Update on bgv impedance studies
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Update on BGV impedance studies. Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi, Plamen Hopchev, Nicolas Mounet, Elena Shaposhnikova. Agenda. BGV design Impedance studies for the LHC

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Update on BGV impedance studies

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Update on bgv impedance studies

Update on BGV impedance studies

Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team

Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi, Plamen Hopchev, Nicolas Mounet, Elena Shaposhnikova.


Agenda

Agenda

  • BGV design

  • Impedance studies for the LHC

  • First studies with 147 mm diameter

  • Studies with smaller diameters and various geometries

  • Conclusions and next steps


Design of new lhc bgv beam gas vertex detector to be installed in ls1

Design of new LHC BGV (Beam Gas Vertex detector)to be installed in LS1

  • request by Plamen, Bernd (BE-BI) and Massimiliano (LHCb)


Agenda1

Agenda

  • BGV design

  • Impedance studies for the LHC

  • First studies with 147 mm diameter

  • Studies with smaller diameters and various geometries

  • Conclusions and next steps


Impedance studies in lhc

Impedance studies in LHC

  • We study the electromagnetic fields generated by the LHC beam when passing through the BGV.

  • These fields perturb the guiding fields, and can lead to

    • Beam instabilities (longitudinal and transverse)  beam losses and/or emittance growth (many occurrence of transverse instabilities in 2012)

    • Beam induced heating of the surrounding  loss of performance, outgassing, deformation, or destruction of the equipment(many examples in 2012: TDI, BSRT, ALFA, MKI, TOTEM, vacuum bellows)

  • In view of higher brightness after LS1, we need to carefully study all planned installation and modifications of LHC hardware.


Agenda2

Agenda

  • BGV design

  • Impedance studies for the LHC

  • First studies with 147 mm diameter

  • Studies with smaller diameters and various geometries

  • Conclusions and next steps


First studies with cst with initial radius of 147 mm

First studies with CST (with initial radius of 147 mm)

Scan over Angle 2

Time domain wakefield simulations

Angle 1=15 degrees

Longitudinal impedance in Ohm (underestimated)

Frequency in GHz

 Many longitudinal resonances whatever the angle from 800 MHz onwards.


Update on bgv impedance studies

Angle IN: 10 degrees

Angle Out: 10 degrees

Angle IN

Angle OUT

With eigenmode solver:

Largest longitudinal mode at ~1 GHz: R~1 MOhm, Q= 40,000

Angle IN: 30 degrees

Angle Out: 10 degrees

Angle IN

Angle OUT

With eigenmode solver:

Largest longitudinal mode at ~1 GHz: R~0.8 MOhm, Q= 65,000

 Very large resonances, despite the longer taper


New geometry smaller radius requested by plamen 130 mm taper in 6 degrees and taper out 30 degrees

New geometry (smaller radius requested by Plamen : 130 mm) : taper IN : 6 degrees and taper OUT: 30 degrees

Re(Zlong)

Frequency (GHz)

Shunt impedance

With eigenmode solver:

Many longitudinal modes after 900 MHz: R~0.07 MOhm, Q between 40,000 and 65,000

Mode number

Still quite large, but factor 10 reduction.

 What is the acceptable limit?


What is the acceptable limit 1 2

What is the acceptable limit (1/2)

  • Limit for longitudinal instabilities

    • Limit from design report in 400 MHz RF system: 200 kOhmfor ultimate intensity, 2.5 eVs longitudinal emittance at 7TeV (E. Shaposhnikova BE/RF-BR).

    • Hard limit below 500 MHz. In principle, less critical above 500 MHz.

    • However, much safer to stay below 200 kOhm for all frequency range


What is the acceptable limit 2 2

What is the acceptable limit (2/2)

  • Limit for beam induced heating:

    • The cooling system should be dimensioned to cope with the power lost in the device

    • Ex: 70 kOhm at 900 MHz with 50 ns beam at 1.6e11 p/b Ploss~ 700 W

    • Ex: 70 kOhm at 1100 MHz with 50 ns beam at 1.6e11 p/b Ploss~ 100 W

    • Ex: 70 kOhm at 1200 MHz with 50 ns beam at 1.6e11 p/b Ploss~ 5 W

 It is critical for both limits to:

 push the mode frequencies as high as possible

 reduce the shunt impedance below 200 kOhm


Agenda3

Agenda

  • BGV design

  • Impedance studies for the LHC

  • First studies with 147 mm diameter

  • Studies with smaller diameters and various geometries

    • Impact of cavity length

    • Impact of taper length

  • Conclusions and next steps


Impact of cavity length on shunt impedance of the highest mode

Impact of cavity length on shunt impedance of the highest mode

  • 106 mm radius (smaller radius push frequencies higher)

  • Copper coating (increases shunt impedance by a factor ~ 6 for 316LN)

Cavity length

  • Not monotonic

  • The length of the cavity should not be too small

  • Frequency of the modes is not plotted, but is also important to assess their effects


Agenda4

Agenda

  • BGV design

  • Impedance studies for the LHC

  • First studies with 147 mm diameter

  • Studies with smaller diameters and various geometries

    • Impact of cavity length

    • Impact of taper length

  • Conclusions and next steps


Importance of taper l 0 5m

L = 0.5 m

Importance of taper (L=0.5m)

l

L

l

  • 106 mm radius (smaller radius push frequencies higher)

  • Copper coating (increases shunt impedance by a factor ~ 6 for 316LN)

 The longer taper, the better


Importance of taper l 1m

L = 1 m

Importance of taper (L=1m)

l

L

  • 106 mm radius (smaller radius push frequencies higher)

  • Copper coating (increases shunt impedance by a factor ~ 6 for 316LN)

l

 The longer taper, the better


Importance of taper l 1 5m

L = 1.5 m

Importance of taper (L=1.5m)

l

L

  • 106 mm radius (smaller radius push frequencies higher)

  • Copper coating (increases shunt impedance by a factor ~ 6 for 316LN)

l

  • The longer taper, the better!

  • The longer cavity length, the better (at least above , complete study ongoing)


Agenda5

Agenda

  • BGV design

  • Impedance studies for the LHC

  • First studies with 147 mm diameter

  • Studies with smaller diameters and various geometries

    • Impact of cavity length

    • Impact of taper length

    • What is the best if total length= 2m?

  • Conclusions and next steps


A more realistic geometry

A more realistic geometry

  • 106 mm radius (smaller radius push frequencies higher)

  • Copper coating (increases shunt impedance by a factor ~ 6 for 316LN)

  • Full length of about 2 m (taper included)

l

L

l

L+2l = 2 m

Cavity length increases

 Taper length decreases


Zoom below the limit

Zoom below the limit

  • The longer the taper, the better (for the symmetric case)

  • Even with copper coating, well below the limit below 1.5 m of flat length (with Ploss of 40 W  is it acceptable from mechanical point of view?).


Conclusions and next steps

Conclusions and next steps

  • There is hope with 106 mm radius!

  • Can the system take ~ 50 W of power loss?

  • Actual mechanical constraints to be added to the next round of simulations  What is feasible?

  • Checks of the transverse impedance


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