| Paper | Title | Page |
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| MOPGW047 | Analysis and Simulation of the "After-Pulse" RF Breakdown | 196 |
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| During the high power experiment of a single-cell standing-wave accelerating structure, it was observed that many RF breakdowns happen when the field inside cavity is decaying after the input rf pulse is off. The distribution of breakdown timing shows a peak at the moment of RF power switches off. A series of simulation was performed to study the after-pulse breakdown effect in such a standing-wave structure. A method of calculating poynting vector over time is proposed in this article to study the modified poynting vector at critical points in the cavity. Field simulation and thermal simulation were also carried out to analyse possible reasons for the after-pulse breakdown effect. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW047 | |
| About • | paper received ※ 14 May 2019 paper accepted ※ 17 May 2019 issue date ※ 21 June 2019 | |
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| WEPRB047 | High-Power Test of a 12 Cell Accelerating Structure Build in Halves | 2912 |
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| An X-band 12 cell travelling-wave accelerating structure has been developed and high-power tested at Tsinghua University in China. This structure works at 2⁄3 π at the frequency of 11.424 GHz. It is a 12-cell constant-impedance structure build in halves and was silver-brazed as a vacuum tight structure. The high power test was conducted at Tsinghua X-band high power test facility [1] with a 50-MW X-band klystron at a repetition rate to 40 Hz. The final input power was 51.23 MW with a 200 ns pulse width, which means an accelerating gradient of 88.58 MV/m was reached. This paper presents the high power test results including the gradient and breakdown history. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB047 | |
| About • | paper received ※ 10 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019 | |
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| WEPRB080 | Optimization of RF Cavities Using MOGA for ALS-U | 3007 |
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Funding: Director of Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 A multi-objective genetic algorithm-based optimiza-tion process has been applied to optimize the RF design of a 500 MHz main cavity and a 1.5 GHz Higher Harmon-ic Cavity (HHC) for the Advanced Light Source upgrade (ALS-U) in Lawrence Berkeley National Laboratory (LBNL). For the main cavity, a significant improvement, compared with the existing ALS cavity, has been achieved in cavity shunt impedance and power loss den-sity simultaneously. The field strengths and distribution of the optimized structure are analysed for further re-search. For the HHC, a cavity with low R/Q has been pre-liminary designed to mitigate the beam instability. This study also serves as an example of how a genetic algo-rithm can be used for optimizing RF cavities. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB080 | |
| About • | paper received ※ 16 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019 | |
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| WEPRB081 | Design Study on Higher Harmonic Cavity for ALS-U | 3011 |
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Funding: Director of Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 The ALS upgrade (ALS-U) to a diffraction-limited light source [1] depends on the ability to lengthen the stored bunches to limit the emittance growth and increase the beam life time. Higher harmonic cavities (HHCs), also known as Landau cavities, have been proposed to in-crease beam lifetime and Landau damping by lengthen-ing the bunch. We present an optimized 1.5 GHz normal conducting HHC design for the ALS-U with a supercon-ducting-like geometry using multi-objective genetic algorithm (MOGA) for lower R/Q. The optimization goal is to reach the required shunt impedance while maintain-ing a relatively high Q value of the cavities. To minimize the coupled bunch instabilities, higher-order mode (HOM) of the HHC as well as corresponding impedance are explored and characterized. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB081 | |
| About • | paper received ※ 16 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019 | |
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| THPRB055 | DAMAGE BEHAVIOR OF TUNGSTEN TARGETS FOR 6 MEV LINEAR ACCELERATORS | 3934 |
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| The target in electron linear accelerator is subjected to high-frequency and intense thermal shocks. Elevated temperatures in the target may lead to target recrystallization, fatigue cracking, creep and vaporization. In this study, experiments were carried out to investigate the damage behaviour of tungsten targets in 6 MeV linear accelerators under pulsed electron beam. The results show that recrystallization occurs after loading 6 MeV electron beam with repetition frequency of 220 Hz, pulse width of 4μs and mean current of 151μA for 248 s. Deformation and cracking caused by recrystallization are observed on the surface of the target. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPRB055 | |
| About • | paper received ※ 14 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019 | |
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| THPTS038 | There-Dimensional Simulation of a C-Band 32-Beam Klystron | 4190 |
| SUSPFO063 | use link to see paper's listing under its alternate paper code | |
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| A 32-beam klystron working at 5.712 GHz has been designed with efficiency of 70% and output power of 3.4 MW. Core oscillations method (COM) is chosen to bunch electrons. The code KlyC is used for 1-D and 1.5-D calculation and a series of parameters are given after optimizing, including the position, frequency, R/Q, Q0 and Qe of cavities. CST/PIC is used to make the final design and coaxial cavities are used. This paper describes 1-D, 1.5-D and 3-D beam dynamics of the klystron, compares their differences, and analyses effect of these differences on efficiency. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPTS038 | |
| About • | paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019 | |
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| THPTS039 | DESIGN OF A COMPACT VARIABLE X-BAND RF POWER SPLITTER | 4194 |
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| This paper presents a design of a compact variable X-band RF power splitter. The RF power splitter includes one input port and two output ports, and the power divi-sion ratio can be adjusted by changing the position of a short circuit piston. This system keeps a good match (less than -40 dB) at any power division ratio. An E-bend waveguide structure is selected to make the geometry more compact (11cm in length, 3.5cm in width and 5 cm in height). Special studies was conducted to sustain a low surface electrical field (maximum 65 MV/m at 100 MW input), and large bandwidth (250MHz). This power split-ter is designed for high-power test stand at Tsinghua Uni-versity. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPTS039 | |
| About • | paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019 | |
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