Luminosity Monitor Status / Beamplug Issues Mark Pitt, Virginia Tech

M. Pitt, Virginia Tech Qweak meeting,Jul’07

Luminosity Monitor Status / Beamplug Issues Mark Pitt, Virginia Tech

• Positioning upstream luminosity monitors so they have the same rate-weighted target distribution as the main detector events

• Linearity studies

• Light yield studies


Luminosity Monitor Locations

• Downstream lumis (eight of them)• small angle (0.7o) – primarily used as “null asymmetry monitor” to monitor helicity-correlated beam properties • will not have acceptance for full target due to “one-plug” beamline design choice

•Upstream lumis (eight of them, or four if budget gets tight)• large angle (9-12o) – primarily detects Mollers – insensitive to beam angle, energy changes• will be used as target density fluctuation monitor

downstream lumis

upstream lumis


Upstream Luminosity Monitors as Target Density Monitors

Ideally, the distribution of detected events for the luminosity monitor will be the same as for the main detector (shown above). In practice, this is somewhat difficult.

M. Pitt, Virginia Tech PAVI 2002, Mainz

Plugs and Beamline Reminder

We are hoping to compare three scenarios:

1 plug2 pluggun barrel

With gun barrel, the beamline / shielding through the minitorus region will be smaller to stop everything that would hit upstream of the end of the QTOR pipe


Proposed Upstream Luminosity Monitor Location Locate the upstream luminosity monitors on the upstream face of the primary collimator; they will detect primarily Mollers at this location. Rates at either location 1 or 2 would be ~ 29 GHz, giving 6 times smaller statistical error than main detectors.


Lumi distribution – location 2

Lumi distribution – location 1 - vacuum

Lumi distribution – location 1

Main detector distribution

Lumi target distribution at upstream location


Cause: multiple scattering of Mollers

Multiple scattering of 20 MeV in electron in : 4 cm of liquid hydrogen ~ 2.1o

3.5 m of air ~ 3.5o


Small Angle Luminosity Monitors

Parameter location 1 location 2 location 3

0.55 +/- .05o 0.65 +/- .05o 0.75 +/- .05o

Total rate/ detector 100 GHz 21 GHz 3 GHz

Dose in 2200 hours 1.8 Grad 0.5 Grad 0.1 Grad

The detector cups will be deep enough toallow access to three different angle rangesr = 15 - 18 cm .5 - .6o r= 18 - 21 cm .6 - .7o

r = 21 - 24 cm .7 - .8o


Lumi distribution – .55o locationLumi distribution – .65o locationLumi distribution – .75o location


Lumi target distribution at downstream location – 1 plug case


Lumi distribution – .55o locationLumi distribution – .65o locationLumi distribution – .75o location


Lumi target distribution at downstream location – 2 plug case


Reminder: Luminosity Monitor: Contribution of Al window

Contribution of aluminum windows to main detector signal is ~ 1% for 3.6 mil

aluminum end windows. Only at large angles is contribution to luminosity

monitor signal the same. So downstream lumi is not perfect either.


Recommendation

• Go with one tungsten plug beamline design BUT don’t design out the possibility of a two-plug solution for the future.

• If a target boiling “normalizer” is actually needed in the experiment, then a two plug + downstream lumi solution MAY be the best.


Luminosity Monitor Components

The luminosity monitors will consist of:• small (4 cm x 10 cm x 2 cm and 3 cm x 5 cm x 2 cm) quartz blocks with an angled edge• air light guide (Anolux Miro IV PVD)• Hammamatsu R375, 2 inch, 10 stage, bialkali photomultiplier read out in “photodiode mode”


Quartz + light guide photon yield tests• Undergraduate Kevin Finelli is just beginning light yield tests of quartz and quartz + light guide combinations with cosmic ray setup.

• Graduate student John Leacock is starting GEANT4 simulations of these; he will focus on the luminosity monitors for the hardware part of his thesis.


Linearity studies – photodetector only

<pe> ~ 29pe ~ 3 ? <pe> ~ 7

pe ~ 4

5 cm x 2 cm x 1 cm quartz coupleddirectly to PMT

5 cm x 2 cm x 1 cm quartz with 30 cm long air light guide

Results imply ~12% transmission in air light guide, comparable to ~ 15% seen in similar size light guide by Hicks, et al. NIMA 553 (2005) 470-482. We still have many further optimizations and tests to do.

main. error than lstatisticasmaller 5 offactor ~ have wouldlumis so

,15.1~7

41~

pe1 ~ is noise excess level,current At

22

pe


• Measurements plagued by instability in AC cathode current • Can only demonstrate linearity of of ~ 0.2% near operating

point.• In principle, 1% non-linearity is good enough (1%) (.1 ppm) ~ 1

ppb = 10-9

Linearity studies – photodetector only

Use Mack/Gericke 2-led technique to

test linearity of photodetector alone

(in “photodiode” mode)


July - Sep. 2007: - continue simulation/optimization of light guides and quartz - finalize quartz/air lightguide dimensions as beamplug/beamline design finalizes

late fall 2007: - place orders for PMT’s and quartz

spring – summer 2008: build and test luminosity monitors

In coordination with JLAB, need to remake the “cups” for the downstream lumisand engineer how the upstream lumis fit into the target region design.

Manpower: - Kevin Finelli (undergrad for Spring/Summer/Fall 2007) - John Leacock (graduate student has joined as thesis student)

Upcoming Work



Budget

Newly projected budget based on recent quotes (and upgrading to 2 x 8 lumisrather than just 8 lumis)

Quartz (~ $1311/bar, 20 bars) $26000PMTs (~ $1198/tube, 20 tubes) $24000Electronics (to JLAB/TRIUMF) $15000Misc. (bases, air light guides, etc) $ 5000

total $70000 (original budget = $15000)

Due to some other savings my NSF grants should still be able to manage this;if I can’t quite do it all, I would likely cut the upstream lumi to 4 lumis (insteadof 8)

Would also like to try to squeeze out a little bit of money for useful additions:

• remotely-controlled shutters to compare rate in PMT to rate from Cerenkov• remotely-controlled linear translation to move one of the downstream lumis radially to find optimum position; rest would be set by hand

Documents

Luminosity Monitor Status / Beamplug Issues Mark Pitt, Virginia Tech