SLAC NATIONAL ACCELERATOR LABORATORY
ACCELERATOR RESEARCH DIVISION
April, 2011
FY2011-Q2 Quarterly Report (Jan-Mar, 2011)
Table of Contents:
1. ARD Administration
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2. Advanced Accelerator Research Department
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3. Beam Physics Department
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4. Accelerator Design Department
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5. Accelerator Physics & Engineering Department
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6. Test Facilities Department
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A U.S. Department of Energy Research Facility Operated Under Contract by Stanford University
Accelerator Research Division Quarterly Report – 2001/Q1
1. ARD Administration
The Invited Accelerator Seminars during the quarter were:
 Mike Borland, APS, “A Comparison of Ultimate Storage Rings as Next Generation X-ray
Sources”
 Claudio Pellegrini, UCLA, “Fifth Generation FEL Light Sources”
 David Robin, LBL, “Novel Design of Gantry Optics for Carbon Cancer Therapy Accelerator”
 Pietro Musumeci, UCLA, “The Development of Relativistic Ultrafast Electron Diffraction: Using
Particle Accelerators to Watch Atoms Move in Real Time”
 Steve Geer, FNAL, “Muon Collider R&D”
These talks are posted on slacportal.slac.stanford.edu/sites/ard_public/ardhq/seminars/Pages/default.aspx.
FACET Construction At the end of the Q1, the FACET project was 80% complete and held 1.3M$ of
management reserve on an estimated cost to complete of 2.6M$. Mechanical installation in Sector 20
began in late Q1 and continued through Q2. At the end of March the project was 93% complete and held
400K$ of reserve on an estimated cost to complete of 1M$. It is expected that FACET construction will
be complete in early May, 2011 with first beam in mid-June.
2. Advanced Accelerator Research Department
AARD – Microwave Group:
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Structure Manufacturing Technology (Collaborative work with CERN & KEK)
o Coordinated the work for two TD24_VG1.8 structures. Finished construction: Structure with
SLAC flanges will be vacuum backed and tested at NLCTA, Structure with KEK flanges will
be held pending discussions with KEK.
o Completed one each from deflector structures T11 and T27. They have been installed at
NLCTA for the Echo-7 experiment.
o Worked to produce a T105 accelerator structure: Job submitted, needed machined parts sent
for quotation, mechanical design for the copper is ongoing.
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Novel Structure Designs
o Working on a Mechanical design structure for test of optimized shaped cavity (three cells –
optimized cavity cell and two coupling cells)
o Completed realistic design including initial mechanical design of accelerator cavity geometry
to be used in parallel-fed standing-wave accelerator structure.
o Finalized the design and now manufacturing a cryogenic system to test normal-conducting
accelerating structures at cryo-temperatures are progressing.

High-Gradient Experiments
o Testing a New PBG structure
o Tested Hard-copper highest-shunt-impedance 1C-SW-A2.65-T2.0-Clamped-Cu-SLAC-#1.
o Tested T18 Structure with a resonant ring
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Manufactured and delivered to collaborators:
o Reiterated on hard-copper-cells for advanced coating to Yale.
o Delivered Mode launchers for Argonne National Lab.
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Accelerator Research Division Quarterly Report – 2001/Q1
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RF Undulators
o Tested RF undulator structure and compared it to simulations with exceptional agreements.
o Designed a new type of end wall termination for the undulator with reduced fields
o Started looking a beam dynamics

Superconducting Material Research
o Continue testing new stratified media based on MgB2
o Continue testing new Nb samples
o Testing the newly fabricated structure cavity for testing residual resistance.
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Publications
o Roark A. Marsh Michael A. Shapiro, Richard J. Temkin, Valery A. Dolgashev, Lisa L.
Laurent, James R. Lewandowski, A. Dian Yeremian, Sami G. Tantawi, “X-Band Photonic
Bandgap (PBG) Accelerator Structure Breakdown Experiment,” Phys. Rev. ST Accel. Beams
14, 021301 (2011) [11 pages].
o
Lisa Laurent, Sami Tantawi, Valery Dolgashev, Chris Nantista, Yasuo Higashi, Markus
Aicheler, Samuli Heikkinen, and Walter Wuensch, “Experimental Study of RF Pulsed
Heating,” Phys. Rev. ST Accel. Beams – (accepted for publication).
AARD – Plasma Group:
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Worked with TFD to develop an integrated layout of the FACET IP area that accommodates
several experimental groups without the need for removal of experimental hardware between
runs.
Worked with TFD and controls department to experimental protection system (EPS) and
necessary interlocks and controls for the plasma oven.
Worked with beam physics department to develop alternate FACET optics to produce shaped
drive bunches for high transformer ratio PWFA experiments at FACET.
Worked with beam physics department to develop optics multi-knobs to introduce x-z and y-z
correlations on the beam at the plasma entrance to make parametric measurement of the electron
hose instability.
Developed a configuration for installation of a one-meter long x-band deflecting cavity in the
FACET beamline upstream of the IP that provides the required experimental resolution (30 fs)
with existing infrastructure and nominal optics.
