Measuring the Electron Beam Energy in a Magnetic Bunch ... - DESY

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The beam shape in the second bunch compressor is also impacted by the addition of the third-harmonic module. The slice emittance of the tail is small, but due to overcompression, transverse tails are generated at the spike of the bunch [32]. This, in addition to the long, longitudinal tail, causes the projected emittance to be significantly larger than the slice emittance. With the third-harmonic module, the projected emittance will be reduced, hopefully enabling a larger portion of the beam to lase With a non-linear energy chirp, the portion of the beam that lases is but a fraction of the sharp, leading spike. While the duration of the spike has been measured with a transverse deflecting cavity (a sort of streak camera) and is
There has been some debate over the cause of this shape, but not much interest in removing it. Because only a slice of the bunch lases in the present machine, without the third-harmonic module, the shape of the rest of the bunch has been irrelevant. This situation, while true now, will not be true when the third-harmonic module is commissioned and the projected emittance becomes almost as important as the slice emittance. Some wondered if the c-shape was the direct result of often simulated but never measured coupler kicks in the first accelerator section. Others believed it was from oft-simulated but never measured wakefields, due to the mirror in the injector. The contribution of linear dispersion induced downstream of the RF gun but before the first accelerator section would be too small to create this effect all by itself, as would the effect of a tilted first accelerator section. To put these effects in a frame of reference, the strength of each effect will be quantified below. Coupler kicks are caused by the forces that the beam experiences when it passes the RF couplers, ports from which the accelerating cavities are filled up with RF waves or from which higher-order modes are removed. The kick arises because the coupler introduces a field asymmetry into the structure. There are two HOM couplers per module, one power coupler, and eight cavities per module. The HOM couplers are oriented in such a way that the kicks of pairs of upstream and downstream couplers should partially cancel one another out, making the power coupler the coupler of concern (Fig. 4.2.2). Without hole With hole cavity field axis Axis (exaggerated) of cavity Figure 4.2.2 Coupler kick concept. A hole in a cavity changes the axis of the cavity field. There are two sets of couplers per accelerating module. They are oriented in such a way that the kicks of pairs of HOM couplers should partially cancel one another. The power coupler produces the strongest kick and it scales with the gradient in the cavity. Estimates for the strength of the coupler kicks in a steady state situation have been made using software that calculates the fields in cavities of arbitrary shape [35]. The coupler 39
Page 1 and 2: Measuring the Electron Beam Energy
Page 3 and 4: Abstract Within this thesis, work w
Page 5 and 6: 9 Synchrotron Light Monitors 9.1 Pr
Page 7 and 8: List of Figures 1.0.1 Magnetic bunc
Page 9 and 10: 5.5.10 Dependence of the slope of p
Page 11 and 12: 8.3.6 RF phase measurement drift wi
Page 13 and 14: where α is the bending angle intro
Page 15 and 16: R 16 ( eBl / 2) d ⎛ ⎞ 1 eff 2 p
Page 17 and 18: 2 Free-electron Lasers The facility
Page 19 and 20: arrival-time and energy prior to a
Page 21 and 22: electrons travel faster than low-en
Page 23 and 24: efore bunch compressor energy chirp
Page 25 and 26: corresponds to terms that are linea
Page 27 and 28: spread will be larger and the trans
Page 29 and 30: (a) (b) Figure 2.3.4 Single chicane
Page 31 and 32: 3 Beam Arrival-time Stabilization A
Page 33 and 34: changes in the amplitude of the kly
Page 35 and 36: The problem of cavity field measure
Page 37 and 38: creates a single point-of-failure s
Page 39 and 40: accelerator section and it was firs
Page 41 and 42: ACC1 ~Gun 3rd ACC2 ACC3ACC4 ACC7 Ac
Page 43 and 44: • The lack of a normal-conducting
Page 45 and 46: ( ) E − E ⎛ E − E ⎜ ⎝ 0 0
Page 47 and 48: 3.7 Second Accelerator Section Jitt
Page 49: 4 Beam Shape in the Bunch Compresso
Page 53 and 54: V T = V cos( k ⋅ z + = V T 0 rf
Page 55 and 56: Upstream of the first accelerator s
Page 57 and 58: Positive bump 5 8 deg off-crest in
Page 59 and 60: E (MeV) 4.75 4.74 4.73 4.72 4.71 4.
