MAMDOUH NASR, PhD
RF Integrity Engineer, Apple Inc.
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RESEARCH INTERESTS
RESEARCH INTERESTS
RF engineering, microwave matching and distribution networks, accelerator physics, computational electromagnetic, multi-radio coexistence, radio wave propagation, quantum mechanics, biomedical devices.
RESEARCH HIGHLIGHTS
RESEARCH HIGHLIGHTS
In my research endeavor, I aim to develop novel approaches for solving complex RF engineering problems ranging from numerical analysis, microwave design, experimental design to material science.
A photo at NLCTA test facility at SLAC National Accelerator Laboratory, USA.
Distributed-Coupling Linear Particle Accelerators (Linacs)
Distributed-Coupling Linear Particle Accelerators (Linacs)
Distributed-coupling Linacs present a topology for Linacs in which the power is distributed to the cavities through a waveguide with periodic apertures that guarantees the correct phases and amplitudes along the structure length. Unlike conventional traveling and standing-wave linacs, the presented topology allows the cavity shapes to be designed without the constraints applied to the coupling between cells to transfer power from one cell to the next. Therefore, the topology permits more degrees of freedom for the optimization of individual cavity shapes in comparison with conventional linacs.
Distributed-coupling Linacs present a topology for Linacs in which the power is distributed to the cavities through a waveguide with periodic apertures that guarantees the correct phases and amplitudes along the structure length. Unlike conventional traveling and standing-wave linacs, the presented topology allows the cavity shapes to be designed without the constraints applied to the coupling between cells to transfer power from one cell to the next. Therefore, the topology permits more degrees of freedom for the optimization of individual cavity shapes in comparison with conventional linacs.
M. Nasr, "Distributed-coupling Linear Particle Accelerators", PhD Dissertation, Stanford University, 2021
S. Tantawi, M. Nasr, Z. Li, C. Limborg, and P. Borchard "Design and demonstration of a distributed-coupling linear accelerator structure." Physical Review Accelerators and Beams 23.9 (2020): 092001.
Multi-mode Linear Particle Accelerators
Multi-mode Linear Particle Accelerators
Accelerating cavities support an infinite number of resonant modes that span many frequency bands and that can be used in particle acceleration. Accelerators, however, are typically designed for single-mode operation, using the fundamental-mode. In multi-mode operation, the accelerating-cells simultaneously utilize two (or more) resonant modes for acceleration, which increases the total accelerating gradient compared to single-mode operation. Moreover, by design, the peak fields for each mode can be crafted not add up simultaneously on the accelerator’s surface, thus reducing the total surface fields. This reduction reduces the breakdown rates in accelerator structures.
Accelerating cavities support an infinite number of resonant modes that span many frequency bands and that can be used in particle acceleration. Accelerators, however, are typically designed for single-mode operation, using the fundamental-mode. In multi-mode operation, the accelerating-cells simultaneously utilize two (or more) resonant modes for acceleration, which increases the total accelerating gradient compared to single-mode operation. Moreover, by design, the peak fields for each mode can be crafted not add up simultaneously on the accelerator’s surface, thus reducing the total surface fields. This reduction reduces the breakdown rates in accelerator structures.
M. Nasr and S. Tantawi, “A novel dual-mode dual-frequency linac design,” in 8th Int. Particle Accelerator Conf. (IPAC’17), Copenhagen, Denmark,14-19 May 2017. JACOW, Geneva, Switzerland, 2017, pp. 1634–1636.
M. Nasr and S. Tantawi, “The design and construction of a novel dual-mode dual-frequency linac design,” in 9th Int. Particle Accelerator Conf. (IPAC’18), Vancouver, BC, Canada, April 29-May 4, 2018. JACOW Publishing, Geneva, Switzerland, 2018, pp. 4391–4394.
Superconducting Distributed-Coupling Linacs
Superconducting Distributed-Coupling Linacs
We extended the distributed-coupling concept to superconducting accelerating structures which can largely benefit from the design flexibility offered by the distributed-coupling technology. While much of the recent research and development effort on superconducting accelerators has focused on material science, we aim to present optimized accelerator geometries that have the promise to reach double the accelerating gradient of existing state-of-the-art designs, while having much lower RF power loss.
