1 brookhaven science associates nsls ii: the accelerator system briefing experimental facilities...

1 BROOKHAVEN SCIENCE ASSOCIATES

NSLS II: the Accelerator System Briefing

Experimental Facilities Advisory CommitteeMay 10, 2007

Satoshi OzakiDirector, Accelerator Systems Division, NSLS II Project


Outline

• Overview of the accelerator system

• Storage ring lattice

– Three-pole Wigglers

– Extra long straights

– Canting of damping wigglers

– Upgrade of energy to 3.6 GeV

• Beam Stability Taskforce activities


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 short and 15 long straights Ultra-Low Emittance (<1 nm) Damping Wigglers (21 – 56 m) Large Dipole Bend Radius (25 m) Provision for IR Source Three-pole wiggler x-ray sources

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


Storage Ring:

• ~791.5 m in circumference

• Double bend achromatic lattice with 15 long straights (~8.4m) and 15 short straights (~6.6m)

• 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)

• Space above the tunnel for power supplies, instrumentation electronics, and other service equipment

Storage Ring Configuration: Proposed Baseline for CD-2


CD-2 Lattice: Half-Superperiod

4S 6S 3S


Storage Ring Functionalities

• 3 GeV, 500 mA 1%• Upgradeable to 3.6 GeV or 700 mA

• Estimated beam life-time: 2 – 3 hours • Top-off injection to achieve better than 1% beam current variation for the heat

load stability

• Ultra-small emittance (x, y) : • Bare Lattice: ~2 nmrad Horizontal & ~0.01 nmrad vertical• Baseline: ~1 nmrad horizontal & ~0.008 nmrad vertical• Fully built-out: ~1/2 nmrad horizontal, ~0.008 nmrad vertical

• High level of reliability and stability of operation

• Magnet Inventory:• 60 dipoles: 2.5 m long, 54 with 35 mm gap, 6 with 93 mm gap• 330 quadrupole magnets: • 390 sextupoles magnets.• 210 corrector magnets


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 in the dipoles with a 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 order of magnitudes higher.

However, 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.


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 a longer straight can give a higher

brightness by a factor 2 ~ 3. However, this gain has not been proven with a detailed analysis.• Because of the odd number of superperiods, it is difficult to add one or two extra-long straights

without grossly disturbing the symmetry we desire to have.• Two ways to implement the extra-long straights:

1. Insert an extra-long straight, the transfer function for which is a unitary matrix for on-momentum particles.

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 standard DBA30 as the CD-2 lattice baseline and use the method 2 when the provision of an extra-long straight becomes necessary.


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 tolerance 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


Pros and Cons of 3.6 GeV Upgrade

• The configuration of the NSLS II includes the energy headroom of 20%, i.e., energy upgrade capability to 3.6 GeV.

• This provision comes almost free for magnetic systems but requires significant increase in the RF power if one maintains the 500 mA current requirement and the number of damping wigglers if one wants to keep the same emittance.

• Advantage of this energy upgrade:

• Extension of the spectra to somewhat higher energy

• Allowance for a longer CPMU without impacting vertical dynamic aperture

• Longer Touscheck life time than at 3 GeV

• Disadvantages:

• Dipole radiation increases by the fourth power of energy

• Wiggler radiation increases by the square of energy

• If current and emittance are to be maintained at 500 mA and ~1 nm, the RF power will have to be increased by about 0.5 MW.

• This is the area where the user input will be valuable.


• 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 joint efforts of Conventional Facilities,

Accelerator Systems, 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)

1 brookhaven science associates nsls ii: the accelerator system briefing experimental facilities...

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