Completed SAREC review of FACET proposals – PWFA proposal received the highest possible
rank from the committee (Excellent).
Delivered Two oral presentations, 6 posters and 7 presentations at PAC11 New York.
Hosted FACET satellite meeting at PAC11 with 35 attendees.
AARD – Laser Group:

NLCTA Beam Tests
o Successfully detected wakefield radiation in 4 different photonic crystal test fibers excited by
the NLCTA electron beam.
o A near-IR spectrometer was used to spectrally analyze the radiation from one of the
commercial fibers within the bandgap region, providing first demonstration of e-beam
coupling to TM modes in an optical scale photonic crystal structure.
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Accelerator Research Division Quarterly Report – 2001/Q1
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A Mach-Zehnder Interferometer was adapted for use with a free-space TEM01* mode, with the
intention of measuring phase length dependence on temperature for TM rather than TE fiber
modes. A TM mode was successfully excited and observed.
Designs completed and parts ordered for construction of a tunable optical parametric oscillator
(OPO) to be used for alignment testing of prototype silicon woodpile accelerator structures in the
4 to 5 micron wavelength region.
Silica gratings with the proper aspect ratio and line spacing for 800nm wavelength operation were
successfully fabricated, and techniques were explored for making a spacer layer to separate two
gratings to create a prototype accelerator structure.
Simulations conducted of newly proposed laser-driven dielectric structure for transverse
confinement of electron beams showing successful excitation of focusing fields by an externally
coupled Gaussian laser pulse.
Simulations performed to model various components of coupling schemes for the woodpile
accelerator structure, indicating up to 70% coupling efficiency from free space Gaussian mode to
on-chip silicon waveguides and 95% efficiency for coupling to accelerating channel by a sidecoupled photonic crystal waveguide T-junction.
AARD – Feedback and Dynamics Group:
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Integration of realistic feedback model into CMAD particle dynamics code - allows evaluation of
instability dynamics, impact of realistic feedback ( bandwidth limits, offsets, noise)
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Testing of 100W 1 GHz amplifiers for upcoming SPS MD - intergration of power stages into 4
GS/sec. excitation system
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LHC MD results focused on longitudinal diffusion from RF system noise
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Sho Uemura ( Stanford Physics) has joined the group as a student RA.
3. Beam Physics Department
Collective Effects:
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Daniel Ratner successfully graduated with thesis defense.
Systematic studies of the emittance exchange. A method is proposed to achieve exact phase space
exchange, i.e. mapping x to z, x' to delta, z to x and delta to x'. The work is documented in a
PAC11 proceedings paper.
A triple modulator-chicane scheme for seeding FELs is proposed. The scheme has the advantage
that ultrahigh harmonics can be generated while simultaneously keeping the energy spread
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Accelerator Research Division Quarterly Report – 2001/Q1
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growth much smaller than beam's initial slice energy spread. The paper is submitted to New
Journal of Physics.
Work on noise and coulomb collision effects in the EEHG.
Work continued on ECHO-7 commissioning. The 5th harmonic at 318 nm with the EEHG
technique was observed in January 2011 and in the following months the in-vacuum UV
spectrometer was tested and observed coherent harmonic radiation at 266 nm from the 800 nm
seed laser.
Work on foil emittance partitioning.
Work on CSR calculations using direct numerical solution of Maxwell’s equations.
Work on wakefield calculation in the interaction region of the ILC.
Study dynamic aperture on low emittance (7nm) optics of SPEAR3;
Study of synchrotron oscillation on cross-correlation on the bunch length measurement in
SPEAR3
Study of the beam ion instability in SPEAR3
Principle study on LCLS fs bunch length measurement using ionization electrons
Simulation of electron cloud in CESRTA
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Talks and papers (with abstracts):
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FEL Physics:
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Finalized LCLS-II CDR and prepared for CDR review.
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A single-shot electron bunch length measurement technique has been tested on the LCLS with ~1
fs resolution achieved.
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A new method is developed to measure the ultra-short soft x-rays pulse length through the
analysis of the statistical properties of the SASE FEL spectra. The method has been
experimentally demonstrated at LCLS. Different x-ray bunch lengths have been measured
keeping the electron bunch charge fixed at 250 pC and manipulating the peak current from 1.5 kA
to 3kA. Bunch length has been also measured for different number of undulators. Finally using
the slotted foil to obtain shorter pulses, x-ray pulse lengths down to 13 fs FWHM have been
measured.
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Investigated the use of x-band deflector to measure single-shot fs electron and x-ray pulse
duration that is applicable to wide operating conditions.
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Worked on optimizing the undulator tapering in a self-seeding scheme to reach terawatts (TW)
FEL for LCLS-II. Empirical solution to have a TW FEL is found to be feasible within the planned
upgrade scheme for the LCLS-II undulator system. Analytical estimate and simulation code
development within Genesis are ongoing.
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Studied the scheme of introducing density modulation on the electron bunch before it enters the
undulator. The density modulation period has been compressed to nm level to generate coherent
soft X-rays.
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Developed a general 3D FEL theory when the transverse beam size varies in the undulator.
