**Research Activity:** **Accelerator and Detector Research**

Division: Scientific User Facilities

Primary Contact: Roger W. Klaffky (roger.klaffky@science.doe.gov;
301-903-1873)

Division Director: Pedro A. Montano

**Portfolio** **Description**:

This activity supports basic research in accelerator physics and x-ray
and neutron detectors. Research seeks to achieve a fundamental
understanding beyond the traditional accelerator science and technology
to develop new concepts to be used in the design of new accelerator
facilities for synchrotron radiation and spallation neutron sources.
Research includes studies of the creation and transport of ultra-high
brightness electron beams to drive Self Amplified Spontaneous Emission
(SASE) Free Electron Lasers (FELs) such as the Linac Coherent Light
Source (LCLS). Collective electron effects as micro-bunch instabilities
from coherent synchrotron and edge radiation are key areas of interest
as they can degrade the beam brightness. Beam bunching techniques such
as magnetic compression or velocity bunching are also vital to the
operation of the LCLS and other FELs. Research is supported to develop
fast THz measurement instruments which will determine the longitudinal
and transverse structure of femtosecond electron bunches leading to an
increase in tuning speed of the various bunch compressive stages at the
LCLS. The Accelerator Test Facility (ATF) at Brookhaven National
Laboratory (BNL) is partially supported so that studies in these areas
can be carried out. In the area of neutron science, there is research to
develop improved high intensity, low emittance proton sources for the
Spallation Neutron Source (SNS) and other accelerator-driven neutron
sources such as the Los Alamos Neutron Science Center (LANSCE). More
efficient proton sources can increase the reliability and lifetime due
to lower RF power requirements. To exploit fully the fluxes delivered by
synchrotron radiation facilities and the SNS, new detectors capable of
acquiring data several orders of magnitude faster are required. Improved
detectors are especially important in the study of multi-length scale
systems such as protein-membrane interactions as well as nucleation and
crystallization in nanophase materials. They will also enable real-time
kinetic studies and studies of weak scattering samples.

**Unique Aspects**:

The accelerator and detector research is carried out to improve the
output and capabilities of synchrotron radiation light source and the
neutron scattering experiments at facilities that are the most advanced
of their kind in the world. Together, they serve more than 7,000 users
annually from academia, Department of Energy (DOE) national
laboratories, and industry, a number that has more than tripled in the
past decade and that can more than double again in the next decade as
current facilities and those under construction are fully instrumented.
These light sources and neutron scattering sources represent the largest
collection of such facilities operated by a single organization in the
world. Conception, design, construction, and operation of these
facilities, which in current costs are in the hundreds of millions to in
excess of a billion dollars, are among the core competencies of the BES
program.

**Relationship to Other** **Programs**:

This activity strongly interacts with BES programmatic research that
uses synchrotron and neutron sources. This includes research in atomic
physics, condensed matter and materials physics, chemical dynamics,
catalysis, geosciences, high-pressure science, environmental sciences,
engineering, biosciences, and much more. It also interacts with other
DOE offices, especially in the funding of capabilities whose cost and
complexity require shared support. The BNL ATF is jointly funded by the
High Energy Physics (HEP) Program and BES. There is also collaboration
with the National Science Foundation (NSF) on Energy Recovery Linac
(ERL) research. There is a coordinated effort between DOE and NSF to
facilitate the development of x-ray detectors. There are ongoing
industrial interactions through DOE Small Business Innovation Research
and Small Business Technology Transfer (SBIR/STTR) Program awards for
the development of x-ray detectors.

**Significant Accomplishments**:

Bunch compression and coherent radiation studies at the ATF using a
University of California at Los Angeles (UCLA) chicane have led to the
first observation of multi-THz coherent edge radiation. Measurements of
phase space distortions from acceleration fields have been carried out
and will serve as a basis for FEL bunch length diagnostics. A
holographic THz Fourier transform spectrometer test bed at Thomas
Jefferson National Accelerator Facility was completed, the first
required step for developing single shot device to completely
characterize bunch shapes. Both of these diagnostic advances are
targeted towards the LCLS. Other research relevant to the SNS includes
the development of an advanced ^3^He neutron detector prototype that has
shown that the ionization mode works in two-dimensions for thermal
neutron detection and is capable of measuring pulse height distributions
with the best ever energy resolution in this mode. Gigabyte per second
data rates will be achievable from this device. There were also advances
in developing a higher output, high brightness H^-^ source for the SNS
that circumvents RF antennae issues. Highly promising results have been
obtained by extracting H^-^ ions directly from a microwave-driven plasma
behind an electrostatic screen filter. The H^-^ ion current extracted
was three times higher that of the present SNS source at comparable
power.

**Mission Relevance**:

This research supports the most fundamental of research needs, i.e., the
need to characterize materials at the atomic and molecular level. In
order to understand, predict, and ultimately control materials
properties, it is necessary to determine the atomic constituents of
materials, the positions of the atoms in materials, and how the
materials behave under the influence of external perturbations such as
temperature, pressure, chemical attack, and excitation by photons,
electrons, and other particles

**Scientific Challenges**:

-   The development of new accelerator concepts is crucial to the design
    and upgrade of synchrotron light sources and neutron scattering
    facilities.

-   In the design and commissioning of new FELs such as the LCLS,
    experimental studies must be conducted on the creation and transport
    of ultra-high brightness electron beams to drive SASE.

-   Start-to-end simulations of the SASE electron source, transport, and
    SASE FEL give details of the physics mechanisms and provide
    benchmark models for the x-ray FEL.

-   New detectors capable of using the high data rates associated with
    high brightness sources will increase beamline efficiencies and user
    throughput.

-   Detectors must also be developed that are capable of acquisition of
    all required x-ray data from a single femtosecond LCLC pulse.

**Funding Summary:**

Dollars in Thousands

[FY 2005]{.underline} [FY 2006]{.underline} [FY 2007
Request]{.underline}

4,000 2,119 3,000

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**Projected** **Evolution:**

X-ray and neutron scattering will continue to play a central role in the
growth of BES programmatic science. The facilities will need continuous
growth in terms of accelerator upgrades, and x-ray and neutron detectors
to fully exploit the high fluxes of x-rays and neutrons. The set of
instruments associated with these facilities provides unique scientific
and technical capabilities, rarely available in other parts of the
world. These facilities need to be kept in an optimal operational mode
in order to maintain and increase the tremendous scientific achievements
they have facilitated.

The SNS will be for years to come the most important neutron spallation
source in the world. It is important to be prepared for full use and
judicious increases in the capabilities of the SNS as recommended by all
advisory committees to DOE. Accelerator and detector research will
enable these upgrades.

The instrumentation and scientific needs required by the future
operation of the LCLS at the Stanford Linear Accelerator Center need to
be identified and addressed. Finally, the LCLS will have properties
vastly exceeding those of current x-ray sources in three key areas: peak
brightness, coherence, and ultrashort pulses. The peak brightness of the
LCLS is 10 orders of magnitude greater than current synchrotrons; the
light is coherent or "laser like" enabling many new types of
experiments; and the pulses are short (230 femtoseconds with planned
improvements that will further reduce the pulse length) enabling studies
of fast chemical and physical processes. These characteristics open new
realms of scientific applications in the chemical, material, and
biological sciences

including fundamental studies of the interaction of intense x-ray pulses
with simple atomic systems, structural studies on single nanoscale
particles and biomolecules, ultrafast dynamics in chemistry and
solid-state physics, studies of nanoscale structure and dynamics in
condensed matter, and use of the LCLS to create plasmas.