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01/07/2005 SN 1 of 16
Estimation of HOM Power in the Interaction Region of ILC
Sasha Novokhatski
Session “Beam RF Effects”ILC MDI Workshop
SLAC January 7, 2005
01/07/2005 SN 2 of 16
Central part of PEP-II IR
01/07/2005 SN 3 of 16
Wake fields go through the fingers into vertex bellows
cavity ~500 W [Stan Ecklund]
01/07/2005 SN 4 of 16
Wake fields are absorbed in ceramic tiles of Q2-bellows
~10 kW [Stan Ecklund]
01/07/2005 SN 5 of 16
IR Model
• Difficulties with 3-d calculations do not allow to do wake field calculations for very short bunches traveling in long structure
• We can use simplified 2-d model which already demonstrated good agreement with HOM measurements (Stan Ecklund) for PEP-II IR:
–HOM power–Bunch length dependence
01/07/2005 SN 6 of 16
PEP-II 2-d model and analog for ILC
Transverse dimensions are two times smaller
01/07/2005 SN 7 of 16
Wakes in IR at different time
01/07/2005 SN 8 of 16
Wakes
01/07/2005 SN 9 of 16
Wakes
01/07/2005 SN 10 of 16
Loss factor for PEP-II IR
Bunch length dependence changes
from
(14-8 mm)
to
-3/2 (6-2 mm)
01/07/2005 SN 11 of 16
Loss factor for ILC IR
Bunch length dependence
(0.3-0.1 mm)
01/07/2005 SN 12 of 16
Shape of RF signal(wake potential)
01/07/2005 SN 13 of 16
Comparison with wake in TESLA
01/07/2005 SN 14 of 16
IP HOM Power 2 2
Incoherent Pow
(
er
) ( )b e eP k I I
Parameters PEP- II ILC
Bunch length [mm] = 13 0.3
Loss factor [V/ pC]= 0.248415883 53.1293034
LER current [A] 2.4 0.025
HER current [A] 1.5 0.025
Time between bunches [nsec] 4.2 337
Power loss (pulse) [kW] 8.357207151 22.3807191
Average 8.357207151 0.044761438
1m, 5 Hz
01/07/2005 SN 15 of 16
ILC IP HOM Power for
smaller bunch length
Parameters ILC ILC
Bunch length [mm] = 0.2 0.1
Loss factor [V/ pC]= 78.7272414 154.203
LER current [A] 0.025 0.025
HER current [A] 0.025 0.025
Time between bunches [nsec] 337 337
Power loss (pulse) [kW] 33.1638505 64.9582
Average 0.066327701 0.12991639
1m, 5 Hz 1m, 5 Hz
01/07/2005 SN 16 of 16
Summary
• Electron and positron bunches produce electromagnetic fields (wakefields) in Interaction Region
• These fields travel for long distance and penetrate inside bellows, pumps and vacuum valves.
• Average power of these fields is not high, however pulse power can reach tens of kilowatt.
• More wake field studies are needed.