Booster bpm’s

Jim Crisp

3/29/06

Plate width and linearity

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40 degree plates

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60 degree plates

with the response linearized along the axis 60 and 20 degree plates become nonlinear in the corners40 degree plates have the least distortioncalculate 0.5db/mm (booster bpm’s are 0.52db/mm)

5

2135][

BA

BA

BA

BAmmX

50 or 25 ohms

• The even mode impedance is most important• 50 ohm 40 degree plates won’t fit in the proposed magnet (60 degree plates worse)

– 3.916” plate ID for 5.465” bpm OD• 25 ohm, 40 degree plates will fit

– 4.5” plate ID 5.228” bpm OD with 1/8” wall

30.0

40.0

50.0

60.0

70.0

5 5.25 5.5 5.75 6

bpm pipe ID [inches]

char

acte

rist

ic i

mp

edan

ce [

oh

ms]

even

odd

40 deg plates

4 3/8" plate ID5.408" ID5.533" OD

50ohm 40deg plates 5.465" bpm OD 1/16" w allestimated plate ID 3.916"

25ohm 40deg plates w ith 4.625" plate ID1/8" w allestimated bpm OD 5.228"

Equivalent bpm• Current booster bpm’s

– 4.625” plate ID, 60 degrees wide, 6” long, 6” bpm OD, – 52.9 ohms even, 44.2ohms odd mode– Vplate/Ibeam 1.4 ohms at 53MHz– 0.52db/mm 30-50MHz and 0.48db/mm at 200MHz

• Proposed bpm– 4.5” plate ID, 40 degrees wide, 16” long

• Ideal (60/40)(50/25)6” = 18” correction magnet 17.5” flange to flange– 25 ohms even 24.2 ohms odd– Vplate/Ibeam = 1.25 ohms at 53MHz (about 10% less)– 0.50db/mm

MHzatc

lZ

I

V

Idt

dtZV

MHzl

c

RCf

pfcZ

l

Z

tC

detectorcapacitive

obeam

plate

beamoplate

ooplate

534.1360

60

360

60

31322

1

1.10

)(

534.1360

60

sin360

60

smallc

l

MHzatc

lZ

c

lZ

I

V

detectorstripline

o

obeam

plate

Beam intensity range• 25 ohms, 40 degrees wide, 16” long

– (Correction magnet is 17.5” flange to flange)• Rf module dynamic range -23.5 to +18.5dbm

– -35 to +27dbm for AM to PM rf module– +1.5db for 100ft RG8 cable– +/-10db for +/-20mm position

• working range of beam intensity– 8.4 to 1060e10– (about the same as now)

dbmVV

AmpsI

eNmRR

cNeMHzI

plate

beam

beam

0.185.2

0.2

13189.752

2)53(

Frequency response

• Peak at wl/c = pi/2 (plates 1/4 wavelength long)– 185MHz for 16” and 492MHz for 6” plates

• Same response for terminated, open, or shorted stripline– 200MHz linac beam 5.00/2.75 ohms (present/proposed)– 37.9MHz at 400MeV 1.06/0.93 ohms– 52.8MHz at 8GeV 1.40/1.20 ohms

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frequency [MHz]

Vp

late

/Ib

eam

[o

hm

s]

40deg, 25ohm, 16" long

60deg, 50ohm, 6" long

Use 50ohms at bpm output to terminate stripline

rf modules

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-5

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5

10

-40 -20 0 20 40

A/B [mm]

A/B

- c

alc(

A/B

) [m

m]

A+B greater than -40db

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A+B [db]

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- c

alc(

A/B

) [m

m]

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A+B [db]

calc

A/B

[db]

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14.1

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4tanln10ln

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1

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01

C

F

V

VVFCFB

A

db

(MI 0.48db/mm Hor, 0.42db/mm Ver)

MI rf module, similar for booster

Wall thickness and magnetic fields

• magnetic fields will be attenuated and delayed inside bpm• round pipe acts like low pass filter (approximate)

– n = 2 for dipole (4 for quadrupole etc)– ρ = 9.0e-7 ohm-m for stainless steel– R = 3” radius– t = 1/8” wall thickness

– f ~ 942Hz t ~ 170usec

– The 4 plates will also distort a changing magnetic field above this frequency

– Frequency where 1/8” = skin depth• f = 22.6KHz

• What are the frequency components of the correction fields?

– (30-50MHz external magnetic fields will never reach the plates)

tR

nf

2

f

Measured fields in pipe• 1/8” wall 2” ID Aluminum pipe• Solid is calculated using Mafia – Ostiguy• Red curve from simple formula• Points are measured with hall probe

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freq [Hz]

amp [db]

1/8" wall 2" ID Al

Cross section• Proposed design• Type N feed through on one end• Short other end• 16” long plates

A few details• Proj 22 Task 1.02.03.01• deliver nearly the same signal to the rf modules

– Lowest intensity 1 turn of 30mA or about 40e10• 24 long and 24 short locations (use same bpm) 60 magnets will be made• Need survey fiducials to measure bpm location in tunnel

– Use same fiducials on bpm test stand– survey position and rotation tolerances?

• Allowable wall thickness / bandwidth of correction fields– Rise times of 2 msec– Eddy current heating may be a problem (correctors ramped at 15Hz)

• radiation exposure over the expected life time?– Few locations measured at 20KRad/month (MRad/lifetime)

• Vacuum acceptance criteria– Flanges should be angled to match bend magnet– Assembly may require a bellows

• Bpm should be made very reliable and thoroughly tested before installation, requires replacing magnet to change

• May request cable strain relief bracket on magnet• Prototype bpm for test June 2006• First 24 required February – April 2007• Installation June 2007