Status: Cooling of the ILC e+ target

by thermal radiation

POSIPOL 2015, Cockroft Institute, Daresbury, UK

2nd September 2015

Felix Dietrich (DESY), Sabine Riemann (DESY), Peter Sievers (CERN),

Gudrid Moortgat-Pick, Andriy Ushakov (Hamburg U)

• Radiative thermal cooling of e+ target• Status

– Target temperature – Design considerations, mechanical issues, eddy

currents– Our next steps

• Summary• Short remark on helicity reversal

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 2

Ti6Al4V

Radiator (Cu)

Cooler (Cu)photons

3Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling

Radiative cooling – considered so far

• Rotating target wheel consists of Ti rim (e+ target) and Cu (radiator)

• Heat path: – thermal conduction

Ti Cu wheel – Thermal radiation of Cu to

stationary water cooled coolers

• Target, radiator and cooler are in vacuum

• Cooling area can be easily increased by additional fins

Felix Dietrich

e+ target for Ecm = 250 … 500GeV

• Ecm and luminosity determine deposited energy

(Pe+ ≤30%)

• Target wheel design appropriate for all Ecm ? – radiative surface A sufficient to remove deposited energies W

for all Ecm?

– Thermal contact Ti-Cu radiator is important (size and quality) Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 4

Ebeam [GeV] Edep [kW] DTmax/pulse [K] Edep [kW] DTmax/pulse [K]

Nominal luminosity High luminosity

120 5.0 66 - -

175 (ILC EDMS) 3.9 125 - -

250 (ILC EDMS) 2.0 130 4.1 195

250 2.3 85 4.6 165

4cool

4radiator TTA~P

A. Ushakov,

Update 2015

A. Ushakov,

2015

s = Stefan-Boltzmann constant = 5.67 × 10-8 W/(m2K4)

e = emissivity = 0.7

G = geometric form factor = 1

Area A of thermal radiation

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 5

4cool

4radiator TTGAP

T[°

C]

A[m2]

Studies so far(ANSYS): Felix Dietrich: – A ≈ 2.8 m2

– ‘outer’ radiator with fins + cooler

– P = 2kW, 4kW

Andriy Ushakov: – A = 1.76 m2

1.51 m2 (Cu) + 0.25 m2 (Ti)– Full copper disc, no fins;

radiation ambient– P = 2.3kW

To be checked: Pol upgrade

Heat transfer target - radiatorTemperature distribution in Ti target depends on

– deposited energy – height of target rim – heat transfer from Ti to Cu radiator, i.e. contact area target-radiator

Details see Felix Dietrich’s talk.

• heat transfer determines also time until equilibrium temperature is reached:

– Photon beam hits after ~7seconds the same position at the target – Thermal diffusion vs time:

• xTi = 0.68 cm for 7s; 2.2 cm for 70s

• xCu = 2.8 cm for 7s; 9.0 cm for 70s

– 7s are not sufficient to remove the heat from target– temperature accumulates over many bunch trains up to equilibrium

Temperature gradient from beam path area to contact surface to radiator

• Heat flux density through Ti – Ci contact – Max power per bunch train: 7kJ/5 = 1.4kJ

average energy deposition in 7s at same target area: 200 W

heat flux density TiCu is 12.5W/cm2 for 16 cm2 Ti-Cu contact surface

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 6

ctx

Ti

Cu

Equilibrium temperature distribution in target

Temperature evolution over time, ANSYS (see also Felix’ talk):• Ecm = 500GeV; Edep = 2.3 kW

• Radiator area ~2.8 m2

• After ~3 hours equilibrium temperature distribution reached

• Target height max temperature Tmax ≈ 680°C (a = 5cm)

Tmax ≈ 570°C (a = 4cm)

Distance beam path to Ti-Cu contact

is important

• Temperature in Cu (near Ti) ≈280°C (a = 5cm), ≈270°C (a = 4cm) Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 7

2cm

a

a = 5cm

a = 4cm

Ti

Cu

Felix Dietrich

Max average temperature in Ti target

(~ area along beam path)

So far, Felix considered a cooling area of 2.8 m2

Max average temperature in target goes down if almost full disc is included in radiative cooling

(+ 0.7m2 without fins)

