STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA
STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA
TABLE 4.2: The three lowest threshold currents in the FEL Upgrade as predicted from MATBBU simulations. Threshold Current (mA) Frequency (MHz) Location 2.1 2106.007 zone 3 cavity 7 10.4 2115.201 zone 3 cavity 6 28.1 1937.698 zone 3 cavity 7 sponding HOM frequencies which cause them. Interestingly, with the machine optics used in the simulation, only a single HOM leads to beam breakup below the nominal 10 mA operating current of the FEL Upgrade Driver. With the predicted threshold current much less than the 10 mA operating cur- rent of the Driver, an opportunity exists to benchmark the simulation codes with experimental data. The importance of this task cannot be overemphasized. With the increasing number of proposed ERL-based accelerator applications (see Fig. 2.1), it is crucial that BBU simulation codes can be used with absolute confidence with respect to their results. Because BBU represents such a hard limit on machine performance, effectively setting an upper limit on the average current, a clear and careful understanding of the instability’s impact on the machine is required. Bench- marking the codes also serves a more fundamental purpose in that it validates the analytic model of BBU. The topic of benchmarking the codes is the subject of Chapter 5. 111
CHAPTER 5 Experimental Measurements of Multipass BBU In May of 2004 BBU was observed in the FEL Upgrade Driver and represents the first time the instability has been observed in an energy recovering linac. Prior to 2004, BBU had been observed in the microtron at Illinois and the recirculating linac at Stanford, both in 1977. Consequently, the FEL Upgrade Driver has become an ideal testbed for gaining a quantitative understanding of beam breakup, which in turn, has allowed BBU simulation codes to be benchmarked with experimental data, and is the subject of this chapter. The Driver has also proved to be valuable for testing the efficacy of a number of BBU suppression techniques which are discussed in Chapter 6 and Chapter 7. 112
- 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
- Page 87 and 88: accelerating gradient at the front
- Page 89 and 90: eason for making the endloops achro
- Page 91 and 92: FIG. 3.7: Illustration of path leng
- Page 93 and 94: 3.5 Longitudinal Dynamics This sect
- Page 95 and 96: FIG. 3.9: The effect of a thin focu
- Page 97 and 98: Under the constraint that each orde
- Page 99 and 100: form of beam breakup not only occur
- Page 101 and 102: 4.1 The Pillbox Cavity Although the
- Page 103 and 104: FIG. 4.2: Electric field (red) and
- Page 105 and 106: where the full 4×4 transfer matrix
- Page 107 and 108: The threshold is inversely proporti
- Page 109 and 110: 4.3 BBU Simulation Codes: Particle
- Page 111 and 112: 6. The second pass beam bunch then
- Page 113 and 114: which excites it. The BBU instabili
- Page 115 and 116: Equation (4.41) is a dispersion rel
- Page 117 and 118: FIG. 4.4: Output from MATBBU showin
- Page 119 and 120: FIG. 4.5: Setup for measuring cavit
- Page 121 and 122: Consequently, depending on the exte
- Page 123 and 124: The projection of the beam displace
- Page 125 and 126: TABLE 4.1: Experimental measurement
- Page 127 and 128: FIG. 4.10: A plot showing the effec
- Page 129: these cryomodules. Modes from these
- Page 133 and 134: threshold current - preferably with
- Page 135 and 136: occurred at approximately 2 mA of a
- Page 137 and 138: FIG. 5.5: FFT of a pure 2106.007 MH
- Page 139 and 140: FIG. 5.6: Illustration to show the
- Page 141 and 142: 5.4 Measuring the Threshold Current
- Page 143 and 144: for the HOM-beam system and is deri
- Page 145 and 146: FIG. 5.10: Schematic of the experim
- Page 147 and 148: FIG. 5.12: A plot of 1/Qeff versus
- Page 149 and 150: measured HOMs in zone 3, a BTF meas
- Page 151 and 152: FIG. 5.16: HOM voltage measured fro
- Page 153 and 154: FIG. 5.18: A plot of the three valu
- Page 155 and 156: the beam’s response in regions wh
- Page 157 and 158: CHAPTER 6 BBU Suppression: Beam Opt
- Page 159 and 160: FIG. 6.1: Schematic of a FODO cell
- Page 161 and 162: plane [85]. Equations (6.7) and (6.
- Page 163 and 164: 6.2.3 Discussion The method of poin
- Page 165 and 166: FIG. 6.3: Beam envelopes (horizonta
- Page 167 and 168: FIG. 6.6: Beam position monitor rea
- Page 169 and 170: FIG. 6.8: A plot of 1/Qeff versus a
- Page 171 and 172: ⎛ ⎞ ⎜ ⎝ 0 0 0 0 0 −1/K 0
- Page 173 and 174: FIG. 6.11: A plot of 1/Qeff versus
- Page 175 and 176: FIG. 6.12: Threshold current for no
- Page 177 and 178: FIG. 6.14: Threshold current utiliz
- Page 179 and 180: TABLE 6.1: Summary of the measured
CHAPTER 5<br />
Experimental Measurements of<br />
Multipass BBU<br />
In May of 2004 BBU was observed in the FEL Upgrade Driver and represents<br />
the first time the instability has been observed in an energy recovering linac. Prior<br />
to 2004, BBU had been observed in the microtron at Illinois and the recirculating<br />
linac at Stanford, both in 1977.<br />
Consequently, the FEL Upgrade Driver has become an ideal testbed for gaining<br />
a quantitative understanding of beam breakup, which in turn, has allowed BBU<br />
simulation codes to be benchmarked with experimental data, and is the subject<br />
of this chapter. The Driver has also proved to be valuable for testing the efficacy<br />
of a number of BBU suppression techniques which are discussed in Chapter 6 and<br />
Chapter 7.<br />
112
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