1Beam Line Review. 17th November 2007

2Beam Line Review. 17th November 2007

3Beam Line Review. 17th November 2007

4Beam Line Review. 17th November 2007

Detector parameters

Fermilab Beam line monitors built to replaced SWICS

Scintillating fibre tracker – readout by multi-anode PMTs

Channel count is 64 (per view)

Fibres may be spaced apart or arranged touching

Range of fibre thicknesses possible

and reading more than 1 fibre out per anode.

Thinner means higher resolution

Thicker means more light

5Beam Line Review. 17th November 2007

Design decisions

1 mm was chosen as a suitable thickness to produce enough light.

1mm readout pitch will only produce a detector 64mm across.

The choice is

• 1mm with gaps

• No gaps and more than 1 fibre per anode

The ability to measure the total integrated flux in the beam guides us to the multi fibre option

6Beam Line Review. 17th November 2007

Monitor dimensions and pitch

UPSTREAM MONITOR

For the upstream monitor grouping in sets of 3mm gives a total size of 192mm

Compared with the specification of 200mm.

A fit to a distribution with 3mm pitch will give a resolution of the mean to better than 1mm as required for beam based alignment.

DOWNSTREAM MONITOR

For the downstream monitor grouping in sets of 8mm gives a total size of 512mm

Compared with the specification of 472mm.

Fitting this will provide a resolution of around 2mm. This is sufficient for the steering of the beam, but is not good enough for beam based alignment which needs 1mm.

Central area 48mm x 48mm at a pitch of 3mm and the rest at a pitch of 8mm. Total size 432*432mm.

Meets beam based alignment requirements for central region and around half the resolution over the rest of the area

7Beam Line Review. 17th November 2007

Readout

UPSTREAM MONITOR

Discriminate and count.Read out scalers once per spill.

If rates too high, go over to integrate and digitise: changing PMT HV gives a way of tuning sensitivity or allowing for PMT saturation.

DOWNSTREAM MONITOR

Discriminate and count.Read out scalers once per spill.

Result is a beam shape, but no particle by particle information – moving the gate would provide a way of measuring time dependant effects if required

Rates with beam but no target are negligible

8Beam Line Review. 17th November 2007

Monitor drawing

9Beam Line Review. 17th November 2007

Background problems

The beam may be bigger than the area of the detector

Fibres running from the “sensitive” area to the PMT are exposed to beam.

Create simple model of smooth beam with independent x and y distributions, and PMTs in the centre. Fibre runs simplified (lengthened)

Compare “true” v “measured” for beams of various widths, both gaussian and top hat (modelled as wide gaussian).

No reliable model of shape in the wings

10Beam Line Review. 17th November 2007

Beam Monitors

sigmaVert=30 sigmaHoriz=30 : Beam Uniform, Larger than chambers

Othogonal Plane - Symmetric Read out - vertical

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Beam Background MeasuredOrthogonal - Symmetric Read out - Horizontal

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Beam Background Measured

sigmaVert=10 sigmaHoriz=10 : Beam Contained

Beams which overhang the edge are measured poorly in terms of width and centroid, but they are poorly defined.

Beams which are well defined are only marginally affected. Corrections are possible.

Inconvenienced but not spoiled

11Beam Line Review. 17th November 2007

Cable Runs

Cable run