T Bradshaw

On behalf of the SCU group

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Planar Undulator -Thermal Requirements

and Heat Loads

Superconducting Undulator Workshop, Rutherford Appleton Laboratory 28th April 2014

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Magnet Operating Point

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Wire Cu:Sc ratio is 0.575:1

Estimations give low minimum quench energies for the magnet ~µJ which is worrying as this effects the magnet stabilityNote that load line is not linear as shown

Need temperatures below 4K to give adequate margin for the conductor

Wire Dimensions NbTi areaTot wire width [mm] 0.36Tot wire height [mm] 0.765Cell Area [mm2] 0.275Insulation thickness 0.025Bare Wire width [mm] 0.31Bare Wire Height [mm] 0.715Bare wire Area [mm2] 0.222PF Area Metal/Cell Area 0.684Area metal [mm2] 0.188Copper part 0.57Scond part 1Area Copper in wire [mm2] 0.068Area NbTi in wire [mm2] 0.120Area of epoxy [mm2] 0.087

Operating pointsCurrent 407.00Curr den Jm NbTi [A/mm2] 3392.14Current density wire cell 1477.85(same as VF calc)Load lineBpeak 3.14Current density NbTi 3392.14Tfrom Graph Tg 4.4Tbath 2

“Load line” is for illustration only – slightly curved in reality

Requirements

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Bore tube

Top Magnet

Bot Magnet

RT

Shield

Shield

RT

The thermal resistances at the end of the bore tube are the bellows assemblies

Concept

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Upper Magnet (1.8K)

Lower Magnet (1.8K)

4K1.8K

RT

50K

12-16K

Current leads

~30-40W

• Cryocoolers at ends of magnet will reduce load on 1.8K stage

• Beam load 30-40W ?

Beam tube cooled by two dedicated cryocoolersWakefield heating uncertain (see later)

Heat load summary

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Magnet 93mW46.9W

Beam tube 41.4W16.2K

55K

4K 0.95W

Breakdown of 2K load – total 93mW ignoring any joint heating

The 1.8K system has a heat lift capacity of 200mW – size should be adequate.Beam tube could be up to 30-40W worst case (see later)

Cryocooler operating points

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Cooler on turret

Coolers on beam tube

...these are approximate positions

There was a study on the use of cheaper 408Ds with lower cooling power – this solution was not feasible as beam tube temperature ended up too high

Wakefield Heating

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From Robert Voutta’s presentation at meeting on 16th January 2013

Image Current Heating in Diamond.doc - Duncan Scott estimates – what we originally worked to.

2.5mm radius 3.5mm radiusSingle (few) bunch 4.18 2.99

MultiBunch, 300mA limit 1.76 1.26MultiBunch – No limit 2.47 1.77

Hybrid 3.10 2.21

We have been following COLDDIAG – instrument on Diamond looking specifically at wakefield heating.

What we were originally working to in terms of heat loads:

Wakefield Heating

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From Robert Voutta’s presentation at meeting on 16th January 2013

Note that these loads are over a 490mm length

Wakefield Heating

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Shamelessly taken from TD-ID-REP-081 by Ed RialLooked at behaviour of cryocoolers and derived heat load from load map and helium pressure controlNote that they have been able to reduce the spread by plotting against a parameter derived from bunch lengths etc… - this is for illustrationNote that DLS wish to increase current from 300mAAlso separation in wigglers is higher than the planar

Numbers are scary:Wiggler I15 getting 20W over full length (1820mm)Wiggler I12 getting 10W over full length (1640mm)

Item Wiggler I12 Wiggler I15Liner length 1640 mm 1820 mm

Magnetic Length 1080 mm 1350 mmAperture height 10 mm 9 mm

Cryocooler Manufacturer Sumitomo Oerlikon LeyboldMaximum Field 4.2 T 3.5 T

Wakefield Heating

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What do we do?

