LSWG day:Impedance and beam induced heating

Nicolas Mounet*, Daria Atapovych, Nicolò Biancacci, Elias Métral, Tatiana Pieloni, Stefano Redaelli, Benoit Salvant

Acknowledgments: Collimation team, BE-BI, TE-ABT, EN-STI, ALFA and TOTEM teams,

Philippe Baudrenghien, Themis Mastoridis, Juan Esteban Mueller, Giulia Papotti, Giovanni Rumolo, Elena Shaposhnikova, Carlo Zannini.

*: now at EPFL

Agenda

• Proposed objectives of MDs• Impedance:– Outcome of MDs in run 1 in a nutshell– Proposals for what would be needed for run 2

• Beam induced heating:– Outcome of MDs in run 2 in a nutshell– Proposals for what would be needed for run 2

• Conclusions

Proposed objectives of impedance/heating MDs

• Mandatory: assess if intensity limits significantly changed during LS1 due to modified/replaced/added devices and to the increase in energy: – 1 consolidated injection dump collimator TDI per beam,– 1 spare primary collimator TCP for beam 1,– 8 new tertiary collimators TCT with buttons and ferrite per beam,– 1 new TCDQ module per beam,– 1 consolidated BSRT mirror per beam,– 4 upgraded MKI injection kickers per beam,– new experimental beam pipes in CMS and ATLAS– All consolidated TOTEM and ALFA pots (+ new TOTEM pots).– + many “smaller” items (e.g. caroussel chamber in 800 mm chambers)

• Very interesting:– Localize impedance sources– Check single bunch stability threshold at injection energy– Check the impedance/heating of other devices (e.g. IR3, IR7, MKD)– Assess the feasibility of reducing/increasing bunch length, changing the bunch profile– Assess the feasibility of optimizing the beta functions to reduce transverse impedance

Agenda

• Proposed objectives of MDs• Impedance:– Outcome of MDs in run 1 in a nutshell– Proposals for what would be needed for run 2

• Beam induced heating:– Outcome of MDs in run 2 in a nutshell– Proposals for what would be needed for run 2

• Conclusions

Impedance: Results from LHC run 1

N. Mounet et al

Discrepancy between measurement and predictions should reduce thanks to the addition of geometric impedance (O. Frasciello and M. Zobov: -15%) and more convergence studies between HEADTAIL and DELPHI (Daria Astapovych)

Collimator impedance model vs tune shift measurements

Accounting for geometric impedance and using more converged simulations reduced the discrepancy by ~30% for collimators. Still ~50 % is missing

N. Mounet et al

Impedance: Results from LHC run 1

• Impedance of moving devices:- Collimation system- TDI- TCDQ very large discrepancy

• Localization

With the LHC accuracy and 2200 turns with an AC dipole, we should be able to detect the TDI IR7 collimators and the TDIs at injection promising!

Example: Horizontal tune while moving the TCSG.6R7 gap

N. Biancacci et al

N. Mounet et al, instability review 2013

Agenda

• Proposed objectives of MDs• Impedance:– Outcome of MDs in run 1 in a nutshell– Proposals for what would be needed for run 2

• Beam induced heating:– Outcome of MDs in run 2 in a nutshell– Proposals for what would be needed for run 2

• Conclusions

Impedance: What we need to prepare run 2 (with single bunches only)

“Mandatory” potential expected or unexpected limitations– Assess total longitudinal effective impedance at injection and top energy for both beams

See presentation of Elena Shaposhnikova

– Assess total transverse imaginary effective impedance at injection and top energy for both beams

By measuring betatron tune shift vs intensity (ideally performed with 8 single bunches of various intensities)

Which requires precise tune measurement (BBQ), bunch length, intensity, chromaticity

– Assess total real effective impedance at injection and top energy for both beamsBy measuring instability growth rate vs chromaticity (ideally performed with 8 single bunches

of various intensities)Which requires tune measurement, bunch length measurement, BCT, chromaticty, Headtail

monitor, operational bunch by bunch damper and instability trigger

– TMCI threshold in both planes for both beams at top energyBy measuring instability threshold at chromaticity~0 (ideally performed with 8 single

bunches)Which requires high bunch intensity from injectors tune measurement, bunch length

measurement, BCT, chromaticity, Headtail monitor, operational bunch by bunch damper and instability trigger

Impedance: What we need to prepare run 2 (with single bunches only)

• Mandatory: checking the impact of modified moving equipment:– Assess TDI jaw longitudinal and transverse impedance– Assess TCDQ jaw longitudinal and transverse impedance (following inconsistency between

model and measurement in 2012)– Assess impedance of new TCTP with buttons and ferrite

Phase error and tune shift while moving the jaws Which requires the phase error application

– Assess impedance of new Roman pots

• “Nice to have”– Attempt localization of impedance– TMCI threshold in both planes for both beams at injection energy– Assess IR7 jaw longitudinal and transverse impedance at injection and top energies– Assess IR3 jaw longitudinal and transverse impedance at injection and top energies– Assess the feasibility of changing beta functions to reduce transverse impedance

• Impedance measurements at top energy would give:– Impact of smaller gap of collimators :

Can they be put closer in special conditions at injection energy? Could avoid the need to rampCould increase the resolution of tune shift measurements

– Impact of increased resistance of copper in beam screens

We should try to learn as much as we can at injection

Agenda

• Proposed objectives of MDs• Impedance:– Outcome of MDs in run 1 in a nutshell– Proposals for what would be needed for run 2

• Beam induced heating:– Outcome of MDs in run 2 in a nutshell– Proposals for what would be needed for run 2

• Conclusions

Heating due to impedance: results from run 1

• Temperature monitoring: all fills were “MDs”, in particular with the voltage increase in the middle of the fills.

• Bunch length reduction (OP test at injection energy in 2012): no obvious show stopper to go to nominal bunch length

• Flattening MD: very promising way to reduce heating on certain equipment (see Elena Shaposhnikova’s talk)

• Synchronous phase error and logged longitudinal beam spectra: very interesting tool to measure heating of moving devices.

Agenda

• Proposed objectives of MDs• Impedance:– Outcome of MDs in run 1 in a nutshell– Proposals for what would be needed for run 2

• Beam induced heating:– Outcome of MDs in run 2 in a nutshell– Proposals for what would be needed for run 2

• Conclusions

Heating: what we need to prepare run 2

• With single bunch/few bunches:– heating should be very small

measure the stable phase error check the delta phase error when moving devices (e.g. TDI), but energy loss

may also be too small to be detected.

• With many bunches– Check impact of intensity, bunch length, bunch shape on temperature (when

monitors installed) and vacuum pressures during regular fills– Check the impact of bunch length changes and flattening (need time for large

thermal capacity equipment), better at top energy since bunch length increases less due to IBS.

– Measure temperature and stable phase error for changing gaps of moving devices vs number of bunches to estimate if the heating is due to broadband or narrow band devices.

Agenda

• Proposed objectives of MDs• Impedance:– Outcome of MDs in run 1 in a nutshell– Proposals for what would be needed for run 2

• Beam induced heating:– Outcome of MDs in run 2 in a nutshell– Proposals for what would be needed for run 2

• Conclusions

Conclusions

• Many needed/interesting MD proposals • Some were not tried before LS1• We should focus on getting MDs for both beams (see Tatiana’s

talk) • Most impedance MDs can be performed on single bunches,

and a large part at injection energy• As proposed by Giulia Papotti, quite a few single bunch

instability MDs, moving devices MDs and scraping MDs could be performed as end of fill with dedicated operational procedures (if OK for MPP and collimation) more statistics.