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

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 @ 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

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

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

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  = 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

Crab cavities: Zholent’s 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 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

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

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 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

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