(Contact jcs@slac.stanford.edu
with comments)
(rev. 4: 9/30/03)
The goals of the E166 Background Test are to transport a low emittance beam through a small aperture tube located at IP1 in the FFTB and to measure the background levels at the locations of the E166 detectors. Success for this test is demonstrated by being able to keep the beam on with the small aperture tube in place (loss levels below the FFTB radiation limits) and by measuring the background levels at each of 5 detectors to be less than 5% of the signal levels anticipated for E166 proper.
Detector and Data Acquisition development and initial check out will be carried out parasitically to scheduled FFTB operations during fall, 2003. Installation and running for the full background studies will be done in the January-March, 2004 time frame.
For the background tests, a beam energy of 28 GeV is sufficient. A 1.2
1
mm id, 1 meter long, thin walled SS tube and a protection collimator will be installed at IP1. Five detectors: two Cerenkov-aerogel flux counters, a Si-W calorimeter, a Si-Pad calorimeter, and a CsI calorimeter will be located about 35 m downstream of IP1. Figure 1 shows the approximate layout of the required equipment in the FFTB enclosure. Shielding for the detectors, including Fe blocks representing the E166 magnetized absorbers, for the background tests is commensurate the full E166 experiment. Table 1 lists the expected E-
166 signal strengths and 5% background levels
Table 1: Expected E-166 Signal Strengths and 5% Background Levels
Detector
CsI †
Si-W
‡
E-166 Signal Strength 5% Backgrnd Level
16 MeV/cm
2
1 MeV/cm
2
500 TeV 25 TeV
Si-Pad ‡
Aerogel Flux Counter, upstream
†‡
500 TeV
 9 
> 5 MeV
 8
25 TeV

> 5 MeV
Aerogel Flux Counter, downstream ††‡
 7 
> 5 MeV
 6 
> 5 MeV
†
P. Schüler memo of September 9, 2003.
‡
 9  ’s per pulse, 4.85 MeV per 
, 2.6% transmission through 15 cm of Fe.
†‡
††‡
 9
9
 ’s per pulse in full spectrum, located upstream of Fe absorber.
 ’s per pulse in full spectrum
, 2.6% transmission through 15 cm of Fe, located downstream of Fe absorber.
Notes:

1. The 0.9 mm aperture of the E-166 undulator is scaled inversely with the square root of the beam energy from the 50 GeV of E-166 proper to the 28 GeV of the background test.
Thus 0.9
mm

50 GeV 28 GeV

0.9
mm

1.20
mm .
Figure 1: Hardware required for the E-166 Background Test

DRAFT September 30, 2003
Parameter
Energy
Beam Current
Beam Requirements
Symbol Value
E n
0 b
28
  10
Units
GeV e-/bunch
Repetition Rate
Emittance f rep

~10

5
Hz m-rad
Bunch Length
Spot Size @ IP1
 z
 *
Time early for installation: February 1, 2004
~ 0.5
50 mm
 m
Time required for installation and non-beam check-out: 2 weeks
Time required to conduct measurements: 9-18 shifts (?)
Run script after installation
Initial Set-Up: 3 Shifts
1.
Tune emittance at end of linac
2.
Transmit nominal 0.5-1.0 mm beam through 2.5 cm beam tube
3.
Measure and reduce backgrounds
4.
Steer bremsstrahlung spot onto target aperture, A t.
5.
Measure noise in detectors: tune, shield as necessary until below Test Goals
Small Spot Tuning: 6 Shifts
1.
Tune emittance at end of linac
2.
Transmit nominal 0.5-1.0 mm beam through 2.5 cm beam tube
3.
Measure and reduce backgrounds
4.
Reduce beam spot to 50
 m
5.
Measure and reduce backgrounds
6.
Steer bremsstrahlung spot onto target aperture, A t.
7.
Measure noise in detectors: tune, shield as necessary until below Test Goals
Small Spot and Small Tube Tuning: 9 Shifts
1.
Tune emittance at end of linac
2.
Transmit nominal 0.5-1.0 mm beam through 2.5 cm beam tube
3.
Measure and reduce backgrounds
4.
Reduce beam spot to 50
 m
5.
Measure and reduce backgrounds
6.
Slide in 1.2 mm id tube into place as per BPM
7.
Measure and reduce backgrounds
8.
Steer bremsstrahlung spot onto target aperture, A t.
9.
Measure noise in detectors: tune, shield as necessary until below Test Goals

