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 With the X-band rf included at a decelerating phase, and with the proper voltage (see below), the compression can be linearized such that a 200-µm rms bunch length is easily achievable with no significant alteration in the temporal distribution. Figure 7.5 shows the simulation, starting from similar conditions as the top row of plots in Figure 7.4, but with some minor S-band phase and voltage adjustments (top row of Figure 7.5), and proceeding through the 20-MV X-band rf (middle row of Figure 7.5), and then through the chicane (bottom row of Figure 7.5). The final temporal distribution is nearly unaltered with the proper X-band rf compensation. The X-band voltage, Vx, required to compensate the non-linear energy-time correlations induced in both the L0 and the L1 linacs, as well as that of the chicane, is given by [8] ⎡ 2 1 λ 2 566 0 1 s T ⎤ E ⎢ − 2 3 ( 1−σ z σ z0) ⎥ − Ei ⎢ 2π R56 ⎥ eVx = ⎣ ⎦ , (7.8) 2 ( λs λx) − 1 where λs and λx are the S-band and X-band, respectively, rf wavelengths (10.50 cm and 2.625 cm), σz0 and σz are the initial and final bunch lengths, and Ei and E0 are the initial and final beam energies at gun and BC1 chicane, respectively. The net deceleration is small due to the large denominator in Eq. (7.8), which stems from the high harmonic number chosen (λs/λx = 4). For parameters R56 ≈ −35.9 mm, T566 ≈ −3R56/2 ≈ +53.9 mm, σz0 ≈ 830 µm, σz ≈ 200 µm, Ei ≈ 7 MeV, and E0 ≈ 250 MeV, the X-band voltage which removes the 2 nd -order energy-time correlation along the bunch after BC1 is Vx ≈ 22 MV. Tracking studies show that this voltage provides a more uniform temporal distribution after BC2 (see Figure 7.6 and Figure 7.7). With the availability at SLAC of high-gradient X-band accelerating structures developed for the NLC project [9], this 4 th harmonic compensation strategy becomes a practical solution for the LCLS. A relatively low rf gradient of 37 MV/m allows a 0.6-meter long section to be used. The mean iris radius is 4.7 mm, which is very large for the typical beam size of 100 µm (see beta functions in Figure 7.14). The transverse wakefields of the X-band structure are strong, but the section is very short. The alignment tolerance of the short X-band structure is therefore ~200 µm, which is not particularly challenging. A similar X-band section is not required at the entrance to BC2, since the quadratic correlation in the bunch after the L2-linac is much less pronounced than that after L1, due to the shortened bunch in L2 with respect to the S-band rf. In addition to linearizing the compression process, the X-band rf also makes the net compression less sensitive to rf gun-timing jitter. Since the net accelerating voltage, as a function of beam arrival time, is more linear when the X-band rf is included, the induced energy-time correlation along the bunch then becomes nearly independent of beam arrival time [8]. This loosens the rf gun-timing jitter sensitivity by nearly a factor of four with respect to that published in the LCLS Design Study Report [16] (see also Figure 7.8). The section will need a dedicated X-band klystron, which is available at SLAC. The existing modulator at 21-2 will be used. 7-10 ♦ A C C E L E R A T O R
7.2.4 Nominal Parameters 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 The nominal design parameters for the LCLS two-stage bunch compression system at a bunch charge of 1 nC are summarized graphically in Figure 7.1 and numerically in Table 7.1 below. A string of five linac sections and two chicane sections are used to compress an 830-µm rms bunch at 150 MeV to 22-µm rms at 14.35 GeV. The final bunch is still under-compressed, so it is actually possible to compress it even further (to
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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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Quantum Yield (electrons/photon) 10
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Bz (T) 0.3 0.2 0.1 1-2002 8560A92 L
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Page 153 and 154: Master Clock 9.917 MHz x8 x6 x6 Df
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Page 169 and 170: γε x,y (µm) 3 2 1 0 3-2001 8560A
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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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Page 220 and 221: β (m) 60 50 40 30 20 10 0 L C L S
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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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