LCLS Conceptual Design Report - Stanford Synchrotron Radiation ...

L C L S C O N C E P T U A L D E S I G N R E P O R T
8.8.1 Electron Beam Collimation and Vacuum Chamber Design
This section analyzes the vacuum chamber and magnetic material with regard to the need for
protection from accidental electron beam losses and discusses the vacuum chamber surface
roughness limits.
8.8.1.1 Beam Parameters Used in These Calculations
It is of vital importance to fully understand the consequences of exposure to the undulator to
the primary electron beam. Of greatest concern is the response of the permanent magnet material
and that of the undulator vacuum chamber to such events. The electron beam parameters (at
injection into the undulator) and geometric dimensions that were used in the analysis are listed in
Table 8.6.
Table 8.6 Parameters used in calculations of the effect of beam losses in the undulator.
Parameter Value
Beam Energy E o = 5–15 GeV
Bunch Charge Q = 1 nC (N = 0.625 × 10 10 e - /bunch)
Repetition Rate Pulse Repetition Rate, PRR ≤ 120 Hz
Average Power P av ≤ 1.8 kW
Beam Transverse Size σ ~32 µm
Magnet Gap g = 6.0 mm
Vacuum Chamber OD = 6.0 mm ,ID = 5.0 mm
Wall thickness t = 0.50 mm
8.8.1.2 Permanent Magnet Material
The material used for this analysis is neodymium-iron-boron (NdFeB) (2-14-1) and its
material properties are listed Table 8.7
Table 8.7 Material Properties of neodymium-iron-boron (NdFeB) (2-14-1)
Property Value
Modulus of Elasticity E = 1.5 × 10 11 N/m 2 (21.74 × 10 6 psi)
Poisson Ratio ν = 0.3
Tensile Strength σ UT = 80 N/mm 2 (11,600 psi)
Coefficient of Thermal Expansion α || = 3.4 × 10 -6 /°C
α ⊥ = –4.8 × 10 -6 /°C
E α || = 5.1× 10 5 (74 psi/°C)
E α ⊥ = 7.2 × 10 5 (104 psi/°C)
Specific Gravity ρ = 7.4 to 7.5 g/cm 3
Specific Heat c = 0.11 cal/(g°C) ≡ 0.46 Ws/(g°C)
8-40 ♦ U N D U L A T O R