T Bradshaw On behalf of the SCU group 1 Planar Undulator - Thermal Requirements and Heat Loads Superconducting Undulator Workshop, Rutherford Appleton Laboratory 28 th April 2014

2 Magnet Operating Point 2 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 stability Note that load line is not linear as shown Need temperatures below 4K to give adequate margin for the conductor Wire Dimensions NbTi area Tot wire width [mm]0.36 Tot wire height [mm]0.765 Cell Area [mm2]0.275 Insulation thickness0.025 Bare Wire width [mm]0.31 Bare Wire Height [mm]0.715 Bare wire Area [mm2]0.222 PF Area Metal/Cell Area0.684 Area metal [mm2]0.188 Copper part0.57 Scond part1 Area Copper in wire [mm2]0.068 Area NbTi in wire [mm2]0.120 Area of epoxy [mm2]0.087 Operating points Current Curr den Jm NbTi [A/mm2] Current density wire cell (same as VF calc) Load line Bpeak3.14 Current density NbTi Tfrom Graph Tg4.4 Tbath2 “Load line” is for illustration only – slightly curved in reality

Requirements 3 Bore tube Top Magnet Bot Magnet RT Shield RT The thermal resistances at the end of the bore tube are the bellows assemblies

Concept 4 Upper Magnet (1.8K) Lower Magnet (1.8K) 4K 1.8K 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 cryocoolers Wakefield heating uncertain (see later)

Heat load summary 5 Magnet 93mW 46.9W Beam tube 41.4W 16.2K 55K 4K0.95W 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 6 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 7 From Robert Voutta’s presentation at meeting on 16 th January 2013 Image Current Heating in Diamond.doc - Duncan Scott estimates – what we originally worked to. 2.5mm radius3.5mm radius Single (few) bunch MultiBunch, 300mA limit MultiBunch – No limit Hybrid 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 8 From Robert Voutta’s presentation at meeting on 16 th January 2013 Note that these loads are over a 490mm length

Wakefield Heating 9 Shamelessly taken from TD-ID- REP-081 by Ed Rial Looked at behaviour of cryocoolers and derived heat load from load map and helium pressure control Note that they have been able to reduce the spread by plotting against a parameter derived from bunch lengths etc… - this is for illustration Note that DLS wish to increase current from 300mA Also 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) ItemWiggler I12Wiggler I15 Liner length1640 mm1820 mm Magnetic Length1080 mm1350 mm Aperture height10 mm9 mm Cryocooler ManufacturerSumitomoOerlikon Leybold Maximum Field4.2 T3.5 T

Wakefield Heating 10 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: Basically proportional to resistivity and inversely proportional to gap – make an attempt to scale from other results …..

Wakefield Heating 11 DeviceOperation Gap [mm] Load[W] Length [m] Q/L [W/m] Adjusted for SCU [W] SCW-1250mA SCW-2250mA ColdDiag 300mA (60x10mm elliptical) CPMU147K CPMU147K CPMU 4K adjusted for resistivity CPMU 4K adjusted for resistivity Duncan Estimates - max Assumed RRR = 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 LonghiBeam Heating in I07 CPMU, DLS report TDI-ID-REP-084, 11/09/13 J.C. Schouten and E.C.M. RialElectron beam heating and operation of the cryogenic Undulator and superconducting wigglers at diamond Ignore adjusted Assumes copper with an RRR=100

Wakefield Heating 12 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 10-6RRRW/m Cu Copper CERN Busbar lower value Cu Plain copper wire Cu Hitachi OFHC C10100 Cu Hitachi OFHC C10200 Al Al 1100 grade Al Al % annealed several days Al Very high purity Al Cooking grade pure Al?

Turret Assembly 13 System is a continuous flow cryostat with a flow of ~10mg/s

Turret details 14 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 15 Turret in preparation

Cryostat Heat Loads 16 StageTemp [K]Heat Load [W] Ambient294 1st Stage nd Stage nd Stage rd Stage 2K 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 17 Struggling to get the correct mass flow – looking at needle valve and trap as flow restrictors

Summary 18 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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