The program has matured over the last two years to the point where we are now commercializing the production of small, inexpensive, novel undulators and planning to upgrade as many CHESS beamlines as possible with more brilliant sources.
For the ERL project, starting in 2009 lead scientist Alexander Temnykh successfully built and tested a 30 cm long Delta Undulator model, Fig. 1 (left), with linac-produced electron beams at the Accelerator Test Facility in Brookhaven National Laboratory. Test results were analyzed and presented at SRI 2010 [1]. The novel Delta design is optimized for a linac-based accelerator, having a round small gap between four magnetic arrays. Presently, Temnykh is collaborating with colleagues at SLAC to design and fabricate 3.2m long Delta undulator as a circular polarization “afterburner” for LCLS [2]. Under this program, a 1 m Delta undulator prototype was built and presently is been tested, Fig. 1 (right).
A critical part of the undulator development program is accurate calibration and tuning of magnetic fields. To make it possible, we developed and built at CHESS a stand and table for precise magnetic field mapping. At present, the stand allows characterization/tuning of undulator magnetic structures up to 2.8m long. The bench provides Hall sensor positioning at the level of 1 micron, and magnetic field measurement errors (normalized) ~5x10-4 or better. This precision yields undulator field optical phase errors resolution of ~ 0.2 deg. At the same time, a new magnetic field measurement technique employing a stretched wire as a magnetic field sensing element (Vibrating Wire technique) was developed [3]. In collaboration with SLAC and using LCLS undulators as a test bench, we carried out experiments which indicated that Vibrating Wire techniques can be efficiently applied for undulator field characterization. Because it employs a stretched wire as a magnetic field sensor, it is very appealing to use for characterization of undulators with small gap/bore such as Delta undulator [4].
Building on these capabilities and expertise, we are now developing and fabricating undulators called CHESS Compact Undulator (CCU) to upgrade existing CHESS beamlines with high-brilliance sources. Just like Delta designs, planar CCUs use small, inexpensive permanent magnets soldered to copper holders (Fig. 2, left), a fixed gap, and tune K to move undulator harmonic energy by simply translating the top magnet array relative to the bottom [1, 5, 6]. A top priority this past year was proving that planar narrow-gap CCU undulators could work in either in-vacuum or out-of-vacuum configurations. Following a successful test of a 1 meter in-vacuum CCU in 2012 [7, 8] a 0.3 meter out-of-vacuum undulator was built this past year by lead engineer Aaron Lyndaker. The device had a fixed gap of 6.5 mm gap, 29.4 mm period, and a variable K from 0 to 2.75 (Fig. 2, right). This length was chosen as a prototype to fit into short straight sections between four bend magnet beamlines.
During September 2013, several design and performance features were tested, including a thin wall vacuum chamber, a new compact sliding joint, a new vacuum chamber taper design, and interactions with stored beams and x-ray beam properties. At the same time, new water-cooled diamond x-ray optics on A-line were subjected to heat loading from 200 milliAmperes beams. The A1 side station utilized a Laue diamond optic that made use of the clamp and heat sinking technology developed by SPring-8 [9]. The A2 station used a CHESS-designed double-crystal diamond monochromator with water-cooling for the first crystal. Both x-ray optics configurations performed well.
Based on the success of these tests, CHESS is planning to replace two existing wiggler sources with CCUs. In 2014, two 1.5 meter canted undulators will replace the current west wiggler. Electron beams passing through the CCUs will illuminate the A1 and A2 stations, while a counter-rotating positron beam will simultaneously produce light in the opposite direction towards G1, G2 and G3. X-ray optics for A-line will initially use water-cooled diamonds, but move to cryogenically-cooled silicon as soon as an optics enclosure is readied. Looking forward to 2015, the F beamline will get two canted CCUs to continue protein crystallography and high-energy programs, but a new independently tunable spectroscopy and microfocus imaging end station is being designed to replace the current F3.
CHESS is working with vendor KYMA S.r.l./Bruker ASC- to produce two CCUs in time for the 2014 summer upgrade. A team from CHESS visited Bruker-KYMA in Fall 2013 to share technology and plans. Over the course of three days, we evaluated plans for a very rapid fabrication cycle to deliver devices by summer 2014, taught them to solder the small permanent magnets into copper holders and tested measuring the magnetic fields of blocks before and after soldering.
Plans for coming year at CHESS include continuing to work on lower emittance machine optics to create smaller x-ray source sizes for CHESS beamlines, and exploring higher energy operations which will improve x-ray flux at high energy applications. In all the next few years are promising to bring exciting deployments of brilliant undulators and beamline upgrades.
References:
[1] A. Temnykh, M. Babzien, D. Davis, M. Fedurin, K. Kusche, J. Park and V. Yakimenko, "Delta undulator model: Magnetic field and beam test results," Nucl Instrum Meth A 649(1), 42-45 (2011).
[2] H.-D. Nuhn, S. Anderson, G. Bowden, Y. Ding, G. Gassner, Z. Huang, E.M. Kraft, Y. Levashov, F. Peters, F.E. Reese, J.J. Welch, Z. Wolf, J. Wu and A. B. Temnykh, "R&D Towards a Delta-Type Undulator for the LCLS," SLAC-PUB-15743 (2013).
[3] A. Temnykh, "Vibrating wire field-measuring technique," Nucl Instrum Meth A 399(2-3), 185-194 (1997).
[4] A. Temnykh, Y. Levashov and Z. Wolf, "A study of undulator magnets characterization using the vibrating wire technique," Nucl Instrum Meth A 622(3), 650-656 (2010).
[5] A. B. Temnykh, "Delta Undulator for Cornell Energy Recovery Linac," Phys. Rev. St Accel Beams 11, 120702 (2008).
[6] A. Temnykh, "Helical PPM Undulator for ERL," 2006, http://www.lns.cornell.edu/public/CBN/2006/CBN06-3/CBN06-3.pdf.
[7] A. Temnykh, T. Kobela, A. Lyndaker, J. Savino, E. Suttner and Y. L. Li, "Compact Undulator for Cornell High Energy Synchrotron Source," Ieee T Appl Supercon 22(3), (2012).
[8] A. Temnykh, D. Dale, E. Fontes, Y. Li, A. Lyndaker, P. Revesz, D. Rice and A. Woll, "Compact Undulator for the Cornell High Energy Synchrotron Source: Design and Beam Test Results," Proceedings of the 11th International Conference on Synchrotron Radiation Instrumentation (SRI), Eds. p., Lyon, France, (2012).
[9] M. Yabashi, S. Goto, Y. Shimizu, K. Tamasaku, H. Yamazaki, Y. Yoda, M. Suzuki, Y. Ohishi, M. Yamamoto and T. Ishikawa, "Diamond Double-Crystal Monochromator for SPring-8 Undulator Beamlines," Synchrotron Radiation Instrumentation: Ninth International Conference (edited by Jae-Young Choi and Seungyu Rah) AIP Conference Proceedings, Volume 879, 922-925 (2007).