Malte Hildebrandt

Malte Hildebrandt

MEG Review Meeting, 20.02.2008

Malte Hildebrandt MEG Review Meeting, 20th Feb 2008

Drift Chamber System• hardware status Run 2007• shutdown activities 2008

Malte Hildebrandt


Installation 2007

• main changes / improvements compared to installation in 2006:

• modifications of support structure ↔ clearance to N2 bag

• new design of gas manifolds ↔ less influence on e+ trajectory

• placed at larger lzl - and larger r - coordinate

• different material (0.5 mm Al → 1 mm PVC)

• 16 / 16 drift chamber modules

• as in 2006: each dc module tested in test setup „aquarium“ (He / C2H6 inside module and Helium outside module)

• cosmics run in lab, modules mounted in support structure→ sort out cable mismatch „inside COBRA“

Malte Hildebrandt


Drift Chamber System

gas manifold ds

„MEG“ target

flange to BTS

dc support

dc15 dc00

Malte Hildebrandt


Alignment – Part 1

• measurement of identification marks wrt reference bolts

(3D touch-sensitive sensor in mechanical workshop)

reference bolt

reference bolt

„connection“ to position of• anode wires and • cathode pattern

(x-y-measuring table in lab)

identification mark identification mark

Malte Hildebrandt


Alignment – Part 2

reference holes in support structure

identification marks on dc module

• surveying of identification marks wrt support structure and beam axis

( survey with theodolite by survey group)

→ 2 vectors:

• connecting line of adjacent holes

• middle of connecting line to identification mark(chamber plane)

Malte Hildebrandt


Chamber Shift

→ ChamberShift in data base

• corrections in x, y, zup to 2 mm

• corrections along vectorof chamber planeup to 6 mrad

-300

-250

-200

-150

-100

-50

0

-350 -250 -150 -50 50 150 250 350

-300

-250

-200

-150

-100

-50

0

-350 -250 -150 -50 50 150 250 350

upstream

downstream

displacement x50

displacement x50

• observation after measurement and survey:

• shift of modules

• tilt of modules

Malte Hildebrandt


Wire Displacement

• mechanical deformation ofdc module / support structure ?

→ survey dc + target system before installation („hanging“)

→ survey after installation in COBRA („sitting“ )

• deviation (wire#) in R and Z of expected hit point to fitted track(including ChamberShift data)

→ measure of wire displacement before alignment procedure

→ after 3 iterations: < 0.01 cm shift tilt

Malte Hildebrandt


Survey of Target

• observation after dc installation (Aug. 2007): target slightly misaligned

→ „survey“ with vertical and horizontal laser projections

→ photos with digital camera and geometrical analysis (PRK)

→ numbers are included in MC

Malte Hildebrandt


Target

Malte Hildebrandt


Survey of Target


→ „survey“ with vertical and horizontal laser projections

→ photos with digital camera and geometrical analysis (PRK)


• before dismounting dc system (Jan. 2008):

→ photogrammetric survey by survey group (no time for theodolite survey)

• several photos from different positions (~1h)

• analysis later with special software and camera calibration

• but: maybe problems due to small angles and glancing intersections

Malte Hildebrandt


Photogrammetric Survey of Target

ruler (absolute scale)

reference points

Malte Hildebrandt


Survey of Target


→ „survey“ with vertical + horizontal laser projections

→ photos with digital camera, geometrical analysis (PRK)


• before dismounting dc system (Jan. 2008):

→ photogrammetric survey by survey group (no time for theodolite survey)

• several photos from different positions (~1h)

• analysis later with special software and camera calibration

• but: maybe problems due to small angles and glancing intersections

before Run 2008: • identification marks on target / frame

• schedule theodolite survey of dc + target (~1d)

Malte Hildebrandt


Drift Chamber Operation

• Cosmic Ray Run 11.-17.10.2007 (1.2 M events)

• z - calibration

• wire positioning, alignment

• gain calibration

• standalone Michel Run (08.-14.11.2007)

→ ultra low (3 M + 2 M events) • x t - calibration

• Michel spectrum

→ low (2 M events) • confirm stable dc operationat „normal“ beam intensity

• tune tracking algorithm

• startup / de-bugging phase (noise, HV & SlowControl vs magnetic field)

• MEG Run

Malte Hildebrandt


Drift Chamber Operation

• standalone Michel Run (08.-14.11.2007)

→ ultra low (3 M + 2 M events) • x t - calibration

• Michel spectrum

→ normal (2 M events) • confirm stable dc operationat „normal“ beam intensity

• tune tracking algorithm

• startup / de-bugging phase (noise, HV & SlowControl vs magnetic field)

• MEG Run

• Cosmic Ray Run 11.-17.10.2007 (1.2 M events)

• z - calibration

• wire positioning, alignment

• gain calibration

Malte Hildebrandt


Disconnected Cables

• missing LV dc6u

• missing signal channels

1 anode wire = signals from both sides (out of 288) 3 anode signals = signal from one side (out of 576) 23 cathode / hood signals (out of 1152)(only one cell with 2 missing cathode signals)

Remark: everything fine during startup, most likely explanation for mishap: • LV cables: stiff and rigid • signal cables: slippery

→ slight mechanical tension→ very slow movement, even we fixed with tape and cable ties→ finally connector slips out of socket

→ improved strain-relief of cables on pcb(design finished, parts under construction)