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Accelerator Research Division Quarterly Report – 2001/Q1
Advanced Computation Group
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Three talks were given in PAC11, including an invited talk about the simulation of the two-beam
acceleration system.
Beam Optics & Non-Linear Dynamics
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We have completed the ERL configuration study. The results of the study were documented in
two papers presented in the PAC 11.
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We continued to design an ultimate storage ring based on the PEP tunnel. Since the last report,
we have added damping wigglers to reduce the equilibrium emittance further down to 15 pm-rad .
Emittance growth due to the intra-beam scattering was about a factor of two at 200 mA beam
current. This extremely low emittance makes the Touschek lifetime much longer than one hour.
That is significant improvement from the baseline design. Currently, we are optimizing the
dynamic aperture of the lattice.
4. Accelerator Design Department
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ILC Systems R&D:
o
In FY11, about 20 SLAC physicists attended the IWLC meeting in Geneva in October, and
12 SLAC physicists attended the ALCPG meeting in Eugene in March. They also attended
meetings of the IDAG and AAP and participated in the change control review process.
o
Electron Source: The group received the KMLabs laser produced under an SBIR at the end of
Q1. A pair of 18W, 515 nm pump lasers will be incorporated into the final stage amplifier of
the KMLabs system to increase the laser output to 3 MHz.
o
Damping Rings: The electron cloud Working Group gave a preliminary recommendation for
ecloud mitigation in Q1. The WG is now preparing a detailed report due by early 2012.
There was also work on the 3.2 km damping ring design, including optics, dynamic aperture
and simulations to assess the impact of reducing the bunch spacing to 3ns. For the CesrTA
program, there was continued work on ecloud build-up simulations and on instability
simulations. This work will be part of the CesrTA phase I report.
o
Accelerator Physics: In FY11, this has mainly involved studies related to the proposed costsaving changes to the baseline design that impact the linacs. In particular, studies were done
on the (1) rf overhead needed to accommodate the ~ 20% spread in sustainable cavity
gradients, (2) configuration of the KCS and RDR rf distribution systems for operation with
half the number of bunches per pulse and (3) operation at higher repetition rates at lower
beam energies, in particular, running at 10 Hz with 125 GeV per beam ‘collision’ pulses
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Accelerator Research Division Quarterly Report – 2001/Q1
interleaved with 150 GeV electron beam pulses that produce positrons at the end of the
electron linac.
o
Machine Detector Interface: The MDI group continued to study the performance of a
platform-based support for the SiD detector and concluded that such a solution was indeed
allowable, given the inter-bunch feedback system. A document “Functional Requirements of
a SiD Platform” was presented at the ALCPG meeting in Eugene Oregon in March 2011.
Progress on this front was labeled one of the most significant accomplishments of the
meeting.
An analysis of HOM induced heating near the IP was completed and presented at the
ALCPG, taking into account the detailed engineering design of the beam pipe in the 7m
surrounding the interaction point. For the ILC bunch structure and bunch length, neither
trapped mode nor resistive wall heating appears to be a problem.
The paperwork required to transfer funds to the University of Michigan to develop a
frequency scanning interferometer based alignment system was completed. Results from new
hardware should be available by the time of the next report.
o
ATF2 Test Facility : At least 2 members of the SLAC ATF2 team participated in all beam
operations during January – March 2011. Beam operations stopped March 11 due to the M9.0
earthquake in Eastern Japan; we expect full operations to commence again from fall, 2011,
after reconstruction and realignment work is completed. There was an ATF2 collaboration
meeting at SLAC in January to discuss progress towards the main ATF2 goals.
The targets on the 4 OTR systems were replaced with Al and Aluminized Kapton targets. The
OTR system is now fully operational and routinely used during tuning operations with a
measurement time of <2 mins (compared with many hours with the wirescanner system).
SLAC is taking a leading role in the development of the readout system for the IP region
cavity BPMs which need to read out the position of the electron beam at the IP waist to very
high precision; ideally <2nm vertically. This will be based on the SLAC digitizer boards
developed for LCLS BPMS
SLAC has worked together with magnet engineers at KEK to now have an accurate computer
model of the ATF2 beamline including a precise description of the measured sextupole and
octupole fields in all the ATF2 magnets. This data will be used to optimize the ATF2 optics
to account for these fields and develop a new magnetic configuration of the machine for
future runs.
o
Ultra-fast ATF2 Extraction Kicker: Progress has been made on demonstrating a new
topology to eliminate the pre-pulse and there was a brassboard circuit demonstration of the
output pulse. A vendor to fabricate a second generation hybrid has been identified and a
conceptual design for an ultra-fast discrete component driver developed.
o
High Availability Controls: The Marx P2 interlock design requirements, design and prototype
fabrication are complete except for high level software. The companion analog Rear
Transition Module board is designed and beginning layout.
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Accelerator Research Division Quarterly Report – 2001/Q1
The major labs in the MicroTCA Standards collaboration now include CERN, DESY, FNAL,
IHEP, IPFN, ITER, LBNL and SLAC, with ESSB (European Spallation Neutron Source
Bilbao) in process of joining. Standards are being reviewed for the MicroTCA extension now
known as PICMG MTCA.4, for the Rear Transition Module (RTM) interface ATCA
PICMG3.8, and on a guideline for a distribution system for precise timing and triggers on the
large-system backplane. The operating system under Linux is developed and operational
including hot-swap capability. MicroTCA was proposed both for the RF and main linac
upgrades needed for LCLS I&II and future experiments using the linac.
