ghosts and satellites measured with the lhc ldm

adam.jeff@cern.ch 1

Ghosts and Satellites measured with the LHC LDM

LUMI days 2012CERN

Adam Jeff

adam.jeff@cern.ch 2

Satellites, Ghosts: definitions

adam.jeff@cern.ch 3

Satellites, Ghosts: definitions

adam.jeff@cern.ch 4

Satellites, Ghosts: definitions

10-4

10-3

10-2

10-1

100

-62.5 -37.5 -12.5 12.5 37.5 62.5Time (ns)

10-4

10-3

10-2

10-1

100

-62.5 -37.5 -12.5 12.5 37.5 62.5Time (ns)

SatellitesGhostsGhosts ≠ debunched beam

adam.jeff@cern.ch 5

Satellites, Ghosts: definitions

DCCT integrates all beam current-> affects fast BCT normalisation

Fast BCT integrates some satellites-> affects relative bunch currents

adam.jeff@cern.ch 6

The LDM: how it works

APD

TDC

synchrotron light

LHC turn clock

Electrical pulse

200

150

100

50

0

x103

1.774661.774651.774641.774631.77462x106

Arrival time

Undulator Dipole• Synchrotron light from BSRT• Dipole and undulator at point 4• Separate system for each beam

7

The LDM: instrument response

10-6

10-5

10-4

10-3

10-2

10-1

100

Nor

mal

ised

cou

nts

2000180016001400120010008006004002000-200

Time (ns)

Laser pulse

Deadtime

Afterpulses Histogram integrated over 1,000,000 pulsesAverage 0.5 photons per pulse

Diffusion tail

adam.jeff@cern.ch 8

The LDM: count rate

adam.jeff@cern.ch 9

The LDM: deadtime correction

Availability of the detector in bin i:

Correction for deadtime:

Correction for deadtime and pile-up:

adam.jeff@cern.ch 10

The LDM: deadtime correction

Availability of the detector in bin i:

Correction for deadtime:

Correction for deadtime and pile-up:

Lab test with pulsed LED

adam.jeff@cern.ch 11

The LDM: afterpulse correction• Trapped charge carriers can generate a false avalanche• Happens at the end of the deadtime or some time after:

- multiple exponential decay, half-life 100ns to few μs• Parameters found by experiment• Correct by subtracting multiple IIRs

adam.jeff@cern.ch 12

Main bunchSatellites

Afterpulsing

Deadtime

Ghost bunches

adam.jeff@cern.ch 13

Corrected for deadtime

14

Corrected for deadtime and afterpulsing

Corrected for deadtime

adam.jeff@cern.ch 15

Average slots & Baseline20

15

10

5

0

463.0462.5462.0461.5461.0x103

3.0

2.5

2.0

1.5

1.0

0.5

0.0

20

15

10

5

0

463.0462.5462.0461.5461.0x103

3.0

2.5

2.0

1.5

1.0

0.5

0.0

20

15

10

5

0

463.0462.5462.0461.5461.0x103

3.0

2.5

2.0

1.5

1.0

0.5

0.0

20

15

10

5

0

463.0462.5462.0461.5461.0x103

3.0

2.5

2.0

1.5

1.0

0.5

0.0

0.35

0.30

0.25

0.20

-10 -5 0 5 10Time (ns)

adam.jeff@cern.ch 16

0.35

0.30

0.25

0.20

-10 -5 0 5 10Time (ns)

0.35

0.30

0.25

0.20

-10 -5 0 5 10Time (ns)

0.35

0.30

0.25

0.20

-11.25 -8.75 -6.25 -3.75 -1.25 1.25 3.75 6.25 8.75 11.25Time (ns)

• Mostly due to under- / over- correction of afterpulsing• Not equal around the ring – but we are only interested in average

0.35

0.30

0.25

0.20

-11.25 -8.75 -6.25 -3.75 -1.25 1.25 3.75 6.25 8.75 11.25Time (ns)

Average slots & Baseline

adam.jeff@cern.ch 17

Average slots & Baseline

10-4

10-3

10-2

10-1

100

-11.25 -8.75 -6.25 -3.75 -1.25 1.25 3.75 6.25 8.75 11.25Time (ns)

Average full slot:The +1 bucket is swamped by the diffusion tail of the main bunch.-4 to -1 and +2 to +5 are counted as satellites.

adam.jeff@cern.ch 18

VdM results: ghost chargeBeam 1 Beam 2

November 2010 n/a 2.5 +2.5/-0.6

March 2011 n/a 0.6 +0.6/-0.2

May 0.18 +0.18/-0.04 0.40 +0.4/-0.1

October 0.69 +0.7/-0.2 0.71 +0.7/-0.2

December f2335 3.1 +3.1/-0.8 2.8 +2.8/-0.7December f2337 2.1 +2.1/-0.5 2.3 +2.3/-0.6

Definition: % of total beam population which is outside the filled slots

adam.jeff@cern.ch 19

VdM results: satellitesBeam 1 Beam 2

November 2010 n/a 0.4 +/- 0.1

March 2011 n/a 0.1 +0.05/-0.03

May 0.02 +0.03/-0.01 0.12 +/- 0.03

October 0.21 +0.06/-0.08 0.57 +0.17/-0.12

December f2335 0.38 +/- 0.1 0.34 +0.1/-0.08December f2337 0.28 +0.08/-0.06 0.29 +0.08/-0.06

Definition: % of filled slot population which is outside the filled bucket or the following bucket

Averaged for whole time of scan and for all filled slots – results for a subset of bunches can be calculated if you ask nicely.

adam.jeff@cern.ch 20

Error inventoryError for ghost charge Error for Satellites

Statistical 10 % 5 %

Baseline uncertainty 12 % 3 %

Emittance dependence 20 % 20 %

Debunched beam 100 % ?! 25 % ?!

Typical values - 68 % CL

Total -25% / +100% -20% / + 30%

LDM baseline correction assumes zero debunched beam- consistent with beam gas and abort gap monitor

adam.jeff@cern.ch 21

LDM vs fBCT

Disagreement between LDM and fast BCT on main bunch populations is usually <2%Occasionally up to 5%, probably due to emittance spread.

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

LDM

- FB

CT

(%)

95x10990858075FBCT

80x109

60

40

20

0

LDM

(nor

mal

ised

)

80x1096040200Fast BCT

y=x

adam.jeff@cern.ch 22

Emittance dependence

• Active area of APD is only 50 microns• Beam spot size ~300 microns• Samples only part of the beam spot

>>> Measured bunch population depends on transverse size

adam.jeff@cern.ch 23

Thanks for your attention