PPAC

1
PPAC

• Jonathan Olson University of Iowa
• HCAL November 11-13, 2004

2
Example of low-pressure PPAC (Parallel Plate
Avalanche Counter)

• Two flat plates
• Separated by 1 mm
• Filled with 80 torr isobutane
• 1000 V between plates
• Operates in avalanche mode
• MIPs often leave no signal
• Showers give large signal directly into 50 O

3
PPAC in HE

• Three flat plates, separated by 1 2 mm
• Middle plate at high voltage
• Outer plates hold atmospheric pressure
• Gas flows in one side and out the other
• Plates can be made of same material as the
  absorber.

Beam In
4
Individual PPAC to replace Scintillators
Beam In
Coax and gas lines extend out of radiation
area No organic materials in high-radiation region
Beam In
5
PPAC Readout
Summing amplifier can be used to add PPAC
signals, increasing the effective size of PPAC
(without increasing the time width of the
signals)
6
Radiation damage
A PPAC can be entirely metal and ceramic so that
it will not be damaged by radiation levels
expected with the SLHC upgrade. Also makes it a
good choice for the ZDC. If PPACs are chosen for
ZDC, we would have a significant investigation
phase prior to HE upgrade
7
Zero Degree Calorimeter
Beam In
The green is solid metal (W). Detectors that
sample the showerare shown in blue.Detector
near front end is for EM shower
8
CONCLUSIONS
PPACs in a ZDC

• Can be made radiation hard.
• Can provide transverse position information.
• Have good energy resolution.
• Have sub nanosecond time resolution.
• Can be integrated to give average luminosity.
• Can be replaced without removing the ZDC.
• ZDC can be left in place for both pp and PbPb

9
Fast signals
Single peak with considerable noise. The noise is
large because of the small size of the signal
using our 137Cs source. With the much larger
signals from high-energy showers, the noise will
be negligible.
10
PPAC ion signal

• Fast electron signal is followed by a small, slow
  (500 ns) signal from ions moving between the
  plates.
• The slow ion signal is easily removed.

11
Ion collection time (1 mm spacing)
12
Double PPAC for Energy Resolution
Poor for single, low-energy heavy ion Current per
mm2 is huge! Same size signal from shower has
good energy resolution. Measure resolution with
double PPAC Look at ratio between two sides
13
Double PPAC for testing energy resolution
14
Ion and electron signals with 2 mm spacing 168 pF
Ion collection time is three times as long with
the 1 mm spacing.
6.2ns
1.6ms
1.3ms
Amplified signal using gamma source.Positive
overshoot is from amplifier.
15
Speed vs Size
For high speed, the RC time constant must be kept
small. Only PPACs of small area are fast, 1 ns R
50 O (coax cable). C is the capacity between
the plates Small PPAC 1 ns C .885 pF
for 1 mm gap and area of 1 cm2 Larger PPAC with
C 168 pF for 2 mm gap and area of 1 cm2
rise time 5 ns fall time 7 nsStill fast
enough for the HE where minimum beam
crossing time is 25 ns.
16
Tests with double PPAC

• Test with EM showers using 80 ps bunches of 7 GeV
  positrons from the Advanced Photon Source, at
  Argonne National Laboratory
• Test with low energy hadron showers using the 120
  GeV proton test beam at Fermilab

17
PPAC Test at ANL

• IOWA double PPAC was tested for energy resolution
  with electron showers from the Advanced Photon
  Source (APS) at Argonne National Laboratory.
• The booster ring of the APS puts out 76 ps
  bunches of 7 GeV positrons at the rate of two per
  second, with 3.6 x 1010 positrons in each bunch.
• In normal operation the positrons are injected
  into the main storage ring where they are used to
  produce synchrotron radiation.
• There are maintenance and development periods
  during which the beam is directed into a beam
  dump. We set up our equipment next to the beam
  line just in front the beam dump.
• The entire beam bunch has an energy of 2.5 x 1020
  eV, or 2.5 x 108 TeV, much more than we needed.
• The PPAC was close to the beam line and so was
  exposed to showers generated by the outer halo of
  the beam striking the beam pipe. Because of the
  small angle between the positrons and the wall of
  the beam pipe, the wall acted as an absorber with
  a thickness of several centimeters. The showers
  were developed in this absorber.

18
Energy Resolution Data of PPAC Test at ANL
Ratio Efront to Eback is constant to within 2
19
120 GeV proton test
Measured signal size (into 50 O, no
amplification) at shower maximum. Maximum signal
from detector placed after 30 cm of iron was 17
mV. TeV hadron showering in copper would give a
much larger signal.
20
No Texas tower effect
With above-atmosphere hydrocarbon gasoccasional
proton from n-p scatteringgives huge signal. In
PPAC, proton hits wall at almost full
energy.PPAC signal mostly from low-energy
electrons. We will test this with detailed
simulations.
21
Simulation Efforts
Investigation using GEANT4