Longitudinal phase space (LPS) provides a critical information about electron beam dynamics for various scientific applications. For example, it can give insight into the high-brightness X-ray radiation from a free electron laser. Existing diagnostics are invasive, and often times cannot operate at the required resolution. In this work we present a machine learning-based Virtual Diagnostic (VD) tool to accurately predict the LPS for every shot using spectral information collected non-destructively from the radiation of relativistic electron beam. We demonstrate the tool’s accuracy for three different case studies with experimental or simulated data. For each case, we introduce a method to increase the confidence in the VD tool. We anticipate that spectral VD would improve the setup and understanding of experimental configurations at DOE’s user facilities as well as data sorting and analysis. The spectral VD can provide confident knowledge of the longitudinal bunch properties at the next generation of high-repetition rate linear accelerators while reducing the load on data storage, readout and streaming requirements.

Experiments using a THz pump and an X-ray probe at an X-ray free-electron laser (XFEL) facility like the Linac Coherent Light Source II (LCLS II) require frequency-tunable (3 to 20 THz), narrow bandwidth (∼10%), carrier-envelope-phase-stable THz pulses that produce high fields (>1 MV cm−1) at the repetition rate of the X-rays and are well synchronized with them. In this paper, a two-bunch scheme to generate THz radiation at LCLS II is studied: the first bunch produces THz radiation in an electromagnet wiggler immediately following the LCLS II undulator that produces X-rays from the second bunch. The initial time delay between the two bunches is optimized to compensate for the path difference in THz transport. The two-bunch beam dynamics, the THz wiggler and radiation are described, as well as the transport system bringing the THz pulses from the wiggler to the experimental hall.

We report observations of an intense sub-THz radiation extracted from a ∼3 MeV electron beam with a flat transverse profile propagating between two parallel oversized copper gratings with side openings. Low-loss radiation outcoupling is accomplished using a horn antenna and a miniature permanent magnet separating sub-THz and electron beams. A tabletop experiment utilizes a radio frequency thermionic electron gun delivering a thousand momentum-chirped microbunches per macropulse and an alpha-magnet with a movable beam scraper producing sub-mm microbunches. The radiated energy of tens of microJoules per radio frequency macropulse is demonstrated. The frequency of the radiation peak was generated and tuned across two frequency ranges: (476-584) GHz with 7% instantaneous spectrum bandwidth, and (311-334) GHz with 38% instantaneous bandwidth. This prototype setup features a robust compact source of variable frequency, narrow bandwidth sub-THz pulses.

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The development of novel mm-wave high-gradient, > 200 MV/m, accelerating structures offers a promising path to reduce the cost and footprint of future TeV-scale linear colliders, as well as linacs for industrial, medical and security applications. The major factor limiting accelerating gradient is vacuum RF breakdown. The probability of such breakdowns increases with pulse length. For reliable operation, millimeter-wave structures require nanoseconds long pulses at the megawatt level. This power is available from gyrotrons, which have a minimum pulse length on the order of microseconds. To create shorter pulses and to reliably detect RF breakdowns we have developed the following devices: a laser-based RF switch capable of selecting 10 ns long pulses out of the microseconds long gyrotron pulses, thus enabling the use of the gyrotrons as power sources for mm-wave high gradient linacs, and a shot-to-shot sub-THz spectrometer with high-frequency resolution, capable of detecting pulse shortening due to RF breakdowns. In this paper, we will describe the principle of operation of these devices and their achieved parameters. We will also report on the experimental demonstration of these devices with the high power gyrotron at the Massachusetts Institute of Technology. In the experiments, we demonstrated nanosecond RF power modulation, shot-to-shot measurements of the pulse spectra, and detection of RF breakdowns.

Super B factories that will further probe the flavor sector of the Standard Model and physics beyond will demand excellent charged particle identification (PID), particularly K/π separation, for momenta up to 4 GeV/c, as well as the ability to operate under beam backgrounds significantly higher than current B factory experiments. We describe an Imaging Time-of-Propagation (iTOP) detector which shows significant potential to meet these requirements. Photons emitted from charged particle interactions in a Cerenkov radiator bar are internally reflected to the end of the bar, where they are collected on a compact image plane using photodetectors with fine spatial segmentation in two dimensions. Precision measurements of photon arrival time are used to enhance the two dimensional imaging, allowing the system to provide excellent PID capabilities within a reduced detector envelope. Results of the ongoing optimization of the geometric and physical properties of such a detector are presented, as well as simulated PID performance. Validation of simulations is being performed using a prototype in a cosmic ray test stand at the University of Hawaii. factory, including results of ongoing detector optimization studies and simulated performance results.

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Free-electron lasers (FEL) and synchrotron sources of high brilliance x-rays have proven to be of tremendous value in basic and applied research. Inverse-Compton sources (ICS) can achieve brilliance matching the requirements of many applications pioneered at those FEL and synchrotron facilitiesincluding phase contrast imaging, macromolecular x-ray crystallography, and x-ray microscopy-but with size, cost, and complexity compatible with a small laboratory. The free-electron laser inverse-Compton interaction compact x-ray source at the University of Hawaii at Manoa is a unique approach to an ICS which employs an FEL as the laser source. We have measured a total average flux of 3.0 × 10 5 photons=second with an average brilliance of 2.0 × 10 7 photons=s mm 2 mrad 2 0.1% of bandwidth (BW) with a peak energy of 10.9 keV from the source. While these results are modest in comparison to the standards set by other IC sources, upgrades to the system have the potential to increase the total average flux to 9.2 × 10 11 photons=second with an average brilliance of 1.9 × 10 12 photons=s mm 2 mrad 2 0.1% BW: comparing more favorably to other sources. We discuss the scientific program, the progress made in design and development, and the achievements of the source to date. We also outline future upgrades and integration needed to yield an enabling source for emerging high brilliance x-ray applications.