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ILC RF system: The SLAC effort is focused mainly on developing lower cost and more reliable
rf components for the main linacs. Areas of research include:
o
Marx Modulator: The P1 Marx backplane was replaced with a more robust version to reduce
corona damage. Also, the P1 Marx continued operation 24/7 at half pulse width while the
capacitor lifetime problem was being studied in a separate test stand. During the > 1000 hours
of operation of the P1 at this narrower pulse width, there have been few faults and no
measureable loss of capacitance. All of the major components for the P2 Marx have been
purchased, and the upgrade of DTI Marx has started.
o
Global RF Distribution: The windows and some of the rectangular waveguide were upgraded
on the 10 m ‘Big Pipe’ section. It recently ran for over 100 hours with no breakdown at 265
MW (at the 280 MW design power, there is a breakdown every few hours). With HEEC
approval, the pipe pressure will be increased from 15 psig to at least 18 psig to see if this
allows for stable operation at higher power. For Phase II of this project, requests for bids for
80 m of new pipe (rated for 30 psig) were placed and a preliminary design completed for a
support system to mount the pipe. Also, the rf design for the required 90 degree waveguide
bend is nearly complete.
o
Local RF Distribution: A second generation, 8-feed, variable power rf distribution system is
being built for FNAL’s second cryomodule. This version has remote-controlled phase shifters
to adjust the power split among the cavities. The first two- feed sub-unit has been cold tested
and will be high power tested soon.
o
Couplers: Two failed cold coupler sections returned to SLAC by FNAL were extensively
examined. These couplers had been returned to CPI for repair after initial inspection at
SLAC, and their resulting ‘fixes’ seem to have caused damage that lead to subsequent
breakdown and copper removal problems at FNAL when they were eventually used to power
SC cavities. Currently, the issue of copper particles coming loose during ultrasonic cleaning
of the copper plated couplers is be examined. For this purpose, various samples (pure copper,
CPI plated copper with and without bead blasting, and SLAC-plated copper) are being
ultrasonically cleaned and the number of copper particles that come loose are being
measured.
o
For the ILC Electron Sources, a Kapteyn-Murnane Laboratories (KMLabs) ILC laser was
shipped to SLAC in Q1 FY11. This laser system was developed by KMLabs under a SBIR
Phase II proposal. Prior to shipment, this laser was observed to produce a full energy ILC
source laser pulse train at 1.5 MHz. A pair of 18W, 515 nm pump lasers will be incorporated
into the final stage amplifier of the KMLabs system to increase the laser output to 3 MHz.
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Accelerator Research Division Quarterly Report – 2001/Q1
The plan developed in conjunction with JLab to demonstrate an ILC specification source
beam at SLAC in FY11 and then at JLab in FY12 has been modified. SLAC will continue
with the ILC source laser development while JLab continues development of a high voltage,
high gradient ILC dc photogun. It has been agreed that SLAC will take the lead in the writing
of the Electron Source chapter for the ILC Technical Design Report.
o
For the ILC Damping Rings, SLAC is coordinating the international Working Group on the
electron cloud R&D. The Working Group gave a preliminary recommendation for the
electron cloud mitigation in October and it is now preparing a detailed report document due
by early 2012. In collaboration with INFN Frascati, we worked on the DR optics and on the
dynamic aperture for the selection of a baseline 3.2 km damping ring design to be included in
the TDR-II. For the CesrTA program, we worked on build-up simulations for quadrupole
and wiggler regions and worked on instability simulations to include radiation damping and
more realistic electron cloud distributions over the CesrTA ring. This work will be part of the
CesrTA Phase I report.
o
For the ILC Machine Detector Interface (MDI) in FY11-Q2, seven MDI meetings took place
and the results were presented at the ALCPG meeting in Eugene, Oregon in March 2011.
Details of the weekly meetings are available at
http://ilcagenda.linearcollider.org/categoryDisplay.py?categId=188.
At the ALCPG meeting the SiD collaboration committed itself to the concept of using a
platform to accomplish push pull operations with the ILD detector. A list of functional
requirements for the platform was developed and presented as input to the ILC Conventional
Facilities group, who are responsible for the detailed engineering of the system. Work
continued on measuring the vibration properties of various concrete blocks to validate the
analysis models, a Frequency Scanning Interferometry (FSI) based alignment system, a reevaluation of SR backgrounds, and an analysis of HOM induced heating near the IP. A grant
request by U. Michigan for FSI work that was submitted to SLAC was finalized.
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FNAL Project X: SLAC received 400 k$ in PX funding from FNAL for FY11. It will be used in
part to study possible 650 MHz, 30 kW rf sources for the PX CW linac, in particular, to examine
solid state sources, which are becoming cost competitive with IOTs. Recently, two US vendors
provided cost estimates for 30 kW and 2 kW 650 MHz solid state sources. For the 3-8 GeV PX
pulsed linac, possible long pulse (up to 25 ms) klystrons and modulators will be examined –
currently design and cost studies of Marx modulators for this application are being done.
