Progress on Helical Undulator for Polarised Positron Production

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Progress on Helical Undulator for Polarised Positron Production Duncan Scott ASTe. C Daresbury Laboratory

Progress on Helical Undulator for Polarised Positron Production Duncan Scott ASTe. C Daresbury Laboratory 26/05/03

Contents l l 26/05/03 Introduction Helical Undulator Designs l Super-Conducting l Pure Permanent Magnet

Contents l l 26/05/03 Introduction Helical Undulator Designs l Super-Conducting l Pure Permanent Magnet Vacuum Issues Further Work Duncan Scott: TESLA Collaboration Meeting 2

Introduction l l l 26/05/03 Looked at different helical undulator designs Two Candidates l

Introduction l l l 26/05/03 Looked at different helical undulator designs Two Candidates l Super-Conducting Wires l Permanent Magnet Helical Carrying out Engineering Feasibility on both designs Duncan Scott: TESLA Collaboration Meeting 3

Super - Conducting Design l Magnet Design for 12 & 14 mm periods: l

Super - Conducting Design l Magnet Design for 12 & 14 mm periods: l Beam Stay Clear 4 mm l Helix Diameter 6 mm Beam Stay Clear Helix Diameter Wire Height Wire Width 26/05/03 Duncan Scott: TESLA Collaboration Meeting 4

Super - Conducting Design l l 26/05/03 Calculated the magnetic field at the SC

Super - Conducting Design l l 26/05/03 Calculated the magnetic field at the SC wires l For 12 mm period this 136% of Short Sample % l For 14 mm period this 69% of Short Sample % l (cf at 100% wires become normal conducting) 14 mm period is the safest option Duncan Scott: TESLA Collaboration Meeting 5

Engineering Design l Prototype former made from cutting grooves into pipe 26/05/03 Duncan Scott:

Engineering Design l Prototype former made from cutting grooves into pipe 26/05/03 Duncan Scott: TESLA Collaboration Meeting 6

Permanent Magnet Undulator Design l l 14 mm Period, 4 mm Bore “Halbach” undulator

Permanent Magnet Undulator Design l l 14 mm Period, 4 mm Bore “Halbach” undulator (Klaus Halbach NIM Vol. 187, No 1) l 26/05/03 PPM blocks create Dipole Field l Rotate many rings to create Helical Field Duncan Scott: TESLA Collaboration Meeting 7

Engineering Design l l l Laminations of half-rings bonded together Made in 5 m

Engineering Design l l l Laminations of half-rings bonded together Made in 5 m sections Arrays are motor driven apart 26/05/03 Duncan Scott: TESLA Collaboration Meeting 8

Cryogenic Temperature Vacuum Problems l l l TESLA requirements of ~10 -8 mbar vacuum

Cryogenic Temperature Vacuum Problems l l l TESLA requirements of ~10 -8 mbar vacuum CO equivalent For the SC magnet this can be achieved As long as the number of photons above 3 e. V hitting the vessel wall is not greater than 1017 s-1 m-1 26/05/03 Duncan Scott: TESLA Collaboration Meeting 9

Room Temperature Vacuum Problems l l 26/05/03 Theoretical maximum for a 5 m long

Room Temperature Vacuum Problems l l 26/05/03 Theoretical maximum for a 5 m long 4 mm bore vacuum pipe is 10 -7 m. Bar A NEG coated vessel is needed No-one has ever NEG coated a 4 mm diameter tube! It is thought to be possible - but not yet achieved Duncan Scott: TESLA Collaboration Meeting 10

Next - Steps l l l Super-Conducting l Look at iron yoke - complicated

Next - Steps l l l Super-Conducting l Look at iron yoke - complicated modelling l Solutions for making the former Halbach l Initial engineering complete l Work with magnet manufacturers to finalise the design Hope to build two ~20 period prototypes (one of each design) to measure the magnetic field this year 26/05/03 Duncan Scott: TESLA Collaboration Meeting 11