Safety

1
Introduction

• Safety
• Requirements
• History
• AC Conductivity
• Chamber Base Materials
• PMOG Statement

2
Safety

• Lifting
• Current design weighs 400 lb, chamber plus jig
  plate, so thought out plans needs to be put into
  place for lifting and assembly
• Fixture incorporates safe lifting and easy
  assembly.

• APS and SLAC Safety
• APS Safety requirements
• Work using ANL ISM process
• SLAC Safety Requirements
• Work also using SLAC ISMS process

3
Vacuum Requirements

• A continuous vacuum chamber will run throughout
  the Undulator System.
• The Vacuum System will be designed to produce an
  average pressure of less than 10-6 torr.
• The maximum time allowed for pump down to reach
  an average pressure of 10-6 torr after Cradle
  replacement is 1 day.
• The vacuum chamber axis shall be aligned to the
  CA (see section 4.7 for definition) to within
  200 µm.
• The beam-stay-clear radius around the CA is 2.3
  mm. The beam-stay clear radius defines the area
  in which the electron beam can be positioned
  without hitting any vacuum chamber components.
  The electron beam will be shut off if its
  position from the CA exceeds 2.1 mm to prevent
  the generation of damaging radiation.
• The material of the vacuum chamber surface seen
  by the electron beam will be aluminum, with a
  minimum thickness of 100 nm. The use of other
  material over very short distances might be
  permissible if approved by the Undulator System
  Physicist. The width of the vacuum chamber will
  be more than 50 larger than its height. The
  inner dimensions of the vacuum chamber inside the
  Undulator Segment shall be 5 mm full height and
  10 mm full width.
• Of importance is the impedance that the vacuum
  chamber presents to the beam. There are three
  main contributors to the impedance of the vacuum
  chamber, i.e., its electrical surface
  conductivity, its surface roughness, and its
  geometric shape. The goal is to keep the
  contribution from surface roughness and geometric
  shape small (less then 10 ) compared to the
  contribution from the finite electrical
  conductivity.
• The surface roughness impedance is dependent on
  the longitudinal spatial spectrum of the surface
  roughness. For each spatial frequency component
  of the surface roughness, the ratio of the
  corresponding spatial wavelength to the amplitude
  will be greater or equal to 300 over the 0.01-10
  mm period range. Structures with periods shorter
  than 10 µm will be kept smaller at amplitude of
  less than 25 nm.
• All vacuum chamber component designs shall be
  submitted to and approved by the Undulator System
  Physicist for impedance evaluation before
  manufacturing.

4
Additional Vacuum Requirements

• These requirements are for the Support and
  Positioning System and they have implications for
  the design of the Bellows.
• The Support and Positioning System is required to
  have a range of motion such that each Quadrupole
  can be moved (0.75 mm old) 1 mm radius in any
  transverse direction from its neutral position,
  independently of other Quadrupoles. The motion of
  the Cradle movers for different Cradles will be
  coupled such that orthogonal position control is
  provided for each Quadrupole. The motion control
  will allow moving a single quadrupole
  independently in horizontal and vertical
  direction without affecting the adjacent
  quadrupoles and without introducing roll to the
  Cradle Assembly. The motion of the other Cradle
  components will be proportional to their position
  on the Cradle so that the Undulator Segment, the
  BPM, and the Quadrupole will stay aligned to the
  CA. The motion will be designed and controlled
  such that the relative alignment information
  between the quadrupole axis and the CA of the
  adjacent Cradle will be maintained.
• The maximum possible range of motion of the
  Quadrupole is not to exceed 1.2 mm from its
  neutral position. The positioning system must not
  exceed this limit under any combination of Cradle
  mover settings, even unintentional.
• The reason for this limitation of the motion
  range is to reduce the possibility that the
  electron beam can hit the undulator vacuum
  chamber due to run-away Quadrupoles.

5
History

• Design has changed over time
• Initial Design Suggested in LCLS CDR
• Stainless Steel Tube with Copper coating
• Copper Tube Design
• Adding Strong Back to improve straightness as
  Undulator now rolls away

6
History
Chamber Strongback
Tubular Chamber 6 mm OD X 5 mm ID
Support

• Stainless Steel with Aluminum Coating

7
AC Conductivity

• Testing
• Pure Copper
• Copper foil (99.999, 100 mm x 100mm x 1 mm) was
  purchased from Good Fellow
• Punch to size then polished by lapping.
• Aluminum coated Stainless Steel 304 (1)
• Mirror finished stainless steel sheet (0.5 mm)
  was supplied from Hwa Yang Stainless Steel Corp.
• Punch to size
• Pure Al sputter coated onto the mirror-finished
  surface

8
Preliminary Kramers-Kronig Analysis
1 meV 8 cm-1
1000 cm-1 10 mm 33 cm-1 300 mm
Figure from Preliminary Reflectivity Data on
Metals By Jiufeng Tu City College of New
York Jan. 26, 2005
9
Chamber Base Materials

• Why Stainless Steel?
• Why not Aluminum?
• Extruded Aluminum
• Taber Metals is not able to do small cross
  section
• Contacted a number of vendors to do extrusion
• Problem with the small size of the order
• Long development to make dies
• Past experience with chamber walls at 1 mm, and
  none with 0.5 mm. Concerns with pipes in
  material
• How to obtain surface finish over full length of
  chamber
• Handling Damage
• Why not Copper?
• Braze Copper
• Need to find furnace large enough for chamber
• Need to polish after brazing
• Concern that flanges will be too soft after
  brazing
• Handling damage
• Aluminum is the preferred surface for chamber

10
What Kind of Stainless Steel?

• Stainless Steel
• Literature
• Experience in other undulator applications
• Permeability

• Stainless Steel 316LN (UNS S 31653)
• Vacuum chamber used in ESRF and CLS, but rebar
  has been a primary application in US.
• Stainless Steel 310 (UNS S 31000)
• Nitronic 33 (UNS S24000, XM-29 )
• Nitronic 40 (UNS S21900, XM-10 )
• 20Cb-3 (UNS N08020)

• Los Alamos Natl Lab
• Title Magnetic Permeability of Stainless Steel
  for Use in Accelerator Beam Transport Systems
  (Source PAC1991 2322).
• Fermi Natl Lab
• Title Magnetic Permeability of Stainless Steels
  at Low Temperature (Source TD-01-065, September
  27, 2001).

11
Permeability of Stainless Steels
Magnetic Measurements
from Magnetic Properties of Undulator Vacuum
Chamber Materials for the Linac Coherent Light
Source by SH Lee presented at FEL2005
12
Project Management Oversignt Group (PMOG) Review
and Comments - 30 Nov. 2005

• The Vacuum Chamber
• The change in material and cross-section has
  forever shifted this component to be near the
  critical path
• We do not yet have a prototype
• Worry about finish (surface roughness and
  durability)
• Also worry about non-zero relative permeability
• Would like a clear fallback position
• Circular cross-section copper as before?
• Response from the PMOG committee on the question
  of the vacuum chamber design.
• The undulator group should concentrate on the
  design of the rectangular vacuum system and not
  worry about backup possibilities. The undulator
  group should measure the vibration
  characteristics of the recently received
  undulator girder. JS