Equipment Safety aspects of the SRF Cavity/He Vessel/Tuner system.Role of the Cavity Tuner to support/deliver equipment safety demands.Modification of the LCLS II pCM Tuner

Yuriy PischalnikovMarch 26, 2015

LCLS II pCM Tuner_V1

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Outline

Review of the Cavity/He Vessel/Tuner system safety (equipment)

Table with anticipated steps during assembly and operation of the CM

* SRF Cavity safety* Tuner active components safety

Modifications introduced into the design the LCLS II Tuner_V1 for pCM (Tuner_V2)

Summary

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I.Gonin/T.KhabiboulineCOMSOL simulation of the cavity/He Vessel/Tuner (brackets) system

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TEM

PERA

TURE

PRO

TECT

ION

The step during cavity assembly or operations

Insu

late

d Va

cuum

, bar

abs

Cavi

ty B

eam

line,

ba

r abs

Heliu

m V

esse

l, ba

r abs

Forces on cavity flange

with absolutely restrained cavity, kN

Cavity lengthwill changes if

flange non-restrained,

mm

Tcav

=300

K REST

RAIN

BRA

CKET

S

0 Cavity is relaxed after HV welding 1 1 1 0 0

1 Cavity/He Vessel Leak Check at MP9 1 1 0 -2.6 -0.6

2 Cavity/He Vessel Pressure test at MP9 1 1 3.3 6.0 1.4

3 Cavity/He Vessel Leak Check in CM/HTS 1 0 0 -3.8 -0.8

4 Cavity/He Vessel leak check in Clean Room 1 0 1 -1.2 -0.25

TUN

ER IN

STAL

LED

ON

CAV

ITY

5 He Vessel pressure test in CM 1 0 3.3 4.9 1.1

6 Start of cooling down CM 0 0 1.5 3.9 0.8

7Linac maintenance (e.g.,

tuner or interconnect access)

1 0 1.4 0 0

8a Tuner access and disconnect (e.g., replace piezo), what is max cryo

system pressure

1 0 0 -3.8 -0.8

8b 1 0 2.5 2.7 0.6

5K 9 End of cooling down 0 0 1.5 3.9 0.8

2K 10 Operating condition 0 0.03 0 0 0

5K 11Worst case cold loss of vacuum accident. Will

piezo and tuner survive?0 0 4 10.4 2.2

Highlighted steps when cavity at 300K will go beyond elastic deformation if do not protected with tuner/safety brackets system.

Impact on the Cavity/He Vessel/Tuner system for various pressure conditions during anticipated steps of assembly and operation of the CM.

Requirements: |∆XT=300K| < 0.6mm

Accident at cold CM Impact on the Tuner/piezo

Safety (restrain) Brackets for Cavity/He Vessel system(serve at steps 0,1,2,3,4 )cavity flange split ring &brackets need to be installed as soon as cavity welded into He Vessel.

Brackets (& flange ring) will remain as part of the system during pressure/leak check; during transportation; at processing facility; inside Clean Room; during test at VTS (and occasional test at HTS /without Tuner-High Q0 test).

Restrain Brackets (& cavity flange split ring) Technical Requirements Specs for Brackets (short) 1). Cavity can't be stretched/squeezed more than 300um.2) Deviations in length of the LCLS II cavity (welded cavity) into He Vessel can be -3mm/+7mm

Pressure/leak check tests with cavities AES018; AES021; AES27 assembled with safety/restraining brackets confirmed that cavities stay in safe elastic deformation range during pressure/leak check tests.

Role of the Safety Restrain Brackets (and Arc) to protect cavity during transportation /assemblyAnalysis & COMSOL simulation performed by Gonin/Khabibouline

Fv=g*ρ corresponding to Earth gravity

Total Displacement

Cavity Support Arc was designed to protect Helium Vessel bellows against transverse acceleration

Cavity limit for transverse acceleration is 3g Bellows limit for transverse acceleration is 23g Detailed analysis demonstrated that cavity is weaker

than bellows in term of transverse acceleration Support Arc not designed to protect the cavity

against axial acceleration (brackets OR tuner will protect cavity)

Cavity displacement and deformation due to gravity is small and not depend on Support Arc installation

Therefore recommended to remove Support Arc from Dressed Cavity assemblySupport Arc will be used only to support cavity inside Clean Room assembly… Arc will be reusable part (made from 304)…Removal of the Arc will increase range of the Slow Tuner

Support Arc

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LCLS II pCM Tuner_V2 (Modification of theTuner_V1) - (1)- Safety Rod

– to protect cavity from excessive stretching during leak check test inside CM

Tuner_V1 designed to tune cavity by “pushing” on the cavity… no any mechanism to prevent cavity from excessive deformation by forces directed inside cavity volume… Step#3

F=3.8kN

Tuner_V1(no safety rod)

Tuner_V2(with safety rod)

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LCLS II pCM Tuner_V2 (Modification of theTuner_V1) –Safety Rod (1) & Piezo Preload tuning mechanism (2)

Small Tuner modification (removing Support Arc, modifying edges of arms) led to increasing tuning range to 1.7mm (on the cavity flange)∆F will increase 450kHz 580kHz

Screw on the Top&Bottom main levers will help to adjust uniform preload of the Top&Bottom piezo-stacks.

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LCLS II pCM Tuner_V2 (Modification of theTuner_V1) –Stepper Motor Limit switches(3) & washers to avoid loosening screws(4)

Equipment safetyLimit switches to prevent hitting “hard stops”.When tuner arm hit “hard stops” forces applied to traveling nut can reach 2-4kN (much above 1.3kN design forces)… traveling nut will be damaged ---experience from first cold test of the Tuner

In the XFEL design “hard stops” will damage harmonic drive…

washers to avoid loosening screws(4)

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Piezostack safety in case of vacuum accident (Step #11)(equipment safety)

Encapsulated piezo designed and manufactured by Physik Instrumente (PI) per FNAL specifications.Blocking Forces 3,8kN

Designated Test of “cold-80K” piezo “6kN survivor” test

Fixture with piezo-capsule was cool-down inside LN2,installed into INSTRON and measured C vs Forces

Piezo Survived 6kN test

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Summary

FNAL LCLS II team reviewed equipment safety aspects of the Cavity/He Vessel/Tuner (C/HV/T) system.

As a result of the review special table was generated. Table presented anticipated steps of assembly and operation of the CM and for various pressure conditions.

Unsafe steps (when any part of C/HV/T system can compromised) were identified.

Tuner design was modified to address uncovered deficiency.

Designated tests were conducted to confirm safe operation of the components of C/HV/T system

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