Loading in 5 sec....

Ali Nassiri and Geoff Waldschmidt Accelerator System Division Advanced Photon SourcePowerPoint Presentation

Ali Nassiri and Geoff Waldschmidt Accelerator System Division Advanced Photon Source

Download Presentation

Ali Nassiri and Geoff Waldschmidt Accelerator System Division Advanced Photon Source

Loading in 2 Seconds...

- 135 Views
- Uploaded on
- Presentation posted in: General

Ali Nassiri and Geoff Waldschmidt Accelerator System Division Advanced Photon Source

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

A Brief Report on the Status of Rf Deflecting Cavity Design for the Generation of Ultra-Short X-Ray pulses at APS

Ali Nassiri and Geoff Waldschmidt

Accelerator System Division

Advanced Photon Source

ICFA Mini-Workshop on

“Frontiers of Short Bunches in Storage Rings”

Laboratori Nazionali di Frascati, 7-9 November 2005

Special thanks to Kenji Hosoyama (KEK), Derun Li and J. Shi ( LBNL), and Tim Koeth (Fermilab) for many productive and useful discussions.

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

Undulator radiation & x-ray optics

L. Assoufid

R. Dejus

D. Mills

S. Shastri

RF

K. Harkay

D. Horan

R. Kustom

A. Nassiri

G. Pile

G. Waldschmidt

M. White

Beam dynamics

M. Borland

Y.-C. Chae

L. Emery

W. Guo

K.-J. Kim

S. Milton

V. Sajaev

B. Yang

A. Zholents, LBNL

* All affiliated with APS except where noted

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

- Introduction
- SC vs. RT option
- Crab cavity modeling
- Summary

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

Can get the same

compression as long as

h*V is constant

V=6, h=4

V=4, h=6

Higher V and lower h: more linear chirp and less need for slits

V=6, h=8

Higher h and lower V: smaller maximum deflection and less lifetime impact

Cavity design and rf source issues

h=7, V<6 MV?

Higher h and maximum V: shortest pulse, acceptable lifetime

Beam dynamics simulation study: h ≥ 4 (1.4 GHz) V ≤ 6 MV (lifetime)

M. Borland, APS ps Workshop, May 2005

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

Parasitic modes (squashed geometry)

TM010

Accelerating mode

TM110h/TE111h

TM011

frequency

TM110v

APS crabbing mode

TE111v

- Vertical crabbing mode (APS): horiz axis “squashed”
- Maximize mode separation for optimized damping
- HOMs above beam pipe cutoff, propogate out
- Lower-order mode (TM010) may strongly couple to beam; freq. below cutoff, adopt KEKB coaxial line strategy (for SC)
- Multiple cells produce multiplicity of parasitic modes (issue for SC)
- Orbit displacement causes beam loading in crabbing mode; adopt KEKB criterion of y = ±1 mm (for orbit distortions ± 0.1 mm)
- Generator power increased to compensate; de-Q to decrease sensitivity

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

- RF sources
- for SC option are available with minimal reconfiguration
- for RT are non-typical and modification is required (1 kHz)

- Cavity fill time vs. susceptibility to phase noise
- Long for SC cavity; makes it less susceptible
- Short for RT structure; makes it more susceptible

- Need to compensate frequency detuning
- Due to pulse heating for RT case
- From microphonics for SC case

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

9 Cells SW Deflecting Structure

- Pulsed heating < 100 deg. C
- BMAX < 200 kA/m for 5 μs pulse (surface)

- Limited available power ≤ 5 MW
- EMAX < 100 MV/m (surface)

V. Dolgashev, SLAC, APS seminar, June 2005

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

- Single-cell vs. multiple-cell SC cavity configurations
- Orbit displacement causes beam loading in crabbing mode; adopt KEKB criterion of y = ±1 mm (for orbit distortions ± 0.1 mm)

Superconducting Deflecting Cavity Design Parameters

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

Coaxial transmission lines

Rejection filter not shown

- Damping load is placed outside of cryomodule.
- Ridge waveguide and coaxial transmission lines transport LOM / HOM to loads
- Efficiency of deQing was simulated by creating the TM010 mode with an axial antenna.
- Stability condition for LOM achieved when Q < 12,900 for 100 mA beam current.
- Unloaded Q of LOM was 4.34e9.
- Coaxial beam pipe damper with four coaxial transmission lines, damped the LOM to a loaded Q of 1130.

