We present a detailed study of the six-dimensional phase space of the electron beam produced by the Cornell Energy Recovery Linac Photoinjector, a high-brightness, high repetition rate (1.3 GHz) DC photoemission source designed to drive a hard x-ray energy recovery linac (ERL). A complete simulation model of the injector has been constructed, verified by measurement, and optimized. Both the horizontal and vertical 2D transverse phase spaces, as well as the time-resolved (sliced) horizontal phase space, were simulated and directly measured at the end of the injector for 19 and 77 pC bunches at roughly 8 MeV. These bunch charges were chosen because they correspond to 25 and 100 mA average current if operating at the full 1.3 GHz repetition rate. The resulting 90% normalized transverse emittances for 19 ð77Þ pC=bunch were 0:23 AE 0:02 ð0:51 AE 0:04Þ m in the horizontal plane, and 0:14 AE 0:01 ð0:29 AE 0:02Þ m in the vertical plane, respectively. These emittances were measured with a corresponding bunch length of 2:1 AE 0:1 ð3:0 AE 0:2Þ ps, respectively. In each case the rms momentum spread was determined to be on the order of 10 À3 . Excellent overall agreement between measurement and simulation has been demonstrated. Using the emittances and bunch length measured at 19 pC=bunch, we estimate the electron beam quality in a 1.3 GHz, 5 GeV hard x-ray ERL to be at least a factor of 20 times better than that of existing storage rings when the rms energy spread of each device is considered. These results represent a milestone for the field of high-brightness, highcurrent photoinjectors.

Characterization of 9-9.5 MeV electron beams produced in the dc-gun based Cornell photoinjector is given for bunch charges ranging from 20 pC to 2 nC. Comparison of the measured emittances and longitudinal current profiles to optimized 3D space charge simulations yields excellent agreement for bunch charges up to 1 nC when the measured laser distribution is used to generate initial particle distributions in simulation. Analysis of the scaling of the measured emittance with bunch charge shows that the emittance scales roughly as the square root of the bunch charge up to 300 pC, above which the trend becomes linear. These measurements demonstrate that the Cornell photoinjector can produce cathode emittance dominated beams meeting the emittance and peak current specifications for next generation free electron lasers operating at high repetition rate. In addition, the 1 and 2 nC results are relevant to the electron ion collider community.

We present the results of transverse emittance and longitudinal current profile measurements of high bunch charge (≥100 pC) beams produced in the DC gun-based Cornell Energy Recovery Linac Photoinjector. In particular, we show that the cathode thermal and core beam emittances dominate the final 95% and core emittance measured at 9-9.5 MeV. Additionally, we demonstrate excellent agreement between optimized 3D space charge simulations and measurement, and show that the quality of the transverse laser distribution limits the optimal simulated and measured emittances. These results, previously thought achievable only with RF guns, demonstrate that DC gun based photoinjectors are capable of delivering beams with sufficient single bunch charge and beam quality suitable for many current and next generation accelerator projects such as Energy Recovery Linacs (ERLs) and Free Electron Lasers (FELs).Linear electron accelerators boast a wide range of current and planned applications in the physical sciences. Examples include: x-ray sources [1-3], electron-ion coolers [4], Ultra-fast Electron Diffraction (UED) experiments [5][6][7][8], and fixed-target nuclear physics experiments [9]. A key feature of many of these applications is the potential to produce beams where the initial beam quality, set by the source, dominates the final beam quality at the usage point. This has lead to the design of a next generation of machines, such as high energy Energy Recovery Linacs (ERLs) [2], and Free Electron Lasers (FELs) [3] which could provide diffraction limited hard x-rays with orders of magnitude brighter beams than modern storage rings. The successful design and implementation of such machines has the potential to impact an impressively broad range of research in physics, chemistry, biology, and engineering.For next generation high energy x-ray sources like the proposed Linac Coherent Light Source-II (LCLS-II) [10], the creation (at MHz repetition rates) and effective transport of multi-MeV beams with high bunch charges (≥100 pC), picosecond bunch lengths, and sub-micron normalized transverse emittances represents a beam dynamics regime previously thought attainable only with RF gun based photoinjectors [11]. In this letter, we challenge this assumption, and show that the DC gun-based Cornell ERL injector can produce cathode emittance dominated beams which meet the bunch charge, emittance, and peak current specifications of a next generation light source. In doing so, we also demonstrate excellent agreement between measurement and simulation of the injector, and show that ultimate optimization of the emittance in high-brightness photoinjectors may require advanced transverse laser shaping along with the use of low intrinsic emittance photocathodes.Before discussing our experimental results, we review the definitions of the key figures of merit for beam quality in high-brightness accelerators relevant for this work: emittance and brightness. For the beam densities encountered in this work (10 17 -10 18 e/m 3 ), classical relativisti...

We present a comparison between space charge calculations and direct measurements of the transverse phase space of space charge dominated electron bunches from a high voltage dc photoemission gun followed by an emittance compensation solenoid magnet. The measurements were performed using a double-slit emittance measurement system over a range of bunch charge and solenoid current values. The data are compared with detailed simulations using the 3D space charge codes GPT and PARMELA3D. The initial particle distributions were generated from measured transverse and temporal laser beam profiles at the photocathode. The beam brightness as a function of beam fraction is calculated for the measured phase space maps and found to approach within a factor of 2 the theoretical maximum set by the thermal energy and the accelerating field at the photocathode.

We measure the tradeoff between the quantum efficiency and intrinsic emittance from a NaKSb photocathode at three increasing wavelengths (635, 650, and 690 nm) at or below the energy of the bandgap plus the electron affinity, hν≤Eg+Ea. These measurements were performed using a high voltage dc gun for varied photocathode surface fields of 1.4−4.4 MV/m. Measurements of intrinsic emittance are performed using two different methods and were found to agree. At the longest wavelength available, 690 nm, the intrinsic emittance was 0.26 μm/mm-rms with a quantum efficiency of ∼10−4. The suitability of NaKSb emitting at threshold for various low emittance applications is discussed.