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X-Band: The SLAC X-band program includes testing CLIC prototype structures, developing and
testing a Dual Mode Cavity to better understand breakdown limitations, developing an X-band
gun (with LLNL) and associated test beamline (XTA), upgrading the X-band systems at NLCTA
in support of other programs there, developing X-band linac designs for light source applications
and designing a more robust 50 MW XL4 klystron. Progress is summarized below.
o
CLIC: The T24 structure was operated for an additional 100 hours longer but no
improvement in breakdown rate was observed. The TD24 structure was assembled using cells
provided by KEK, and will be tested next.
o
Dual Mode Cavity: Stn 1 and Stn 2 were configured to power the two cavity modes
independently. The results showed that the breakdown rate increased significantly for a fixed
surface electric field when the pulsed heating from the TE mode was increased above about
50 degC. These results were presented at PAC11.
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Accelerator Research Division Quarterly Report – 2001/Q1
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o
X-band Gun: Construction was started for the 5.59 cell X-band gun (Mark 1) and assembly
was completed of a partially fabricated gun (the 5.5 cell Mark 0) from an earlier project. This
latter gun will be tested without beam in ASTA in FY11-Q3 to measure breakdown rates and
dark currents. At LCLS, studies were done to improve the bunch emittance from their S-band
gun by using a truncated-Gaussian-shaped laser pulse.
o
XTA: A new beamline in NLCTA (called XTA) is being constructed to test X-band rf guns.
The design for this beamline is nearly complete, a number of the parts have been ordered and
the control system, which will use many of the data acquisition modules developed for LCLS,
has been mostly defined.
o
NLCTA Upgrades: The spectrometer magnet bend angle was increased (from 12 to 30
degrees) to improve resolution. Also, the fabrication of two deflecting cavities was completed
and waveguide and other rf components (e.g., phase shifters and loads) that will power them
from Stn 1 and Stn 3 were prepared.
o
Light Sources: For an all-X-band linac, bunch energy linearization can be achieved using the
T566 component of the first bunch compressor chicane if higher harmonic rf is not available.
Several options for such a linearization system were simulated and shown to provide high
current bunches similar to those in LCLS.
o
Linac Optimization: A study was completed of optimized S, C and X-band TW structures for
the cases of short (50 ns) and long (1250 ns) bunch train operation with low beam loading.
The latter case is applicable to the proposed MaRIE project at LANL (they visited SLAC and
we visited LANL this Quarter to discuss this project). The results show that X-band has the
advantage of providing a higher gradient with equal (long pulse) or higher (short pulse) rf-tobeam efficiency. This work was presented in an invited talk at PAC11.
o
XL4 Klystron: A program was started to design a longer (6 cell vs 4 cell) output section for
the XL4 klystron with the goal reducing the surface fields by about 15% - this will hopefully
lead to more robust operation of the tube at 50 MW. A design has been completed and
currently studies are underway to see if other modes will be excited by the beam.
LARP: For the collimator project in FY11 Q2, we:
o
Finished the final rotation tests of the 20-sided rotatable collimator jaws in test mode. Test
mode means that the jaws were free to rotate without their cooling tubes attached to fixed
points and forced to wind up during rotation. The baseplate with now welded steel jaw
supports was lowered onto the two jaws while they rested on a granite table. The jaws were
attached with the final version of the rotation bearing housing, nuts and spacers. The final
versions of the rotation drives, anti-backlash pawl assemblies, rhodium coated RF "wipers",
BeCu RF foils and thermistors holders were attached to the jaw ends. These last 3 items are
designed to provide 0.1 mOhm resistance between the jaw surface and the end of the vacuum
tank for each rotation of the jaw. This was tested and after considerable tuning, achieved. The
post which holds the claw that actuates the rotation mechanism was welded to the baseplate.
The jaw translation drive mechanism was checked for limits of travel and limit switches and
various hard stops tuned for proper interaction with the actuator. The rotation actuation was
reconfirmed under load. A fixture to rotate the entire assembly in phi was designed, built &
installed. This allowed us to put the baseplate in the correct position for each test in a very
safe and controlled manner. At this point everything was disassembled. Each end of each
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Accelerator Research Division Quarterly Report – 2001/Q1
facet of each jaw had 3 lines scribed to allow for optical alignment through ports in the
vacuum vessel and the jaw facets numbered with a punch. The cooling tubes coming out of
the collimator jaws were carefully bent to 90 degrees.
o
Completed final assembly and rotation tests in a mode where the tubes must be twisted during
rotation (and thus the number of such tests are limited). The baseplate was lowered onto the
jaws for a final time capturing the cooling tubes through minimal clearance feedthroughs in
the baseplate. The jaws were reattached to their moveable supports with the bearing housings
and then the unit rotated to its normal orientation of jaws up, baseplate down. The housings
were tack welded in place. The rotation drives and pawls were remounted. The RF foils and
thermistor holders with thermistors were attached and functioning verified. The first rotation
test with tube twist was performed; alignment was excellent before and after; gear
functioning was flawless. Resistance measurements were as before. Then the molybdenum
rotation housing was tack welded via steel support wire to prevent any future movement and
its mounting screws welded to each other with a thin steel plate. The actuator claw was tack
welded to its support post. A second pair of rotation tests were performed successfully and
the decision to place the unit inside its vacuum vessel was made.
