts ) 1 Ptsrad(65K) = 2.8 W/m Ptscond(65K) = 1.4 W/m CD - June 23, 21 VLHC workshop on the beam tube vacuum 16

17 Cooling loop:thermal shield and Beam screen in series ( T ) = f ( T ) P ( T ) + f ( T ) [ 2 P ( T )] + f ( T ) [ 2 P ( T, T ) 1] P2 Q ts ts ts ts bs bs bs cb cb bs cb + We estimate that.5 W/m is the additional heat load, Q1, on the two cold bores due to resistive heating in the magnet, beam gas scattering, radiation from the shield, conduction through the cold mass supports. Power at the plug (W) Optimization refrigeration cost for PSR=5 W/m ~ 1% of economy for 97 K compared to K optimum BS temp (K) synchrotron rad power (W/m/beam) cooling surface (mm 2 ) Beam screen temperature (K) Installed Power 1.4 MW CD - June 23, 21 VLHC workshop on the beam tube vacuum 17

18 Cooling loop optimization Optimal beam screen temperature (K) PSR (W/m) Optimal beam screen temperature (average) for a beam screen in series with the thermal shield Optimal thermal shield temperature (Calculated independently from the beam screen cooling system) Operating wall power plug (W/m) - No beam screen in series Thermal shield temperature (K) CD - June 23, 21 VLHC workshop on the beam tube vacuum 18

19 Cooling loop optimization Parameters calculated for a luminosity of cm -1.s -1-1, with 4.7 W/m of SR power: 1- the optimal beam screen temperature if in series w/ thermal shield T1_BS opt = 97 K 2- the optimal thermal shield temperature if in series w/ beam screen T1_TS opt = 83 K 3- the optimal thermal shield temperature w/o beam screen T_TS opt = 63 K 4- the one beam screen + one cold bore operating wall plug power Ptotbs(82.7K) = 64.8 W/m 5- the thermal shield (only) operating wall plug power PtsRT(82.7K) =37.1 W/m CD - June 23, 21 VLHC workshop on the beam tube vacuum 19

20 Cooling loop optimization Parameters calculated for a luminosity of cm -1.s -1-1, with 4.7 W/m of SR power: 6- the beam screen + cold bore operating wall plug power PtotRT(97K) =224.6 W/m 7- the thermal shield + cold mass operating wall plug power PtsRT(82.7K) = 197 W/m 8- the VLHC total operating wall plug power PRT_BScold = 61.8 MW 9- the VLHC total operating wall plug power w/ the safety and overcapacity factor Power_BScold = 1.4 MW CD - June 23, 21 VLHC workshop on the beam tube vacuum 2

21 Ref: Fermilab-TM-2149 Design Study for a Staged VLHC Shield supply Shield return pipe pipe Thermal shield Beam screen and thermal shield Magnet cold mass (in transfer line) (magnet) (two beams) (transfer line) Temp in (K) Press in (bar) Temp out (K) Press out (bar) Predicted heat load (W/m) Heat uncertainty factor Design heat load (W/m) Distance (m) Design total heat (kw) Design mass flow (g/s) Design ideal power (kw) K equiv design power (kw) Efficiency (fraction Carnot) Efficiency in Watts/Watt (W/W) Nominal operating power (kw) Overcapacity factor Installed operating power (kw) Percent of power 1.% 12.6% 17.9% 5.8% 59.4% Total installed operating power for one 1 km string (MW) 4.7 Total installed 4.5 K equivalent power for one 1 km string (kw) 21.2 Number of above "strings" in accelerator 24 Operating wall plug power for cryogenics for entire accelerator (MW) 85.7 Installed wall plug power for cryogenics for entire accelerator (MW) Installed 4.5 K equivalent power for entire accelerator (kw) 58.9 Installed number of LHC system equivalents 3.5 From Tom Peterson CD - June 23, 21 VLHC workshop on the beam tube vacuum 21

22 RT Solution: 2 g/s of water to keep a 2 K gradient along the beam screen DP= 1 bar thermal shield around the beam screen If the thermal shield is cooled in series w/ the cold mass then Tts=95 K X-section water + X-section He = 22 % + 12% >28 % available for the 4 aperture magnets Save 27 % of the refrigeration cost Installed Power 76.1 MW Need to increase the aperture of the magnet ==> not a realistic solution CD - June 23, 21 VLHC workshop on the beam tube vacuum 22

23 RT 5 1 K beam screen Total refrigeration power (W/m) K beam screen Plots for P SR = 8.5 W/m Temperature of the thermal shield (K) Save 27 % of the refrigeration cost Installed Power 76.1 MW Need to increase the aperture of the magnet ==> not a realistic solution CD - June 23, 21 VLHC workshop on the beam tube vacuum 23

24 Beam screen design Cold bore updated dimensions: 5/53 mm LHC beam screen Operating temperature : 5 K to 2 K Cooling tube: ID=3.7 mm,.53 mm thick, developed with high manganese and high nitrogen content stainless steel grade (commercial name Boehler P56). This steel grade needs a magnetic permeability of < 1.5 at temperatures of 5-2 K Preliminary VLHC beam screen proposal 8 tubes (3.7 mm id / 4.5 mm od), screen (44 mm id / 46 mm od) and cold bore (49 mm id / 52 mm od); CD - June 23, 21 VLHC workshop on the beam tube vacuum 24

25 VLHC2-BS 6W/m-12% DESIGN Beam-screen: 32.5 mm OD 1mm SS.5 mm brass/ss supports Extruded SS cooling channel (.5 mm wall thickness) Aperture: 2x3 mm 2µm Cu layer - co-laminated 9-11 K*, bar* 6.6 g/sec GHe 12 pump. slots/m 1.5x8mm-rounded Accelerator & Technology Seminar Fermilab, June 12, K. Ewald 1.5 mm cold-bore, 34 mm ID P. Bauer Synchrotron Radiation and Vacuum issues in the VLHC2 * refers CD - June to 23, a m half-cell VLHC workshop on the beam tube vacuum 25

26 ALTERNATIVE SOLUTIONS From Pierre Bauer 14 GHe CB wall Power per beam (W/m) GHe H 2 O BS CB BS BSTS PS C. Darve synchrotron rad power (W/m/beam) CB Accelerator & Technology Seminar Fermilab, June 12, P. Bauer Synchrotron Radiation and Vacuum issues in the VLHC2 CD - June 23, 21 VLHC workshop on the beam tube vacuum 26

27 Acknowledgement - Tom Peterson - Berthold Jenninger - Nicolaas Kos - Tom Nicol CD - June 23, 21 VLHC workshop on the beam tube vacuum 27