J. C. Sheppard
Rev.0: 9/18/03
Question: How much detector shielding is required for E-166?
Answer: A background attenuation of about

8 in front of the CsI should be sufficient. This corresponds to about 80 radiation lengths of lead (~ 45 cm). Simulations need to be done to better define the requirements and predict the performance.
Discussion:
As a worst case scenario, assume that the beam loss in the vicinity of the undulator tube is at the 1 W continuous loss, radiation safety limit of the FFTB. Furthermore, assume that this loss generates a uniform background that fills the 3m by 3m tunnel cross sectional Area and illuminates everything downstream. Also, assume that the beam is running at f b
= 30 Hz, E
0
= 50 GeV, and n b
=
 10
e- per bunch. The total beam power is P
B
:
P
B q n f b
E
0
 
19   10    10 
2413 W. (1)
The 1 W loss corresponds to a beam loss of
 n b
,
 n b

1 W
2413 W n b
4.1 10 6 e per bunch. (2)
And, the background flux per pulse is F :
F

 n E b 0
Area

 6   10 eV

300 cm

2

2.3
TeV cm
2
. (3)
For the full E166 test, the signal in the CsI is estimated to be about 16 MeV cm
2
. A signal-to-noise ratio of 200 (for the actual experiment) corresponds to a noise level of
N

80 keV cm
2
. The required attenuation of the background flux is the ratio
 
N F :
 
N

F
80 keV
2.3
TeV

3.5 10

8
. (4)
L. Keller recently did a pair of low statistics EGS runs of sending 50 GeV electrons into
20 and 40 radiation lengths (r.l.) of Pb and looking at the total transmitted energy. The 20 r.l. case gave an attenuation of 1 10

2 and the 40 r.l. case gave an attenuation of

4
.

So, 80 r.l. of Pb should give the correct amount of attenuation. R. Pitthan points out that
Pb is a good neutron emitter and warns that some level of borated shielding should be included. The attenuation of the Fe in front of the CsI has not been included in the estimate of

or of the required lead thickness. The Fe reduces the background flux by an additional factor of about 6. In the background experiment, we are aiming for a signalto-noise ratio of 20 not 200 and the beam energy is down by a factor of about 2. The background experiment requires a factor of 20 less attenuation than the full E-166. One could low ball the background test by only installing about 30 r.l. of lead. I do not recommend this unless we are pushed in the direction of substandard shielding for some reason.
In addition, the 1 W continuous loss scenario generates to a noise signal transmitted through a 3 mm id hole of the target collimator, A t
, onto the

counters of
F
 
2.3
TeV cm
2
  
1.5
mm

2 
162 GeV . (5)
This energy is equivalent to 33,000 5-MeV photons compared to the E-166 undulator signal of
 9
incident photons of energy greater than 5 MeV and the expected signal in the SiW gcal of 500 TeV. Hence, the 3 mm id hole in the shielding should not result in an unacceptable background levels on the photon detectors (aerogel FC’s and gcal).

Overall Responsibilities: K. McDonald, J. Sheppard
Run Coordinator: J. Sheppard, V. Bharadwaj
Beamline and Shielding: J. Sheppard, D. Walz
Compatibility w/ other
experiments: J. Sheppard, D. Walz
Detectors:
Si-W, Si-G10:
Cerenkov aerogel:
Wm. Bugg, S. Berridge
K. McDonald
CsI/PMT, CsI/Diodes: A. Stahl
DAQ (incl. MCCstat): G. Bower, A. Weidemann (w/ P. Anthony, Z. Salata)
Cable Plant: G. Bower, C. Hast
BPMs:
Motors, LVDTs, Video:
SCP Database:
J. Sheppard, S. Smith
J. Sheppard, tbd Controls
J Sheppard, Controls or NLC staff
Radiation Physics Coord.: V. Bharadwaj, H. Vincke
Simulations:
GEANT3/4
FLUKA
EGS (as needed)
Beam Tuning:
Global Scheduling:
G. Bower, Y. Batygin, R. Xxxxx
V. Bharadwaj, J. Sheppard (A. Fasso, H. Vincke)
J. Sheppard
FJ Decker, R. Iverson, J. Sheppard, Ops
J. Sheppard, K. McDonald, E. Paterson, J Seeman