J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-20061 of 20

Studies with a TPC and development of a procedure

to measure ion feedback

James Inman – Radford UniversityDan Peterson - Cornell University

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-20062 of 20

Equipment, Amplifiers and Electronics

Micromegas

GEM

Wires (Multi-Wire-Proportional-Chamber)

High voltage system:-20 kV module, 2 channels-2 kV module, 4 channels

Readout:VME crateStruck FADC

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-20063 of 20

Sample data taken with Cornell TPC

25 MHz , 40 ns 2048 time buckets (81.92 µs)

ArCO2 (10%) , 300V/cmGas gain: ~ 300

Micromegas event – raw (no smoothing)tracks

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-20064 of 20

Implementing Program in Visual C++

Design Goals:

• Maintain functionality of old program

• Allow for analysis of ion feedback

• Interactive control

• Optimize run speed

track

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-20065 of 20

TPC Data Analysis Program – Block Diagram

Form1 - GUI Initialize event class

Load channel pad configuration data file

Load analysis configuration data file

Get TPC data file name

Open data-file-list file, load list of TPC data file names

Create ROOT File? Initialize ROOT components

Load event from TPC data file

Analyze event

Plot event

Open TPC data filePulses & Event

Tracks

Ion FeedbackFill ROOT tree

or

Create ROOT file

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-20066 of 20

TPC Data Analysis Program - Data Files

Channel Pad Configuration

• Contains information about the layout of the TPC (# rows, #pads, …)

• Maps the channels of data in the TPC data files to the pad board layout (channel# -> (row, pad))

• Contains the geometry of the padboard, used for track fitting and plotting

Analyze Configuration

• Has 3 sets of 35 input parameters that are used to analyze data

• Data smoothing (smoothwidth)

• Pulse identity (thresh, recoverwidth)

• Track fitting (pad pulse sharing)

MAP! N

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-20067 of 20

TPC Data Analysis Program - ROOT

Create an ntuple tree

• A tree stores data

• TTree object consists of branches that can hold any type of data from integers to classes

• Branches are filled for each event

Create ROOT file

• Contains ROOT objects (in particular my TTree)

• ROOT is run in “interactive” mode (root.exe) and file is opened to make cuts on the data and then plot histograms

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-20068 of 20

Ion Feedback Measurement

Positive ions are created in the amplification and drift back into the field cage.

Ion feedback is expected to besuppressed with theGEM or Micromegas devicesrelative to MWPC.

We measured ion feedback on the field cage termination plane, for individual tracks.

This is a different method than used by other groupsand will allowa more direct comparative measurement of ion feedback in the various devices.

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-20069 of 20

Ion Feedback MeasurementWire Amplifier

Field cage termination plane

Located between field cage and amplifier (next slide)

Wire amplifier produces large feedback signal this is why it is unsuitable for use in the ILC

It is used as a starting point for measuring ion feedback

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-200610 of 20

Field Cage Termination

Single Field Cage Termination Double Field Cage TerminationThe field cage termination provides a close to uniform potential plane while still being transparent

It would not collect ion signal; ions drift past the plane into the field cage

Allows for an area to be defined with a reverse electric field

This reduces transmission of elections from track and allows for ions drifting back into the field cage to be collected on wires

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-200611 of 20

Transmission Coefficient

0

20

40

60

80

100

120

140

160

0 100 200 300 400 500

Voltage (-Volt)

Puls

e H

eigh

t (co

unts

)

Transmission coefficient of electrons through double field cage termination wires using Micromegas

~40% transmission at bias voltage of -450 V

~60% of the ion feedback should be detected by the field cage termination wires

-300

V/c

m

0 V/

cm

+30

0 V/

cm

Single Grid(maximum transmission)

Partial Transmission Mode

Bias Voltage (-V)

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-200612 of 20

40% Transmission Mode, 5mm Drift

Pulse observed on field cage termination, is this ion feedback?

X-axis is in units of data buckets

Top 6 traces are from pad board, data collected at 20ns/bucket (82 µs)

Bottom traces are from FCT, data collected at 320ns/bucket (655 µs)

Logic pulses identify pulse threshold crossings

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-200613 of 20

40% Transmission Mode, 5mm Drift

Average pulse delay time is 202 µs with σ = 8.7 µs

Average relative pulse height is 6.0%

0

2

4

6

8

10

12

14

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Relative Pulse Height (%)#

Even

ts

Average: 5.5%

Initial Results calculated by hand, not fun

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-200614 of 20

“Full” Transmission Mode, 5mm Drift

Pulse still observed on field cage termination

By observation pulse looks smaller

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-200615 of 20

“Full” Transmission Mode, 5mm Drift

Average pulse delay time is 207 µs with σ = 9.3 µs

Average relative pulse height is 4.2%

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-200616 of 20

“>Full” Transmission Mode, 5mm Drift

Pulse still observed on field cage termination; decreased signal to noise ratio makes pattern-recognition difficult

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-200617 of 20

“>Full” Transmission Mode, 5mm Drift

Average delay time is 216 µs with σ = 21 µs

Average relative pulse height is 2.6% (reduced by 43%)

Pulse Height is effectively controlled by bias voltage applied to field cage termination

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-200618 of 20

40% Transmission Mode, 7mm Drift

Change the ion drift distance to see if the pulse changes accordingly

Pulse observed on field cage termination with a noticeably later time

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-200619 of 20

40% Transmission Mode, 7mm Drift

Average pulse delay time is 245 µs with σ = 7.9 µs (5mm – 202 µs)

Pulse delay time increase of 21% (40% drift distance increase)

Average relative pulse height is 7.4% (5mm – 6.0%)

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-200620 of 20

Results / Next

Created a new display and analysis program in Microsoft C++ that can be used to analyze ion feedback

Ion feedback was measured from a wire amplifier which has a large gain (x300)

An attempt to measure ion feedback from the double layer GEM amplifier was made; however, the GEM has an expected gain that is 10% of the wire amplifier and only 5% of the ion feedback

Plan to make a pulsing voltage bias on the field cage termination to allow full transmission of electrons and then pulse field to collect ions, need pulsing circuit and electronic amplifiers that can withstand pulsing bias

Smaller diameter wires on the field cage termination would increase field near wire increasing feedback signal (20 µm -> 8 µm)

A triple layer GEM would provide much more signal amplification

Make more measurements of ion feedback ;measure ion feedback for various amplifier devices.

J. Inman, “Studies with a TPC … measure ion feedback” , REU presentation, 08-Aug-200621 of 20

Acknowledgements

I would like to thank Dan Peterson of Cornell University for being my mentor and guiding me through my research expeirence. Thanks to Tarek Anous for his encouragement, programming assistance, and daily entertainment. Thanks to Chris Macklin for getting me started with ROOT and to LEPP Computing. Thanks to all the other REU students for adding plenty of excitement and support. And much thanks to Rich Galik for his dedication to the REU program and genuine interest in the success of all the REU students.