Accelerator Physics Studies for Generating Short

Radiation Pulses at the Diamond Light Source

Introduction Short pulses low alpha optics Short

pulses crab cavities

- R. Bartolini
- Diamond Light Source Ltd

SBSR05, INFN-LNF, 7 November 2005

Diamond (July 2005)

SBSR05, INFN-LNF, 7 November 2005

Diamond nominal optics (working point 27.22,

12.36)

3 GeV Storage Ring (561.6 m) 24 cells DBA

lattice 18 short straights (5 m) 6 long straights

(8 m) emittance 2.7 nm ?y 1.5 m in short s. ?x

10 m _at_ injection point Qx 27.22 Qy

12.36 ?1 1.7 ? 104 ?2 1.9 ? 103 Lifetime

gt 10 h 7 beamlines in phase 1 (2007) Commissioning

2006

SBSR05, INFN-LNF, 7 November 2005

Low Alpha optics (I)

?z 2.83 mm (9.4 ps)

? 1.7?104 V 3.3 MV ?? 9.6 ?104

?z ? 0.3 mm (1 ps)

? (low_alpha_optics) ? 106

- linear optics requirements

?x (_at_ injection) ? 10 m optic not too dissimilar

from nominal (?y in the straight sections lt 3

m) flexibility in the choice of the working point

(while keeping low ?) emittance can be relaxed

- non-linear optics requirements

correct chromaticity AND ?2 while ensuring good

DA for injection off-momentum DA at least ?2 no

lifetime issues

SBSR05, INFN-LNF, 7 November 2005

Low Alpha optics (II)

? 106 Qx 21.22 Qy 12.36 ?x0 1.74 ?y0

-2.42 ?20 1.17?102 ?x 36.2 nm

? 106 Qx 30.22 Qy 12.36 ?x0 3.63 ?y0

-2.37 ?20 3.97?103 ?x 3.68 nm

LA_1

LA_2

SBSR05, INFN-LNF, 7 November 2005

Transverse dynamics for LA_1

Used three sextupole families to correct the

chromaticities and ?2 to zero One family had to

reverse the polarity (upgrade on the machine

needed)

- other 5 sextupole families were used
- to increase the on-momentum DA
- On-momentum DA is barely acceptable (at least ?10

mm in H are needed!) - to achieve ?2 off-momentum aperture with good DA

SBSR05, INFN-LNF, 7 November 2005

Off-momentum dynamics for LA_1

? 10 mm H DA is achieved up to ? 2 off momentum

DA for 2

SBSR05, INFN-LNF, 7 November 2005

Momentum Aperture for LA_1

Momentum aperture low alpha optics

Touschek Lifetime with 7 mm ID V gap 45 h for 10

?A in single bunch 6.2 mA in 2/3 filling (624

bunches)

Microbunch instability threshold

6D

Ib ? 1 ?A for ?z0 0.3 mm

4D

SBSR05, INFN-LNF, 7 November 2005

Low alpha optics Work in Progress

? 106 ?2 106 ?3 2?102

need to understand better the effect of higher

order terms in momentum compaction and the effect

of longitudinal to horizontal coupling

SBSR05, INFN-LNF, 7 November 2005

Crab cavities Zholents scheme

Thanks to M. Borland, K. Harkay (APS) SBSR05,

INFN-LNF, 7 November 2005

Analytical estimate of achievable compression

Assuming a linear RF slope, Gaussian beams and

linear compression, bunch length 10 ps the

minimum achievable x-ray pulse duration is given

by

Thanks to M. Borland, K. Harkay (APS) SBSR05,

INFN-LNF, 7 November 2005

Solutions with no lattice modification

4? in V

Crab cavities are located at 1.1 m from the

centre of the long straight

420 ?rad V kick

Thanks to M. Borland, K. Harkay (APS) SBSR05,

INFN-LNF, 7 November 2005

Modified lattice to allow for extra-space in the

long SS

4? in V

Crab cavities are located at 2.5 m from the

centre of the long straight The optics of a

superperiod is modified to restore the 4?

vertical phase advance between the crab cavities

Linear optimziation perforned with ELEGANT

Thanks to M. Borland, K. Harkay (APS) SBSR05,

INFN-LNF, 7 November 2005

Comparison of DA for modified lattice

on-momenutm DA is slightly reduced but still

about 20 mm in H

Thanks to M. Borland, K. Harkay (APS) SBSR05,

INFN-LNF, 7 November 2005

Comparison of momentum aperture for modified

lattice

Momentum aperture

Touschek lifetime 6D, 1 coupling, 7 mm ID gap

Nominal lattice 13.3 h Modified lattice 12.8 h

The effect of the crab cavity has to be included

(WIP)

Thanks to M. Borland, K. Harkay (APS) SBSR05,

INFN-LNF, 7 November 2005

RF parameters choice

- compression is the same as long as hV is

constant - choice of h is limited by the requirement of a

linear chirp - choice of V is limited by the maximum deflection

achieved and its impact on lifetime - Tracking studies with ELEGANT were performed to

assess the RF voltage limits (zero length TM110

cavity) - h6 (3 GHz) and 1.25 MV is acceptable a voltage

of 1.5 MV generate particle losses in the

vertical plane. - The maximum deflection is 400 ?rad

Thanks to M. Borland, K. Harkay (APS) SBSR05,

INFN-LNF, 7 November 2005

First analysis of emittance degradation

Tracking studies with ELEGANT to assess emittance

degradation showed no significant effect the

vertical and horizontal emittance

Thanks to M. Borland, K. Harkay (APS) SBSR05,

INFN-LNF, 7 November 2005

Crab cavities compression results

ELEGANT can simulate photon ray tracing and

optimize the parameter of the compression optics

to minimize the X ray pulse length

Achievable compression for different slit opening

and crab cavity voltage

Transmission for different slit opening and crab

cavity voltage

Thanks to M. Borland, K. Harkay (APS) SBSR05,

INFN-LNF, 7 November 2005

Crab cavities ongoing work

Looks feasible to get sub-ps x-ray pulses with

very good transmission Lattice asymmetry doesnt

introduce major problems Emittance degradation is

modest More simulations are needed to assess the

effect of lattice errors Impedance issues have

still to be addressed (machine impedance and HOM

in crab cavity)

Thanks to M. Borland, K. Harkay (APS) SBSR05,

INFN-LNF, 7 November 2005

Conclusions

- Preliminary studies were carried out to

demonstrate the feasibility of different schemes

to generate short pulses in the diamond storage

ring. - Low alpha optics with acceptable dynamic aperture

was identified. - Crab cavities schemes are very promising and well

suited to Diamond lattice - Thanks to G. Wuestefeld (BESSY-II) M. Borland,

K. Harkay (APS).

SBSR05, INFN-LNF, 7 November 2005