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

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well the beam couples to the antenna and how well the properties of the current pulses generated in the antenna can be measured. In this thesis, the design and characterization of a pickup antenna and pulse measurement system was completed in order to measure the position of an electron beam over a range of 10 cm and with a resolution below 2 μm. Expanding the range, even to the 40 cm required by the XFEL chicanes, should also be possible with this design. Typical beam position measurements achieve few-micron resolution over a fewmillimeter range. The monitor system developed within this thesis work represents a new and unique tool in the spectrum of accelerator diagnostics. Several types of pickups were considered for this task: a pin that detects the ringing in a cavity, an array of closely spaced striplines oriented in the direction of the beam, and a rod in a coaxially shaped channel oriented perpendicularly to the direction of the beam. In the end, the perpendicularly oriented pickup was constructed and utilized with two different types of pulse measurement systems, one of which made use of highfrequency electronic techniques and the other which made use of an optical technique involving Mach-Zehnder electro-optical modulators and the pulses from a master laser oscillator. Both techniques delivered the required resolution, but each had unique advantages and disadvantages. Particular emphasis is placed on the cost and robustness of the high-frequency electronic system compared to the lower potential for systematic error of the optical system. Understanding the influence of the shape of the beam on chicane beam position measurements is also critical. For this reason, simulations of the beam transport from the start of the accelerator up to the middle of the chicane were undertaken in order to predict the likely beam properties at the Free-electron LASer in Hamburg, FLASH. The impacts of beam shape, charge, position jitter, and accelerating RF properties were also investigated. Measurements were undertaken to verify the predictions of these simulations and benchmark the measurements against those of an existing synchrotron light detection scheme and a beam arrival-time monitor scheme. 4
2 Free-electron Lasers The facility at which the experiments were performed is the Free-electron LASer in Hamburg (FLASH). FLASH consists of an RF photo-injector electron source, superconducting RF accelerator sections, two magnetic bunch compressors, and an undulator section (Figure 2.1). ACC 1 ACC 23 ACC 456 Undulators GUN Diag. BC2 BC3 Figure 2.1 Free-electron LASer in Hamburg (FLASH) including RF gun (GUN), superconducting RF accelerator sections (ACC1-6), two bunch compressors (BC2-3) and an undulator section. The electron beam is produced in the RF photo-injector, accelerated, compressed, accelerated and compressed again, and finally sent through the undulator magnets, producing FEL light pulses with wavelengths between 6 and 40 nm for experimenters [2, 3]. Experimenters use the pulses of light to, among many other sorts of experiments, take pictures of molecules with crystallographic and pump-probe methods. The pulses range in duration from 10 to 50 femtoseconds with the possibility of making them as short as a few hundred attoseconds [4]. If experimenters cannot synchronize their measurement equipment to the beam within these time-scales, they cannot directly make 5
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: R 16 ( eBl / 2) d ⎛ ⎞ 1 eff 2 p
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 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
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BPM BAM More power at lower frequen
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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
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None of the designs suffered from a
Page 87 and 88:
pickup functions appropriately over
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35 Measured BPM Vertical amplitude
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2.5 Beam position 2 position (cm) 1
Page 93 and 94:
L( x0 , t) U 0 ( t) = λ( x0 , t) (
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1 x beam = ) xdtdx Q ∫∫λ ( x,
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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
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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
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
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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
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using the RF limiter. This might be
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compared. The length of the cable c
Page 147 and 148:
eplaced with fiber. The advantage o
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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
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out. This was done in two ways: by
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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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Measuring the Electron Beam Energy in a Magnetic Bunch ... - DESY

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