Measuring the electron beam energy in a magnetic bunch compressor

Within this thesis, work was carried out in and around the first bunch compressor chicane of the FLASH (Free-electron LASer in Hamburg) linear accelerator in which two distinct systems were developed for the measurement of an electron beam's position with sub-5 μm precision over a 10 cm range.One of these two systems utilized RF techniques to measure the difference between the arrival-times of two broadband electrical pulses generated by the passage of the electron beam adjacent to a pickup antenna.The other system measured the arrival-times of the pulses from the pickup with an optical technique dependent on the delivery of laser pulses which are synchronized to the RF reference of the machine.The relative advantages and disadvantages of these two techniques are explored and compared to other available approaches to measure the same beam property, including a time-of-flight measurement with two beam arrival-time monitors and a synchrotron light monitor with two photomultiplier tubes.The electron beam position measurement is required as part of a measurement of the electron beam energy and could be used in an intra-bunch-train beam-based feedback system that would stabilize the amplitude of the accelerating field.By stabilizing the accelerating field amplitude, the arrival-time of the electron beam can be made more stable.By stabilizing the electron beam arrival-time relative to a stable reference, diagnostic, seeding, and beam-manipulation lasers can be synchronized to the beam. ZusammenfassungIm Rahmen dieser Doktorarbeit wurden an dem Freien Elektronen Laser FLASH, in Hamburg, zwei unterschiedliche Techniken zur Vermessung der transversalen Elektronenstrahlposition in magnetischen Schikanen mit einer Auflösung von 5 μm über einen 10 cm breiten Meßbereich, entwickelt.Eine diese Technik basiert auf der Bestimmung der Ankunftszeiten zweier kurzer elektrischer Signale, welche beim passieren des Elektronenstrahls an einer Hochfrequenzantenne erzeugt werden, mittels Hochfrequenzelektronik. Die zweite Technik verwendet kurze Laserpulse, die zur Hochfrequenz des Beschleunigers synchronisiert sind, um die Ankunftszeiten der elektrischen Antennensignale mit hoher Präzision zu ermittelt.Die Vor-und Nachteile dieser beiden Methoden werden in dieser Arbeit theoretisch und experimentell untersucht und verglichen mit anderen Methoden, wie zum Beispiel, der Detektion der Flugzeitdifferenzen des Elektronenstrahls durch die magnetische Schikane oder der Positionsbestimmung der Elektronenpakete durch optische Synchrotronstrahlung. Die Messung der transversalen Elektronenstrahlposition in einer magnetischen Schikane ist ein direktes Maß für die Elektronenstrahlenergie und kann für ein schnelles Regelungssystem zur Stabilisierung der Beschleunigungsgradienten genutzt werden.Durch die Stabilisierung der Beschleunigergradienten kann eine Stabilisierung der Ankunftszeit des Elektronenstrahls relative zur Synchronisationsreferenz der Anlage erzielt werden.Dies verbessert entscheidend Experimente die auf das seeden oder manipulieren des Elektronenstrahls durch externe Laserstrahlen angewiesen sind.8.3.6 RF phase measurement drift without temperature control, without disturbances (people in room).8.3.7 Out-of-loop measurement drift without temperature control and without disturbances (people in room).9.1.1A synchrotron light monitor system with CCD screen.9.1.2A picture of the beam as imaged with the synchrotron light camera.9.2.1 Two Photomultipliers used to measure the beam position in the chicane.10.1.1 Measurements of energy stability in the chicane taken by the coarse and fine HF front-ends of the chicane BPM plotted with energy setpoint values from the upstream accelerating module.10.2.1 Correlation between the measurements of the beam position in the chicane taken by the chicane BPM (labeled EBPM) and the photomultiplier tube monitor (PMT).10.2.2 Fine HF front-ends position measurement and photomultiplier tube position measurement in good agreement.10.2.3 Fine HF front-ends position measurement and photomultiplier tube position measurement in poor agreement.10.3.1 Fine HF front-ends position measurement and photomultiplier tube position measurement.10.4.1 Optical (EOM) front-end position measurement and photomultiplier tube position measurement along with a time of flight measurement involving 2 BAMs and a line showing how the setpoint of the gradient changed.10.4.2The beam energy was changed by 0.3 % with the accelerator gradient setpoint and the beam energy measured by the chicane BPM changed by a comparable amount.10.4.3 Optical (EOM) front-end chicane BPM measurement and photomultiplier tube BPM measurement along with a time-of-flight measurement involving 2 BAMs and a line showing how the setpoint of the gradient predicted an energy change of 0.1%.10.4.4The beam-arrival time upstream of the chicane measured with both the transversely mounted stripline BPM installed in the chicane and with a button-type pickup BAM installed upstream of the chicane.10.4.5 Optical (EOM) front-end position measurement, 10.4 GHz front-end measurement, photomultiplier tube position measurement, time-of-flight measurement involving 2 BAMs and the setpoint of the gradient are plotted together over several hours.