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 8

A

A

4

1

T

T

Heat flux through Ti-Cu contact

Andriy Ushakov (2014) P = 5.17 kW, eCu = 0.7, eTi = 0.25

max heat flux thru Ti-Cu contact

≈ 10 W/cm2

Felix Dietrich: P = 2.3 kW, eCu = eTi = 0.7

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 9

Ti

Cu

2cm

4cm

Ti

Cu

2cm

5cm

Ti Cu Ti Cu

Stress at Ti-Cu contact• Thermal expansion and resulting distortion/stress at the Ti-Cu contact

depends on temperature profile in radiator and target

aTi = 8.6 × 10-6/K aCu = 16.5 × 10-6/K– Max temperature in Ti wheel ~500°C Dh ~ 0.43%– Max temperature in Cu radiator (near Ti-Cu contact) is ~200°C Dr ~

0.33%

• Additionally, stress due to centrifugal force – Not yet taken into account

• Heat transfer at contact depends on– Surface roughness– Contact pressure– Are there substances, vacuum-capable, to minimize thermal resistance?– Bolted Ti-Cu contact seems to be better than brazed contact

contact must stand thermal fluctuations without degradationRiemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 10

Simulation (prel.) by A. Ushakovbrazed Ti-Cu contact assumed

P= 5170W,

eCu = 0.7, eTi = 0.25

v.Mises stress <200MPa

Stress at Ti-Cu contact Simulation (prel.) by A. Ushakovbrazed Ti-Cu contact assumed

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 11

• v.Mises tress at Ti –Cu contact <200MPa • Max values (ANSYS) appear at

outermost region of contact.

Ti target

Cu radiator

Stress at Ti-Cu contact• Thermal expansion and resulting distortion/stress at the Ti-Cu contact

depends on temperature profile in radiator and target

aTi = 8.6 × 10-6/K aCu = 16.5 × 10-6/K– Max temperature in Ti wheel ~500°C Dh ~ 0.43%– Max temperature in Cu radiator (near Ti-Cu contact) is ~200°C

Dr ~ 0.33%

• Heat transfer at contact depends on– Surface roughness– Contact pressure– Are there substances, vacuum-capable, to minimize thermal resistance?

Contact must stand thermal fluctuations without degradation

Bolted Ti-Cu contact is ok, brazed contact is not– bolting at 10 MPa could allow frictionless, lateral thermal expansion maintaining

the at the thermal contact (P. Sievers)

To be done: implement ‘real’ contact in ANSYS simulations.

experimental tests Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 12

Mechanical aspects• Mass of the wheel (Cu radiator) ~100 kg• Energy E stored in the wheel ≈ 0.5MJ safety rules !

I = moment of inertia ~ 20kgm2

w = angular frequency

• Stress (average) in radiator due to centrifugal force ~112 MPa

(1/0.4 = formfactor for this shape of flywheels)

• Stress at the radiator fins due to centrifugal force– mass of one fin: ~4kg– Centrifugal force: F = m w2 r ~ 80 kN– Stress at each fin = F/A ~ 5 MPa

Next steps:• Alternative (lighter) radiator material? • Design optimization with smaller (no?) fins

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 13

MJ5.02

IE

2

m

E

4.0

1

• In principle, Ti keeps its stability in the temperature range 200 - 635°C (http://form-technik.biz/titan-material-eigenschaften/)

• Stability of Cu decreases with temperature, but this shouldn’t be a problem for T ~ 200 and choice of special alloy – Permanent stress due to tangential force creeping effects ? to

be checked

• Thermal expansion slightly changed momentum of inertia wheel slows down slightly if no correction

• Non uniform average temperatures around the wheel non symmetric thermal deformations unbalances – Temperature raise up to equilibrium (~3h) could cause imbalances– unbalances have to be monitored and corrected; has to be discussed with

engineers

• Long term material degradation due to irradiation must be tested experimentally

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 14

Eddy currents• B field at the target additional heat load • Eddy current tests at UK

• Zang, http://research-archive.liv.ac.uk/1445/2/ZangLei_Sept2010_1445.pdf , .

• Bailey et al., Proceedings of IPAC2010, Kyoto, Japan

expect ~8 kW energy deposition in the Ti rim

rotating with 2000rpm through a field of B = 0.5T

ILC: duty cycle of 5×1/1000 (5×1ms), – heat load is only 8W per bunch train distributed to a

length of ~10cm of the spinning rim

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 15

Eddy current estimations (P. Sievers)

Input:• Target velocity v = 100 m/s• magnetic pulse: flat top, duration of 1 ms; rise and fall times of

about <0.2 ms. • B = 0.5T at target, considered as constant over radius of 10 mm• repetition rate 5 Hz.• target cross section: height h = 2 cm, thickness d = 1.4 cm • Electrical conductivity (Ti-alloy): σ= 5.3×105 1/(W m)

Results:– Torque t = F×R = 37 Nm– Average power: W = F v = 7.4 kW;

duty cycle 5∙10-3 W = 37 W– High momentum of inertia of the wheel slow

mechanical response Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 16

Eddy currents …

• In addition: intermittent force (~100N in 1ms) on the target shaft and bearings resulting from the pulsed braking power

tight control of the wheel velocity, the motor

torque and damping if possible

vibrations could be important and have to be

studied

Conclusion • No problem with eddy currents at undulator source. • In case of longer duty cycle values have to be updated.