o
Welded the vacuum tank to the baseplate and leak checked, sealing the cooling tube
penetrations with 4 cylinder-covers equipped with O-rings. Leak rates of 1e-10 mbar-l/sec
were achieved. The rest of the period was spent arranging for someone to do the copper tubecopper feedthrough TIG brazes.
o
Other LARP efforts: A wide-band feedback system is proposed to stabilize intra-bunch
instabilities driven by electron-clouds or transverse mode coupling (TMCI) in the CERN
SPS. In support of this project, SLAC has started to work on incorporating into the C-MAD
code a detailed and realistic model of the intra-bunch feedback system to analyze its impact
on the beam emittance and stability. The objective is to simulate the feedback control by
using 16 samples per bunch to process the feedback algorithm, which is equivalent to a 2.6
Giga-Samples/sec sampling frequency in the ADC/DACs and processing channel, which is at
the limit of the available technology. With a realistic model of the hardware, it will be
possible to design a feedback system suitable for suppressing electron cloud and TMCI.
A grooved insert has been installed into in a dedicated test area of the CERN SPS beam line.
We received the preliminary results of short tests made in March. The measured electron
cloud current signal for the grooved insert was a factor of 2 to 15 lower, depending on the
beam parameters, than a reference smooth metallic surface of the same material.
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SuperB: No further work was done on the Super-B project pending direction from the DOE.
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End Station A: We (Mauro Pivi and the Test Facilities Department) are working on reestablishing the End Station A Test Beam (ESTB) at SLAC. A small fraction of the 13.6 GeV
electron bunches from the Linac Coherent Light Source (LCLS) will provide test beam
capabilities in the large End Station A (ESA) experimental hall for accelerator instrumentation
tests, accelerator R&D, particle and particle astrophysics detector research, linear collider
machine and detector interface studies, radiation-hard detector development and material damage
studies.
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Accelerator Research Division Quarterly Report – 2001/Q1
Currently the plan includes the installation of one kicker magnet with a stainless steel chamber in
the Beam Switch Yard during Spring 2011. This will allow early commissioning of the kicker
system with the bunches deflected into a beam line upstream of End Station A. As soon as a new
Personal Protection System for ESA is completed later this summer, and a new beam dump is
installed in ESA, a low energy beam will be run into ESA to start commissioning of the complete
test beamline. In late October, we will install four new kicker magnets with ceramics chambers
(to reduce eddy currents) in the Beam Switch Yard and start operating the ESTB at higher beam
energy in November.
In March, we hosted the first ESTB Workshop, which attracted 50 attendees from 16 outside
institutions, underlining the broad interest by the community for a beam test facility. Ahead of the
workshop, we received eight proposals with requests for beam time.
5. Accelerator Physics & Engineering Department
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ATF2: The ATF2 is a test facility designed to demonstrate the linear collider final focus optics
using the low emittance beam from the ATF damping ring at KEK in Japan
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The ATF2 non-linear optical system requires the development of new tuning algorithms
which are tested on a simulator, then implemented on the accelerator. A new tuning algorithm
that does not require an operating spot size monitor was developed and tested in simulation
because the laser spot size monitor (developed by Tokyo University) has been unreliable in
recent runs.
The ATF2 uses 37 C-band cavity BPMs with electronics designed by SLAC, cavities
constructed by KEK and Pohang and algorithms and software developed at RHUL. The
cavity BPM system including the IP BPMs were commissioned this quarter.
Work at the ATF2 was halted by the disastrous March 11 earthquake which caused some
damage to ATF ring and ATF2. This quarter we expect to find out KEK’s plans for ATF2.
CLIC has become more heavily involved with ATF2 and is doing optics optimization using
MADX/MAPCLASS and investigating ultra-low beta* / ultra-high chromaticity optics, and
new final focus quads.
CTF3: The CTF3 facility at CERN is designed to demonstrate the high current drive beam
generation and two-beam acceleration required for the CLIC collider
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The CLIC drive beam BPM design was completed and prototypes are being fabricated.
The CLIC main beam BPMs conceptual design is underway with possibilities of a common
design with LCLS_II and the Pohang XFEL.
Studies of the transverse and longitudinal wakes of both main beam and drive beam BPMs
were done
Conceptual design of readout electronics for CLIC beam instrumentation is underway.
Calculation of beam impedances for damping ring, combiner ring, and drive beam turnaround
tapered stripline kickers is underway.
Writing of Conceptual Design Report (CDR) sections on BPMs and beam instrumentation is
underway.
An initial feasibility study is underway for a CLIC quadrupole stabilization demonstration
experiment at JLAB. The CLIC design requires main beam quadrupole magnetic field centers
to be stabilized to less than 2nm rms in a bandwidth 2 - 25 Hz. This is considered a
“feasibility issue” and performance should be demonstrated.
