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

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measurement is limited by the injector phase jitter. This means that 0.07 is a rather pessimistic value for the phase jitter of the first accelerator section, since it represents more the jitter between the phase of the gun laser and gun RF. The true value of the first accelerator section jitter could be anywhere between 0.01 and 0.07, but based on principles of the regulation algorithm, the amplitude jitter should always be ~1.8 times the phase jitter [19], so for future calculations, we will assume a phase jitter of 1e-4 or 0.02 degrees. These numbers are also only applicable for short bunch trains and 1 nC bunch charge. When long bunch trains with 3 nC were used in the 9 mA experiment for ILC research, due to the large beam loading effect, the energy jitter of the bunches at the end of the bunch train was ten times worse than the energy jitter of the bunches at the beginning of the bunch train [24]. While the combination of a new down-conversion front-end [22], reference injection [21] and system identification [11] could conceivably stabilize the cavity amplitude jitter and drift to within 1e-5 for short bunch trains in a well tuned machine, it is unclear what the system performance would be under more typical circumstances. Using the present machine as an example, the best results are different from the typical results for short bunch trains by about a factor of 2. For long bunch trains the difference can be a factor of 10-30 A beam-based feedback system is being developed to complement this cavitybased system because beam-based measurements can often provide a more accurate measure of how much energy the beam gained in the cavity than a measurement of how much energy the cavity lost when the beam traversed it. The reason for this is that the beam-based measurement can often be accomplished in one location, with one pickup and one set of electronics, while the cavity measurement requires a sum of signals from many different pickups in an RF vector sum. The beam-based measurements can also be drift-free relative to an optical reference which is used to synchronize various laser systems through optical cross-correlation. It is not possible to use an RF reference to synchronize the beam to lasers with femtosecond precision. The beam position monitor developed in this thesis is ideally suited for use in a beam-based feedback system because it provides beam energy measurements with
creates a single point-of-failure system that is not robust enough for long-term operation, especially since the high resolution monitors have such a limited dynamic measurement range. Ideally, multiple systems should be used simultaneously, so that if one measurement is out-of-range, another system can step in. An architecture that takes beam-based and reference tracking information into account in the cavity controller is depicted below in Fig. 3.1.3. FPGA Setpoint From ADC: Cav1 Cav2 … Vector sum Ref. Injection Bunch Length Meas. Arrival Time Meas. Feedforward Matrix old Feedforward Matrix new MO To DAC BLM BAM Figure 3.1.3 A desired FPGA algorithm structure incorporating reference injection and beam-based information. gain So far, there has only been a description of what the module controller can do with respect to amplitude and phase stability, but we have not given a description of what it must do in terms of beam arrival time stability. This is determined by the relation of the accelerator RF parameters to the bunch compressor parameters and this is described in the following section. 3.2 Arrival-time Changes after a Bunch Compressor The equation 3.2.1 gives a good representation of how an incoming arrival-time jitter, Σ t0, is altered by transport through an accelerating module followed by a bunch compressor (Fig. 3.2.1). Σ 2 2 1 2 ⎛ R56 σ ⎞ A ⎛ C −1 = Σ 2 0 + ⎜ ⎟ t t + ⎜ C c0 A ⎝ C ⎝ ⎠ 2 ⎞ ⎟ ⎠ ⎛ ⎜ ⎝ c0k σ ϕ rf ⎞ ⎟ ⎠ 2 (3.2.1) 25
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: The problem of cavity field measure
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 and 50: 4 Beam Shape in the Bunch Compresso
Page 51 and 52: There has been some debate over the
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
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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
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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
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strengths of the peaks seen in Fig.
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algorithm required to select the ph
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Downmixers for EBPM BPM-L BPM-R BPM
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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
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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
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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
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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
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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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