D. Asner, J. Conway, S. Greenwald, J. Kim, Y. Li, V. Medjidzade, T

D. Asner, J. Conway, S. Greenwald, J. Kim, Y. Li, V. Medjidzade, T

49th ICFA Advanced Beam Dynamics Workshop October 8 –12, 2010
In Situ SEY Measurements at CesrTA
D. Asner, J. Conway, S. Greenwald, J. Kim, Y. Li, V. Medjidzade, T. Moore, M. Palmer, C. Strohman
Introduction
Measuring secondary electron yields (SEYs) on technical
surfaces in accelerator vacuum systems provides essential
information for many accelerator R&D projects, such as the ILC
Damping Rings, regarding to electron cloud growth and
suppression. As a part of CesrTA research program, we
developed and deployed SEY in-situ measurement systems.
Two such SEY systems were installed to expose samples with
direct and scattered synchrotron radiation (SR), and the SEYs of
the samples were measured as a function of SR dosages. In this
poster, we describe the in-situ SEY measurement systems and
the initial results on bare aluminum (6061-T6) and TiN-coated
aluminum samples.
Sample
System Schematic
Horizontal In Situ SEY
Station in L3 of CesrTA
CESR beampipe
In Situ SEY Stations
Sample
Isey
Gun
Sample
~2nA
Ip
20-1500V
Gate valves
-20V
Gun
power
supply
Keithley
6487
Beampipe
It
Sample Inserted for Exposure
Sample retracted for measurement
PC
•
Electron gun
(inside crotch)
•
Magnetic manipulator
(electrically insulated
from crotch)
•
•
• 2 samples in beam pipe, one horizontal in the radiation strip,
one at 45° beneath radiation strip.
• Samples are retracted periodically during accelerator accesses
Hardware components controlled
and their SEYs measured in situ.
remotely via LabVIEW software on PC
• SEY at 9 grid points on sample measured (right), with incident
Gun energy cycled from 20-1500eV with
angles 20˚ (pts. 1, 2, 3), 25˚ (pts. 4, 5, 6), & 30˚ (pts. 7, 8, 9).
current ~2nA and beam size ~0.5mm
•
A
typical
measurement
(~
1.5-hr)
can
be
easily
accomplished
in
Ip is measured with 150V bias before and
a normal accelerator access, to minimize disruption to CESR
after It is measured
operations.
It measured with -20V bias
Initial Results – SEY vs. Beam Doses
TiN-Al Sample
2/2/2010
1.0
10
22
10
Photon Dose (photons/m)
23
10
23
24
10
10
3
Horizontal "Fresh"
Horizontal "N2 Vent"
45 deg "Fresh"
45 deg "Contaminated"
1.6
24
10
4 5 6
2
3
10
4 5 6
2
450
1.6
1.4
3/23/2010
1.2
1.0
EMAX (eV)
Secondary Electron Yield
1.4
400
3/2/2010
1.2
350
1.0
0.6
0.6
400
800
1200
1600
0
Primary Electron Energy (eV)
800
0.001
1200
Primary Electron Energy (eV)
9/2/2010
9/3/2010
9/21/2010
1.5
1.0
10/5/2010
0.5
0
400
800
1200
18
10
9/2/2010
1600
Primary Electron Energy (eV)
10
100
300
10
1000
2
3
4
5
6 7 8 9
2
3
4
5 6 7 89
100
1000
Total Beam Dose (Amp·Hr)
19
10
20
21
10
22
10
Photon Dose (ph/m)
23
10
18
10
10
380
19
10
20
21
10
22
10
23
10
10
2.6
2.0
9/3/2010
360
2.4
9/4/2010
1.5
2.2
2.0
1.0
9/7/2010
340
320
1.8
0.5
6061-T6 Aluminum
Horizontal Sample Data
6061-T6 Aluminum
o
45 Sample Data
1
Photon Dose (ph/m)
8/31/2010
Secondary Electron Yield
2.0
0.1
SEY Peak Beam Processing - Al6061-T6
2.5
8/31/2010
0.01
Total Beam Dose (Amp·Hr)
Al6061-T6 Sample
2.5
0.0
400
Emax (eV)
0
0.0
0
400
800
1200
1.6
1600
Primary Electron Energy (eV)
300
Horizontal
45 Degree
1.4
Measured Current &
SEY Calculator/Plot
Scanning Parameters
& Controls
LabVIEW
Block Diagram
• Hardware is controlled by LabVIEW GUI developed at Wilson Lab, incorporating
existing Kimball Physics Electron Gun and Keithley 6487 Picoammeter software.
• Developed software includes:
-Synchronizing gun power supply voltages and bias voltages
-Automating electron beam energy scanning and raster scan subroutine while
recording current from ammeter
-Automating SEY calculation and plotting subroutine
280
0.001
0.01
0.1
1
10
Electron Beam Dose (Amp•hr)
Angular Dependence of Peak SEY in TiN-coated
Horizontal Sample
Keithley
Controls
0.8
5/25/2010
SEYmax
Secondary Electron Yield
1.4
21
1.8
2/23/2010
1.6
20
10
at 45 Orientation
1.8
1/14/2010
Secondary Electron Yield
19
o
1.8
0.8
Photon Dose (photons/m)
TiN Coated Aluminum
Gun Parameters
TiN Coated Aluminum Sample
@ Horizontal Orientation
1.2
SEY Peak Beam Processing – TiN-Al
2.0
Peak SEY
2.0
Control & Data Acquisition System
0.001
0.01
0.1
1
10
Electron Beam Dose (Amp•hr)
D-0.030)
• Data shows a steady (~
decrease
in SEY peak with increased beam dosage
(D) for both types of samples
• 45° system has a consistently higher
SEY than the horizontal system for TiNcoated sample
• Measured SEY peak is dependent on
incident angle (left figure).
Conclusions & Future Work
• Measured the SEYs from 6061 alloy are much lower than reported values
from 6063 alloy. We plan to do comparison using our in situ systems
• Measure the SEY of a sample cut from an extruded aged (30+ years)
6063 aluminum CESR chamber
Plot
showing
angular
• Comparing SEY while suppressing E-cloud with solenoid magnetic field
generated. dependence of SEY
• Measuring in situ various coated samples (such as NEG thin film,
amorphous/diamond-like carbon, etc) provided by collaborators
• Building and testing in situ SEY systems for the FNAL Main Injector
Supported by the National Science Foundation (Contract No. PHY-0734867) and the Department of Energy (Contract No. DE-FC02-08ER41538)
LEPP, the Cornell University Laboratory for Elementary-Particle Physics, has joined with CHESS to become the Cornell Laboratory for Accelerator-based Sciences and Education (CLASSE).
LEPP's primary source of support is the National Science Foundation. Visit us on the web at: www.lepp.cornell.edu