Release Date
August 23rd, 2023
Open Date
September 20th, 2023
Due Date(s)
October 18th, 2023
Close Date
October 18th, 2023
Topic No.


L-Band Buncher/Modulator for X-Band Accelerator


Department of DefenseN/A


Type: SBIRPhase: BOTHYear: 2023


The Department of Defense (DoD) is seeking proposals for the development of a compact, high current, L-band modulator/buncher with broad bandwidth capability for an X-band accelerator. The modulator/buncher should be designed to provide L-band modulated electron beams of arbitrary waveform to the X-band accelerator, with consistent capture efficiency across a variety of lower frequency modulated electron beams. The design should include a transition into X-band cavities for integration with the accelerator. The project will involve extensive modeling, simulation, and theory, and Phase II awardees will fabricate the modulator and integrate it with an X-band accelerator for testing. Phase III will involve refining the design, scaling it to S-band, and potentially integrating it onto a ruggedized platform for field testing. The project falls under the Directed Energy critical technology area and is restricted under export control laws. The solicitation is open until October 18, 2023. For more information, visit the solicitation link.



The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Deliver a compact (up to 2m), high current, L-band modulator/buncher with broad bandwidth (>20% fractional bandwidth) capability to the Air Force Research Laboratory (AFRL). This capability is beyond the scope of what has traditionally been done with bunchers since providing a broad bandwidth is atypical. The buncher/modulator should be designed such that it is optimized to provide L-band modulated electron beams of arbitrary waveform (given Fourier limitations) to a state-of-the-art X-band accelerator (peak beam current 75-250 mA delivered over a 3 us macropulse with length of ~1m). Designs should provide consistent capture efficiency (>25%) going into the X-band accelerator across a variety of lower frequency (DC through L-band) modulated electron beams. The current to the accelerator should ensure that the accelerator can output 75-250mA. This design should include a transition into X-band cavities such that it is integrable with an X-band accelerator.The design should provide broadband modulation within L-band to an input electron beam with arbitrary amplitude modulation containing frequency content from DC to 1 GHz. Designs can include advances in cathodes - the requirement is that they can be operated such that modulated high frequency electron pulses are possible and integrable with X-band buncher/accelerator cavities.

DESCRIPTION: The performance of this work should include extensive modeling/simulation/theory of modulator/buncher designs and methods for integration with X-band accelerator cavities. This could include use of software such as HFSS and CST for full wave electromagnetic design, Parmela, ASTRA, GPT, and TRACK for particle tracking, and particle-in-cell software such as CST, Hellweg, or MAGIC for self-consistent study of beam dynamics. Those advancing to Phase II will need to fabricate the modulator and integrate it with an X-band accelerator. Final beam acceleration tests can be performed at AFRL's facilities and will include measurements of key performance parameters such as degree of modulation, bandwidth, and capture efficiency. Improvements to design may be required. Those advancing to Phase III will need to refine their designs, scale them from L-band to S-band and integrate the new design with the X-band accelerator. Final beam acceleration tests for Phase III will proceed as in Phase II with emphasis on key performance parameters.

PHASE I: Phase I awardees should design and simulate an L-band modulator/buncher which can effectively produce arbitrary amplitude, L-band modulation on arbitrary input waveforms with frequency from DC to 1 GHz. Designs must be scalable to higher frequency bands. Various approaches can be taken with the design and may include cavities and waveguides (including folded waveguides, tapered bunchers, etc.), or multi-section bunchers incorporating both and other elements such as choppers. Input beams to the modulator should be modulated through gridded or gridless cathodes, modulated photoinjection into accelerator/buncher cavities or any other viable techniques, which can produce distinct and arbitrary on/off cycles from DC to 1 GHz. Required performance parameters will include bandwidth of operation and degree of modulation and should be addressed with modeling/simulation/theory. Other key performance parameters will vary by design choice but should be demonstrated using theory/simulation. Examples of key performance parameters could include shunt impedance, current/current density handling, capture coefficient/efficiency, length of modulator/buncher section and plots of phase space. The modulator/buncher should not exceed 2m in length in order to maintain compactness. A transition between the modulator and X-band accelerator cavities should be designed such that there is minimal loss of electrons/energy. Full-wave, particle-in-cell analysis of electron propagation and electromagnetic fields should be performed showing performance across L-band. Identify commercial off-the-shelf components including electron gun, pulsed power, L-band RF amplifier or oscillators, or design in-house system(s). Provide quarterly reports to AFRL and write a final Phase I report presenting the modulator design and all modeling, simulation, and theory work (including raw data) indicating the device's progress towards meeting Topic Objectives. Provide a plan to carry out Phase II.

PHASE II: Phase II awardees should fabricate modulator designs and purchase/build electron guns, pulsed power supplies, L-band RF sources, or other required equipment to experimentally demonstrate buncher design. Designs can be demonstrated using limited frequency points (e.g. 2 frequencies which represent performance for the full bandwidth). Experiments should demonstrate feasibility of modulator and data for key performance parameters as described in Phase I should be collected and compared to theory/simulation. Designs should be optimized through experimentation to match, as near as possible, the theoretical/computational results. Final integration of modulator with X-band accelerator may be performed in AFRL's facilities. Quarterly reports should be sent to AFRL. A final report should be written to include modulator design, verification of all required/key performance parameters including raw data, standard operating procedures, and analyses of experiments vs. simulation/theory. A plan for Phase III should be provided.

PHASE III DUAL USE APPLICATIONS: Phase III awardees will refine their designs and scale the modulator to S-band. The system may also be integrated onto a ruggedized platform for field testing. Improvements to system performance may be required. Quarterly reports to AFRL should be written discussing design and integration of modulator and accelerator and overall performance of the modulator/accelerator system. A final report will be delivered to AFRL which will include a summary of all work performed in Phase III.


  1. Kutsaev, S. V., et. al, "Compact X-Band electron linac for radiotherapy and security applications," 2021.;
  2. Kutsaev, S. V., et. al, "Electron bunchers for industrial RF linear accelerators: theory and design guide," 2021.; Mishin, A. V., "Advances in X-Band and S-Band Linear Accelerators for Security, NDT, and Other Applications," 2005.

KEYWORDS: Buncher; Modulator; Linear accelerator; RF Linac; Electron Beams; Directed Energy