STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA

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TABLE <strong>OF</strong> CONTENTS Page Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix CHAPTER 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1 Energy Recovering Linear Accelerators . . . . . . . . . . . . . . . 3 1.2 Superconducting Radio Frequency Technology . . . . . . . . . . . 5 1.2.1 Figures of Merit . . . . . . . . . . . . . . . . . . . . . . . . 7 1.2.2 ERLs Utilizing SRF Technology . . . . . . . . . . . . . . . 9 1.3 Historical Development of ERLs . . . . . . . . . . . . . . . . . . . 10 1.3.1 Jefferson Laboratory and ERLs . . . . . . . . . . . . . . . 12 1.4 Fundamental ERL Challenges . . . . . . . . . . . . . . . . . . . . 15 1.4.1 Injector . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.4.2 Machine Optics . . . . . . . . . . . . . . . . . . . . . . . . 16 1.4.3 Superconducting RF . . . . . . . . . . . . . . . . . . . . . 16 1.5 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 iv
2 CEBAF with Energy Recovery . . . . . . . . . . . . . . . . . . 20 2.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.1.1 CEBAF Overview . . . . . . . . . . . . . . . . . . . . . . . 21 2.2 Issues and Challenges . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.2.1 Phase Delay Chicane and Beam Dump . . . . . . . . . . . 25 2.2.2 Machine Optics . . . . . . . . . . . . . . . . . . . . . . . . 27 2.2.3 SRF Induced Effects . . . . . . . . . . . . . . . . . . . . . 28 2.2.4 Balancing Linac Energy . . . . . . . . . . . . . . . . . . . 32 2.3 Transporting Beam to the Energy Recovery Dump . . . . . . . . . 33 2.3.1 Setting the Path Length . . . . . . . . . . . . . . . . . . . 33 2.4 Transverse Emittance . . . . . . . . . . . . . . . . . . . . . . . . . 36 2.4.1 Emittance Measurement Using a Quadrupole Scan . . . . . 37 2.4.2 Measuring Beam Sizes . . . . . . . . . . . . . . . . . . . . 40 2.4.3 Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.4.4 Emittance Measurement Using Multiple Monitors . . . . . 48 2.4.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.5 Measuring Beam Profiles of the Energy Recovered Beam . . . . . 52 2.6 Measuring Energy Spread . . . . . . . . . . . . . . . . . . . . . . 54 2.7 Response of the RF System . . . . . . . . . . . . . . . . . . . . . 57 2.8 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 3 The Jefferson Laboratory 10 kW FEL Upgrade Driver . . . . 62 3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 3.2 Injector and Injection Line . . . . . . . . . . . . . . . . . . . . . . 65 3.3 Linear Accelerator . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.4 Recirculator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 3.4.1 Recirculation Endloops . . . . . . . . . . . . . . . . . . . . 68 v
Page 1 and 2: STUDIES OF ENERGY RECOVERY LINACS A
Page 3: DEDICATION To my wife Danielle and
Page 7 and 8: 5.2 HOM Power . . . . . . . . . . .
