VVS Prototype Construction at Fermilab

Erik Ramberg26 February,2002

• Design issues for VVS• Details of VVS prototype design• Schedule and Budget• Testing the VVS prototype

VVS design issues

• The Vacuum Veto System must:– Satisfy inefficiency requirement as

function of photon energy

– Be efficient with respect to mechanical, readout and other system wide parameters (i.e. hermeticity, stability, etc.)

– Reside in a vacuum

– Be mechanically stable and easy to construct

• The prototype will be able to test most of these issues except energy dependence of inefficiency

34 VVS modules of 2 different sizes

Prototype Design Details

• Mechanical design (size, #layers, support, etc.)

• Scintillator

• Fiber

• Lead

• Tyvek

• Fiber connector and window

• PMT and electronics

Mechanical Design Specifications

• The smaller VVS module has an inner radius of 30 cm and outer radius of 70 cm. (Since effective radiation length for combined material is 3.6 cm., this gives more than 10 rad. lengths depth)

• 80 layers of 1 mm Lead / 5 mm Scintillator This gives sufficient light output and sampling frequency and makes each module 50 cm active, 50 cm empty.

• Each VVS module is subdivided into 16 phi sectors for spatial measurement.

• Each phi sector is split longitudinally in half so that a steel plate can be inserted for supporting the load. Fibers do not cross this boundary.

Alternate PMT’s with every layer to reduce PMT related inefficiencies

Stagger layers to minimize cracks

Scintillator and Fiber• The collaboration is still deciding

issues of scintillator and fiber procurement. These issues will not be resolved for some time.

• For the prototype, we will go with a well studied standard, namely Bicron BC404 scintillator read out with Bicron BCF92 WLS fiber.

Cosmic Ray Light Yield Setup in Lab 6

Fiber Spacing and Placement

• We have defined a standard of scintillator/fiber geometry for light yield measurements:

Example of Scintillator Light Yield Study

Fiber Spacing and Placement (cont.)

• But fiber spacing changes as a function of radius for our tile wedges. Therefore a somewhat arbitrary decision has to be made for fiber spacing.

• We have chosen 16 fibers per tile for the prototype, which reflects a reasonable upper limit for the final design.– This gives approximately 1 cm average

spacing.– If we use bent fibers, then 12 or 16 are natural

numbers of grooves per tile. – The base of the tile is approximately 12 cm.

• Light yield studies of fiber and scintillator will be performed independently of prototype construction, with comparisons of standard tile geometry.

Lead and Tyvek layers

• Both lead and Tyvek layers will span multiple phi sectors for ease of construction and minimization of cracks

• Lead will be purchased already cut to size – in our case spanning 2 phi segments.

• Tyvek may be type 1055B, with enhanced reflectivity in the UV (although manufacture process has changed since studies performed)

From: Stoll “Investigation of Reflective Properties of Tyvek Papers”; Phenix note #245

16 fibers from each tile are collected into a connector and polished

20 connectors from each longitudinal half of each phi sector are collected into a PMT bundle. (4 bundles from each phi sector)

Each tile is now a separate object, not intrinsically connected to any other tile

Fiber Connectors

Proposal for PMT window on vacuum vessel and connection to fibers

This element is still being debated. Final design can proceed in parallel with procurement and fabrication of scintillator and fiber.

PMT Choice, Placement and Fiber Routing

• PMT will be 2” diameter, with type unspecified as yet.

• The prototype will have 8 active PMT’s, and 4 inactive placeholders.

• Fiber routing, with alternate layers going to separate PMT’s, is shaping up to be a nightmare. A model for fiber routing is being developed by the Technical Division of Fermilab.

Electronics

• Phototubes will be read out into standard CAMAC DAQ system, with both ADC and TDC information.

• If ready by the time of test beam, we will also read signal into QIE integrator.

VVS Prototype Budget

• Cost of prototype:– Scintillator: $ 27.7 K

– Scint. Machining 8.4

– Fiber: 3.8

– Fiber alum. and polish: 3.7

– Finished Lead: 3.8

– Tyvec: .5

– Vacuum box material: 2.1

– Vacuum box machining: 4.0

– PMT (10 tubes)+base: 3.5

– PMT mounting hardware: .8

– Motion control stand: 2.5

_____

– Total $ 60.8 K

Schedule

• Scintillator and fiber arrival: April 1

• Finish machining Scint

and fiber: May 15

• Lead and material for

vacuum box arrive: April 15

• Finish machining box: May 31

• Finish PMT mounts: June 15

• Start installation: July 1

• Finish installation: Aug 1

• Mechanical shakedown: Aug 15

• Finish vacuum tests: Sept 1

• Finish cosmic ray tests: Sept 21

• Ship to JLAB: Oct. 1 ?

Test Beam Plans

• We have confirmed with JLab Hall-B participants that we will be welcome to test our detector using the tagged photon beam sometime “in the fall”.

• We need to communicate with them in detail our plans for this test.

• We envision several weeks of running at Jlab.