CERN/JINR Collaboration Alignment with Laser

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CERN/JINR Collaboration Alignment with Laser

N. Azaryan, I. Bednyakov, J. Budagov, B. Di Girolamo, V.

Glagolev, M. Lyablin, A. Pluzhnikov, G. Trubnikov (CERN

& JINR)

1^st MUonE Collaboration meeting at CERN – 25-26 March 2019

Be Target

Si detectors

50-70cm 10cm

µ e αe

0< αe<100mrad

α_µ

αµ < 5mrad

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Outline

§ Initial discussions and requirements

§ Laser Reference Line 1 (LRL1) for alignment within a module

§ Laser Reference Line 2 (LRL2) for alignment of all 60 modules

§ Online long-term monitoring of alignment

§ Laser Reference Line 2 parallelism adjustment w.r.t. the muon beam direction

§ Feedback need and future steps

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Initial discussions and requirements

§ Informal contacts with G. Venanzoni setting up possible requirements

§ Requirement 1: MUonE module, the quantum

§ Requirement 2: MUonE full setup of 60 modules

§ Requirement 3: real-time monitoring of full setup

§ Requirements 4: mutual parallelism of the 240 plates (60 times (1 Be target + 3 Si modules)) within 20 µrad

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Quantum, Full System, Scope

Be Target

Si detectors

50-70cm 10cm

µ e αe

0< αe<100mrad

αµ

αµ < 5mrad

Module

30-45m

…….

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Proposed solution

§ LRL1 to adjust target and detectors in the module: 20 µrad parallelism to ensure

measurement precision at 5 µrad level

§ LRL2 to adjust all modules along a line: same requirements

§ Online control of modules angular position in space: 1 µrad precision in determination of angular positioning during data taking

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LRL1: principle and expectations

§ Parallel Plates (PPs) mounted on the Target

and Detectors supports allow to align sequential each module to reach precise positioning of the laser spot on the center of a quadrant

photodiode. Iterative procedure

Laser Δ

PP optical plate4

Laser beam

Quadrant Photoreceiver

Laser spot θ

d PP optical plate3

PP optical plate2 PP optical plate1

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LRL1 higher precision

§ Laser light collimated and focused (F = 1 m) to have a spot with d = 80 µm

§ The light travels inside a tube to reduce laser beam scattering in air

Laser

Collimator

δ

F D

Lens Tube Quadrant Photodiode

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LRL1 expectations

§ ∆= # · %&' ( · 1 − ^{+,- .}

/⁰1-23 . ⁰

§ n is the refraction index of PP

§ PP thickness d = 3 cm

§ Let’s find K(q) from D = K(q) q ^PPs

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LRL1 expectations

§ For q in the interval 0-10^-2 rad the K ~ 0.01 quite constant

§ For d = 3 cm, q = 5 µrad the laser beam will be shifted by D

= 0.05 µm

§ From our publications the measurement precision for the laser spot shift on the quadrant photodiode is:

∆_"= $

8 &_' ∆(

(

Where D_l = 80 µm laser spot, DU is ADC noise, U is the sum of all four signals from the quadrant photodiode. For our

thermostabilized and RF shielded 24-bit ADC DU/U ~ 10^-4

Therefore D_n ~ 3 nm and the precision for each plate alignment is q_n = D_n/K ~ 0.3 µrad, good enough to achieve parallelism of the plates within 20 µrad

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LRL1 specific constraints and PP “precision”

§ Length of LRL1 ≤ 2 m

§ Use of a tube to confine the laser light improving precision

§ Limit precision coming from PP manufacturing within 2.5 µrad

Windows and Optical Flats LASER GRADE PLANE PARALLEL WINDOWS, ≤10 ARC SECONDS: PW1

Specifications

Product Code: PW1 Optical Material:

Standard Grade Corning 7980 1-D (Fused Silica) or N-BK7

Diameter Tolerance: +0/–0.25mm Thickness Tolerance: ±0.25mm Wedge Tolerance: ≤10 arc seconds Chamfer:

Ø ≤ 50.8mm: 0.35mm leg width at 45° nominal Ø > 50.8mm: 0.85mm leg width at 45° nominal Surface Quality: 10-5 scratch-dig per MIL-PRF-13830b Transmitted Wavefront Error (TWE): < λ/10 p-v at 633nm Clear Aperture: ≥85% of central diameter

PW1 windows are polished on two sides, with a wedge of ≤10 arc seconds and are manufactured to handle high power applications.

They form the foundation for several coated products, such as, beamsplitters, output couplers, harmonic separators, dichroic mirrors, and partial reflectors.

X Extremely parallel wedge X ≤10 seconds of arc

X Minimal angular deviation of transmitted beam X Minimum misalignment errors when window is repeatedly

inserted and removed

LASER GRADE PLANE PARALLEL WINDOW Standard Grade Corning 7980 1-D (Fused Silica)

