Tevatron IPM

10/3/2003 Andreas Jansson - Tevatron IPM review 1

Tevatron IPM

Primary signal, electron transport, amplification, detection…


Overview

• Primary signal levels (# of electrons)

• Electron transport to detector

• Separation of protons and pbars

• Amplification and detection

• Avoiding parasitic signals


5-10

kV (

60-1

20 k

V/m

)

~1kV

~100V

RF screen

Electron suppression grid

High voltage plate

Electron source (e-gen or hot wire)

Anode board

“Faraday cage”

Microchannel plate

IPM schematic

e-

I+

B


Estimation of ionization

• Tev gas composition:– 42% H2 – 42% H2O – 16% N2

• Production rate (Sauli)– H2 5.9 cm-1

– H2O 15 cm-1 (est)– N2 10 cm-1

• Gives 1.3 10-2 cm-1 torr-1, or about 1000e for a 10 cm detector at 3 108 torr and 2.7 1011 protons.


Electron Transport

-0.02 -0.01 0 0.01 0.02

-0.02

-0.01

0

0.01

0.02

-0.001 -0.0005 0 0.0005 0.001 0.0015

-0.001

-0.0005

0

0.0005

0.001

0.0015

• Simulated electron transport in E+B field, to understand and minimize peak broadening.

• Home-cooked Mathematica code adapted from a program by A Hahn


Electron energy distribution

• Energy distribution MC generator from A. Hahn.

• Distribution approximately 1/T2.

• Sharply peaked at low energies, long tail which essentially generates background.

350

0

50

100

150

200

250

300

3.0E+20.0E+0 5.0E+1 1.0E+2 1.5E+2 2.0E+2 2.5E+2

Electron Energy Spectrum (eV)

Fig. from A. Hahn


Transverse displacement

-0.4 -0.2 0 0.2 0.4Devaiation mm0

2

4

6

8

10

12

14

borP.

sneD.

protons at injection

-0.4 -0.2 0 0.2 0.4Devaiation mm0

2.5

5

7.5

10

12.5

15

17.5

borP.

sneD.

pbars at injection

-0.4 -0.2 0 0.2 0.4Devaiation mm0

2

4

6

8

borP.

sneD.

protons at flattop

-0.4 -0.2 0 0.2 0.4Devaiation mm0

2.5

5

7.5

10

12.5

15

borP.

sneD.

pbars at flattop

B=0.2 T, E=100kV/m


Signal time structure

-5 0 5 10Timens0

20

40

60

80

100

120

140

stnuoC

protons at injection

-5 0 5 10Timens0

20

40

60

80

100

120

140

stnuoC

pbars at injection

-5 0 5 10Timens0

200

400

600

800

1000

1200

stnuoC

protons at flattop

-5 0 5 10Timens0

100

200

300

stnuoC

pbars at flattop

B=0.2 T, E=100kV/m


Magnetic field spec

• 0.2 T is adequate for protons at flat-top (worst case).

• Field uniformity should be 1% or better.

• Field must be compensated (less than 0.1 mm residual orbit distortion).

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 0.05 0.1 0.15 0.2 0.25

TIPM Data e- 10/30/97

Ratio Measured/Input Sigma

Ra

tio M

ea

sure

d/In

pu

t Sig

ma

Applied B (Ts)

Fig. from A. Hahn


Magnet designs

• Electro- vs Permanent magnet– Electromagnet preferred since

field can be varied and turned off

• 2 vs 3-bump– Limited by tolerances, use

simpler 2-bump.

• Single “Self-compensating” vs separate C-magnets – Cheaper to use commercially

available c-magnets

Fig. from V. Kashikin


How to separate p’s and pbars

• Helix separation is barely enough, and helix is undergoing modifications– Don’t rely on helix for separation!

• Time separation is 0-198ns, depending on location, and collection time typically 2-3ns.– Time gating can be used!– Implies single bunch resolution


How to gate?

• MCP too slow for single bunch gating (recharge time ~100us, according to Burle)!

• Gating clearing voltage is impractical (~10000V).

• Partially gated clearing voltage would simply act as a delay.

• Use fast readout electronics (gated integrator)!


MCP gain limitations

• The output current from the MCP should be limited to 10% of the bias current to avoid ‘field distortion saturation’.

• “Extended dynamic range” MCPs have bias currents of 4-14 uA/cm2 (at maximum gain).

• This gives a max signal per bunch on a 0.25 mm by 10 cm anode strip of 0.4-1.3 106 electrons (60-200fC).

• Effectively limits gain to ~10000 for the expected signal levels (if using high end plates).


