New optics for the PSB measurement line J.L. Abelleira Thanks to B. Mikulec, G.P. De Giovanni, Jean-Francois Comblin MSWG, 13 Feb 2015

Summary The PSB measurement line (BTM) and its upgrade New Optics for the PSB measurement line BTM measurements with present system and future beams

The PSB measurement line (BTM) 3 grids for emittance measurement from PS BOOSTER

New Optics of the PSB measurement line With the purpose of reducing the beam size at some specific locations, only the strength of the quadrupoles BT.QNO40, BT.QNO50, BTM.QNO05, BTM.QNO10, BTM.QNO20. have been retuned, for the four configurations: 1.Dump optics (Isolde) 2.Horizontal measurement optics (large DX) 3.Horizontal measurement optics (small DX) 4.Vertical measurement optics (Half) beam sizes computed as With (NORMGPS beam)

Condition for emittance measurments Three grids for horizontal emittance measurement: BTM.BSGH01, BTM.BSGH02, BTM.BSGH03 For optimum emittance measurements α x (BTM.BSGH02) = 0 Minimize dx 2 +dx’ 2 (*); 60  of horizontal phase advance between grids 60°

1. Dump optics BTM.BHZ10

1. Dump optics Beam size reduced from 55.7 mm to 36.2 mm BTM.BHZ10

1. Dump optics CurrentProposed

2. Hor. measurement optics (large Dx) BTM.QNO20

2. Hor. measurement optics (large Dx) Beam size reduced from 65.1 to 52.2 mm BTM.QNO20 Beam size reduced from 47.0 mm to 36.2 mm BTM.BHZ10 Same size as for the dump optics

2. Hor. measurement optics (large Dx) CurrentProposed D X [m]D’ X αXαX β X [m]dx 2 +dx’ 2  X [degrees] BTM.BSGH BTM.BSGH BTM.BSGH D X [m]D’ X αXαX β X [m]dx 2 +dx’ 2  X [degrees] BTM.BSGH BTM.BSGH BTM.BSGH Conditions are improved current optics (Ring 3) Proposed optics (Ring 3)

3. Hor. measurement optics (small Dx)

Beam size reduced from 53.3 to 52.2 mm BTM.QNO20 Same size as for the large-Dx measurement optics Beam size 32.9 mm BTM.BHZ10 Side effect: beam size enlargement

2. Hor. measurement optics (small Dx) Current Proposed D X [m]D’ X αXαX β X [m]dx 2 +dx’ 2  X [degrees] BTM.BSGH BTM.BSGH BTM.BSGH D X [m]D’ X αXαX β X [m]dx 2 +dx’ 2  X [degrees] BTM.BSGH BTM.BSGH BTM.BSGH current optics (Ring 3) proposed optics (Ring 3)

4. Ver. measurement optics

Beam size reduced from 38.8 to 36.1mm BTM.BHZ10 Same size as for the dump optics Side effect: beam size enlargement

4. Ver. measurement optics Current Proposed D Y [m]D’ Y αYαY β Y [m]dy 2 +dy’ 2  Y [degrees] BTM.BSGV013.0e-33.9e e-30 BTM.BSGV e e BTM.BSGV e e D Y [m]D’ Y αYαY β Y [m]dy 2 +dy’ 2  Y [degrees] BTM.BSGV01 3.4e-33.7e e-30 BTM.BSGV e e BTM.BSGV e e current optics (Ring 3) proposed optics (Ring 3)

Beam size comparison Beam size only gets bigger after BTY.BVT101. The plots represent the maximum beam envelopes for the 4 optics. Ax/Ay [mm] currentproposed BT.QNO4057.0/24.7 BT.QNO5039.7/ /33.5 BT.BHZ1034.5/ /36.1 BTM.QNO0528.4/ /37.4 BTM.BHZ1035.3/ /36.2 BTM.QNO1044.2/ /37.1 BTM.QNO2065.1/ /39.8 BTY.BVT / /28.3 ElementMADXcurrent g 2.0 GeV [T/m] proposed g Max 2.0 GeV [T/m] gg BT.QNO40kbtqno % BT.QNO50kbtqno BTM.QNO05kbtmqno BTM.QNO10kbtmqno % BTM.QNO20Kbtmqno %

BTM measurements Currently the emittance (in each plane) is measured with 3 SEM grids separated by 2.5 m Wire separation 1 mm 0.5 mm

BTM measurements Three SEM grids (σ 1, σ 2, σ 3 ) determine 3 parameters : beta, alpha and emittance. The precision on the measurement comes from the precision on the beam size determination. A general rule is to have at least 3 points per sigma (wire separation < σ) However, this depends on the center location Wire separation = 1σ

LIU minimum beam sizes in SEM grids σ X [mm] LHCσ X [mm] probeσ x [mm] BCMSGrid sep [mm] Current optics BTM.BSGH BTM.BSGH BTM.BSGH Proposed optics BTM.BSGH BTM.BSGH BTM.BSGH LHC beam : ε N,x = 1.63  m, σ  =1.5x10 -3, E k = 2.0 GeV probe beam: ε N,x = 1  m, σ  =1.07x10 -3, E k = 2.0 GeV BCMS beam : ε N,y = 1.19  m, σ  =1.1x10 -3, E k = 2.0 GeV σ y [mm] LHCσ y [mm] probeσ y [mm] BCMSGrid sep [mm] Current optics BTM.BSGV BTM.BSGV BTM.BSGV Proposed optics BTM.BSGV BTM.BSGV BTM.BSGV Vertical measurement: The beam size is always > wire separation Small Dx horizontal measurement:

WS vs SEM grids Comparative measurements have been done to asses the reliability of the SEM grids measurements Probe beam at 1.4 GeV LHC beam : ε N,x ~ 0.5  m, σ  =4.65x10 -4, E k = 2.0 GeV Wire Scanner (WS)

Vertical plane Wire scannerSEM grids ε N [mm mrad] INCA ε N [mm mrad] from adjustment ε N [mm mrad] INCA ε N [mm mrad] from adjustment ε N [mm mrad] from adjustment (restricted to 2σ) Wire scannerSEM grids ε N [mm mrad] INCA ε N [mm mrad] from adjustment ε N [mm mrad] INCA ε N [mm mrad] from adjustment ε N [mm mrad] from adjustment (restricted to 2σ) set of measurements with WS at 15 ms/, vertical plane set of measurements with WS at 10 ms/ vertical plane INCA gives always larger emittances (~20-40 %) for the SEM grids When adjustment is made taking only 2sigma, there is a better good agreement Error analysis to be done, but measurement in SEM gives higher values

Horizontal plane Wire scannerSEM grids ε N [mm mrad] INCA ε N [mm mrad] from adjustment ε N [mm mrad] INCA ε N [mm mrad] from adjustment ε N [mm mrad] from adjustment (restricted to 2σ) X set of measurements with WS at 15 ms/, horizontal plane However, in the horizontal plane, there is a strong disagreement (it could come from a wrong value of dispersion)

Conclusions The new optics offers better conditions for emittance measurements Considerable reduction of the specifications for the vertical GFR in BTM.BHZ10 Optics will be checked with present energies in a MD Future beam sizes still above grid separation In principle, new SEM grids with less wire separation is not justified To be checked out the exact loss in precision in emittance measurement