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Accelerator Research Division Quarterly Report – 2001/Q1
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FACET: FACET is a SLAC project to use the front 2 km of the linac, damping rings and positron
system to generate high peak current test beams for plasma wakefield acceleration and other
experiments.
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The preparation of the Sector 0-20 systems, damping rings and FACET experimental area is
continuing and is completed in time for the scheduled turn-on.
FACET feedbacks are under development and expected to be ready to start commissioning
for beam turn-on.
The Pyroelectric detectors for the FACET bunch length monitors have been fabricated and
the remainder of the system is expected to be completed next quarter.
The SAREC committee decided that the FACET THz source required more science
motivation. The THz power produced at FACET will be measured, but plans to transport the
THz to an experimental area are on hold.
Beamline models and MAD decks are being updated.
LCLS: The SLAC X-ray FEL system, now providing user beams.
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Due to a calculation error, the X-ray beam divergence from the LCLS is 2x larger than
originally estimated and overfills the hard X-ray mirrors. A design was developed to install a
Be focusing lens in the X-ray diagnostics chamber (“ST0”). Unfortunately the commercial
UHV motion system was delivered very contaminated and could not be installed. We expect
to have parts from an alternate vendor installed next quarter.
The phase cavity timing noise problem that developed last quarter was tracked down to a
loose cable in a RF chasis and has been corrected. New phase cavity electronics designed to
operate at low charge have been installed and will be ready for operation at the end of the
down.
Short bunch (few-femtosecond) operation of the LCLS based on low charge (20-40pc) and
the slotted spoiler is regularly used by experimenters, however the existing diagnostics cannot
resolve bunches below 20 femtoseconds. A conceptual and optical design of a single shot
broad-band (6-50um) infra-red spectrometer for bunch length measurement was completed.
Fabrication of this system has been delayed by parts delivery times, but tests are expected to
begin next quarter.
The slotted-foil ultra-short X-ray pulse generation system is being upgraded with a new high
precision foil to allow shorter pulses and more flexibility.
The thermal-acoustic X-ray energy monitor has passed vacuum testing and will be ready for
beam operation after the down.
The LCLS THz source was used to demonstrate both linear and non-linear autocorrelation
scans.
A THz pump / X-ray probe test is being designed to be installed in the Undulator hall. This
will demonstrate the feasibility of this type of experiment before the THz line to the NEH is
constructed.
The Be solid attenuators are being replaced with diamond and Silicon to reduce beam
distortions. Some attenuators will be ready at beam turn-on, others are waiting for material
delivery.
The noise performance of the LCLS gas attenuator was found to be partially due to issues
with photomultiplier saturation and pulse timing changes with beam energy / gas pressure.
The PMTs are being replaced with high-signal tubes and the software is being modified to
allow gate timing and PMT high voltage to be automatically adjusted for different operating
conditions. A wiring problem on the gas detector solenoids was also found and corrected.
This work is expected to be completed next quarter.
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Accelerator Research Division Quarterly Report – 2001/Q1
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LCLS_II: The LCLS_II is a project to construct a new XFEL facility at SLAC to provide
additional capacity for more simultaneous user experiments.
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The LCLS_II CDR was completed and presentations for the CD-1 review are being finalized.
LHC: Large Hadron Collider at CERN.
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The LCLS orbit response calculation is now able to fit BPM gain and roll angles of BPMs,
quadrupoles and corrector magnets. This will allow better characterization of the LCLS
optics.
A high resolution screen and optics were installed in PR18 in the A-line which allowed fewfemtosecond temporal resolution measurements.
A total of 4 thin Be foils have been damaged in the undulator / beam dump area. APE is
investigating alternatives to Be in these applications and has put a hold on installing more Be
foils in the vacuum chamber.
APE has been supporting the LINAC upgrade project to convert the RF system from SLC to
EPICS.
The fast feedback pulse by pulse control system is being used to develop semi-noninvasive
pulse-stealing diagnostics.
The LHC synchrotron light monitor is used to measure beam profiles and to detect particles
in the abort gap. Upgrades to the optical system were installed during the shutdown this
winter.
The forward proton detector system at LHC requires few-picosecond timing stability over
several hundred meters. Last quarter a copy of the coax distribution system developed for
LCLS demonstrated the required stability (scaled with cable length). Further development is
waiting for funding from LHC or LLNL.
