update on bgv impedance studies alexej grudiev, berengere luthi, benoit salvant for the impedance...
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![Page 1: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/1.jpg)
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.
![Page 2: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/2.jpg)
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
![Page 3: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/3.jpg)
Design of new LHC BGV (Beam Gas Vertex detector)to be installed in LS1
• request by Plamen, Bernd (BE-BI) and Massimiliano (LHCb)
![Page 4: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/4.jpg)
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
![Page 5: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/5.jpg)
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.
![Page 6: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/6.jpg)
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
![Page 7: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/7.jpg)
First studies with CST (with initial radius of 147 mm)
Many longitudinal resonances whatever the angle from 800 MHz onwards.
Angle 1=15 degrees
Scan over Angle 2
Time domain wakefield simulations
Frequency in GHzLong
itudi
nal i
mpe
danc
e in
Ohm
(und
eres
timat
ed)
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Angle IN: 10 degreesAngle Out: 10 degrees
Angle IN: 30 degreesAngle Out: 10 degrees
With eigenmode solver:Largest longitudinal mode at ~1 GHz: R~1 MOhm, Q= 40,000
With eigenmode solver:Largest longitudinal mode at ~1 GHz: R~0.8 MOhm, Q= 65,000 Very large resonances, despite the longer taper
Angle IN Angle OUT
Angle IN Angle OUT
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New geometry (smaller radius requested by Plamen : 130 mm) : taper IN : 6 degrees and taper OUT: 30 degrees
With eigenmode solver:Many longitudinal modes after 900 MHz: R~0.07 MOhm, Q between 40,000 and 65,000
Still quite large, but factor 10 reduction. What is the acceptable limit?
Frequency (GHz)
Re(Z
long
)
Shun
t im
peda
nce
Mode number
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What is the acceptable limit (1/2)• Limit for longitudinal instabilities
– Limit from design report in 400 MHz RF system: 200 kOhm for 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
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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
![Page 12: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/12.jpg)
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
![Page 13: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/13.jpg)
Impact of cavity length on shunt impedance of the highest mode
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
Cavity length
• 106 mm radius (smaller radius push frequencies higher)• Copper coating (increases shunt impedance by a factor ~ 6 for 316LN)
![Page 14: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/14.jpg)
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
![Page 15: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/15.jpg)
Importance of taper (L=0.5m)L
l
lL = 0.5 m
The longer taper, the better
• 106 mm radius (smaller radius push frequencies higher)• Copper coating (increases shunt impedance by a factor ~ 6 for 316LN)
![Page 16: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/16.jpg)
Importance of taper (L=1m)L
l
lL = 1 m
The longer taper, the better
• 106 mm radius (smaller radius push frequencies higher)• Copper coating (increases shunt impedance by a factor ~ 6 for 316LN)
![Page 17: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/17.jpg)
Importance of taper (L=1.5m)L
l
lL = 1.5 m
The longer taper, the better! The longer cavity length, the better (at least above , complete study ongoing)
• 106 mm radius (smaller radius push frequencies higher)• Copper coating (increases shunt impedance by a factor ~ 6 for 316LN)
![Page 18: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/18.jpg)
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
![Page 19: Update on BGV impedance studies Alexej Grudiev, Berengere Luthi, Benoit Salvant for the impedance team Many thanks to Bernd Dehning, Massimiliano Ferro-Luzzi,](https://reader030.vdocuments.us/reader030/viewer/2022032702/56649f4c5503460f94c6c81e/html5/thumbnails/19.jpg)
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)
Cavity length increases Taper length decreases
Ll
l
L+2l = 2 m
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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?).
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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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