Ø (mm) t (mm) Transmitted

Wavefront Error

p-v at 633nm PART NUMBER

12.7 1.0 < λ/4 PW1-0504-UV

12.7 3.175 < λ/10 PW1-0512-UV

12.7 6 .35 < λ/10 PW1-0525-UV

19.1 6 .35 < λ/10 PW1-0725-UV

25.0 6 .0 < λ/10 PW1-2506M-UV

25.4 2.0 < λ/4 PW1-1008-UV

25.4 3.175 < λ/10 PW1-1012-UV

25.4 6 .35 < λ/10 PW1-1025-UV

25.4 9.525 < λ/10 PW1-1037-UV

38 .1 6 .35 < λ/10 PW1-1525-UV

50.0 10.0 < λ/10 PW1-5010M-UV

50.8 6 .35 < λ/10 PW1-2025-UV

50.8 9.525 < λ/10 PW1-2037-UV

76 .2 12.7 < λ/10 PW1-3050-UV

101.6 12.7 < λ/10 PW1-4050-UV

152.4 25.4 < λ/10 PW1-6010-UV

N-BK7

Ø (mm) t (mm) Transmitted Wavefront

Error p-v at 633nm PART NUMBER

12.7 6 .35 < λ/10 PW1-0525-C

25.0 6 .0 < λ/10 PW1-2506M-C

25.4 6 .35 < λ/10 PW1-1025-C

50.0 10.0 < λ/10 PW1-5010M-C

50.8 9.525 < λ/10 PW1-2037-C

γ = δ

% 2⁄ δ=₍₎^'

D = 5 cm

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LRL2 working principle

§ We propose to add an additional support in the MUonE module for holding a semitransparent mirror M2 and to add a final mirror M1 after the 60^th module

§ The LRL2 working principle is based on the positioning of the M2s in all modules once LRL1 has enabled the alignment of all plates in the module

Base O Module1

Base O Module60

…

^M1

ST mirror M2

Laser beam L1 of the LRL2

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LRL2 optical schema

§ A cube beam splitter allows to split the primary laser light in two beams L1 and L6

§ L1 is reflected by the mirror M1 and the L2 beam is read back by a quadrant photodiode

§ The laser beam and the optical cube are adjusted to have The reflected L4 and L5 beams centered on the quadrant photdiode

§ The position of the reflected L2 beam will determine the

M1

Laser

Laser beam Quadrant Photodiode

The optical cube face 1 The optical cube face 2

M2

Lm

L1 L2 L3

L4

L5 L0

L6

L

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LRL2 constraints and precision

§ All planes (Target and Si modules) have to be

interconnected with the Baseplate O carrying the M2 semi-transparent mirror

§ Optical cube manufacturing precision deviation from p/2 is d < 5 arcmin (1.5 10^-3 rad), with a cube edge size of D_c = 10 mm, the divergence m between the centers of the L4 and L5 laser beam spots is m = D_cd < 15 µm

Optical Cube

L1

Δс

L4

L5 L6

δ m

Spots of the laser beam Quadrant Photodiode

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LRL2: impact of laser light propagation in air

§ The rms value of the laser beam spot d_n in air has been measured experimentally by JINR team up to 50 m and extrapolated to 100 m

§ Experimental data up to 100 m exist and confirmed the extrapolation

Estimation d_n(100 m) ~ 350 µm

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LRL2: impact of laser light propagation in air

§ In our case we propose to keep the distance between the beam-splitting cube and the first M2 mirror to 2 m, therefore the laser path for the L1 beam and reflected L2 is in total 4 m:

§ d_n(4 m) = 6 µm

§ The angular precision for the positioning of the M2

mirror can be estimated based on the L1 length of 2 m as:

§ q_n(L = 2 m ) = √(m² + d_n²)/L = 8 µrad

§ Increasing L the precision will improve, but the influence of propagation in air will increase (d_n)

§ At 35 m, for the last M2 mirror

§ d_n(70 m) = 160 µm and q_n = 4.3 µrad

§ Therefore all elements will be aligned at worst within 8 µrad, respecting the requirement of < 20 µrad

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Real life implementation

§ Requirement of machining precision ± 0.01 mm for support to ensure precise mounting of Parallel

Plates

Over 50 cm it will ensure 20 µrad by construction

Be-Target or Si-detector PP-plate

Common plane surface for Be-Target or Si-detector and PP plate

Common Basement for Be-Target or Si-detector and PP plate Common basement O

Lml

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Positioning of the plates

§ The positioning of the plates is achieved using off-the-shelf elements with the swap for higher precision differential positioners 0.5 µm per

division

Platform dimension 112x115 mm², 0.5 µm per division equivalent to 4.5 µrad per division

With accurate positioning (1^o) on a common support the LRL1 takes

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Long-term and online control system during data taking

§ Basic unit: 2 PP at fixed position at ~ Brewster angle to let the Laser beam direction untouched.

Repeating 60 times we will have 240 beam impacts with power loss of 50%

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§ The angle of this basic unit has to be controlled with high precision via a Precision Laser

Inclinometer

In this case D_l = 1 cm for which D_n ~ 0.4 µm

With L_i, distance between the surface of the liquid mirror and the quadrant photodiode, of 20 cm q_n = D_n/2L_i = 1 µrad

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§ By measuring the 60 inclinometers output one can monitor if there is any displacement > 20 µrad for any module

§ LRL2 and the inclinometer use the same laser source

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Muon beam parallelism with LRL2

§ For brevity we do not describe here the system based on the use of two positioner at the start of the experiment and at the end at a distance of 35 m

§ Parallelism with 40 µrad is achievable provided a muon divergence within 20 µrad

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Conclusions and next steps

§ The systems described are based on available instruments and off-the-shelf components from usual vendors

§ A basic estimation of the cost can be done

§ If the proposal is sound (i.e. the expected

accuracies are suited) for the collaboration we need to have expression of interest letters to CERN and JINR teams to be later formalised with a collaboration agreement/MoU

§ A close collaboration with the mechanical design of the target and modules has to be