Rejectionfilter

Coaxialtransmissionline

Excitationantenna

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

Deflecting mode filter

Waveguide to damper load

- Deflecting mode creates surface currents along the coaxial beam pipe damper, but does not propagate power.
- When a resistive element is added, there is substantial coupling of power into the damping material.
- A radial deflecting mode filter rejects at ~ -10 dB.
- Performance improvement pursued as well as physical size reduction.

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

- Ten single-cell cavities with KEK-type coaxial beam pipe damper and rejection filter
- Ion pump/valves/bellow assembly will need at least 0.4m on both sides of the cavity assembly.
- The total space required by the following physical arrangement is ~ 2.6 m.
- Beam impedance considerations may require different cavity configuration
- Upstream/Downstream location of coaxial beam pipe damper may be significant
- Downstream location may increase beam impedance excessively
- Configuration change would require additional space

Input Coupler

Coaxial Damper

Rejection Filter

Coaxial Beam Pipe

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

- Alignment of coaxial beam pipe dampers (CBD) will be difficult.
- Thickness of (CBD) as modeled is 4mm which includes the cooling channel. Rigidity and mechanical stability and cooling capabilities are questionable
- Rejection filter may be difficult to implement efficiently.
- Results of stress analysis of cavity performed by KEK required stiffening of KEK cavity - tuning by deformation was abandoned.
- CBD also functions as tuner in KEK design. This will require a separate adjustable CBD for each cavity.
- CBD tuner will require more space and increase complexity

- KEK locates CBD on the upstream side of the cavity due to possible impedance issues – will require more space.

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

- Waveguide dampers are placed near cavity to intercept leakage fields of the LOM*+
- LOM couples to waveguide and is strongly damped Qext= 500.
- Other monopole modes also couple to TE10 waveguide mode and are strongly damped.

Power Flow and Efield vector plot of LOM

* A. Nassiri, APS/ANL

+ D. Li, LBL

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

- Coaxial input coupler considered to permit variable coupling.
- Deflecting dipole mode couples to waveguide as TE20 mode and is rejected by > 30 dB in current configuration due to waveguide cutoff frequency.
- “Degenerate” deflecting mode couples to TE10 waveguide mode and is strongly damped.
- Asymmetric cavity may no longer be necessary depending on HOM spectrum.

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

Input Coupler

Waveguide Damper

Coaxial Damper

- Ten single-cell cavities with waveguide damper.
- The total space required by ten single-cell cavities in the following physical arrangement is ~ 2.4 m assuming ion pump/valves/bellow assembly installed on both ends.
- Additional dampers may be required based on full HOM analysis

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

- Feasibility study completed
- SC rf technology chosen

- Finalize RF system design, refine simulations
- Observe assembly and testing of KEKB crab cavities in 2005, 2006
- Model impedance effects (parasitic modes, head-tail)
- Conduct proof of principle tests (beam dynamics, x-ray optics)
- Chirp beam using synchrobetatron coupling (transient) (W. Guo)
- Install 1 MV RT S-band structure, quarter betatron tune (M. Borland, W. Guo, A. Nassiri) (AIP)
- Install warm model of SC rf cavity (passive), parasitic mode damping (K. Harkay, A. Nassiri) (AIP)

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005

- We believe x-ray pulse lengths ≤ 1 ps achievable at APS
- SC RF chosen as baseline after study of technology options
- Recent simulation results on LOM and HOM damping are encouraging.
- Input coupler design is underway
- Beam impedance calculation may have appreciable effect on final design
- Proof of principle R&D is underway: beam/photon dynamics
- Operational system possibly ≤ 4 yrs from project start

A. Nassiri, G. Waldschmidt APSINFN – LNF 8 November2005