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 17

Magnetic Bearings• No news yet• Experience exists over 30 years for the use of

magnetic bearings (see P. Sievers’ talk @POSIPOL’14) • Industrial suppliers are SKF/Gemany/Calgary/Canada and

KFZ/Juelich/Germany• Loads above 100 kg with more than 7000 rpm are possible• Temperatures of up to 300°C can be accepted by the bearings• Active vibration control of the axis at the magnetic bearings is

available• Thermal barriers should be arranged to prevent heat flowing into the

rotation axis • Very precise velocity control is standard

• Prototype with magnetic bearings for cooling with sliding pads is also benchmark for radiative cooling

We should agree the parameters to be tested Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 18

Our next steps• Temperature evolution in the whole system • stress at the wheel (including radiator) • optimize system (target + radiator) to be flexible for all

energies and luminosities– Thermal contact target-radiator– Aspects important for magnetic bearings (forces,

imbalances,…)– Figure out safety factors

• Target material tests – We get support from German Ministry of Science– Period: July 2015 – 2019 (manpower)– DESY Zeuthen: 1 postdoc 2016/17 (2 years)

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 19

Material tests at MainzFirst step:• Tests at MAMI

– 3.5kW beam power, E=3.5MeV

– No problems with radiation protection

– Study material response to cyclic load

Later step • Tests at MESA (>2017), E≈15MeV

Simulations to prepare tests will be done by DESY/ Uni HH; preparation and set up of experiments will be done in Mainz

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 20

K. Aulenbacher

Summary• Radiative cooling should work, no showstopper identified• Scheme is under study & optimization

– Prototyping :• Desired: design an experimental mock up in real size • DESY/Uni HH: no hardware resources

Collaboration with ANL/… ?!– Material tests at Mainz (e- beam)

• Also important: polarization issues– Upgrade to higher polarization– Spin flipper

• Our Resources– Manpower:

• Felix Dietrich (master student, until autumn 2016), • Andriy Ushakov (contract until 2017(+)), • SR. + postdoc @ Zeuthen from 2016• Peter Sievers 21Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling

Last but not least: helicity reversal for e+ILC project meeting at DESY, 28 Sept 2015:

Nick Walker presented news from ILC AD&I status

… spin flipper…

OTDR:ur statement concerning spin flipper:• Helicity reversal is essential to control systematic errors

second rotator line is required• Design exists – see L.I. Malysheva et al., “The Design of spin-

rotator with a possibility of helicity switching for polarized positron at the ILC,” Proc. IPAC’12, (TUPPR003)

• Depolarization in damping ring is very difficult– See talks of L. Malysheva and Valentyn Kovalenko at previous e+

source meetingsRiemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 22

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 23N. Walker, B. List; DESY ILC project meeting 28 Sep 2015

Spin flipper

L.I. Malysheva et al., http://accelconf.web.cern.ch/AccelConf/IPAC2012/papers/TUPPR003.PDF

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 24

– Studies done so far for sc solenoid (8.32m)

– Have to be updated for nc 40m solenoid

Last but not least: helicity reversal for e+ (cont’d)

ILC project meeting at DESY, 28 Sept 2015:

Nick Walker presented news from ILC AD&I status

… spin flipper…

Our statement concerning spin flipper:• Helicity reversal is essential to enhance luminosity and to control

systematic errors second rotator line is required

• Design exists – see L.I. Malysheva et al., “The Design of spin-rotator with a possibility of helicity switching for polarized positron at the ILC,” Proc. IPAC’12, (TUPPR003) http://accelconf.web.cern.ch/AccelConf/IPAC2012/papers/TUPPR003.PDF

• Depolarization in damping ring is very difficult– See talks of L. Malysheva and Valentyn Kovalenko at previous e+

source meetingsRiemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 25

Thank you!

Riemann, Dietrich, Sievers, Ushakov POSIPOL 2015: Status radiative thermal e+ target cooling 26