Tevatron IPM
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Transcript of Tevatron IPM
10/3/2003 Andreas Jansson - Tevatron IPM review 1
Tevatron IPM
Primary signal, electron transport, amplification, detection…
10/3/2003 Andreas Jansson - Tevatron IPM review 2
Overview
• Primary signal levels (# of electrons)
• Electron transport to detector
• Separation of protons and pbars
• Amplification and detection
• Avoiding parasitic signals
10/3/2003 Andreas Jansson - Tevatron IPM review 3
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
10/3/2003 Andreas Jansson - Tevatron IPM review 4
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.
10/3/2003 Andreas Jansson - Tevatron IPM review 5
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
10/3/2003 Andreas Jansson - Tevatron IPM review 6
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
10/3/2003 Andreas Jansson - Tevatron IPM review 7
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
10/3/2003 Andreas Jansson - Tevatron IPM review 8
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
10/3/2003 Andreas Jansson - Tevatron IPM review 9
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
10/3/2003 Andreas Jansson - Tevatron IPM review 10
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
10/3/2003 Andreas Jansson - Tevatron IPM review 11
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
10/3/2003 Andreas Jansson - Tevatron IPM review 12
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)!
10/3/2003 Andreas Jansson - Tevatron IPM review 13
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).
10/3/2003 Andreas Jansson - Tevatron IPM review 14
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#
10/3/2003 Andreas Jansson - Tevatron IPM review 15
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!
10/3/2003 Andreas Jansson - Tevatron IPM review 16
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
10/3/2003 Andreas Jansson - Tevatron IPM review 17
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 .
10/3/2003 Andreas Jansson - Tevatron IPM review 18
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.
10/3/2003 Andreas Jansson - Tevatron IPM review 19
Bonus slides
Just in case
10/3/2003 Andreas Jansson - Tevatron IPM review 20
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
10/3/2003 Andreas Jansson - Tevatron IPM review 21
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
10/3/2003 Andreas Jansson - Tevatron IPM review 22
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
10/3/2003 Andreas Jansson - Tevatron IPM review 23
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.