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RF cavities have been designed and constructed that simultaneously and exclusively resonate many harmonic TMono modes. These modes are axially symmetric and have their electric field maximum along the cavities bore. A periodic beam passing through a harmonic cavities bore excites these modes whose superposition can be measured at the cavities antenna with a sampling oscilloscope. Processing the detected waveform with the harmonic cavities transfer function yields the Fourier series of the beam, and a near real-time, non-invasive measurement of the beams longitudinal bunch shape and duration. Experiments have been performed on the 130 kV injector at the Thomas Jefferson National Accelerator Facilities Continuous Electron Beam Accelerator Facility. The harmonic cavities sensitivity was near 1 mV/μA and measured beam bunches ranging in width from 45 to 150 picoseconds (FWHM). These measurements were in close agreement with measurements made using an invasive bunch measurement system as well as predictions by a particle tracking simulations., Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain

As part of the CEBAF 12 GeV upgrade at Jefferson Lab, a new experimental hall was added to the existing three halls. To deliver beam to all four halls simultaneous-ly, a new timing pattern for electron bunches is needed at the injector. This pattern change has consequences for the frequency of the lasers at the photogun, beam behavior in the chopping system, beam optics due to space charge, and setup procedures. We have successfully demonstrated this new pattern using the three existing drive lasers. The implementation of the full system will occur when the fourth laser is added and upgrades to the Low Level RF (LLRF) are complete. In this paper we explain the new bunch pattern, the challenges for setting and measuring the pattern such as 180° RF phase ambiguity, addition of the fourth laser to the laser table and LLRF upgrade., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

Polarized photocathodes with higher Quantum efficiency (QE) would help to reduce the technological challenge associated with producing polarized beams at milliampere levels, because less laser light would be required, which simplifies photocathode cooling requirements. And for a given amount of available laser power, higher QE would extend the photogun operating lifetime. The distributed Bragg reflector (DBR) concept was proposed to enhance the QE of strained-superlattice photocathodes by increasing the absorption of the incident photons using a Fabry-Perot cavity formed between the front surface of the photocathode and the substrate that includes a DBR, without compromising electron polarization. Here we present recent results showing QE enhancement of a GaAs/GaAsP strained-superlattice photocathode made with a DBR structure. Typically, a GaAs/GaAsP strained-superlattice photocathode without DBR provides a QE of 1%, at a laser wavelength corresponding to peak polarization. In comparison, the GaAs/GaAsP strained-superlattice photocathodes with DBR exhibited an enhancement of over 2 when the incident laser wavelength was tuned to meet the resonant condition for the Fabry-Perot resonator., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

Operating the JLab polarized electron source with high reliability and long lifetime requires vacuum near the XHV level (, Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

Polarized positron beams have been identified as either an essential or a significant ingredient for the experimental program of both the present and next generation of lepton accelerators (JLab, Super KEK B, ILC, CLIC). An experiment demonstrating a new method for producing polarized positrons has been performed at the Continuous Electron Beam Accelerator Facility at Jefferson Lab. The PEPPo (Polarized Electrons for Polarized Positrons) concept relies on the production of polarized e⁻/e⁺ pairs from the bremsstrahlung radiation of a longitudinally polarized electron beam interacting within a high Z conversion target. PEPPo demonstrated the effective transfer of spin-polarization of an 8.2 MeV/c polarized (P~85%) electron beam to positrons produced in varying thickness tungsten production targets, and collected and measured in the range of 3.1 to 6.2 MeV/c. In comparison to other methods this technique reveals a new pathway for producing either high energy or thermal polarized positron beams using a relatively low polarized electron beam energy (~10MeV) .This presentation will describe the PEPPo concept, the motivations of the experiment and high positron polarization achieved., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA