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Managed by UT-Battellefor the Department of Energy
SNS BLM System Overview Detectors, Measurements, Simulations
Alexander Zhukov
Saeed Assadi
SNS/ORNL
2 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
Liquid Hg Target
SNS Accelerator Complex
Front-End:Produce a 1-msec
long, chopped, H- beam
1 GeV LINAC
Accumulator Ring: Compress 1 msec long
pulse to 700 nsec
Ion Source2.5 MeV 1000 MeV87 MeV
CCLCCL SRF, =0.61SRF, =0.61 SRF, =0.81SRF, =0.81
186 MeV 387 MeV
DTLDTLRFQRFQ
RTBT
HEBT
InjectionExtraction
RF
3 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
BLMs at SNS Major MPS device
– Fast MPS – abort the current beam pulse within 10 μS (hardware – analog integrator), not applicable to RTBT
– Slow MPS – keep average loss reasonable
Diagnostic device - machine tuning
Activation “planning” Activation decaying
Activation buildup ?
Halo measurement with the help of WS
Detectors used
– Ion chambers ~300+
– Neutron detectors ~30+
– Low level neutron detector 8
– PMTs ~10+
4 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
Ion Chambers
Argon filled, 113 cc volume, 2 kV bias.
Response 70 nC/Rad
Slow ~1 μS (charge collection)
Voltage Dependence
1.0E+03
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
6.0E+05
7.0E+05
8.0E+05
0 500 1000 1500 2000 2500 3000 3500
Volts
bit
s/A
BLM334
BLM317
5 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
Neutron Detector
35 mm poly moderator
Li (n,alpha)
Scintillator
PMT
104 – 108n/cm2/s
0.03eV - 3MeV
6 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
Low Level Neutron Detector
85 mm poly moderator
B (n,alpha)
Counter
102 – 104n/cm2/s
0.03eV-10 MeV
7 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
PMT
Scintillator
PMT
Response 50 pC/MeV
Fast ~10 nS
8 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
ND
IC
1 mS
Neutron Detector vs. Ion Chamber
Commons– Analog output
– Same electronics, low level software, MPS interface
Differences
– Distance range: IC – local, ND remote
– HV controlled dynamic range for NDs
– Neutron signal originates from beam loss only, in contrast there are several x-ray sources
– Waveform shape (neutron moderation in NDs)
Proton Energy, MeV
9 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
Challenges: Low energy part of linac
low energy beam (<20MeV)– IC not sensitive enough
– ND sensitive, but hard to calibrate (no sufficient experimental data for reliable simulation)
– Still the biggest issue
– PMTs are supposed to help
Warm linac PMTs
10 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
Challenges: WF subtraction
– Cavity X-rays give significant input to loss signal
– The software subtracts the RF only waveform (the beam rep rate is 59.9 Hz to allow one reference signal per 10 seconds)
– Fast MPS is compromised
1 mS
X-ray
Beam loss
11 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
NoiseBLM
PMT
HV OFF
PMT
BLM
Loss
HV ON
Challenges: RTBT noise
RTBT noise/EM interference with the beam or image current
• Problem is present with beam only• Gets worse with beam charge increase
12 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
Challenges: RTBT noise (continued)
Low Level NDs
• Counter output (solves noise issue)• Registration of time distribution effectively increases dynamic range• Capable of registering losses from 1 mini-pulse• Need time to collect statistics 10 s ~ 600 pulses
1 mini -pulse
150 mini -pulses
saturation
10 mS
13 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
WS and halo studies
Loss / WS conversion constant
Attempt to improve WS performance in halo part
• Special scintillating fiber• Ordinary IC• Scan of loss signal vs WS position gives good measurement around the beam center, but halo shape isn’t really detectable• Optimized fiber is being designed
14 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
shutdown begins
Activation decaying
• NDs in SCL• HV ramped up• Using gamma sensitivity
15 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
Standard IC & ND amplifier– High channel density– Obsolete parts (big problem!)– 3 gains jumper settable
VME ADC– 24 bits for dynamic range (~10 bits digitizing noise)– High channel density– 100 kS sampling rate
VxWorks based EPICS running WF subtraction at 60 Hz
PMT custom made amplifier/HV boards + cRIO + LabVIEW RT
Low Level ND LabVIEW on Windows
Electronics and Low Level Software
Cu
rren
tly
run
nin
g p
rod
uct
ion
sys
tem
16 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
Electronics and Low Level Software Future
FPGA based WF subtraction– Test with cRIO based PMTs currently installed– Increase of sampling rate is desirable
Choosing FPGA platform– VxWorks vs. PXI vs. cRIO ?
Smart devices for higher beam availability– Every detector has its own hot pluggable data acquisition
board– Complete replacement of 1 channel should not affect other
channels (no beam downtime)– Full remote configuration: all setup data come from one
source (Oracle)
17 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
High Level SoftwareLossviewer2 (XAL application)
BLM statistics web site
18 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
Simulations (MC transport codes)
High Energy
Hadrons (primary protons, cascade hadrons)
MCNPX, SHIELD,
G4, MARS
Low Energy Neutrons MCNPX, G4
Electromagnetic Showers MARS,
EGS4, G4
Low Energy electromagnetic interactions
EGS4, G4
Beam PARMILA
Low Energy Protons MCNPX
MARS, SHIELD, G4
RF, dark current
???
FC428
0
5E+15
1E+16
1.5E+16
2E+16
2.5E+16
3E+16
3.5E+16
4E+16
4.5E+16
ND622
ND611
ND524
ND512
ND334
ND317
ND248
ND224
ND160
ND130
n/s
/4P
I
Ultimate goalRecreate the loss location and absolute valueusing BLM measurements
Proton Energy, MeV
19 Managed by UT-Battellefor the Department of Energy A. Zhukov SNS BLM System Overview Detectors, Measurements, Simulations WGF04 - HB2008 8/26/2008
Thank you!