LCLS Conceptual Design Report - Stanford Synchrotron Radiation ...

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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 7.1 Introduction and Overview In order to reach SASE saturation in a reasonable length undulator, a high electron peak current is required. For a radiation wavelength of 1.5 Å, an undulator period of 3 cm, and an undulator parameter of K ≈ 3.7, the desired electron beam should have a peak current of 3.4 kA, energy of 14.3 GeV, and transverse normalized rms ‘slice’ emittance of ≤1.2 µm. A longitudinal ‘slice’ of the electron beam is defined by the FEL slippage length (~0.5 µm in this case). These values correspond to an rms bunch length of 22 µm and charge of 1 nC, which is not possible in present rf photo-injectors due to space charge limitations. Therefore the bunch is accelerated and compressed in a series of linacs and magnetic chicanes. The accelerator must preserve the transverse emittance produced by the rf photo-injector. A slice emittance growth of
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 L0) is a new section installed in an existing off-axis enclosure adjacent to the beginning of sector- 21. L0 is composed of two 3-m RF structures and accelerates the ~1-mm long bunch from the rf gun to 150 MeV. The space-charge emittance compensation is also finalized in L0 (see Chapter 6). The transport line following L0 (low energy ‘dog-leg’ or DL1) provides energy and emittance diagnostics and includes a bending section for injection into the SLAC linac at a 35˚ angle. Linac- 1 (L1) accelerates the bunch “off-crest” to 272 MeV and generates a nearly linear energy correlation along the bunch to initiate the first stage of compression. A short X-band rf section (LX), immediately following L1, is used to linearize the compression by removing the quadratic energy-time bunch correlation generated in L0 and L1. It operates at 180˚ and decelerates the beam by 22 MeV setting the BC1 compression energy at 250 MeV. The linearization allows strong compression in the first stage while maintaining a fairly uniform temporal distribution along the bunch. The first bunch compressor is a 4-dipole chicane (BC1, located at the start of linac sector-21), which shortens the bunch to 0.20 mm rms. Linac-2 (L2) then accelerates the bunch to 4.54 GeV, also at an off-crest phase, which maintains the desired linear energy correlation. The second compressor is another 4-dipole chicane (BC2, at the end of linac sector-24) which compresses the bunch to its nominal final value of 22-µm rms. The very high peak current generated by the compression in BC2 can drive a micro-bunching instability [3], [4], which can damage both the slice emittance and the slice energy spread. In order to damp these effects, a very strong one-period superconducting wiggler is placed just upstream of the BC2 chicane in order to increase the incoherent energy spread of the beam. An increase to 3×10 −5 rms (from 3×10 −6 at 4.54 GeV without wiggler) is sufficient to suppress the instability without adding too much energy spread for the 1.5-Å SASE FEL. This is described in more detail in Section 7.4.2. β 1/2 (m 1/2 ) 25 20 15 10 5 0 1/2 β x 1/2 β y η x η y 200 400 600 S (m) 800 1000 1200 Figure 7.2 Twiss parameters for the <strong>LCLS</strong> accelerator from linac-0 exit to undulator entrance. The first compressor, BC1, is at S ≈ 30 m and the second, BC2, is at S ≈ 400 m. 0.3 0.2 0.1 0 −0.1 −0.2 −0.3 η (m) A C C E L E R A T O R ♦ 7-3
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Linac Coherent Light Source (LCLS)
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L C L S C O N C E P T U A L D E S I
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Preface This Conceptual Design Repo
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Table of Contents 1 Executive Summa
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6. Two experiment halls L C L S C O
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2.7.1.7 Conventional Facilities L C
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3 TECHNICAL SYNOPSIS Scientific Bas
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5 TECHNICAL SYNOPSIS FEL Parameters
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and the total peak beam power L C L
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5.4.2.2 Case II - High Charge Limit
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∆P ∆I sat pl / P / I sat pk L C
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5.9 Summary L C L S C O N C E P T U
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6 Injector TECHNICAL SYNOPSIS The i
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εn,x (µm) 4 3 2 1 4-2001 8560A95
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Page 139 and 140: Quantum Yield (electrons/photon) 10
Page 141 and 142: Bz (T) 0.3 0.2 0.1 1-2002 8560A92 L
Page 153 and 154: Master Clock 9.917 MHz x8 x6 x6 Df
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Page 165 and 166: B z (kG) 3 2 1 4-2001 8560A91 L C L
Page 169 and 170: γε x,y (µm) 3 2 1 0 3-2001 8560A
Page 171 and 172: γεx,y (µm) yn 10 0 -10 -10 0 10
Page 173 and 174: σ γ /γ 0 (percent) ∆N/N 0.02 0
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Page 177 and 178: Table 6.5 PARMELA Output Parameters
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Page 181 and 182: ∆E/E 0 (%) ∆N/N 0 -1 -2 0.02 0
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Page 204 and 205: 〈∆E/E 0 〉 /% I pk /I pk0 0.1
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economic reasons. L C L S C O N C E
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Phase [deg. S-band] L C L S C O N C
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New Solid-State Sub-Booster and Ele
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7.8.2 Bunch Length Diagnostics L C
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Magnet String Location Existing, Ne
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8.1 Overview 8.1.1 Introduction L C
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Mu in the pole, for mu
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Gasload (Torr-l/sec-cm) (x10 -12 )
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8.10.4 Conclusion L C L S C O N C E
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x θ j > 0 L C L S C O N C E P T U
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Quad ∆X/µm Quad ∆Y/µm −500
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∆X/µm ∆Y/µm L C L S C O N C E
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8.13.2 Undulator Cell Structure L C
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9.2 Layout and Optics 9.2.1 Experim
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Fast Valve L C L S C O N C E P T U
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0.01 10 -4 10 -6 10 -8 10 -10 10 -1
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Table 9.5 Mirror requirements L C L
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Refractive Focusing System L C L S
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Pulse Split/Delay L C L S C O N C E
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Figure 9.20 LCLS Ion Chamber L C L
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9.4.3.2 Pulse Length L C L S C O N
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9.4.3.6 Divergence L C L S C O N C
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10 Conventional Facilities TECHNICA
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1-2002 8560A198 Linac Center Line L
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Figure 10.6 Near hall floor plan 10
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11 Controls TECHNICAL SYNOPSIS The
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11.5.3 Motion Controls L C L S C O
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12.1 Procedural Overview L C L S C
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13 Environment, Safety and Health a
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Table 13-1 Hazard Identification an
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13.1 Ionizing Radiation The design
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Table 13-2 Minimum Training Require
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13.10 SLAC References L C L S C O N
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L C L S D E S I G N S T U D Y R E P
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15 TECHNICAL SYNOPSIS Work Breakdow
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A A.1 FEL-Physics A.1.1 Performance
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A.2 Photo-Injector A.2.1 Gun-Laser
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A.2.3.2 Electron Beam L C L S C O N
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A.2.4.7 Vacuum L C L S C O N C E P
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A.3.8 DL-2 A.3.8.1 Subsystem L C L
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A.4 Undulator A.4.1 Undulator A.4.1
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B Control Points B.1 Injector Contr
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C Glossary ACO Anneaux Collisions O
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