We extended the distributed-coupling concept to superconducting accelerating structures which can largely benefit from the design flexibility offered by the distributed-coupling technology. While much of the recent research and development effort on superconducting accelerators has focused on material science, we aim to present optimized accelerator geometries that have the promise to reach double the accelerating gradient of existing state-of-the-art designs, while having much lower RF power loss.
M. Nasr, P. Welander, Z. Li, and S. Tantawi, “The Design of Parallel-Feed SC RF Accelerator Structure,” in 10th Int. Particle Accelerator Conf. (IPAC’19), Melbourne, Australia, May 19-24, 2019.
P. Welander, M. Nasr, Z. Li, and S. Tantawi, “Parallel-feed SRF accelerator structures,” in 9th Int. Particle Accelerator Conf. (IPAC’18), Vancouver, BC, Canada, April 29-May 4, 2018. JACOW Publishing, Geneva, Switzerland, 2018, pp. 3835–3837.
Genetic Optimization of Accelerating Cavities
Genetic Optimization of Accelerating Cavities
Over the past decades, accelerator scientists have made significant advances in the technology of particle accelerators, which has lead to state-of-the-art fabrication techniques and simulation tools. Combining these advancements with modern computational power has enabled great flexibility to the optimization of accelerator geometries. We presented a new geometrical optimization approach for accelerating cells. This approach provides a wider design space and enhanced geometries compared to conventional re-entrant shapes for the accelerating cells, defined using circular or elliptical curvatures.
Over the past decades, accelerator scientists have made significant advances in the technology of particle accelerators, which has lead to state-of-the-art fabrication techniques and simulation tools. Combining these advancements with modern computational power has enabled great flexibility to the optimization of accelerator geometries. We presented a new geometrical optimization approach for accelerating cells. This approach provides a wider design space and enhanced geometries compared to conventional re-entrant shapes for the accelerating cells, defined using circular or elliptical curvatures.
M. Nasr and S. Tantawi, “New geometrical-optimization approach using splines for enhanced accelerator cavities’ performance,” in 9th Int. Particle Accelerator Conf. (IPAC’18), Vancouver, BC, Canada, April 29-May 4, 2018. JACOW Publishing, Geneva, Switzerland, 2018, pp. 4395–4397.
Cryogenic Operation of Normal-Conducting Particle Accelerators
Cryogenic Operation of Normal-Conducting Particle Accelerators
We presented an experimental demonstration of the high-gradient operation of an X-band, 11.424 GHz, 20-cells linear accelerator (linac) operating at a liquid nitrogen temperature of 77 K. The tested linac was previously processed and tested at room temperature. Low-temperature operation increases the yield strength of the accelerator material and reduces surface resistance, hence a great reduction in cyclic fatigue could be achieved resulting in a large reduction in breakdown rates compared to room temperature operation. Furthermore, temperature reduction increases the intrinsic quality factor of the accelerating cavities, and consequently, the shunt impedance leading to increased rf-to-beam efficiency and beam loading capabilities. We verified the enhanced accelerating parameters of the tested accelerator at cryogenic temperature using different measurements including electron beam acceleration up to a gradient of 150 MV=m, corresponding to a peak surface electric field of 375 MV=m. We also measured the breakdown rates in the tested structure showing a reduction of 2 orders of magnitude compared to their values at room temperature for the same accelerating gradient.
We presented an experimental demonstration of the high-gradient operation of an X-band, 11.424 GHz, 20-cells linear accelerator (linac) operating at a liquid nitrogen temperature of 77 K. The tested linac was previously processed and tested at room temperature. Low-temperature operation increases the yield strength of the accelerator material and reduces surface resistance, hence a great reduction in cyclic fatigue could be achieved resulting in a large reduction in breakdown rates compared to room temperature operation. Furthermore, temperature reduction increases the intrinsic quality factor of the accelerating cavities, and consequently, the shunt impedance leading to increased rf-to-beam efficiency and beam loading capabilities. We verified the enhanced accelerating parameters of the tested accelerator at cryogenic temperature using different measurements including electron beam acceleration up to a gradient of 150 MV=m, corresponding to a peak surface electric field of 375 MV=m. We also measured the breakdown rates in the tested structure showing a reduction of 2 orders of magnitude compared to their values at room temperature for the same accelerating gradient.
M. Nasr et. al. “Experimental demonstration of particle acceleration with normal conducting accelerating structure at cryogenic temperature”, Physical Review Accelerators and beams 24.9 (2021): 093201.
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