Page 61 and 62: leads one to suspect that as in the
Page 63 and 64: vacuum feedthroughs, the buttons we
Page 65 and 66: J image − ⎡ ⎛ ⎞ ⎤ = ⎢ +
Page 67 and 68: sensitivity of 8 and 20 mm diameter
Page 69 and 70: 1 v phase = . (5.1.21) LC Finally,
Page 71 and 72: some locations. Nevertheless, it is
Page 73 and 74: BPM BAM More power at lower frequen
Page 75 and 76: arrival-time monitor with and witho
Page 77 and 78: 5.2 Cavity BPM Cavity BPMs (Fig. 5.
Page 79 and 80: t=0 Z 0 t=L/c Z 0 2L Figure 5.3.1 L
Page 81 and 82: 0.2 nC beam charge and can handle b
Page 83 and 84: T1-T2=T3 X=T3*c T1 T2 Figure 5.5.2
Page 85 and 86: None of the designs suffered from a
Page 87 and 88: pickup functions appropriately over
Page 89 and 90: 35 Measured BPM Vertical amplitude
Page 91 and 92: 2.5 Beam position 2 position (cm) 1
Page 93 and 94: L( x0 , t) U 0 ( t) = λ( x0 , t) (
Page 95 and 96: 1 x beam = ) xdtdx Q ∫∫λ ( x,
Page 97 and 98: 0 BPM beam width dependence arrival
Page 99 and 100: 100 Vertical y position sensitiviy
Page 101 and 102:
Such an x-y tilt was measured with
Page 103 and 104:
10 5 head x [mm] 0 tail -5 -5 -4 -3
Page 105 and 106:
3.5 x 10-3 Horizontal Charge Distri
Page 107 and 108:
The problem that could arise due to
Page 109 and 110:
around their zero-crossings in orde
Page 111 and 112:
v i ( i i i t) = A sin(2π f t + θ
Page 113 and 114:
strengths of the peaks seen in Fig.
Page 115 and 116:
algorithm required to select the ph
Page 117 and 118:
Downmixers for EBPM BPM-L BPM-R BPM
Page 119 and 120:
While this option was not built and
Page 121 and 122:
A Peltier element acts as a heat pu
Page 123 and 124:
For the measurement shown in Fig. 7
Page 125 and 126:
2 1.5 1 BC2 x position (mm) 0.5 0 -
Page 127 and 128:
0 BC2 arrival time (ps) 1.5 1 0.5 0
Page 129 and 130:
eality check BC2 PMT EBPM and PMT p
Page 131 and 132:
EBPM and PM positions (mm) 6 5 4 3
Page 133 and 134:
If a limiter or nothing at all is u
Page 135 and 136:
Depending on the arrival-time of th
Page 137 and 138:
20mW to BAM FARADAY 8m 80/20 60mW W
Page 139 and 140:
can be placed anywhere prior to the
Page 141 and 142:
Insulation Peltier element on metal
Page 143 and 144:
using the RF limiter. This might be
Page 145 and 146:
compared. The length of the cable c
Page 147 and 148:
eplaced with fiber. The advantage o
Page 149 and 150:
Photodetector Photodetector Two las
Page 151 and 152:
RF-Lock Box for FLASH MLO Synchroni
Page 153 and 154:
In Fig. 8.3.4, the spectral noise d
Page 155 and 156:
Mixer Output (fs) 40 20 0 -20 MLO R
Page 157 and 158:
For a frame of reference concerning
Page 159 and 160:
(Fig. 9.1.2). This method proved to
Page 161 and 162:
N λ ∞ ∫ ω / ω Δω 9 3 ( ω)
Page 163 and 164:
Finally, we can use this, together
Page 165 and 166:
The highest energy resolution (ΔE/
Page 167 and 168:
Good agreement between the RF chica
Page 169 and 170:
10.3 Out-of-loop Vector Sum The out
Page 171 and 172:
out. This was done in two ways: by
Page 173 and 174:
1.8 1.6 stripline button 1.4 Upstre
Page 175 and 176:
10 Conclusion and Outlook Six disti
Page 177 and 178:
Appendix A The derivation of Eqs. 3
Page 179 and 180:
Solving Eq. 8 for E 1 ’ provides
Page 181 and 182:
Higher order terms and the 3 rd -ha
Page 183 and 184:
∂t ∂V 2 2 ⋅ ΔV 2 1 = T1 '( E
Page 185 and 186:
References [1] P. Castro. “Beam t
Page 187 and 188:
[28] H. Schlarb et al., “Beam bas
Page 189 and 190:
[55] C. Gerth, personal communicati
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Measuring the Electron Beam Energy in a Magnetic Bunch ... - DESY

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