3.
ADVANCED SOURCES FOR ACCELERATOR FACILITIES
The Office of Basic Energy
Sciences, within the DOE’s Office of Science, is
responsible for current and future synchrotron radiation light source, free
electron laser, and spallation neutron source user
facilities. This topic seeks the
development of technology to support the particle and radiation sources needed
for these user facilities. Grant
applications are sought only in the following subtopics.
a. Electron Gun Technology—Grant applications are sought to develop
novel electron gun features including:
(1) Robust cathode materials suitable
for production of low emittance electron bunches at high repetition rate using laser excitation. Intrinsic normalized emittance
of the electron beam must be of order 10-7 m-rad, in bunches of order 100 pC
charge, duration of approximately 10 ps, and with
quantum efficiency of 10-2 or greater. Materials should be robust to environmental
conditions, have small dark current under applied electric fields of order
10-100 MVm-1, and have long lifetime.
(2) Accelerating structures supporting
electric fields of 10-100 MVm-1 at
a cathode surface, allowing laser excitation of the cathode material and rapid
acceleration of the emitted electrons with minimal emittance
growth, and having an electron bunch repetition rate of 1 MHz or greater. Combined with suitable cathode materials and a
photocathode laser, the system should be capable of producing low emittance (less than 1 mm-mrad normalized) electron bunches at a minimum 1 MHz repetition
rate, with up to 1 nC charge per bunch.
Questions - contact Roger Klaffky (roger.klaffky@science.doe.gov)
b. High Brightness Sources of Negative
Hydrogen Ions—Grant applications are sought to develop high-current, high
brightness sources of negative hydrogen ions.
The goal is the production of ~70 mA of H-
with a normalized emittance of
0.2
p mm.mrad,
or about 100 mA, with a normalized emittance of 0.35 p mm.mrad. These currents and emittances
have to be achieved for 1 ms long pulses at 60 Hz. The current should remain constant within ~5%.
The lifetime as well as the meantime-between-failure should exceed several
weeks. Of special interests are highly
efficient ionization technologies that can produce such beams with moderate
power levels (< 40 kW peak power).
Questions - contact Roger Klaffky (roger.klaffky@science.doe.gov)
c. Undulator Radiation Sources—Advanced undulator radiation sources are required for current and
future light sources. Grant applications
are sought for the development of:
(1) Superconducting undulators
(SCUs) that can generate tunable, monochromatic x-ray
beams in the 2-30 keV photon energy range from medium-energy
(2-3 GeV) synchrotrons. These requirements demand that the undulators have a short period (around 1.5 cm) and high
peak magnetic fields (around 1.6 tesla). The permanent-magnets commonly used in undulators do not produce sufficiently high magnetic fields
to fully cover the desired photon energy range without gaps in the
spectrum. Development efforts are
underway at several National Laboratories and in industry to develop SCUs that promise to overcome these deficiencies. However, current designs suffer from an
inability to operate without quenching in the presence of the heat induced by
the stored electron beam current and by synchrotron radiation encountered in
modern synchrotron light sources. This heat
load can be up to 10 watts per meter of undulator
length. Novel ideas for SCU design,
construction, and thermal management are needed to meet these challenging
requirements.
(2) Cryogenically-Cooled Permanent
Magnet Undulators (CPMUs).
When permanent magnet materials are cooled to low temperatures they exhibit a
larger coercivity (5-10%) for convenetional
materials like NdFeB or CoSm,
and up to 20% for more exotic materials.
To make use of this effect, undulators must be
cooled to cryogenic termperatures and in the cooled
down stage, magnetic measurements and adjustments of the PM must be
.performed. This requires a complex
design.
(3) High coercivity
permanent magnet materials for CPMUs. To take full advantage of CPMUs
sintering and manufacturing procedures need to be developed for permanent
magnet material like PrFeB, which exhibits large
increases in coercivity at cryogenic
temperatures.
(4) New superconducting materials for undulator applications.
Three types of materials promise a considerable enhancement of undulator performance:
·
High temperature superconducting
materials such as YBCO which operate at about 90K would allow current densities
up 100kA/mm^2. The challenge here is to optimize the conductor design to
maximize the current density and the transport current. A next step would lead
to the development of the coil manufacturing techniques based on such
materials.
·
Thin film high temperature
superconducting materials such as MgB2 which are operated at ~39K may become a
good material for undulator magnets as the mechanical
properties will be determined by the substrate material. The issue is the
production of the thin films and the choice of optimum substrate materials.
·
APC (artificially enhanced pinning
center) NbTi Superconductor which would allow
super-high current densities exceeding the Jc of
conventional NbTi superconductor by a large factor (14 kA/mm2 @
2 T). The high
current density might offer in particular an advantage for design magnet coils
for undulator magnets.
(5) Undulators
with period < 1 cm. The resonant condition for undulator
radiation at short wavelength (approximately 1 nm), with low energy electron
beams (of 1-2 GeV), requires undulators
with period that is shorter than generally available on existing synchrotron
radiation sources. Undulator designs are sought with
K-value ~1, impedance shielding of pole faces, and a gap of greater than 2.25
mm.
Questions - contact Roger Klaffky (roger.klaffky@science.doe.gov)
Subtopic
a References:
1.
Ben-Zvi,
Search
by author.)
2.
Proceedings of the Future Light Source Workshop (FLS2006),
available at: http://adweb.desy.de/mpy/FLS2006/proceedings/index.htm)
3.Y. Li and J.
Lewellen, 'Generating a Quasiellipsoidal Electron
Beam by 3D Laser-Pulse Shaping,' Phys. Rev. Lett. 100, 078401 (2008).
4.C. Limborg-Deprey and P.
Bolton, “Optimum electron distributions for space charge dominated beams in photoinjectors,” Nucl. Instrum. Methods A 557, 106 (2006).
5.
Subtopic b References:
.1.
Stockli, M., “The Development of High-Current and
High Duty-Factor H- Injectors,” presented at
LINAC’06,
stockli@ornl.gov)
Subtopic
c References:
1.
Casalbuoni, S., et al., “Generation of X-Ray
Radiation in a Storage Ring by a Superconductive Cold-Bore
In-Vacuum
Undulator,” Physical Review Special Topics:
Accelerators and Beams, 9(1), January 2006.
(ISSN:
1098-4402) (Full text available at: http://prst-ab.aps.org/onecol/PRSTAB/v9/i1/e010702)
2.
Bernhard, A., et al., “Planar and Planar Helical Superconductive Undulators for Storage Rings: State of the
Art,”
Proceedings of EPAC 2004,
http://accelconf.web.cern.ch/AccelConf/e04/PAPERS/MOPKF025.PDF)
3.
T. Hara et al., “Cryogenic Permanent Magnet Undulators,”
Physical Review Special Topics: Accelerators
and Beams,
7(5), May 2004. (ISSN: 1098-4402