STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA

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LIST <strong>OF</strong> FIGURES Figure Page 1.1 Schematic of a generic light source based on an energy recovering linac driver. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 A CEBAF 5-cell cavity with a waveguide higher-order mode coupler (left) and fundamental power coupler (right). . . . . . . . . . . . . . . 6 2.1 Energy versus average current for machines which have demonstrated energy recovery (black) and for proposed machines (red). . . . . . . . 22 2.2 Schematic of the CEBAF accelerator. . . . . . . . . . . . . . . . . . . 23 2.3 Additional hardware installed to energy recover the beam in CEBAF. 24 2.4 A picture of the energy recovery phase delay chicane to the left of the nominal straight ahead CEBAF beamline. . . . . . . . . . . . . . . . 26 2.5 The dump and instrumented beamline during installation. . . . . . . 27 2.6 Horizontal (red) and vertical (green) beta functions for the accelerating pass through north linac (top) and the accelerating pass through the south linac (bottom). . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.7 Horizontal (red) and vertical (green) beta functions for the decelerating pass through north linac (top) and the decelerating pass through the south linac (bottom). . . . . . . . . . . . . . . . . . . . . . . . . . 30 2.8 Illustration of the cryomodule RF feed geometry used to minimize the FPC induced dipole kick. . . . . . . . . . . . . . . . . . . . . . . 32 2.9 Images of the beam at various locations in the machine. . . . . . . . . 35 xii
2.10 Illustration of quadrupole scan method to measure the transverse emittance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 2.11 A 3-wire scanner oriented at 45 ◦ with respect to the horizontal plane. 41 2.12 A typical wire scan near the extraction region showing six distinct peaks as a result from a 3-wire scanner passing through two copropagating beams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.13 A schematic of the 2L21 and 2L22 regions of CEBAF and the location of the quadrupoles used to measure the emittance. . . . . . . . . . . . 43 2.14 Measured data for extracting the horizontal (left) and vertical (right) emittance at an energy of 56 MeV. . . . . . . . . . . . . . . . . . . . 45 2.15 Measured data for extracting the horizontal (left) and vertical (right) emittance at an energy of 20 MeV. . . . . . . . . . . . . . . . . . . . 45 2.16 Beam profiles of the 56 MeV energy recovered beam at the dump. . . 53 2.17 Beam profiles of the 20 MeV energy recovered beam at the dump. . . 53 2.18 Schematic illustrating the effect of an RF crest phasing error on the fractional energy spread. . . . . . . . . . . . . . . . . . . . . . . . . . 56 2.19 The GASK signal measured with (blue) and without (red) energy recovery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 2.20 The measured normalized transverse emittance at various locations in CEBAF for the Einj = 56 MeV configuration. . . . . . . . . . . . . 60 2.21 The measured normalized transverse emittance at various locations in CEBAF for the Einj = 20 MeV configuration. . . . . . . . . . . . . 60 3.1 Schematic of the 10 kW FEL Upgrade Driver. . . . . . . . . . . . . . 64 3.2 Layout of the DC photocathode gun and injection line. . . . . . . . . 66 3.3 A single 7-cell cavity with a coaxial higher-order mode coupler (left) and a waveguide fundamental power coupler (right). . . . . . . . . . . 67 3.4 View of the second (as seen by the beam) Bates style endloop in the FEL Upgrade Driver. . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 xiii
Page 1 and 2: STUDIES OF ENERGY RECOVERY LINACS A
Page 3 and 4: DEDICATION To my wife Danielle and
Page 5 and 6: 2 CEBAF with Energy Recovery . . .
Page 7 and 8: 5.2 HOM Power . . . . . . . . . . .
Page 9 and 10: ACKNOWLEDGMENTS First and foremost
Page 11: 6.1 Summary of the measured effects
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
Page 57 and 58: where σ2 is the rms beam size meas
Page 59 and 60: eams. The effects of varying the qu
Page 61 and 62: FIG. 2.12: A typical wire scan near
Page 63 and 64:
quadratic fit and a multiple regres
Page 65 and 66:
ting the data is difficult. Without
Page 67 and 68:
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
Page 77 and 78:
FIG. 2.19: The GASK signal measured
Page 79 and 80:
FIG. 2.20: The measured normalized
Page 81 and 82:
CHAPTER 3 The Jefferson Laboratory
Page 83 and 84:
FIG. 3.1: Schematic of the 10 kW FE
Page 85 and 86:
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
Page 103 and 104:
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
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[22] L. Merminga, in Proceedings of
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[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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