Main Injector IPM results

Horizontal MI IPM: Em ittance versus MCP voltage

0

5

10

15

20

25

30

35

40

45

50

750 850 950 1050 1150 1250 1350

MCP bias (Volts)

Em

itta

nce

(p

i mm

mra

d)

0

4500

9000

18000

22500

27000

31500

36000

40500

49500

54000

58500

63000

67500

saturation

Turn#


Single vs Dual plate

• Current IPMs (at Fermilab) use dual plates (Chevron).

• For a given gain, a Chevron saturates at a smaller signal (smaller voltage).

• A single plate can deliver ~10000 gain.

• Use single plate!


Parasitic beam signals

• MCP electrons are collected on anode strips

• Electric field of beam can couple directly to anode strips!

• Such signals would be capacitively coupled and average to zero.

• How big are they?

IPM Response

-110.00

-100.00

-90.00

-80.00

-70.00

-60.00

-50.00

-40.00

-30.00

0 100 200 300 400 500

Freq(MHz)

db

aluminum plate w /cutout aluminum plate w /f ine screen Strips

Micro Plate Micro Plate Screen

Measurements on booster IPM


Avoiding parasitic signals

• Faraday cage and RF screening mesh give significant overall reduction (any effect on desired signals?).

• Avoid any low frequency (< 200 MHz) resonances in anode strips/cabling.

• Change HV capacitors (used for shorting HV detector components to ground at high frequencies) to surface mounted .


Summary

• Fairly good understanding of where the issues are• Some tests still to be done

– MCP test stand• Gain uniformity, test calibration device, effect of RF

screening mesh…

– RF coupling• Try to remove all resonances from the Booster can.

• Repeat tests on RR IPMs that were recently removed.


Bonus slides

Just in case


Booster IPM measurements

Anode strip RF coupling to beam current

-110

-100

-90

-80

-70

-60

-50

0 100 200 300 400 500

Frequency (MHz)

s1

2 (

dB

)

simulated resonance (L=0.7 uH) simulated no resonance (no inductance)

fine screen pcb caps shorted shielded output w/copper gnd fine screen110 -8 210 -8 310 -8 410 -8 510 -8 610 -8

-10000

10000

20000

110 -8 210 -8 310 -8 410 -8 510 -8 610 -8

-100000

-50000

50000

100000

150000

200000

Residual: 10 pC

Residual: 2 fC

L=0.7 uH

L=0.07 uH


Proton/pbar space separation

• Although the helix separation has improved, there is still significant overlap in the projected profiles

• Helix can change again(?).

• Don’t rely on helix alone to separate beams!

-15 -10 -5 5 10 15

-15

-10

-5

5

10

15

= 20 mm mradp/p = 7.5 10-4


Proton pbar time separation

• Time difference between protons and pbars are in the range 0-198 ns, depending on location.

• Collection time 2-3 ns.• Gate on single

bunches!3145 3150 3155 3160

255075

100125150175200

BATD91

2PS0ED1

4VGD1

3PS0ED1

1DNEGODD1

MGOD0E1

1DNEGODD2

A7LLEBD1

ELLOC2RD5

LCHU10EM1

LCVU10EM1

2LLOC2RD5

LCH10E1

LCV10E1

2LLOC2RD6

LCHD10EM1

LCVD10EM1

ELLOC2RD6

A7LLEBD2

1DNEGODD3

PGOD0E1

1DNEGODD4

4PS0ED1

1DNEGODD5

PGOD0E2

1DNEGODD6

5PS0ED1

1DNEGODD7

1PMGOD0E1

0EM1

2PMGOD0E1

1DNEGODD8

6PS0ED1

KPMADHPD1

NI3D2

KPMADVPD1

NI3D3

PMADHBPD1

NI3D4

PMADVBPD1

7PS0ED1

A7LLEBD3

ELLOC2RD7

LCHU20EM1

LCVU20EM1

2LLOC2RD7

LCH20E1

LCV20E1

2LLOC2RD8

LCHD20EM1

LCVD20EM1

ELLOC2RD8

A7LLEBD4

ELLOC2RD9

LCHU30EM1

LCVU30EM1

2LLOC2RD9

LCH30E1

LCV30E1

2LLOC2RD01

LCHD30EM1

LCVD30EM1

ELLOC2RD01

A7LLEBD5

UPPMADHD2

NI3D5

UPPMADVD2

8PS0ED1

4VGD2

9PS0ED1


Pros and cons of single plate

• Higher saturation limit, due to higher operating voltage

• Cheaper• Simpler• Same plate lifetime as

for Chevron

• Larger gain dispersion• Limited gain, but:

– Much smaller primary signals would be limited by statistics (esp. pbars), hence it is better to boost too low primary signals with injected gas.

Documents

Tevatron IPM