1. R. Bartolini Diamond Light Source Ltd
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

2. SBSR05, INFN-LNF, 7 November 2005
Diamond (July 2005)
SBSR05, INFN-LNF, 7 November 2005

3. 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 injection point
Qx = 27.22; Qy = 12.36
1 = 1.7  10–4; 2 = 1.9  10–3
Lifetime > 10 h
7 beamlines in phase 1 (2007)
Commissioning 2006
SBSR05, INFN-LNF, 7 November 2005

4. Low Alpha optics (I) linear optics requirements
 = 1.710–4; V = 3.3 MV;  = 9.6 10–4
z = 2.83 mm (9.4 ps)
 (low_alpha_optics)  10–6
z  0.3 mm (1 ps)
linear optics requirements
x injection)  10 m; optic not too dissimilar from nominal (y in the straight sections < 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

5. SBSR05, INFN-LNF, 7 November 2005
Low Alpha optics (II)
 = 10–6;
Qx= 21.22; Qy = 12.36
x0 = –1.74; y0 = -2.42; 20 = 1.1710–2
x = 36.2 nm
 = 10–6;
Qx= 30.22; Qy = 12.36
x0 = –3.63; y0 = -2.37; 20 = 3.9710–3
x = 3.68 nm
LA_1
LA_2
SBSR05, INFN-LNF, 7 November 2005

6. 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

7. 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

8. 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

9. Low alpha optics: Work in Progress
 = 10–6; 2 = 10–6; 3 = –210–2; …
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

10. Crab cavities: Zholent’s scheme
Thanks to M. Borland, K. Harkay (APS)
SBSR05, INFN-LNF, 7 November 2005

11. 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

12. 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

13. 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

14. 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

15. Comparison of momentum aperture for modified lattice
Nominal lattice Modified optics
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

16. RF parameters choice
compression is the same as long as h*V 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)
h=6 (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

17. 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

18. 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

19. Crab cavities: ongoing work
Looks feasible to get sub-ps x-ray pulses with very good transmission
Lattice asymmetry doesn’t 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

20. 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