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

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Central part of PEP-II IR

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Wake fields go through the fingers into vertex bellows

cavity ~500 W [Stan Ecklund]

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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

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Wakes in IR at different time

01/07/2005 SN 8 of 16

Wakes

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Wakes

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Loss factor for PEP-II IR

Bunch length dependence changes

from

(14-8 mm)

to

-3/2 (6-2 mm)

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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)

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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.