Dipole Vacuum Chambers Stefan Wilfert GSI Helmholtz-Zentrum für Schwerionenforschung mbH Vacuum systems/ Magnet technology Planckstrasse 1 64291 DARMSTADT 05.05.2011 dfkgajklajklgadg 1 Stefan Wilfert, 5th MAC, 09.05.2011
I Introduction II Dipole chamber designs 1. Chamber with supplementary cooling tubes (measurements and methods for optimization) 2. Chamber with contact cooling (Measurements and methods for optimization) III Aspects of material choice IV Summary and conclusions 05.05.2011 dfkgajklajklgadg 2 2
Introduction Introduction Introduction Vacuum physical requirements on the magnet chambers � appr. 885 m of the 1084 m long beam line are operated at cryogenic temperatures � appr. 644 m are represented by magnet chambers (dipole, quadrupoles, sextupoles,….) � appr. 373 m are represented by dipole chambers � UHV/XHV generation will be realized by cryogenic wall pumping (cryopumping) and additional cryosorption pumps (for H 2 +He) � effective cryopumping requires wall temperatures lower than 20K Chamber design must be optimized in terms of � Field quality (avoiding the distortion of main guidiance field) � low wall temperatures during magnet ramping to preserve the effectiveness of cryopumping � beam dynamics aspects 05.05.2011 dfkgajklajklgadg 3 3
Dipole chamber design Dipole chamber design Dipole chamber design Great problem: unless special cooling measures, due to the fast magnet ramping eddy currents heat up the chamber wall to temperatures > 80K 80K max. dynamic vacuum pressure: p H2 ~ 5.10 -12 mbar @ 5K, static vacuum pressure: p H2 < 10 -12 mbar @ 5K Demand: T cham < 20K Length of chamber: 3.45 m Free aperture: 120 x 60mm 2 Wall thickness: 0.3mm Rib thickness: 3.0 mm 05.05.2011 dfkgajklajklgadg 4 4
Two different dipole chamber layouts Two different dipole chamber layouts Two different dipole chamber layouts Solution: chambers must be cooled Design I: Beam pipe with supplementary cooling tubes Design II: Beam pipe with contact cooling via the cold yoke 05.05.2011 dfkgajklajklgadg 5 5
Dipole chamber design I with different positions of Dipole chamber design I with different positions of Dipole chamber design I with different positions of supplementary cooling tubes supplementary cooling tubes supplementary cooling tubes 1 3 19.6° electrically insulated 18.0° electrically insulated electrically 4 insulated 2 05.05.2011 dfkgajklajklgadg 6
Dipole chamber design I Dipole chamber design I Dipole chamber design I with supplementary cooling tubes with supplementary cooling tubes with supplementary cooling tubes 24 top & buttom 22 lateral 20 18 T (K) 16 14 12 10 40 42 44 46 48 50 52 54 56 58 x (mm) Calculated by: LH picture shows the eddy current density. As shown in RH Shim (GSI) picture, the optimum position of 4 cooling tubes was for 2c cycle calculated computationally. The results shows that the optimum position is 52 mm from the center of magnet. At this positions the maximum temperatures on the lateral sides and top/bottom, are ~ 16 K. 05.05.2011 dfkgajklajklgadg 7
Dipole chamber design I Dipole chamber design I Dipole chamber design I with supplementary cooling tubes with supplementary cooling tubes with supplementary cooling tubes Calculated by: Shim (GSI) for 2c cycle Problem: non- Reinforcing ribs electrically insulated DN125 CF cooling tubes generate LHe fange additional unwanted cooling harmonics (multipoles) tubes in the magnetic beam guidiance field! 05.05.2011 dfkgajklajklgadg 8 8
Dipole chamber design I Dipole chamber design I Dipole chamber design I with supplementary cooling tubes with supplementary cooling tubes with supplementary cooling tubes 1 Fa. Reuter, Alzenau BINP, Novosibirsk 2 Length of chamber: 3.35 m Bend for Aperture: 120 x 60mm 2 Straight Wall thickness: 0.3mm BINP for BNG Rib thickness: 3.0 mm magnet Magnet Test sample by Fa. Reuter, Alzenau 05.05.2011 dfkgajklajklgadg 9 9
Dipole chamber design I: Measurements on temperature Dipole chamber design I: Measurements on temperature Dipole chamber design I: Measurements on temperature and partial pressure conditions under static conditions and partial pressure conditions under static conditions and partial pressure conditions under static conditions The generated residual gas atmosphere H 2 contains (in absense of He) only hydrogen p H2 = 3·10 -12 mbar measured @ RT p H2 = 1.5·10 -13 mbar @15K 05.05.2011 dfkgajklajklgadg 10
