Проектные параметры усовершенствованного резонатора для ВЧ-фотоинжекторов

Приведены расчетные характеристики резонатора для ВЧ-фотоинжекторов, работающих на частоте 1300 МГц в сочетании сильных электромагнитных полей и длинного ВЧ-импульса. Конструкция усовершенствованного резонатора использует апробированные решения, но содержит существенные изменения. В ячейки резонатора введены ВЧ-датчики. Проведена оптимизация характеристик резонатора по отдельным характеристикам. Но основное внимание уделено учету взаимного влияния процессов и поиску оптимальных решений по комплексу параметров резонатора в целом.Наведено розрахункові характеристики резонатора для ВЧ-фотоінжекторів, що працюють на частоті 1300 МГц у сполученні сильних електромагнітних полів і довгого ВЧ-імпульса. Конструкція вдосконаленого резонатора використовує апробовані рішення, але містить істотні зміни. В осередки резонатора уведені ВЧ-датчики. Проведено оптимізацію характеристик резонатора по окремих характеристиках. Але основна увага приділена обліку взаємного впливу процесів і пошуку оптимальних рішень із комплексу параметрів резонатора в цілому.During development and operation of DESY L-band RF gun cavities, desires for further improvements were formulated. The next step of development is based on the proven advantages of existing cavities, but includes very significant changes. The L-band 1.6 cell RF gun cavity is intended for operation in pulse mode with unique combination of high RF fields and long RF pulse. Each cavity cell is equipped with RF probe. The cavity design is improved to gain an advantage over existing cavities in certain parameters. But main attention paid for coupled optimization to improve the cavity parameters in total. The design ideas and expected results are described

Chirp mitigation of plasma-accelerated beams using a modulated plasma density

Plasma-based accelerators offer the possibility to drive future compact light sources and high-energy physics applications. Achieving good beam quality, especially a small beam energy spread, is still one of the major challenges. For stable transport, the beam is located in the focusing region of the wakefield which covers only the slope of the accelerating field. This, however, imprints a longitudinal energy correlation (chirp) along the bunch. Here, we propose an alternating focusing scheme in the plasma to mitigate the development of this chirp and thus maintain a small energy spread

High Precision Temperature Control of Normal-conducting RF GUN for a High Duty Cycle Free-Electron Laser

High precision temperature control of the RF GUN is necessary to optimally accelerate thousands of electrons within the injection part of the European X-ray free-electron laser XFEL and the Free Electron Laser FLASH. A difference of the RF GUN temperature from the reference value of only 0.01 K leads to detuning of the cavity and thus limits the performance of the whole facility. Especially in steady-state operation there are some undesired temperature oscillations when using classical standard control techniques like PID control. That is why a model based approach is applied here to design the RF GUN temperature controller for the free-electron lasers. A thermal model of the RF GUN and the cooling facility is derived based on heat balances, considering the heat dissipation of the Low-Level RF power. This results in a nonlinear model of the plant. The parameters are identified by fitting the model to data of temperature, pressure and control signal measurements of the FLASH facility, a pilot test facility for the European XFEL. The derived model is used for controller design. A linear model predictive controller was implemented in MATLAB/Simulink and tuned to stabilize the temperature of the RF GUN in steady-state operation. A test of the controller in simulation shows promising results

Report on Gun Conditioning Activities at PITZ in 2013

Recently three RF guns were prepared at the Photo Injector Test Facility at DESY, location Zeuthen PITZ for their subsequent operation at FLASH and the European XFEL. The gun 3.1 is a previous cavity design and is currently installed and operated at FLASH, the other two guns 4.3 and 4.4 were of the current cavity design and are dedicated to serve for the start up of the European XFEL photo injector. All three cavities had been dry ice cleaned prior their conditioning and hence showed low dark current levels. The lowest dark current level as low as 60 amp; 956;A at 65MV m field amplitude has been observed for the gun 3.1. This paper reports in details about the conditioning process of the most recent gun 4.4. It informs about experience gained at PITZ during establishing of the RF conditioning procedure and provides a comparison with the other gun cavities in terms of the dark currents. It also summarizes the major setup upgrades, which have affected the conditioning processes of the cavitie