Engineering Division1

M321/M331 Mirror Switchyard Design Review

Tom Miller11-29-2006

Engineering Division2

Basic layout of M321/M331 mirror switchyard

Engineering Division3

x

y z

M321

M331

Figure 4: Coordinate system of mirror switchyard

Alignment / stability tolerance and mechanical steps for M321 and M331

DimensionAlignment tolerance Mechanical step Stability tolerance

X 100m 38m 19m

Y 1mm N/A 0.5mm

Z 300m N/A 150m

x 1o N/A 0.5o

y 1mrad 30rad 15rad

z 24rad N/A 12rad

x

y z

M321

M331

Figure 4: Coordinate system of mirror switchyard

Alignment, resolution and stability requirements

(Roll)

(Pitch)

(Yaw)

Engineering Division4

Basic Optic Design

Single optic for M321 and M331 with diagnostic pass – through. Mounting details are omitted

One optic versus twoSingle optic advantages:•No mechanisms for alignment between M321 & M331•Lighter and more rigid optic and mounting for better stability•Smaller required translation due to compact design•Faster setup and commissioning due to fixed angle between M321 & M331

Single optic disadvantages: •Up-front cost of the optic. This can be offset by reduced mechanism and setup costs if optics are not routinely damaged•Manufacturing tolerances on the relationship between the two optical surfaces must be good for quick replacement of the optic.

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Maximum Required Motions

Translations(x):(Single optic)RIXS Rotated: 12.01mm outboundARPES Rotated: 17.97mm inboundTotal: 29.98mm (nominal)

Pitch (Thetay ):(Single or dual optics, RIXS & ARPES)High Res grating: +/-259 microradians High Flux grating: +/-168 microradians

Roll (Thetaz ):(Single or dual optics, RIXS & ARPES)+/- 5 milliradians

RIXS rotated ARPES rotated

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Mechanism Fundamentals

Initial concept:

Mount the optic(s) rigidly in the chamber and translate the chamber with a single slide and pitch and roll with struts to steer the beam.

Advantage: • Familiar approach• Easy installation survey. The optic(s) can be accurately fiducialized in a lab

and those numbers used for installation alignment.

Disadvantages:• Input and output bellows are required. Large and variable off-axis forces act

on the translation slide and rotation mechanisms• If pumping is added to the chamber, the pump must move with the

chamber or be bellows isolated. This will result in a large mass offset from the slide or more non-constant bellows forces. Both solutions result in poorly placed variable forces.

• Pitch and roll motions intrinsically couple to all other motions.• Parasitic motions from variable off-axis forces may make high resolution

encoder readings meaningless

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Mechanism Fundamentals

New concept:

Mount the chamber rigidly and move the optic(s)

Advantages: • Bellows forces are small and self-cancelling • Pitch corrections are nominally independent of roll• Translations are nominally independent of pitch and roll• Any force required for translation is small and almost directly in line with

the linear bearings in the stages.• All sources of backlash in the mechanism are spring loaded in the axis of

freeplay. • Pitch and roll are flexure-based motions and therefore very repeatable• Large pumps can be mounted beneath the tank with no effects on motion. • Small off-axis forces will make encoder readings more meaningful• The moving masses are small and the mechanisms optimized for stiffness.

The vibrational modes of the mechanism are thus above 200Hz.• All mechanism parts are stainless steel or cast iron. This should yield good

thermal stability.

Engineering Division8

Mechanism Fundamentals

New concept: Mount the chamber rigidly and move the optic(s)

Disadvantages:• Unfamiliar design• Roll couples to pitch and translation. 1 milliradian of roll induces 200

microradians of pitch for ARPES, 100 microradians of pitch for RIXS and 0.13 microns of translation. Intrinsic roll errors should be very small, and thus the roll corrections should also be small, so pitch coupling should not be a problem. Translation coupling will be insignificant.

• Pitch couples to translation. 250 microradians of pitch results in 9 microns

of translation at the nominal reflection point. The large pitch changes required for grating selection also have an associated ~1.5mm translation, so this number is acceptable.

• Installation surveys of the optic will be relatively imprecise. The orientation of the optic to outside fiducials must be determined after the optic is mounted in the tank. The in-vacuum fiducials are close together and difficult to survey in the tank.

Engineering Division9

Mechanism Overview

Engineering Division10

Translation Mechanism

Engineering Division11

Chamber pass-through

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Roll Mechanism

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Pitch Mechanism

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Mirror details

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Center Section

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Pitch Hinge Details

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Micro-e Encoder Scale

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Center Section Mounting

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Pitch Mechanism First mode

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Spring stress at 1mRad pitch

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Demagnification spring deflection with 1mRad pitch

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Roll Mechanism first mode

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Cost estimate

Fab and purchases: $78,000Assembly (200hrs) : $20,000

Total: $100k