Dipole chamber design I: Measurements on temperature Dipole chamber design I: Measurements on temperature Dipole chamber design I: Measurements on temperature and partial pressure conditions under static conditions and partial pressure conditions under static conditions and partial pressure conditions under static conditions If T cham > 20K, pressure rises rapidly from 10 -12 mbar to 10 -6 mbar range, i.e. 6 orders of magnitude! 05.05.2011 dfkgajklajklgadg 11
Dipole chamber design I: Measurements on temperature Dipole chamber design I: Measurements on temperature Dipole chamber design I: Measurements on temperature and partial pressure conditions during magnet ramping and partial pressure conditions during magnet ramping and partial pressure conditions during magnet ramping 3,0 3,0 1.22s t d 2,5 2,5 magnetic field B [T] 2,0 2,0 1,5 1,5 1,0 1,0 0,5 0,5 0,0 0,0 t cyc 0 1 2 3 4 5 6 time t [sec] Measurements during magnet ramping cycle similar to 2c (most critical cycle) magnet ramping cycle 05.05.2011 dfkgajklajklgadg 12 He mass flow rates through the cooling tubes of (d m /d t ) He = 0,33g/s 12
Dipole chamber design I: Measurements on temperature Dipole chamber design I: Measurements on temperature Dipole chamber design I: Measurements on temperature and partial pressure conditions during magnet ramping and partial pressure conditions during magnet ramping and partial pressure conditions during magnet ramping � chamber responds immediately to magnet ramping with an increase in temperature � depending on ramping cycle, chamber walls heat-up from 5…6.8K to maximum temperatures of max.12K � only He and H 2 are released from the chamber walls � all other residual gases remain stuck to the cold walls � Helium desorbs completely from the walls (no wall- pumping!!!) � -> Cycles 2a, 3a, 4, and 5 and less critical Measurements during different ramping cycles (2a, 3a, 4, 5) 05.05.2011 dfkgajklajklgadg 13 He mass flow rates through the cooling tubes of (d m /d t ) He = 0,33g/s 13
Dipole chamber design I Dipole chamber design I Dipole chamber design I with supplementary cooling tubes with supplementary cooling tubes with supplementary cooling tubes Can we reduce the eddy current losses generated by the cooling tubes by changing the cooling pipe dimension? Cooling pipe dimension time (mm) average Calculated by: loss Shim (GSI) outer thickness (watt/m) for 2c cycle diameter 5 0.5 3.88 18 3.6 0.3 3.09 16 reduced cooling pipe dimension 14 Temperature (K) minimize heat loss by ~20% compared 12 to previous design 10 0.5 mm However, even lower heat loss, the 0.3 mm 8 temperature is increased about ∆ T ≅ + 1.0 K at the top and lateral side 6 Losses are reduced of beam tube. As expected, the cooling But temperatures are higher 4 efficiency is decreased by smaller heat transfer cross section. -1 0 1 2 3 4 5 6 7 8 05.05.2011 dfkgajklajklgadg 14 circumference (cm) 14
Methods to reduce the losses Methods to reduce the losses Methods to reduce the losses induced by cooling tubes induced by cooling tubes induced by cooling tubes In order to reduce eddy current losses and to avoid a conductor loop inside the magnet, the whole cooling tube circuit must be completely electrically insulated from the chamber . Two consequences: i) the outer surface of the cooling tubes has to be covered with a thin ceramic film (e.g. 150µm aluminium oxide Al 2 O 3 ) ii) Secondly, the electrical loop represented by a closed metallic cooling circuit must be electrically interrupted b y the use of an electrical insulating transition piece 05.05.2011 dfkgajklajklgadg 15 15
Dipole chamber design I Dipole chamber design I Dipole chamber design I with supplementary cooling tubes with supplementary cooling tubes with supplementary cooling tubes Calculated by: Shim (GSI) >18 K for 2c cycle ~ 5 K Using a chamber with only 2 cooling tubes (on each lateral side), most of the chamber surface shell is above 18K -> critical for cryopumping 05.05.2011 dfkgajklajklgadg 16 16
Specified dipole chamber design with 4 Specified dipole chamber design with 4 Specified dipole chamber design with 4 insulated supplementary cooling tubes to be tendered insulated supplementary cooling tubes to be tendered insulated supplementary cooling tubes to be tendered 5.3 mm 5.0 mm ∆ T ≅ + 1.7 K T = + 1.7K cooling tube Al 2 O 3 ceramic layer LHe (~150 µm) chamber wall Voltage breaker ~16 K ~ 5.5 K 05.05.2011 dfkgajklajklgadg 17
Comparison of different dipole chamber designs Comparison of different dipole chamber designs Comparison of different dipole chamber designs with supplementary cooling tubes with supplementary cooling tubes with supplementary cooling tubes 1 2 3 4 05.05.2011 dfkgajklajklgadg 18 18
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