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MOPH11 |
Beam Dynamics of Grided Electron Gun in Distributed X-ray Sources | |
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| Distributed X-ray sources, a single vacuum chamber containing multiple x-ray sources, open the way to innovative system concepts in x-ray and CT. This paper proposed a novel electron beam focusing scheme for distributed x-ray sources. The sources used dispenser cathode as electron emitter, mesh grid to control emission current, and two electrostatic lenses for beam shaping, focusing and deflecting or not. Because the mesh is a non-linear optical system, after beam passes the mesh, the beam emittance grows. In order to minimize this emittance growth, the first lens was placed behind the mesh. The second lens, called focusing lens, with two semi-ellipses opening make the beam shaping, deflecting or not. If the voltages of two semi-elliptical electrodes are different, the beam will deflect after passing through the focusing lens. The voltage difference between the two semi-elliptical focusing lens is set to +V, 0, -V. Then three focal spots will be obtained on the anode target. So that we can use fewer cathodes to get more sources, thereby reducing cost and the difficulty of thermal management, increasing the count of focal spots and improving the image quality. | ||
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| MOPH24 | Electromagnetic and Mechanical Design of High Gradient S-band Accelerating Structure in TTX | 83 |
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| Thomson scattering x-ray source is an essential scien-tific platform and research tool in x-ray imaging technol-ogy for various fields. Upgrading plan that replacing the 3-meter S-band old linac with shorter high-gradient struc-ture in Tsinghua Thomson scattering X-ray source (TTX) is undergoing so far, aiming to enhance accelerating gradient from 15MV/m to 30MV/m. Detailed parameters of couplers and electromagnetic simulation results of whole acceleration structure are presented in this paper. Finally, mechanical structure and further upgrading re-search on energy with X-band structures are also discussed. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SAP2017-MOPH24 | |
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TUPH05 |
Experimental Observation of External Injection Acceleration by a Laser Produced Wake using a RF Photogun Based Linac | |
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| External injection of beams into plasma accelerators and acceleration with minimal degradation of their quality provide a promising route to make plasma acceleration a realistic technology for applications. In the past two years, we have carried out a lot of preparatory work for the external injection acceleration experiment in Tsinghua University. An ultrafast TW Ti:sapphire laser system is synchronized with a 45 MeV RF photogun based linac with a sub-200fs (RMS) time jitter between the laser pulse and the electron bunch. Here we present the first-time observation of external injection acceleration by a laser produced linear wake. Stable 32-MeV, 1~2-pC electron beams from the linac were compressed by a Chicane, focused to a 200-um radius (RMS) and then injected into the linear wakefield excited by the 10TW, 30fs laser. The preliminary experimental results show that up to 20% electrons can be accelerated and the maximum energy gain reaches 0.35 MeV in a 6-mm long plasma by optimizing the plasma density and the laser focal plane position with respect to the plasma, corresponding to an average gradient of about 60 MV/m, which are in reasonable agreement with 3D PIC simulations. | ||
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TUPH06 |
Experimental Demonstration of Energy-chirp Reduction by a Plasma Dechirper | |
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The first experimental study is presented using a low density plasma dechirper to reduce a correlated energy chirp from the 41.5-MeV, 300-fs (RMS) beam at the linac in Tsinghua University. The plasma dechirper operates through the interaction of the electron bunch with its near linear self-wake to dechirp itself, leading to a reduction in energy spread. The experimental results demonstrate that the projected FWHM energy spread of the beam can be reduced from 1.2% to 0.9% with a 12 mm long plasma dechirper, which are in good agreement with full three-dimensional particle-in-cell (PIC) simulations. Theoretical analyses and simulations indicate that by optimizing the plasma density and length, the plasma dechirper can also be used to completely remove the characteristic energy chirp of the ultra-short high-current bunch generated from plasma based accelerator, such that its energy spread can be reduced from one percent level to 0.1 percent level [1]. Application of such a simple and effective method can significantly improve the beam quality and provide the path to realize the future compact free electron lasers and colliders driven by plasma based accelerators.
[1] Y. P. Wu, X. L. Xu, et al., "A plasma dechirper for electron and positron beams in plasma-based accelerators", to be submitted to Scientific Reports |
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