Page 9 and 10: ACKNOWLEDGMENTS First and foremost
Page 11 and 12: 6.1 Summary of the measured effects
Page 13 and 14: 2.10 Illustration of quadrupole sca
Page 15 and 16: 5.1 Successive frames in time (prog
Page 17 and 18: 6.8 A plot of 1/Qeff versus average
Page 19 and 20: ABSTRACT An energy recovering linac
Page 21 and 22: CHAPTER 1 Introduction An increasin
Page 23 and 24: FIG. 1.1: Schematic of a generic li
Page 25 and 26: FIG. 1.2: A CEBAF 5-cell cavity wit
Page 27 and 28: The solution to Eq. (1.3) is U(t) =
Page 29 and 30: y reducing the impedance of HOMs, a
Page 31 and 32: Despite its success, this method of
Page 33 and 34: design parameters, most notably ach
Page 35 and 36: 1.4.2 Machine Optics The second cat
Page 37 and 38: analytic model elucidates many impo
Page 39 and 40: CHAPTER 2 CEBAF with Energy Recover
Page 41 and 42: FIG. 2.1: Energy versus average cur
Page 43 and 44: FIG. 2.3: Additional hardware insta
Page 45 and 46: FIG. 2.4: A picture of the energy r
Page 47 and 48: dipoles and beam diagnostics such a
Page 49 and 50: FIG. 2.7: Horizontal (red) and vert
Page 51 and 52: FIG. 2.8: Illustration of the cryom
Page 53 and 54: linac and θNL is the RF phase. The
Page 55 and 56:
2.4 Transverse Emittance One of the
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where σ2 is the rms beam size meas
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eams. The effects of varying the qu
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FIG. 2.12: A typical wire scan near
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quadratic fit and a multiple regres
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ting the data is difficult. Without
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primary source of error is measurin
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identified, although the phase dela
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TABLE 2.3: Comparison of Twiss para
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the results of the fits. The vertic
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FIG. 2.18: Schematic illustrating t
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FIG. 2.19: The GASK signal measured
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FIG. 2.20: The measured normalized
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CHAPTER 3 The Jefferson Laboratory
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FIG. 3.1: Schematic of the 10 kW FE
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FIG. 3.2: Layout of the DC photocat
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accelerating gradient at the front
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eason for making the endloops achro
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FIG. 3.7: Illustration of path leng
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3.5 Longitudinal Dynamics This sect
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FIG. 3.9: The effect of a thin focu
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Under the constraint that each orde
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form of beam breakup not only occur
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4.1 The Pillbox Cavity Although the
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FIG. 4.2: Electric field (red) and
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where the full 4×4 transfer matrix
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The threshold is inversely proporti
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4.3 BBU Simulation Codes: Particle
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6. The second pass beam bunch then
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which excites it. The BBU instabili
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Equation (4.41) is a dispersion rel
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FIG. 4.4: Output from MATBBU showin
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FIG. 4.5: Setup for measuring cavit
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Consequently, depending on the exte
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The projection of the beam displace
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TABLE 4.1: Experimental measurement
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FIG. 4.10: A plot showing the effec
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these cryomodules. Modes from these
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CHAPTER 5 Experimental Measurements
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threshold current - preferably with
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occurred at approximately 2 mA of a
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FIG. 5.5: FFT of a pure 2106.007 MH
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FIG. 5.6: Illustration to show the
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5.4 Measuring the Threshold Current
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for the HOM-beam system and is deri
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FIG. 5.10: Schematic of the experim
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FIG. 5.12: A plot of 1/Qeff versus
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measured HOMs in zone 3, a BTF meas
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FIG. 5.16: HOM voltage measured fro
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FIG. 5.18: A plot of the three valu
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the beam’s response in regions wh
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CHAPTER 6 BBU Suppression: Beam Opt
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FIG. 6.1: Schematic of a FODO cell
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plane [85]. Equations (6.7) and (6.
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6.2.3 Discussion The method of poin
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FIG. 6.3: Beam envelopes (horizonta
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FIG. 6.6: Beam position monitor rea
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FIG. 6.8: A plot of 1/Qeff versus a
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⎛ ⎞ ⎜ ⎝ 0 0 0 0 0 −1/K 0
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FIG. 6.11: A plot of 1/Qeff versus
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FIG. 6.12: Threshold current for no
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FIG. 6.14: Threshold current utiliz
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TABLE 6.1: Summary of the measured
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CHAPTER 7 BBU Suppression: Feedback
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FIG. 7.1: A schematic of the feedba
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FIG. 7.4: A coaxial 3-stub tuner us
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All of these considerations are con
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FIG. 7.6: Generic layout for a feed
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in Section 4.2.1, however, in the p
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FIG. 7.7: The threshold current as
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FIG. 7.8: Threshold current versus
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FIG. 7.10: The threshold current as
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CHAPTER 8 Conclusions The work pres
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le were experimentally measured. Du
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APPENDIX A The Pillbox Cavity Start
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FIG. A.1: A pillbox cavity exhibiti
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Ez(ρ, φ) = ψ(ρ, φ) = E0Jm(γρ
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FIG. B.1: Relationship of the S-par
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FIG. C.1: Impedance and frequency o
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FIG. C.5: Impedance and frequency o
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BIBLIOGRAPHY [1] M. Tigner, Nuovo C
Page 217 and 218:
[22] L. Merminga, in Proceedings of
Page 219 and 220:
[50] C. Hernandez-Garcia et al., in
Page 221 and 222:
[79] L. Merminga et al., in Proceed
Page 223 and 224:
VITA Christopher D. Tennant Christo
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