Dispersion Measurements in the PSB Measurement Line PSBBTxBTM

Dispersion Measurements in the PSB Measurement Line (PSB-BTx-BTM) V. Forte, G. P. Di Giovanni, G. Guidoboni MSWG 21 st October 2016

Motivations • Scope: Understand harmonize the emittance measurements performed in the PSB rings using the wire-scanners with the ones in the BTM line using 3 SEM grids. • Beam: LHC 25 -type with an intensity of ~165 E 10 ppb. • The WS application currently uses as input the optics and dispersion values from MADX: • Measurement performed at C 796 (before the extraction bump is ON). • Filter at 0. 5% and PM 900 -950 permill. • Horizontal/Vertical Dispersion = -1. 4658/0 m. • The SEM GRIDs uses as input the dispersion values from MADX, different for each ring. • Average of 20 consecutive measurements. Ring/Plane Intensity [E 10 p] WS Emittance [mm] SEM GRID [mm] WS speed R 1 H 164. 9 ± 2. 5 1. 615 ± 0. 068 1. 913 ± 0. 021 15 m/s R 1 V 164. 5 ± 1. 6 1. 869 ± 0. 024 1. 860 ± 0. 020 10 m/s R 2 H 167. 2 ± 1. 6 2. 066 ± 0. 051 2. 100 ± 0. 045 15 m/s R 2 V 166. 5 ± 1. 6 1. 967 ± 0. 057 1. 957 ± 0. 043 15 m/s R 3 H 164. 2 ± 1. 7 1. 607 ± 0. 044 1. 786 ± 0. 019 15 m/s R 3 V 165. 9 ± 1. 7 1. 955 ± 0. 048 1. 828 ± 0. 022 15 m/s R 4 H 163. 8 ± 2. 5 1. 973 ± 0. 071 2. 131 ± 0. 069 15 m/s R 4 V 164. 0 ± 1. 6 2. 034 ± 0. 092 2. 032 ± 0. 037 15 m/s 2

Dispersion Measurement • Record the change of position of BPMs, of WS and SEM GRID distributions centroid, while varying the frequency of the PSB internal generator (BA. EXTREFFREQ). • Nominal setting is 1746270 Hz. The measured value oscillates within few Hz around the value set. • The value is varied within ± 500 Hz. • Dp/p = -(1/h. PSB)* Df. REV/f. REV, h. PSB=ac-1/g 2 • The compaction factor is taken from MADX. • In the PSB Rings the TRIM 1+4 was active, but not the BR 4. BDL. 3

Horizontal Dispersion R 1 4

Horizontal Dispersion R 1 5

Horizontal Dispersion R 1 6

Horizontal Dispersion R 2 BTMS Electronics 7

Horizontal Dispersion R 3 Calibration Issue? BI Experts looking into it 8

Horizontal Dispersion R 4 9

Vertical Dispersion R 1 10

Vertical Dispersion R 2 11

Vertical Dispersion R 3 12

Vertical Dispersion R 4 13

Dispersion Measurements Summary Ring/Plane WS [m] SEM GRID 1 [m] SEM GRID 2 [m] SEM GRID 3 [m] R 1 H -1. 3619 -1. 5515 -0. 052911 +1. 4290 R 1 V -0. 0919 0. 32782 -0. 0262 -0. 39807 R 2 H -1. 3884 -1. 2368 +0. 038622 +1. 2936 R 2 V -0. 0114 0. 25384 0. 062838 -0. 12573 R 3 H -1. 3634 -1. 1798 +0. 039221 +1. 2243 R 3 V -0. 0299 0. 029354 0. 027425 0. 04821 R 4 H -1. 3827 -1. 5313 -0. 14812 +1. 1998 R 4 V -0. 1101 0. 034784 0. 14163 0. 30977 14

Dispersion Measurements Comparison Ring/Plane WS Emittance MADX Input [mm] WS Emittance Measured Disp. [mm] SEM GRID [mm] Dp/p [E-3] R 1 H 1. 615 ± 0. 068 1. 735 ± 0. 068 1. 913 ± 0. 021 1. 01 R 1 V 1. 869 ± 0. 024 1. 857 ± 0. 024 1. 860 ± 0. 020 / R 2 H 2. 066 ± 0. 051 2. 167 ± 0. 051 2. 100 ± 0. 045 1. 07 R 2 V 1. 967 ± 0. 057 1. 960 ± 0. 057 1. 957 ± 0. 043 / R 3 H 1. 607 ± 0. 044 1. 765 ± 0. 044 1. 786 ± 0. 019 1. 17 R 3 V 1. 955 ± 0. 048 1. 954 ± 0. 048 1. 828 ± 0. 022 / R 4 H 1. 973 ± 0. 071 2. 079 ± 0. 071 2. 131 ± 0. 069 1. 06 R 4 V 2. 034 ± 0. 092 2. 026 ± 0. 092 2. 032 ± 0. 037 / 15

Preliminary Observations • Results compatible with the measurements done while injecting in the PS, see V. Forte’s talk. • Horizontal dispersion from MADX model matches better the data in Ring 1 and 4. • Accounting for the measured dispersion in the calculation of the emittance improves the agreement between the WS and SEM grid measurements in several rings/planes. • The discrepancy observed in R 1 H and R 3 V is still to be understood… among several other things. • Not reported here, but an emittance blow-up of 2 -3% induced by the WS could be systematically measured at the SEM grid while doing a synchronized measurement with the WS. • For instance the effect of multiple coulomb scattering at low energy from the WS studied in details by E. Benedetto and M. Kowalska, see http: //tinyurl. com/jn 3 twqn Work to be continued… 16