Integrated high efficiency bunch shaping techniques for SWFA Demonstrator
Purpose of the research: In the Collinear Wakefield Acceleration (CWA), which is one important variant of the SWFA (structure-based wakefield accelerator), an important parameter that describes the performance of the wakefield accelerator is the transformer ratio R, which characterizes the efficiency of the energy transfer from the drive bunch to the witness bunch (a higher R is preferred under a certain main beam current). Another important figure of merit is the accelerating gradient. In principle, high R and high gradient cannot be achieved simultaneously for a CWA using a given drive charge [1]. Increasing the drive bunch charge with a specifically shaped temporal profile becomes the most attainable solution to achieve high R and high gradient. The existing bunch-shaping methods fall into three categories: laser shaping, emittance exchange, and correlations between the energy and one of the other coordinates. These methods require either (i) dispersive elements (e.g., a dipole magnet), which can generate coherent synchrotron radiation, or (ii) beam shaping near the cathode, which can distort the beam profile due to space-charge effects. These collective effects significantly decrease the shaping quality as the bunch charge increases. None of the existing methods are currently capable of shaping high-charge bunches. The purpose of our research is to develop a method of producing high-charge shaped bunch, and thus to enable the demonstration of high gradient, high transformation acceleration. Scope of the research: We proposed to use a new Coherent Synchrotron Radiation (CSR)-free longitudinal bunch shaping method, which primarily includes two transverse deflecting cavities, a quadrupole magnet, and a mask in a straight beamline configuration, thus avoiding the impact of collective effects (CSR in particular) on the shaping process. The method also will integrate the laser-shaping technique as a pre-shaper to reduce the beam loss at the mask, and thus increase the overall bunch-shaping efficiency. Results of the research: In Phase I, we have successfully completed all of the proposed tasks and the two main deliverables: 1) simulation of the full experimental layout based on the use of wakefield-driven short-pulse deflectors; 2) high power RF test of the short-pulse traveling-wave deflector that was developed for the bunch-shaping experiments that are to be carried out in Phase II. An RF deflecting voltage exceeding the required deflecting voltage was achieved (conditioned to 200-MW rf input; 100 MW is required for the bunch-shaping experiment). The results in Phase I have laid down a solid foundation for the next Phase of the project. The results of Phase I will be presented at the AAC2022 workshop. Near-term application: The first application of the technologies developed in this project is the Energy Doubler Demonstrator that is proposed for the Argonne Wakefield Accelerator (AWA) facility. It will use two 0.5-m-long corrugated-waveguide CWA modules with TR~5 in order to boost the main beam energy to 150 MeV.
- Research Organization:
- Euclid Beamlabs LLC
- Sponsoring Organization:
- USDOE Office of Science (SC), High Energy Physics (HEP)
- Contributing Organization:
- Argonne National Laboratory
- DOE Contract Number:
- SC0021733
- OSTI ID:
- 1871031
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- DOE-Euclid-21733
- Country of Publication:
- United States
- Language:
- English
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