1 brookhaven science associates nsls-ii: the accelerator systems briefing nsls-ii project advisory...

1 BROOKHAVEN SCIENCE ASSOCIATES

NSLS-II: the Accelerator Systems Briefing

NSLS-II Project Advisory CommitteeMay 24, 2007

Satoshi OzakiDirector, Accelerator Systems Division, NSLS-II Project


Outline

• Activities since the last PAC

• The accelerator systems

• Storage ring

–Harmonic number and circumference

–Re-arrangement of multipoles

–Three-Pole Wigglers

–Long and short straight sections

–Canting of damping wigglers

–Extra long straights

• Beam Stability Taskforce activities (Sam Krinsky)

• Response to comments and recommendations from the last PAC

• Near term staffing plan


The Accelerator Systems Division Activities

• Made good progress in the advanced conceptual design of the accelerator systems, taking recommendations from many reviews and advisory committees, and additional requirements.

• Design parameters for the external booster were fixed, and a concept for the procurement of the system was developed.

• The storage ring (CD-2) lattice has been put under a configuration control within the Division and will be released in a matter of days, after a few final refinements.

• Realistic storage ring hardware has been incorporated in the lattice design, including hardware for the insertion device straights.

• A more refined 3D simulation of the magnetic field, particularly for the interference between adjacent multipoles as well as a 3-Pole Wiggler and the dipole next to it.

• Visits to potential manufacturers of magnets, vacuum chambers, etc are being carried out to access their capabilities.

• An R&D experiment for vibrating wire alignment is under way, using multipole magnets borrowed from the Swiss Light Source.


NSLS-II Concept Concept

NSLS-II Machine Concept• New 3 GeV Electron Storage Ring• Large Circumference (791.5 m), H = 1320• “Compact” (~158m, H=264) booster • Large Current (500 mA)• Superconducting RF• Top-Off Operation• DBA30 Lattice (15 fold symmetric)• 15 short and 15 long straights• Ultra-Low Emittance (<1 nm)• Damping Wigglers (21m) (full built-out – 56 m)• Large Dipole Bend Radius (25 m)• Provision for IR Source (3 pair of Wide Gap D)• Three-pole wiggler x-ray sources

Technical Challenges• Lattice Design: dynamic aperture, energy acceptance• Source Stability: vibrations, thermal issues, feedback• Impedance Budget: Small gap (5 mm) ID tapers, etc• Insertion Device: CPMUs, EPUs, SCUs(?)


Storage Ring Harmonic Number and Circumference

• Recommendation of the 2nd Accelerator Systems Advisory Committee: “Rationalize the harmonic number of the storage and booster

rings.”

• RF Frequency = 499.68MHz

• HSR = 1320 (= 2 x 2 x 2 x 3 x 5 x 11): 791.472 m for SR circumference

• HBR = 264 (= 2 x 2 x 2 x 3 x 11): 158.944 m for BR circumference

• A large largest-common-denominator LCD): • A shorter dwell time for the injection time matching (~10 sec)

• Easily factorable H: • A wider range of fill patterns, particularly for a mixing of timing bunches

in a bunch trains.

• H = 1320 is particularly convenient for synchronization to mode-locked lasers


Storage Ring:• Circumference: ~791.472 m• Double bend achromatic lattice

with 15 long straights (~8.4m) and 15 short straights (~6.6m)

• Vacuum and other hardware for an insertion device will take away ~2.2 m from ID straight length

• Long straights for beam injection, RF, Damping Wigglers, and other insertion devices

• Short straights for narrow gap undulators for high brightness beams

• Space for 3-Pole Wigglers just upstream of the second dipole (length ~0.4m X 2) Impact of fifteen 3-Pole Wigglers is an enlargement of emittance by ~10%

Storage Ring Lattice Configuration


CD-2 Lattice: Half-Superperiod

4S 6S 3S


Three-Pole Wigglers

• The weak bend of dipoles: good for soft X-ray beamlines.

• A larger number of hard X-ray beams is desired, particularly with the transfer of the NSLS beamlines in mind.

• Studied a short hard-bend sector for the dipoles with minimal success.

• Introduce 3-Pole Wigglers at the upstream end of the second dipoles.

