Negative Ion TPC
as the LC Main Tracker
G. Bonvicini, Jan. 2003
• Overview
• Early Simulations (by A. Schreiner)
• Also in the collaboration J. Martoff and
R. Ayad (Temple), D. Snowden-Ifft
(Occidental)
What is a NITPC?
• It is a TPC where the primary ionization and the
avalanche are made of electrons, but the drift is
done by negative ions
• Uses any electronegative gas, with thermal
electron capture and ion stripping (at high E)
cross section of order 10^7 Barn, and
appreciable gain
• Three such gases are known: CS2, biacetyl and
methylchloride
• NI gas tubes first studied and operated in 1953
NITPC in modern times (post 1995)
• Developed by J. Martoff
and collaborators
• DRIFT collaboration
(1998-): 1m3 NITPC to
study dark matter (seeks
annual, daily, and
directional signature of
dark matter) (Boulby, UK)
– a very robust detector
• DRIFT-II proposed: 9m3
He/CS2 80/20 detector
Properties of the NITPC
• Thermal diffusion at all E)
fields:   70 m E (LkV(cm/ cm
)
• Good gain (10^4 at 7700V)
• Drift velocity approx. 20m/sec
(at 1 kV/cm) drift
• Negligible Lorentz angle allows
radial, azimuthal drift
• Properties conspire to allow
“single electron detection”
• Extreme photon and electron
quenching
Motivation of the NITPC
• Improve event information by detecting single
electrons (F. Villa, NIM 217, 273,1983, J. Huth
and D. Nygren, NIM 241, 375, 1985, G.
Bonvicini, Hellaz Note 93-01) – momentum
resolution, two-track separation, and tracking
efficiency
• Decrease material and cost through the use of
novel detector planes
• Keep alive the TPC option for the far future (E=1
TeV)
Simulations
•
•
•
•
In progress
One event is 1+GByte
GEANT4 crashes on events this big
We are writing an algorithm to reject
background hits before tracking
• Main tracker for TESLA discussed below
• Temporarily, we have abandoned the axial
and radial TPC and concentrated on the
azimuthal TPC
Parameter
TPC
NITPC
objective
Central Tracker in Tesla;
B=3 Tesla
geometry
azimuthal: r=0.5-2m,
z=-2.7-+2.7m
material
gas: Ar(100%)
Comments
gas:
He/CS2(80/20)
+6·0.5% X0
(membr)
For multiple scattering
33 cm
NITPC is devided into
12 sectionsazimuthally
and TPC into 2 along z
0.4 mm
for E=1kV/cm in NITPC
<ldrift>
1.35 m
l_dif(<ldrift>)
4 mm
tr_dif(<ldrift>)
0.68 mm
Ns of
samples/track
144
104
Ni of ioniz. e
per
measurement
140
1
z_meas
3 mm
azim_meas
0.1 mm
0.4 mm
depends on the gas
meas=dif/SQRT(Ni)
(Here are only 2% of background at Tesla)
5-section axial TPC
12-section azimuthal TPC
read out planes do not
produce background at all
regular TPC
TPC detector plane (azimuthal
TPC)
• A modified version of a
Micromegas detector
plane (GorodetzkyGiomataris)
• Blue pads are ganged
NW-SE, white pads are
ganged NE-SW (angle to
wire is 60 degrees)
• Hits are recorded as a
triplet
TPC backgrounds (TESLA)
• Incoherent noise
backgrounds   3
• Approximately
2X10^9 “wire pixels”
due to long drift
• Pulse height
matching: 1) stripstrip; 2) wire-(s1+s2)
(not done yet)
Backgrounds comparison vs
regular TPC (TESLA)
• A regular TPC will see 19
times less backgrounds
at TESLA
• Factor of 2 less hits in
NITPC due to gas density
• Factor 1.6 from linac veto
• The rest (at least a factor
6) will have to come from
higher B-field
Simulated wire occupancies
(backgrounds = 6XNLC)
Using Maruyama’s ntuples, FADC
bucket = 100 nsec, no cuts)
background
signal in background
average strip
occupancy is 11%
radius [cm]
Momentum resolution
comparison with reg. TPC
(both large TPC, using Bruce
Schumm’ s program, red=NITPC,
blue=reg. TPC)

Space charge
• An issue if a wire/strip detector plane is
used
• For gain = 10^4, n=3X10^7, V=100 kV,
Delta(V)=17V
• Some drift velocity saturation also helps
Conclusions
• The NITPC niche: small, low cost, low
material, very competitive momentum
resolution and pattern recognition
• Working point is relatively well defined
• Early studies point to manageable
backgrounds