Strong wiggler field assisted amplification in a second-harmonic waveguide free electron laser

As a technique to reduce the size of compact waveguide free electron lasers (FELs) operated from microwave to the far infrared, a longitudinal interaction mechanism was recently proposed to operate waveguide FELs at the second harmonic. With a gain formulation based on Madey’s theorem in the limit of small wiggler field, it was shown analytically that second harmonic waveguide FELs can reduce significantly the electron energy required for radiation at a given frequency. As it is advantageous to operate second harmonic waveguide FELs with strong wiggler field, Madey’s theorem is used here to reformulate their interaction gain for strong wiggler fields up to [....] with the axial electron velocity Taylor expanded to the eighth order of the wiggler field. Given that Madey’s theorem has not been established for second harmonic waveguide FELs, their interaction gain is also formulated independently by solving their pendulum equation without recourse to Madey’s theorem. These two gain formulas are not analytically identical, but numerically they lead to an excellent agreement over a wide range of system parameters, thus confirming the applicability of Madey’s theorem. The interaction analyses presented form a thorough and detailed description of second harmonic waveguide FELs in the small-signal regime and for wiggler field that is both practical and beneficial

Nonlinear amplification in a second-harmonic waveguide free-electron laser

This paper describes the results of numerical simulation of second-harmonic waveguide free-electron lasers (FELs) from the small-signal regime to the large-signal regime. Aimed at reducing the size and hence the cost of compact waveguide FELs operated from the microwave to the far infrared, these unconventional waveguide FELs can substantially decrease the minimum electron energy required for strong FEL radiation at a given frequency while increasing the small-signal gain. This contribution focuses on their saturation behaviors, taking into consideration variation in wiggler field and electron-energy spread. Depending on the roundtrip power loss within the FEL cavity and the initial electron-energy spread, the computed relationship between interaction gain and in-cavity power can be used to maximize the output power at a given electron current. Furthermore, it is found that gain degradation due to electron-energy spread remains relatively unchanged regardless of radiation power and wiggler field

Sedative-sparing effect of acupuncture in gastrointestinal endoscopy: systematic review and meta-analysis

ObjectiveThis study aimed to perform a systematic review and meta-analysis to identify the efficacy of acupuncture therapy (including manual acupuncture and electroacupuncture) performed before or during gastrointestinal endoscopy with propofol as the main sedative, compared with placebo, sham acupuncture, or no additional treatment other than the same sedation.MethodsA systematic search was performed through PubMed, Embase, Web of Science, Cochrane Library, Chinese Biomedical Databases (CBM), Wanfang database, China National Knowledge Infrastructure (CNKI), SinoMed, and Chinese Scientific Journal Database (VIP) to collect randomized controlled trials published before 5 November 2022. Bias assessment of the included RCTs was performed according to Version 2 of the Cochrane risk-of-bias tool for randomized trials (RoB 2). Stata16.0 software was used to perform statistical analysis, sensitivity analysis, and publication bias analysis. The primary outcome was sedative consumption, and the secondary outcomes included the incidence of adverse events and wake-up time.ResultsA total of 10 studies with 1331 participants were included. The results showed that sedative consumption [mean difference (MD) = −29.32, 95% CI (−36.13, −22.50), P < 0.001], wake-up time [MD = −3.87, 95% CI (−5.43, −2.31), P < 0.001] and the incidence of adverse events including hypotension, nausea and vomiting, and coughing (P < 0.05) were significantly lower in the intervention group than in the control group.ConclusionAcupuncture combined with sedation reduces sedative consumption and wake-up time compared with sedation alone in gastrointestinal endoscopy; this combined approach allows patients to regain consciousness more quickly after examination and lower the risk of adverse effects. However, with the limited quantity and quality of relevant clinical studies, caution must be applied until more high-quality clinical studies verify and refine the conclusions.Systematic review registrationhttps://www.crd.york.ac.uk/prospero/display_record.php?, identifier: CRD42022370422