• The similar radiation power level as the dipole beamline at NSLS, but with a brightness more than 2 orders of magnitudes higher.

However, the impact of 3-Pole Wigglers to the storage ring is finite:

• 40 cm of space for the wiggler and another 40 cm on the opposite end of the dispersion straight, and repeat it for all sectors to maintain the symmetry added 24 m to the lattice length.

• Addition of the radiation in the non-achromatic region results in ~10% emittance growth for 15 3-Pole Wigglers.

• Small but a finite interference between the magnetic field of the dipole and 3-Pole Wigglers (~2/10,000 in dipole field integral), which can be easily compensated with trim current or changing 3-Pole to 5-Pole.


Canting of Damping Wigglers

• A 7 m long damping wiggler can be divided into two ~3 m long wigglers with canting magnets in between.

• The DW absorber system can handle the radiation with the total fan angle of 6 mrad.

• ± 0.25 mrad beam deviation from its nominal orbit and an additional ± 1 mm machining and alignment tolerances can be allowed. The electron beam is dumped by interrupting RF if it deviates more than ± 0.25 mrad.

Possibilities are:

• Straight DW (7m long) with ±3 mrad fan as with 100 mm period DW

or

• 2 mrad canting of two DW (~3 m long) with ±2.3 mrad fan as with 80 mm period DW

~12 kW

~53 kW


Extra-long Straight Sections

• There have been on-going discussions for the extra-long straight sections.• The idea behind this has been that it would be nice if an extra long straight can

give a higher flux by a factor 2 ~ 3. However, this gain as well as the soundness of such a straight has not been proven with a detailed analysis.

• Two ways to implement the extra-long straights:1.Insert an extra-long straight, the transfer function for which is a unitary

matrix for the on-momentum particles. This may impact the momentum acceptance, thus impacting the Touschek life-time.

2.Create extra-long straights by shortening short straights in adjacent cells in the standard DBA30 configuration.

• While keeping extra-long straights as the stretch goal of the Project, we have decided to consider the standard DBA30 as the CD-2 lattice baseline and use method 2 when the provision of an extra-long straight becomes necessary.


• The beam stability required: 10% or less of the beam size (~3m)• Settling and vibration (natural and self-inflicting) of the accelerator tunnel and

experimental hall floor/beamlines • Temperature stability• Mechanical engineering consideration• Magnet power supply and RF noise issue• Closed orbit correction with slow and fast feedback• Achievement of good stability must be a joint effort of Conventional

Facilities, Accelerator System, and Experimental Facilities Groups

• Beam Stability Workshop: April 18-20, 2007: Sam Krinsky• External Participants

• Extensive experience and lessons learned:

Beam Stability Requirement

M. Boege (SLS/PSI) J. Byrd (ALS/LBL)J. Chen (Taiwan) Y. Dabin (ESRF)R. Hettel (SSRL/SLAC) Chair J. Jacob (ESRF)J. Maser (APS/ANL) R. Mueller (BESSY)D. Shu (APS/ANL) J. Sidarous (APS/ANL)O. Singh (APS/ANL) C. Steier (ALS/LBL)


ASD Response to the First PAC Comments

• Organization Structure (Neutron Target vs. ID’s):In the case of the neutron target, the proton beam that hit the target is wasted, while in the case of ID’s, the electrons that passed through an ID have to remain in the storage ring while maintaining their specific property required for the stable and high brightness operations. Namely, ID’s, including the damping wigglers, are a part of the storage ring lattice, therefore they impact the electron beam quite strongly, especially for a 3 GeV ring. For this reason we have the insertion device group in the Accelerator Systems Division.

1. Reducing the horizontal beam size by lowering the value of the beta function is essential for many coherent imaging/diffraction beamlines. This flexibility should be built in the lattice from the beginning.

There are a number of competing factors in the lattice design. On the one hand, we wish to maintain maximum flexibility with many knobs, a robust dynamic aperture, and ultra small emittance. On the other hand, the economics dictate that the number of quadrupoles and sextupoles be minimized. Reduction of the horizontal function would have been easier with the quartet of quadrupoles as in the CDR lattice, but we anticipate reduction by a factor of 2 can be achieved even with triplet quads for insertion straights.