• Suspicion is that most of the heating is not wakefield heating – it is due to small cavities that are absorbing rf

- Need to ensure that the beam tube is as clean as possible- Roughness ≈ skin depth – a few microns- Transitions – Steps less than 100 microns, minimise gaps

• We don’t have a good handle on the size of the heating- have made provision for extra cryocoolers – likely discontinuities are at the ends of the beam tube which is where we have situated the cryocoolers

- have a good margin of safety on the cooling power• Need to keep following the COLDDiag and DLS measurements:

2 2 2

0 0

avs

I cPR d

L lMf

Basically proportional to resistivity and inversely proportional to gap – make an attempt to scale from other results …..

Wakefield Heating

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Device Operation Gap [mm]

Load[W] Length [m]

Q/L [W/m]

Adjusted for SCU [W]

SCW-1 250mA 10 9.5 1.824 5.21 20.03

SCW-2 250mA 9 11.8 1.64 7.20 24.91

             

ColdDiag 300mA (60x10mm elliptical)

10 9 0.49 18.37 70.64

             

CPMU 147K 7 38 2 19.00 51.15

CPMU 147K 5.2 50 2 25.00 50.00

             

CPMU 4K adjusted for resistivity

5.2 44 2 22.00 1.27

CPMU 4K adjusted for resistivity

9 56 2 28.00 1.24

Duncan Estimates - max

Assumed RRR = 60 5 5 1 5 9.62

The Cryogenic Permanent Magnet Undulator (CPMU) results were taken with beam tube at 147K (TDI-ID-REP-084). If we assume that the RRR of the copper used was about 100 and the wakefield heat is proportional to resistivity then the heating effect should be reduced by a factor of about 40. This seems to give anomalous results.The “adjusted for SCU” column assumes a 1/gap dependancy and for the CPMU a proportionality to resistivity. The SCU parameters are gap = 5.2mm and length = 2m.

Duncan Scott Engineering Tolerances Study and Image Current Heating in a Superconducting Planar Undulator for Diamond  

Emil Longhi Beam Heating in I07 CPMU, DLS report TDI-ID-REP-084, 11/09/13J.C. Schouten and E.C.M. Rial Electron beam heating and operation of the cryogenic

Undulator and superconducting wigglers at diamond

Ignore adjusted

Assumes copper with an RRR=100

Wakefield Heating

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Different materials and different RRRs will give very different beam heating – if we are understanding the numbers…..

Probably will end up gold plating – only require a few microns which is the skin depth at these frequencies

  Ohm cm x 10-6 RRR W/m  Cu 1.7 150.0 2.80Copper CERN Busbar lower valueCu 1.7 40.0 10.50Plain copper wireCu 1.7 100.0 4.20Hitachi OFHC C10100Cu 1.7 500.0 0.84Hitachi OFHC C10200Al 2.9 14.0 51.18Al 1100 gradeAl 2.65 414.0 1.58Al 99.995% annealed several daysAl 2.65 1000.0 0.65Very high purity Al 2.65 160.0 4.09Cooking grade pure Al?

Turret Assembly

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System is a continuous flow cryostat with a flow of ~10mg/s

Turret details

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Aim is to test the turret assembly for cooling power and operation – there are some wrinkles that we need to understand.We are also testing the current leads, thermometry and thermal balances.

Turret details

15Turret in preparation

Cryostat Heat Loads

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Stage Temp [K] Heat Load [W]

Ambient 294  1st Stage 55 48.12nd Stage 415 16.2 41.42nd Stage 415 4 0.953rd Stage 2K 1.8 0.110

• Cryostat uses HTS leads to limit load on 4K stage

• Beam tube is assumed at 12-16K and a load of 40W from beam heating

• Using 3 x Sumitomo RDK-415 coolers. One on turret and two on the beam tube

Cryostat Tests

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Struggling to get the correct mass flow – looking at needle valve and trap as flow restrictors

Summary

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• Conductor requirements are for ~2K.• MQE for the conductor is a bit worrying.• Using a continuous flow cryostat to get ~200mW (require

~100mW).• Not sure of beam/wakefield heating – allowed for worst

case. Will probably need plating.• Turret works – but flow needs looking at.

Looking at thermal aspects of bath to magnet interface – test programme.

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END