History of Crystal Extraction at the SPS RD

History of Crystal Extraction at the SPS (RD 22) Walter Scandale CERN Geneva, 07 March 2005 CARE-HHH-APD-CC 05 workshop 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 1/18

The ante-fact - Aachen 1990 Giuseppe Fidecaro’s request: t t t Provide 7 Te. V/c extracted beams for B-physics in LHC Provide an appropriate Insertion Region Use silicon bent crystals to assist crystal extraction My answer: t t t W. Scandale, Proc. LHC Workshop, eds G. Jarlskog and D. Rein, Aachen, 1990, vol. III p. 760. IR for extraction difficult but feasible Request to evaluate the crystal channeling efficiency Proposal of an experiment in the SPS to test extraction feasibility and the proton interaction with the superficial crystal layer 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 2/18

The RD 22 proposal 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 3/18

The RD 22 collaboration Contactperson Spokesperson 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 4/18

The experimental set-up Goniometer with a stepsize of 2 µrad Stepping Motor with a stepsize of 50 µm The RD 22 Collaboration, CERN DRDC 91 -25 Special tank located the upstream empty half-cell of the long straight section # 5 in the SPS - total length of the set-up about 20 m t t t t Two Si crystals 3 cm long, bent by about 8. 5 mrad, mounted on goniometers 3 scrapers (2 horizontal and 1 vertical) to find the beam position and horizontal angle Laser monitoring system for the alignment of the crystals Scintillators to estimate extracted beam intensity Scintillator hodoscope to estimate horizontal and vertical extracted beam profile Miscrostrip gas chamber 0. 1· 0. 1 mm 2 pixel size Cs. I scintillating screens 0. 2· 0. 2 mm 2 pixel size (later) a scintillator horizontal fisc to measure the extracted beam profile; thickness initially 1 mm, later 0, 2 mm. 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 5/18

The basic crystal A. A. Asseev et al, Nucl. Inst. Meth. A 330 (1993) p 39 Eff. =54± 2 % Eff. =33± 5 % Silicon crystal t 30 mm long, t Serpukov style holder Eff. =16± 3 % Test in single pass mode F. Costantini, Nucl. Inst. Meth. A 333 (1993) p 125 Main drawbacks t Varying radius of curvature t Anticlastic vertical bending 7 March 2005 The RD 22 Collaboration, CERN DRDC 94 -11 walter scandale, History of Crystal Extraction at the SPS (RD 22) 6/18

The “perfect” crystal The RD 22 Collaboration, CERN DRDC 94 -11 The U-shaped crystal t More constant radius of curvature t Less anticlastic curvature 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 7/18

The goniometer and the laser Use of the laser table t Crystal pre-aligned t Continuous monitor of the crystal alignment Goniometer with a stepsize of 2 µrad Stepping Motor with a stepsize of 50 µm The RD 22 Collaboration, CERN SL-95 -088 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 8/18

The halo formation set-up The RD 22 Collaboration, CERN DRDC 91 -25 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 9/18

The impact parameter The RD 22 Collaboration, Phys. Lett. B 357 (1995) 671 -677 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 10/18

The two mode of extraction Kick mode t Impact parameter 0. 1 to 5 mm larger that the amorphous layer t Enhanced single pass extraction t Large extraction rate t Difficult to estimate losses and channeling afficiency t Not a parasitic mode The RD 22 Collaboration, CERN DRDC 92 -51 Diffusion mode 7 March 2005 Diffusion mode t Impact parameter < 1 µm smaller that the amorphous layer t Controllable diffusion speed t Controllable extraction rate t Easy to estimate losses and channeling afficiency t Parasitic mode t Difficult to predict b and b’ walter scandale, History of Crystal Extraction at the SPS (RD 22) 11/18

Extraction efficiency The basic crystals The RD 22 Collaboration, CERN DRDC 94 -11 7 March 2005 t Large channeling efficiency measured t Consistent with simulation expectation t Large angular response related to multi-turn effect walter scandale, History of Crystal Extraction at the SPS (RD 22) 12/18

Extraction efficiency The U-shaped crystals t Higher channeling efficiency measured t Consistent with expectations (better surface cutting; no anticlastic curvature) t Large angular response (multi-turn effect) The RD 22 Collaboration, CERN SL-95 -088 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 13/18

Extraction efficiency The crystal with 30 µm thick amorphous layer The RD 22 Collaboration, Phys. Lett. B 357 (1995) 671 -677 In diffusion mode t Average impact parameter varying from 0. 05 to 1 µm t Maximum impact parameter varying from 0. 5 to 10 µm t b is much smaller that the size of the amorphous layer t The only possible extraction mechanism should be driven by the multi-pass effect 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 14/18

Energy dependence G. Arduini et al. , CERN SL 97 -031 and SL 97 -055 Dechanneling vs beam energy t Critical angle c p-1/2 t Dechanneling due to hits on e- and dechanneling due to bending --> LD p --> LB = LD (1 -F)2 Channeling probability Scattering angle t Gaussian distribution t < > = 0 t Multiple scattering and dechanneling determine the energy dependence of the extraction efficiency t For a given beam energy and crystal bending angle there is an optimal crystal length t Extrapolations of crystal efficiency to the LHC beam energy are reliable (but they depend to some extent on the assumed size of the amorphous layer, which is not known) 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 15/18

Ion extraction efficiency G. Arduini et al. , CERN SL 97 -036 and SL 97 -043 t Angular scan smaller than with protons t Electromagnetic breakup cross section large t Multiturn effect smaller than with protons 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 16/18

Conclusive remarks Primae of RD 22: t Channelling efficiency consistently of the order of 10 % (more than an order on magnitude larger than in previous experiments) t Experimental evidence of multiturn effect in extraction mode t Robust method to evaluate the extraction efficiency t Experimental validation of simulation code at high energy t Extraction of Led ions t All these results were never exploited for collimation t neither for HEP in collider mode Why a new experiment ? ---> Round Table discussion t The experience at U 70 is very promising t There is a strong incentive to propose collimation upgrade (we need however guidance from RHIC ad FNAL experiences) and to exploit crystal in LHC experiments t Considerable improvement were made in crystal production l More homogeneous bending radius using strip crystals with anticlastic curvature (the Russian way) l “perfect” surface with no amorphous layer using chemical hatching (the Italian way) 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 17/18

Some Literature t W. Scandale, Proc. LHC Workshop, eds G. Jarlskog and D. Rein, Aachen, 1990, vol. III p. 760. t The RD 22 Collaboration, CERN DRDC 91 -25 t The RD 22 Collaboration, CERN DRDC 92 -51 t A. A. Asseev et al, Nucl. Inst. Meth. A 330 (1993) p 39 t The RD 22 Collaboration, CERN DRDC 94 -11 t The RD 22 Collaboration, CERN SL-95 -088 t The RD 22 Collaboration, Phys. Lett. B 357 (1995) 671 -677 t G. Arduini et al. , CERN SL 97 -031 and SL 97 -055 t G. Arduini et al. , CERN SL 97 -036 and SL 97 -043 7 March 2005 walter scandale, History of Crystal Extraction at the SPS (RD 22) 18/18