In 2010 the DCCT used to measure average current in the LHC rings showed fill-pattern
sensitivity. The modifications implemented during the year-end shutdown, a repartioning of
gain and bandwidth profiles and an improvement of RF bypassing, appears to have solved
saturation problems. Beam tests this quarter have shown sufficient available headroom to
meet LHC needs until the 2013 shutdown. Additional benefits include improved signal
monitor bandwidth and improvement in matching of behavior of the devices in the
accelerator with the one in the lab. The LHC fast current transformer showed position
sensitivity, the cause of which has been identified, and a proposed solution is seen to work in
the lab, but has not yet been implemented
NLCTA: Test accelerator using X-band RF
o The operation of the NLCTA has been limited by the lack of automated tuning and feedback
systems which has made it difficult to reproduce beam conditions. Scripts and high level
applications from LCLS are being adapted for use at NCLTA. These include profile monitor
and emittance GUIs and the Schottky scan script.
o NLCTA / ECHO decks and models are being updated to include the new spectrometer and Xband TCAVs
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Accelerator Research Division Quarterly Report – 2001/Q1
6. Test Facilities
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ASTA report: The ASTA facility includes two s-band 50 MW klystrons who output can be
combined, a variable length pulse compressor with an output of up to 500 MW and an extremely
flexible RF system that is well suited for fast turnaround of experiments. The ASTA bunker’s
shielding is rated for up 100 MeV beam energies. At present is used extensively for testing of all
sorts of short RF structures and for testing materials that can be used in RF structure manufacture.
With a modest upgrade ASTA can be used to test RF guns. The past quarter activities in ASTA
were:
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Operations for the High Gradient structure tests (see also AARD-Microwave report,
PETS2 and C10-VG0.7.5).
Planning for relocation of the cryogenic test stand into the ASTA vault.
Planning for upgrading facility for 24/7 and for remote operations from the NLCTA
control room. 24/7 operation requires design and installation of a fire-suppression system
for the modulators. Remote operations require upgrading the ASTA control system to
EPICS and upgrading the monitoring systems for remote readout and display. Parts for
the remote operation of ASTA have been purchased and are being installed. The fire
suppression system is under design review by SLAC.
A design for a spectrometer magnet can be use to characterize dark current coming out of
an RF gun.
Continuation as last quarter
NLCTA report: The NLCTA facility is housed in End Station B (ESB). At its heart is a former
320 MeV x-band linac (from the NLC project) with an s-band injector and an output beam line
and dump. The accelerator components are in their own enclosure inside the ESB hall. The past
quarter activities using NLCTA were:
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Provide beam for E163 and the ECHO experiments (see also AARD-Laser for more
E163 information).
Provide a home for testing x-band RF. (see???)
Continued to rebuild the x-band two-pack for future use in the NLCTA accelerator as
power source for one transverse cavity, and long term testing of XL4 klystron tubes.
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Accelerator Research Division Quarterly Report – 2001/Q1
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Continued upgrading the NLCTA beam line with addition of two transverse cavities for
increasing the beam energy spread and improved slice emittance measurement for the
ECHO-7 experiment.
Refurbished the dump spectrometer to a factor 3 better resolution.
Started to convert the NLCTA control system to EPICS, which will allow a more
homogeneous integration with higher level beam applications provided by the controls
department.
Continued the design of a new x-band test station in the beam dump area. This station
will have an x-band gun and some beam acceleration capability.
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FACET User Area report: In anticipation of FACET construction completion (see status in ARD
Administration section), planning on the experimental user area and the purchase of a trailer for
FACET users is proceeding. Detailed installation planning for the user experiments has started.
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End Station A: It is planned to have a new electron test beam in ESA (End Station Test Beam,
ESTB). Comissioning of the ESTB is expected in Winter of 2011. This test beam will provide the
full range of electron energies up to 13.6 GeV, and intensities from single particles to .25 nC/
bunch. It will be used primarily for detector R&D and machine developments. The designs for
kicker magnets and ceramic beam pipes to extract and transport beam from the LCLS linac to
ESA have been completed and are being fabricated. The implementation of the PPS system for
ESA has been started. A one day workshop on March 17, 2011 was met with overwhelming
response of 50 participants from 16 institutions. Eight test beam requests were submitted. The
first official user run is now scheduled for February 2012.
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End Station B: In addition to housing the NLCTA, ESB also supports a range of high power RF
source development activities (in collaboration with the Accelerator Design Department and
others).
o MARX modulator testing. The failure of the MARX modulator capacitors under full load
has led to a study to measure capacitor aging. In the meanwhile the MARX modulator is
being run at reduced pulse width but with same power.
o The Cluster-Klystron concept prototype was installed on the NLCTA enclosure roof and
tested. Planning for a full scale test (160 meter big pipe) installed in the ESB has started.
o The two-pack system LLRF has been upgraded and modulator mods have been made to
facilitate design testing by AED’s Power Conversion Department. A fire suppression
system for the two-pack system has been installed.
o TTF3 coupler testing.
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Continuation as last quarter
ECHO Experiment: Echo-7 is a proof-of-principle echo-enabled harmonic generation (EEHG)
experiment which is being performed at the NLCTA at SLAC. The experiment aims to test the
physics of the EEHG concept and demonstrate scaling. The 3rd, 4th, 5th, 7th, and possibly 15th
harmonic of a 1590nm seed laser will be generated through the EEHG scheme. In contrast to
other schemes for generating harmonic bunching (e.g. HGHG), higher harmonics can potentially
be reached with EEHG; in fact, due to the remarkable up-conversion efficiency, soft x-rays may
be reached directly from a UV seed laser.
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After a successful summer 2010 run which provided a qualitative confirmation of the
ECHO theory, planning for an experiment aimed at making quantitative measurements by
summer of 2011 are underway
Continuation as last quarter
For technical improvements: see NLCTA
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