→ additional test after inserting dc support structure, before closing endcap

disconnected patchpanel insideopen DS endcap

Jan 2008

Malte Hildebrandt


O2 SensorsUS endcapDS endcap

dc

O2

O2

O2 O2

O2

• Alphasens O2 sensors : • metal / air battery: I proportional O2 concentration

→ calibration with 20.8 % O2 → U0 = R·I0

→ “aging”: exposed to 20.8 % O2 → I0 = I0(t)

• powerfull tool to monitor Helium concentration inside COBRA and to „identify“ leaks

He_in He_in

He_out He_out

Malte Hildebrandt


DC HV Problems

• 6 dc modules showed frequent HV trips (1850V) when cHe_COBRA >97 %

MC: influence on • stopping distribution and • reconstructed momentum resolution of e+

→ decission: air admixture to „adjust“ 95 % < cHe_COBRA < 97 %

• but: due to trips slight deterioration during run… → situation end of run: 16 / 32 planes operated at 1850 V

11 / 32 planes operated at 1800 V 5 / 32 planes not operational (<1700 V)

→ recent activities (since beginning of January):• dc support structure moved out of COBRA

• test setup „aquarium“ installed and operational in E5• „weakest“ dc module dismounted → optical inspection

suspicious spot: sealing of HV connection to pcb

outside

?

Malte Hildebrandt


HV Connection

anode decoupling capacitorshood readouthood Vernier pattern

pre-amplifier cardsHV connection to pcb

Malte Hildebrandt


Anode PCB

Malte Hildebrandt


Next Steps

• 1st test with „weakest“ dc module in „aquarium“: HV trip reproduced → new sealing

→ stable operation with 1875 V at 99.7 % Helium in „aquarium“ (O2-sensor)

• all dc modules with planes labled „not operational“:• dismount from support structure → optical inspection• redo sealing of HV connection• confirm HV stability in test setup „aquarium“

next steps:

• no activities scheduled for planes operated at 1850 V

→ depending on success of these activities:

• all dc modules with planes operated at 1800 V: • dismount from support structure • check / redo sealing (• confirm HV stability in aquarium)

Malte Hildebrandt


y = 2.710E-04x

R2 = 1.000E+00

0

2000

4000

6000

8000

10000

12000

0.0E+00 5.0E+06 1.0E+07 1.5E+07 2.0E+07 2.5E+07 3.0E+07 3.5E+07

Current vs Beam Rate

• two different settings for stopping rate :

ultra low: 5.0 · 106 /s

normal : 3.1 · 107 /s

dc4AIanode [nA]

stop rate [Hz]

Malte Hildebrandt


but: slight saturation visible

• only ~10 V voltage dropdue to 1 M resistor and10 A

→ saturation due to high gain and space charge effects ?

→ analysis of pulse heigth or charge distribution 6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0

1550 1600 1650 1700 1750 1800 1850 1900

Current vs HV

dc4A, low rateln(Ianode)

HV [V]

• normal stopping rate 3.1 · 107 /s

• HV scan from 1600 V to 1850 V

→ Ianode shows exponential relation as a function of HV !

Malte Hildebrandt


Wire Hit Rates

→ why is 1st cell of plane A and plane B much higher than expected ?

→ why is 1st cell of plane A higher than 1st cell of plane B ?

data

MC

•

H.Nishigushi

normal rate, dc08

cut condition for charge : > 0.6 V·ns

Malte Hildebrandt


Drift Lines from Track

A B

anode wire potential wire (GND)

A B

Malte Hildebrandt



A B

anode wire

A B

potential wire (GND)

Malte Hildebrandt



A B

anode wire

A B


Malte Hildebrandt



A B

anode wire

A B


Malte Hildebrandt


MC + Data

MCH.Nishigushi

data•

normal rate, dc08

cut condition for charge : > 0.6 V·ns

→ after implementation of „cell 0 geometry“ in MC:

→ still some work to do understand further discrepancies

Malte Hildebrandt


Charge Distribution

run 6092, 6093, low rate

H.Nishigushi

wire 0 wire 1

wire 8

wire 2

wire 3 wire 4 wire 5

wire 6 wire 7

Malte Hildebrandt


Current, Gas Gain

• dE/dX, → energy deposition along track

w-value → primary ionisation along track

track length → primary ionisation per traversing particle

rate, surface → Iprimary ionisation

Iprimary ionisation x gas gain = Imeasured

data: • (single wire hite rates) too large due to contributions of small pulses on wire 0

• estimation of correction factor 0.9 (Ch.Topchyan):

→ gas gain ~4.4·105 @ 1850 V

What is the reason for the small pulses?

• low collection efficiency? • GARFIELD

• attachment / recombination ? • data analysis

• accumulated charge (innermost anode wire): ~1 C / cm / 8 months → monitor chamber parameters

Malte Hildebrandt


PSI Savety

• dc gas system: • fire protected cabinet with ventillation system to operate 50l bottle ethane

• E5 gas warning system: • in total 8 sensors:3 sensors for O2

4 sensors for C2H6

1 sensor for H2

Malte Hildebrandt


Conclusion

• dc hardware problems have huge impact on overall performance of

dc system

→ exchange / repair broken pre-amplifier cards

→ improve strain-relief of LV and signal cables

→ repair bad potting of HV connection on dc modules to ensureHV stability in pure Helium environment

→ in parallel: construction of 2nd spare module (dc18)remark: dc17 available in laboratory (completely tested)

Date post:	13-Jan-2016
Category:	Documents
Upload:	mio
View:	31 times
Download:	2 times

Malte Hildebrandt

Documents