# Presentation: 362660

## NSLS II Lattice and Accelerator Configuration Review5/11-5/12/06

- C. Bocchetta
- M. Boege
- M. Borland
- M. Cornacchia
- M. Eriksson
- T. Roser
- C. Steier

## Charge to Committee

- Can the proposed design meet the requirements in terms of
- Emittance
- dynamic aperture (injection efficiency)
- Lifetime (momentum aperture)
- Reliability and availability
- Comments and advice on proposed solutions, such as,
- Soft bends and damping wigglers at 3 GeV
- Booster in same tunnel as ring
- IR ring  concept
- Utilization of 15m straights

## General Comments

- Committee was impressed by
- Amount of work accomplished to date
- Quality of the presentations
- Performance goals appear achievable with design presented
- Proposed lattice design combines
- Innovative ideas for a new light source (damping wigglers and soft bends)
- Informed by experience from state-of-art existing facilities

## Lattice

- Proposes to achieve horizontal emittance about 5 times smaller than existing hard x-ray sources
- Achieved by
- Moderate focusing --- no sacrifice of dynamic aperture
- Damping wigglers
- Soft bends
- This is a plausible approach
- Given the chosen approach, the circumference appears justified in order to meet performance goals

## Lattice Continued

- Reliance on damping wigglers puts burden on beam dynamics with their associated nonlinearities and realistic lattice errors
- Preliminary studies look promising
- Presented plan for further studies looks sound, but should include
- More realistic (startup) errors for alignment
- Demonstration of workability with long/multiple devices in short and long straights
- Dispersion and beta function errors
- Coupling between planes
- Correction scheme including BPM/corrector layout
- Damping wigglers provide supplement for dipole sources
- Reduces impact of occupying straight sections
- Consider moving vertical working point below half-integer

## Intrabeam Scattering Effects

- Proposed design is in a new regime for Touschek scattering
- Is there any new physics lying in wait?
- Cross-check IBS results
- Consider ATF/KEK results for comparison
- 2~3 hour lifetime appears suitable for operation, however
- Is momentum aperture properly determined in lifetime calculations?
- Some tracking results show aperture < +/- 3%
- Nonlinear coupling important in presence of very small gaps
- Lower betatron coupling may *enhance* lifetime

## Gas Scattering

- Presumably Touschek-dominated, but should evaluate gas scattering lifetime
- Look at all-over NEG-coated system
- Evaluate fast-ion instability in light of small vertical emittance

## Collective Effects

- We compliment the team on a very good start
- Concerned about scaling of impedance with *number* of small gap devices
- Chromaticity to fight TMCI is not “free”
- Impact on DA can be serious
- Study optimization of sextupoles for various chromaticities
- Consider feedback as an alternative
- Does impedance-driven microwave instability dominate CSR?
- Agree with use of third-harmonic cavity
- Phase/shape transients need further study
- Be aware of possible impact on crab scheme

## Injector

- Linac concept incorporates redundancy
- 600 MeV linac required only by IR source
- A lower energy linac will be cheaper, more reliable
- Endorse putting booster in ring tunnel
- Will provide small injected beam emittance, which is good for top-up
- Endorse study to ensure ring/booster cross-talk is controlled
- Clarify the booster operating mode
- Use of a thinner injection septum is strongly encouraged

## Rf System

- Appreciate that team plans to take advantage of latest light source's SC rf experience
- Development of dual-antennae feed would be a valuable contribution to the community
- Tailor rf design to momentum aperture needs of this machine
- Take advantage of LLRF developments at other labs

## Technical Concerns

- Magnet design option to consider
- Optimization of physical aperture
- Minimization of magnet mass
- Higher vibration frequency
- High different between accelerator and experimental floors could be concern
- Different weight may result in different settlement rates
- Appreciate thoughts on magnetic measurements of in-vacuum devices
- Use of cryogenic PM undulators is endorsed
- Encourage attention to stability aspects of mechanical design

## IR Ring

- Committee favors a completely new ring
- However, phased approach may involve improvements to existing ring
- E.g., rf system
- Study impact on other systems of higher current, shorter bunches
- Recommend optimized lattice in direction of increased number of ports
- Consider more than four superperiods