R&D Meeting, March 23th, 2017 1

Review on Crab Test at SPS

Facility

Salvador Sosa

Old Dominion University

ssosa006@odu.edu

R&D Meeting, March 23th, 2017 2

Material from the 6th HL-LHC Collaboration Meeting (Nov 2016)

– https://indico.cern.ch/event/549979/

Crab Cavity SPS Test (Jan 2016)

– https://indico.cern.ch/event/463435/

4th Joint HiLumi LHC-LARP Annual Meeting (Nov 2014)

– 2017-2018 CC Validation Run: Status and Issues, A. McPherson

– https://indico.cern.ch/event/326148/contributions/1711560/attachm

ents/633139/871382/SPS_Crabs_HL_LHC.pdf

This presentation composed of…

R&D Meeting, March 23th, 2017 3

Cavity validation with beam (field, ramping, RF controls, impedance)

– Operation of such type of cavities in high current and high energy CW (proton) circular

machines has not been done before.

Cavity Transparency

– Injection, capture, acceleration where the cavities are carefully counter-phased.

– Ultra-precise control of cavity voltage and phase guarantees the preservation of beam

quality throughout the cycle.

Collimation, machine protection, RF noise, emittance growth, non-linearities, Instrumentation

and interlocks.

Guarantee the operation of cavities with a trip rate significantly below the LHC availability. To

validate this is in SPS is pre-requisite both with and w/o beam.

Unlike electrons, there are many aspects (emittance growth, machine protection, RF non-

linearity, instabilities) where proton beam tests are the only conclusive answer.

Goals of CC Test at SPS

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Impact of (Cost & Schedule) Reviews

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▪ SPS Tests

▪ Prepare & test one cryomodule in the SPS before 2018

▪ SPS-LSS6 dedicated test stand for beam tests in 2018

▪ Integration almost complete, installation starts in 2 months

▪ LHC

▪ ½ system (16 cavities) as a new baseline

▪ New production strategy with industry starting 2017

▪ UK pre-series cryostat & US contribution (10 RFD dressed Cav)

▪ RF power infrastructure reduction to 40 kW-CW (80 kW peak)

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SPS Tests Program – Weekly Schedule

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EN-MME BE-RF/SRF EN-ACE TE-CRG TE-VSCBE-RF

Cavity #1

ready

22/12/16

Cavity #2

ready

02/02/17

Cavity #2

pieces

produced

28/10/16

Cavity #1

pieces

produced

03/10/16

String

assembled

27/07/17

CM

assembled

06/12/17

CM

commissioned

In SPS

23/02/18

Missing

12 days

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MD Parameters

• For crab cavity tests with proton beams in the SPS

Units Value

Energy GeV 26 − 450

Coast Energy GeV 55, 120, 270

Intensity p/bunch 0.05 − 1.3 × 1011

RF Voltage MV 3.0 − 7.0

4th Harmonic Voltage MV 0.0

Bunch Length ns < 2.0

Longitudinal Emittance eVs 0.35 − 0.5

Betatron Tunes 26.12, 26.18

𝛽𝑥,𝑦 m 40, 80

Dispersion m −0.5

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Prototype Cryomodules

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Vertical crossing for ATLAS,

first one to go to SPS 2018

Horizontal crossing for CMS

Cavities starting 2017

300K

10−10mbar~10−7mbarAtm Pressure

2K − 80K

2K2K

300K

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Mechanical Parameters

• SPS between QDA.61710 – MST61779

• In the SPS alignment tolerances are generally more relaxed. However

the tighter tolerances derived for the LHC are kept for validation.

Units Value

Total Cryomodule length m 2.9

Total Bypass length m 9.5

Cavity Aperture mm 𝟖𝟒

Transverse Cavity Alignment

mm ≤ 0.5

Transverse Tilt degrees < 0.3

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Cavity Parameters

Two cavity types (Ver & Hor) (ATLAS & CMS)

Vertical cavities will go first in the SPS

Units Value

Frequency MHz 400.79

Number of Cavities 2

Kick Voltage/cavity MV 3.4

R/Q (linac convention) Ω ∼ 400

Max RF Power kW 40 (80)

Cavity detuning kHz ±100 (−60)

Cavity bandwidth Hz 800

DQW RFD

Pictures courtesy EN-MME

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SPS Cavities, 2K Volume

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Bulk Nb cavities, Dipolar symmetry

𝑉𝑇 = 3.4 MV (𝐸𝑝, 𝐵𝑝 ≤ 40 MV/m, 70 mT)

Stored energy ~ 10 − 12 J

CERN insourced DQW production

Nov 2015

DQW RFD

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Dressed Cavities (2K volume)Fundamental

Power Coupler

Tuning

Mechanism

HOM

Coupler

(Niobium)

Hel-Vessel

(Titanium)

CavityCold

Magnetic

Shield

Tuner frame

(Titanium)

Pickup HOM

HOM

Main Mechanical interfaces:

He-vessel: Bolted-welded concept

Cold magnetic shield

Tuner: Sym. tuning with warm actuation

Three point support + alignment system

Main RF interfaces

1 FPC: Single ceramic coaxial line

3 HOMs: Two stage filter, coaxial

1 PU: Cu-Nb for field probe + HOM

Similar concept for RFD with different HOM interfaces

Some Final Comments• A new paradigm on SC compact deflecting cavities will soon

be validated with the highest energy protons for the first

time in the world

• There is an intense level of activity on many fronts

• USLARP & UK collaborations were an integral part w/o

which it SPS tests be impossible

• The design choices for the CM & RF services (after many

iterations) are robust. We have validated most important

elements by prototyping (cavity, tuner, He-vessel…)

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R&D Meeting, March 23th, 2017 15

Extra Slides

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Test Program Summary

• In-situ cryomodule RF commissioning/testing in park position

• RF commissioning with low-intensity beam, 1-12 bunches

• Establish proper RF parameters (operating frequency, amplitude, and phase)

• Verify that CCs are transparent (cavity counter-phasing and detuning)

• High intensity single bunch up to 4x72 trains

• Impact on cavity performance (including transient behavior), impedance, stability

& machine protection as a function of beam current; interlocks

• Verify cavity stability over many hours (relevant for LHC physics fill)

• Long-term behavior of coasting beams in the SPS with 1-bunch

• Study the effects of cavity drifts, emittance growth, non-linear effects such as RF

multipoles

Goal of this meeting to define a detailed & prioritized program that would

constitute the success of the SPS tests and min goals for 2018

l/4 TEM Cavity – BNL (Ilan Ben-Zvi)

• Cavity is very short in the direction of opposing beamline.

• Nearest HOM is far away.

400 MHz Cavity Comparison

RF Dipole (ODU)

4-Rod(UK)

¼ Wave (BNL)

Cavity Radius [mm]

147.5 143/118 142.5

Cavity Length[mm]

~600 ~500 ~400

Beam Pipe [mm]

84 84 84

Peak E field 33 29.5 32.3

Peak B- Field 56 59.5 57.3

RT/Q 287 915 318