ANL, Argonne, Illinois, USA
Fermilab, Batavia, Illinois, USA
We report recent pulse-duration measurements of the APS PC Gun drive laser at both second harmonic (SH, 527 nm) and fourth harmonic (FH. 263 nm) wavelengths. The drive laser is a Nd:Glass-based CPA with the IR wavelength (1053 nm) twice doubled to obtain UV output for the gun. A Hamamatsu C5680 streak camera and an M5675 synchroscan unit are used for these measurements; the synchroscan unit is tuned to 119 MHz, the 24th subharmonic of the linac operating frequency. Calibration is accomplished both electronically and optically. Electronic calibration utilizes a programmable delay line in the 119 MHz rf path. The optical delay employs an etalon with known spacing between reflecting surfaces; this etalon is coated for the visible, SH wavelength. IR pulse duration is monitored with an autocorrelator. Fitting the streak camera image projected profiles with Gaussians, UV rms pulse durations are found to vary from 2.1 ps to 3.5 ps as the IR varies from 2.2 ps to 5.2 ps.
Fermilab, Batavia, Illinois, USA
Northern Illinois Univerity, DeKalb, Illinois, USA
Northern Illinois University, DeKalb, Illinois, USA
Sokendai, Ibaraki, Japan
BYU-I, Rexburg, USA
KU, Lawrence, Kansas, USA
The low-energy section of the photoinjector-based electron linear accelerator at the Fermilab Accelerator Science & Technology (FAST) facility was recently commissioned to an energy of 50 MeV. This linear accelerator relies primarily upon pulsed SRF acceleration and an optional bunch compressor to produce a stable beam within a large operational regime in terms of bunch charge, total average charge, bunch length, and beam energy. Various instrumentation was used to characterize fundamental properties of the electron beam including the intensity, stability, emittance, and bunch length. While much of this instrumentation was commissioned in a 20 MeV running period prior, some (including a new Martin-Puplett interferometer) was in development or pending installation at that time. All instrumentation has since been recommissioned over the wide operational range of beam energies up to 50 MeV, intensities up to 4 nC/pulse, and bunch structures from ~1 ps to more than 50 ps in length.
Fermilab, Batavia, Illinois, USA
Although beam centroid information at the MHz-micropulse-repetition rate has routinely been achieved at various facilities with rf BPMS, the challenge of recording beam size information at that rate is more daunting. The Integrable Optics Test Accelerator (IOTA) ring being planned at Fermilab has ~8 MHz revolution rates. To simulate the IOTA synchrotron radiation source temporal structure, we have used the UV component of the drive laser of the Fermilab Accelerator Science and Technology (FAST) Facility. This laser is normally set at 3 MHz, but has also been run at 9 MHz. We have configured our Hamamatsu C5680 streak camera in a framing camera mode using a slow vertical sweep plugin unit with the dual axis horizontal sweep unit**. A two-dimensional array of images sampled at the MHz rate can then be displayed on the streak tube phosphor and recorded by the CCD readout camera at up to 10 Hz. As an example, by using the 10 microsecond vertical sweep with the 100 microsecond horizontal sweep ranges, 49 of the 300 micropulses at 3 MHz are displayed for a given trigger delay in each of six images. Example 2D image arrays with profiling examples will be presented.
**Hamamatsu C5680 product web page.
Fermilab, Batavia, Illinois, USA
Commissioning at the SCRF accelerator at the Fermilab Accelerator Science and Technology (FAST) Facility has included the implementation of a versatile bunch-length monitor located after the 4-dipole chicane bunch compressor for electron beam energies of 20-50 MeV and integrated charges in excess of 10 nC. The team has initially used a Hamamatsu C5680 synchroscan streak camera. An Al-coated Si screen was used to generate optical transition radiation (OTR) resulting from the beam's interaction with the screen. The chicane bypass beamline allowed the measurements of the bunch length without the compression stage at the downstream beamline location using OTR and the streak camera. The UV component of the drive laser had previously been characterized with a Gaussian fit σ of 3.5-3.7 ps**. However, the uncompressed electron beam is expected to elongate due to space charge forces in an initial 1.5-m drift from the gun to the first SCRF accelerator cavity. We have observed electron beam bunch lengths from 5 to 14 ps (σ) for micropulse charges of 60 pC to 800 pC, respectively. Commissioning of the system and initial results with uncompressed and compressed beam will be presented.