ASD Response to the First PAC Comments - 2

2. The beamline front end and a double redundancy (duplicate beam stops, duplicate safety shutters, duplicate PSS, etc).

We will present the beamline front end designs in this meeting. The accelerator safety rule is clear about the requirement of the double redundancy for the PSS system. We agree that it is necessary to reach a clear understanding with DOE soon on whether dual beam shutters are required or not.

3. The operation of x-ray BPMs on undulator beamlines.Our 3 GeV beam and tight alignment tolerances should reduce this radiation impact significantly. However, in view of the importance of photon BPM for sub-nm stability requirement, we plan to include a provision to shift the ID beamline from the line-of-sight from the insertion device straights in the storage ring layout. This, however, will have to be done carefully to keep the achromaticity of insertion straights for emittance damping and dynamic aperture control.

4. Top-up operation should be fully planned and included in the project scope and the project SAD should include all the requirements to perform top-up.

We agree that this is a critical issue that should be addressed in the design stage of the storage ring. Sam Krinsky was at the ALS/SSRS top-off safety review, and came back with a number of lessons learned.



5.There have been phenomenal improvements in undulator technology and the quality of available magnet materials suitable for x-ray FELs.

Improvement in some of the undulator technology and available magnetic material will be useful for us. Here again, we should note the different requirements between the undulator for FEL that is a one-pass device and that for the storage ring that have to satisfy the storage ring lattice condition

6.Procurement risks from overloaded qualified venders. The PAC would like to hear the planned approach at the next review with a complete risk analysis including an assessment of foreign currency risk exposure.

Yes, this is a significant risk issue. Presently, many of the prospective providers of the accelerator components are relatively busy with many accelerator projects in the world. Their status at the time of our procurements, i.e., in 2009 to 2011, is completely unpredictable, but we, so far, do not identify other major projects that may be running at the same time, and seriously impacting their capacity. The best way to reduce this risk is to begin procurement early, but the current funding profile prediction may rule out this possibility.



7. It is PAC's opinion that basic diagnostics for qualifying undulators and optics metrology capability should be part of the project.

The development of a well equipped insertion device laboratory has been one of major R&D activities beginning with the current fiscal year. Start-up of this program was delayed to the next fiscal year due to the continuing resolution and subsequent funding reduction.

8. The provision of the synchrotron infrared (IR) program at the NSLS, with its half dozen beamlines, is one of the features of the facility that makes it unique in the world. The way to provide a strong IR component at NSLS-II problem needs to be explored in much more detail, and contingency plans considered for maintaining it (including restoring the earlier plan for moving the existing IR ring to the facility).

We acknowledge that the IR beam program is an important one in the NSLS II era. We have reasonably good expectations that the storage ring will perform well with 3 pairs of wide gap (93 mm) dipoles for IR with a judicious simulation of the magnetic field of both narrow gap and wide gap.


Accelerator Systems Division Staffing

Current (FTE)

MOU and Contract

Requisitioned

Scientific Staff 10 1 1 Mechanical Engineer 4 4 3 Mechanical Designer 4 1

Vacuum Scientist 1

Electrical Engineer 1 1 2 Electrical Designer 2

Pulsed Power Engineer 0.5

RF Scientist/Engineer 1 LBNL 2 Controls Scientist/Engineer 0.5 2

Instrumentation Scientist/Eng 1 2

Total 22 7 14

• With formal recognition of the NSLS II Project, we began to have staff members dedicated to the Project since the beginning of FY 2007

•Notable Additions: F. Willeke from DESY: to arrive this summer as Director of ASD,•George Ganetis (SMD), Dick Hseuh (CA-D), Erik Johnson (NSLS)

: We have a candidate

: Relatively easy to find

: Very difficult to find


Summary

• We have made good progress in the design of the accelerator systems.

• The current lattice design incorporates the realistic ring hardware and typical beam front ends including absorbers.

• A high level project schedule, based on the anticipated funding profile, has been fixed, we will begin re-establishing the schedule for the accelerator system construction.

• The refinement for the cost estimate will follow the scheduling activity, to be completed well in advance of the November Lehman Review.

• Plan to hold technical design review of various subsystems of the accelerator system this summer.

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