HOM Issues in LER Ring and IR. Recent measurements and calculations

PEP-II Machine Advisory Committee Meeting SLAC,

April 15-17, 2004

HOM Issues in LER Ring and IR.HOM Issues in LER Ring and IR.Recent measurements and calculations.Recent measurements and calculations.

Sasha Novokhatski

SLAC

15-April-2004 PEP-II MAC Session 2SN

More LER & HER currents –More LER & HER currents – more HOM Heating more HOM Heating

LER ring– TSP feed-through & Bellows – Vacuum pumps & NEGs (new)

HER ring– Bellows (new)

Interaction region– Vertex bellows & near bellows


Fight against high temperaturesFight against high temperatures

Water and air cooling– Fans for bellows in all LER and HER regions– Special cooling for vertex bellows

Damping High Order Modes by water cooled RF absorbers– HOM absorber in LER arc chamber

Improving RF screens


HOM measurements and HOM measurements and computer simulationscomputer simulations

HOM spectrum measurement:– Signals from BPMs– RF antenna near TSP feed-through– RF antenna near HV cable in vacuum pumps

HOM power measurement:– Thermocouples on input and output water

cooling system with water-flow measurement

Computer simulation:– Calculations with MAFIA and other wake field

programs


HOM absorber in region 4HOM absorber in region 4

HOM Absorber

TSP

1162

Bellows2012


Absorber: ceramic tiles with large Absorber: ceramic tiles with large loss tangent and water cooling tubeloss tangent and water cooling tube


Effect of absorberEffect of absorberon TSP feed-throughon TSP feed-through

Temperature

LER current

Nov. 2002-Apr. 2004


TSP in the next arc chamber 1153TSP in the next arc chamber 1153

Nov. 2002-Apr. 2004


Analog TSPs in region 12 do not Analog TSPs in region 12 do not have high temperatureshave high temperatures

Artem KulikovHOM detectors

installed in June 2003


HOM spectrum measurement: antenna HOM spectrum measurement: antenna and spectrum analyzer near TSP 1163and spectrum analyzer near TSP 1163


HOM power measurement: digital HOM power measurement: digital water flow meter and thermocoupleswater flow meter and thermocouples


Power Power relationsrelations

2 1360

3.8

200

RF

bunches

VP Z I

MV N

Z Ohm

Prediction for HOM power

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 1000 2000 3000 4000

LER current [mA]

HO

M p

ow

er [

W]

V=3.2MVN=1200

V=3.8MVN=1360

V=5.6MVN=1700

V=6.4MVN=1715

Now we are here


The hottest bellows in the LERThe hottest bellows in the LER

LER Bellow 2012 PR04with ‘super” fan

Nov. 2002-Apr. 2004


Examples of RF modes. S. WeathersbyExamples of RF modes. S. Weathersby

Magnetic field Electric field


Proposal for absorber for arc bellowsProposal for absorber for arc bellows

Copper buttons

Absorber tiles

Water cooling tubes


MAFIA . Stephen Weathersby computation.

1.E+01

1.E+02

1.E+03

1.E+04

1.4E+09 1.9E+09 2.4E+09 2.9E+09 3.4E+09 3.9E+09 4.4E+09

frequency [Hz]

Q wall-mag

3-az-mag

no abs mag

Comparison of 1-tile thick covered Comparison of 1-tile thick covered flange absorber with azimuthal 2x3-tile flange absorber with azimuthal 2x3-tile mount and the no absorber Q values.mount and the no absorber Q values.


HOM spectrum HOM spectrum in IP region. in IP region.


Vertex bellowsVertex bellows

Bellow

Cavity

bunch field ‘‘Mode Converter”


Vertex bellows. RF Modes .Vertex bellows. RF Modes .Stephen Weathersby computation.


Quadruple modeQuadruple mode


Damping HOMs in vertex bellows. Damping HOMs in vertex bellows. Simulation study by S. Weathersby.Simulation study by S. Weathersby.

Decreasing Q-value of a bellow cavity by placing absorber

Best position of absorber.

Low Q decreases power dissipation.

10

0

1 022

1 0

0 1

20 1

1

1

in

4(1 )

( )

4 /

(1 / )

cav

waveguide

cav inc inc

cav inc

Reflection from cavity

ZQQ

Z Q

Power a cavity

Q QP P P

Q Q

Q QP P

Q Q


Power dissipation a bellow cavityPower dissipation a bellow cavity

Q/QbettaPower in cavity 0.01 0.04

0.1 0.330.2 0.560.5 0.890.7 0.97

1 12 0.895 0.56

10 0.3315 0.2320 0.18

Power in cavity

0

0.2

0.4

0.6

0.8

1

1.2

0 1 2 3 4 5 6 7 8 9 10

Q0/Qbetta


Absorber on the one side does not well damp modes!

Vertex Bellows

1.00E+00

1.00E+01

1.00E+02

1.00E+03

3.00E+09 5.00E+09 7.00E+09 9.00E+09 1.10E+10 1.30E+10

Frequency

Q-v

alu

e

no absorber mag mag

no absorber elec mag

mag mag

mag elec


Absorber on the other side. Still not good damping.


Q value

10

100

1000

10000

4.0E+09 5.0E+09 6.0E+09 7.0E+09 8.0E+09 9.0E+09 1.0E+10 1.1E+10 1.2E+10 1.3E+10

frequency [Hz]

QQ Cu no absorber

Q absorber 0.5mm

Q absorber 1.0mm

Q absorber 1.25mm

Q absorber 1.5mm

Absorber on the wall


Power in a cavityPower in a cavityX Power in cavity

0.01 0.0392120.1 0.3305790.2 0.5555560.5 0.8888890.7 0.968858

1 12 0.8888895 0.555556

10 0.33057915 0.23437520 0.181406

Power in cavity

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10

Q0/Qbetta


HOMs in vacuum pumpsHOMs in vacuum pumps


Vacuum pump (LER PR2:3044) HOM Vacuum pump (LER PR2:3044) HOM spectrum. Frequency range 0-10 GHzspectrum. Frequency range 0-10 GHz

Antenna in HV connector


Frequency range 3-6 GHzFrequency range 3-6 GHz


Q-value estimationQ-value estimation

0

5

10

15

20

25

30

-1 -0.5 0 0.5 1 1.5 2 2.5 3

Delta Frequency [MHz]

Sp

ectr

um

F=4.046119 GHz Breit-Vigner Q=6100

02468

101214161820

-1 -0.5 0 0.5 1

Delta frequency [MHz]

Sp

ectr

um

F=5.236GHz Breit-Vigner Q=12000


RF screen for vacuum pumpRF screen for vacuum pump


RF screens for NEGsRF screens for NEGs


Other screenOther screen


SummarySummary

More water and air coolingDamping High Order Modes by water

cooled RF absorbersSimulation studies on improvement of

beam chamber elements and RF screens

Documents

HOM Issues in LER Ring and IR. Recent measurements and calculations