**A.H. Lumpkin et al., Proceedings of FEL14, MOP021, Basel, Switzerland, www. JACoW.org
Fermilab, Batavia, Illinois, USA
Washington University in St. Louis, St. Louis, Missouri, USA
X-ray phase contrast (XPC) imaging is an emerging technology that holds great promise for biomedical applications due to its ability to provide information about soft tissue structure *. The need for high spatial resolution at the boundaries of the tissues is noted for this process. Based on results from imaging of relativistic electron beams with single crystals **, we proposed transferring single-crystal imaging technology to this bio-imaging issue. Using a microfocus x-ray tube (17 kVp) and the exchangeable phosphor feature of the camera system, we compared the point spread function (PSF) of the system with the reference P43 phosphor to that with several rare earth garnet single crystals of varying thickness. Based on single Gaussian peak fits to the collimated x-ray images, we observed a four times smaller system PSF (21 microns (FWHM)) with the 25-mm diameter single crystals than with the reference polycrystalline phosphor's 80-micron value. Initial images of 33-micron diameter carbon fibers have also been obtained with small crystals installed. Tests with a full-scale 88-mm diameter single crystal (patent-pending configuration) are being planned.
*A. Appel, M.A. Anastasio, and E.M. Brey, Tissue Eng. Part B Rev 17 (5), 321 (2011).
**A.H. Lumpkin, et al., Phys. Rev. ST-AB 14 (6), 060704 (2011).
Fermilab, Batavia, Illinois, USA
The University of Texas at Austin, Austin, Texas, USA
Private Address, Silver Spring, USA
Recent measurements of betatron x-ray emission from quasi-monoenergetic electrons accelerating to 500 MeV within a laser plasma accelerator (LPA) enabled estimates of normalized transverse emittance well below 1 mm-mrad and divergences of order 1/gamma [1]. Such unprecedented LPA beam parameters can, in principle, be addressed by utilizing the properties of linearly polarized optical transition radiation (OTR) that provide additional beam parameter sensitivity. We propose a set of complementary measurements of beam size and divergence with near-field and far-field OTR imaging, respectively, on LPA electron beams ranging in energy from 100 MeV [2] to 2 GeV [3]. The feasibility is supported by analytical modeling for beam size sensitivity and divergence sensitivity. In the latter case, the calculations indicate that the parallel polarization component of the far-field OTR pattern is sensitive to divergences from 0.1 to 0.4 mrad (σ) at 2 GeV, and it is similarly sensitive to divergences from 1 to 5 mrad (σ) at 100 MeV. We anticipate the signal levels from charges of 100 pC will require a 16-bit cooled CCD camera. Other practical challenges in the LPA will also be discussed.
1.G. R. Plateau et al., Phys. Rev. Lett. 109, 064802 (2012).
2.Hai-EnTsai, Chih-Hao Pai, and M.C. Downer, AIP Proc. 1507, 330 (2012)
3.Xiaoming Wang et al., Nature Communications 4,1988(2013).
Northern Illinois University, DeKalb, Illinois, USA
Fermilab, Batavia, Illinois, USA
Northern Illinois Univerity, DeKalb, Illinois, USA
Masking a dispersive beamline such as a dogleg or a chicane [1, 2] is a simple way to shape a beam in the longitudinal and transverse space. This technique is often employed to generate arbitrary bunch profiles for beam/laser-driven accelerators and FEL undulators or even to reduce a background noise from dark currents in electron linacs. We have been investigating a beam-modulation of a slit-masked chicane, which was deployed for crystal-channeling experiments at the injector beamline of the Fermilab Accelerator Science and Technology (FAST) facility. With a nominal beam of 3 ps bunch length, Elegant simulations showed that a slit-mask with slit period 900 um and aperture width 300 um induces a modulation with bunch-to-bunch space of about 187 um (0.25 nC), 270 um (1 nC) and 325 um (3.2 nC) with 3 ~ 6% correlated energy spread: An initial energy modulation pattern has been observed in the electron spectrometer downstream of the masked chicane using a micropulse charge of 260 pC and 40 micropulses. Investigations of the beam longitudinal modulation are planned with a Martin-Puplett interferometer and a synchro-scan streak camera at a station between the chicane and spectrometer.
[1] D.C.Nguyen, B.E.Carlsten, NIMA 375, 597 (1996)
[2] P.Muggli, V.Yakimeno, M.Babzien, et al., PRL 101, 054801 (2008)