Cryogenic Experts Meeting (19 ~ ) Heat transfer in SIS 300 dipole MT/FAIR – Cryogenics Y. Xiang, M. Kauschke

Heat transfer through laser cutting holes (M. Wilson, TU Dresden and GSI ); Temperature margin check-up for the SIS 300 dipole IHEP design by using 2D ANSYS simulation; Optimization of the interlayer cooling channel and its connection channels based on 3D ANSYS calculation Heat transfer analysis of 1-phase and 2-phase helium recooling process in one 300 Tm dipole; Conclusions Outline Cryogenic Experts Meeting (19 ~ )

Concerns on large thermal resistance due to big helium space underneath the Kapton insulation of coil cables Fig 1: Gas bubble formed where Kapton wrap bulges away from cable at the edges. Martin Wilson Report GSI 5 (25 Jan 2001) A calculation of 0.35 K temperature rise through a stagnant gas film, assuming the film to be 0.5mm thick.

Two types of Laser cutting holes on cable insulation Fig 2: Edge view of the cable with holes cut by Jena University Martin Wilson Report GSI 17 (5 Feb 2004)

Heat transfer through a hole in the electrical insulation by CFD analysis M. Hieke, H. Quack ( ) Helium layer thickness: 20  m w (m/s) k tot without hole (W/m 2 K) k tot with hole (W/m 2 K) Helium layer thickness: 500  m w (m/s) k tot without hole (W/m 2 K) k tot with hole (W/m 2 K) Fig. 2 – CFX model for helium flow above insulation with a hole and temperature contours (helium layer 500  m, average velocity 0.1 m/s) heat transfer coefficient (total)

2D ANSYS analysis at GSI about the influence of cooling hole on helium flow and heat transfer ( )

Type A _ cooling hole of nominal width 630 micrometers Type B _ cooling hole of nominal width 400 micrometers Thickness of the four layers Kapton : 88 micrometers Thickness of the helium space underneath the four layers Kapton : 31 micrometers Thickness of the four layers Kapton : 102 micrometers Thickness of the helium space underneath the four layers Kapton : 19 micrometers Depth of the helium groove in the superconductor : 100 micrometers The measurement shows the depth of the helium space underneath the Kapton layers is about 20 ~ 30 micon. For the cured cable it may be even smaller. Observation and measurements for the cooling holes on cable insulation with microscope at GSI ( )

purposes: to check the temperature margin of the magnet design at IHEP, Moscow optimization the interlayer cooling channel dimensions to ensure enough temperature margin for the magnet operation Note: The cross section of the 2D model has ellipse shape because the coil is cut at 45 degree direction with respect to the magnet axis. 2D ANSYS analysis at GSI on the temperature margin check-up for SIS T IHEP design ( ) In the model no cooling holes on the insulation! no helium space underneath the insulation! supercritical helium (light blue), NbTi coil turns (violet), SS304 wedges (dark blue) and 0.1 mm polyimide film of insulation (not shown).

Ramping conditions of 6 T superconducting SIS 300 dipole (IHEP design) "Design of 6T superconducting dipoles for the SIS 300" IHEP report Power loss curve over one cycle Power loss curve over five cycles

Temperature profile of the inner and outer coil layers and helium flow in the interlayer cooling channel at certain time during the ramping Temperature profile at end of 5 ramping cycles Interlayer cooling channel connection channel outlet annular channel connection channel inlet Highest temperature occurs in the coil blocks of outer layer with many turns (poor cooling conditions) High temperature occurs also at the turns of outer layer close to the pole (high field region); SS304 wedges help cooling the neighboring turns

Temperature profile and its changes of inner-, outer-turn layers and helium flow during the ramping Animation video of temperature profile during 5 ramping cycles Time history of temperature changes at three positions in the turns and of the helium flow nearby during ramping The calculated temperature margin of the first pole turn by ANSYS is about 0.9 K if the critical temperature for this turn is 5.69 K (IHEP 2005 report). This fits the results in the IHEP 2005 report.

Temperature profile in the pole turn region and helium flow velocity when the highest temperature is reached during ramping (80 s) Temperature differences between the coil cable and the helium are : ~ 0.3 K at the outler layer in the pole region; ~ 0.1 K at the first turn of inner layer in the pole region; They are dominated by the temperature drop on Kapton insulation The average helium velocity in the interlayer is about 0.01 m/s which corresponds to the mass flow rate of g/s

purpose: to allow as much the helium mass flow into the interlayer cooling channels as possible so as to improve the cooling performance Optimization of the interlayer cooling channel and its connection channels based on 3D ANSYS calculation

Optimization results discussion helix channel connection channel annular channel Dimension of fishbone channel [mm] 1 x 42 x 4 Dimension of connection channel [mm] 0.5 x 20.5 x 42 x 21 x 42 x 22 x 4 Velocity in fishbone channel [m/s] ~0.018~0.037~0.042~0.056~0.033~0.047 Mass flow rate fishbone channel [g/s] Temperature margin [K] * Mass flow rate is kept constant at 38 g/s in the annular channel which is of 5 mm gap. The best combination is that both the helix channel and connection channels have the same height and width.

Investigation of 1-phase and 2-phase helium recooling process in SIS 300 dipole Cooling concept of SIS 300 dipole (origins from HERA [and UNK] dipole) One example to show how important is the recooling process Test results of temperature profile of one Tevatron dipole (cryogenics 37, 1997)

Heat transfer coefficients of supercritical helium, liquid helium (nucleate boiling and convection) and vapor in 2-phase recooling over 3 m dipole length Engineering Data Book III, Chapter 10, Boiling heat transfer inside plain tubes,

Temperature profile of 1-phase and 2-phase helium over 3m recooling process in one 300 Tm dipole Parameters of LHC dipole heat exchanger has been used for the simulation 0.11 K 0.06 K Heat load for one dipole: 15 W

SIS 300 dipole – guiding plate for better recooling performance

The influence of part load operation on heat transfer coefficients in 2-phase recooling process 100 % load50 % load

The analysis shows that the Laser cutting holes technology is an effective way to improve the cooling performance but further investigation is needed on the other aspects (strength under rapid ramping, electric insulation characteristics estimation, etc.); Observation and measurements for the cooling holes on cable insulation shows the contribution of thermal resistance by helium space underneath the cable insulation can be neglected; Temperature margin check-up for the SIS 300 dipole IHEP design and optimization of the interlayer cooling channel and its connection channels have been successfully done; Heat transfer of 1-phase and 2-phase helium recooling process in one 300 Tm dipole has been simulated and ways to improve recooling performance has been discussed. Conclusions Cryogenic Experts Meeting (19 ~ )