managed by ut-battelle for the department of energy sns blm system overview detectors, measurements,...

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


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+


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


Neutron Detector

35 mm poly moderator

Li (n,alpha)

Scintillator

PMT

104 – 108n/cm2/s

0.03eV - 3MeV


Low Level Neutron Detector

85 mm poly moderator

B (n,alpha)

Counter

102 – 104n/cm2/s

0.03eV-10 MeV


PMT

Scintillator

PMT

Response 50 pC/MeV

Fast ~10 nS


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


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


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


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


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


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


shutdown begins

Activation decaying

• NDs in SCL• HV ramped up• Using gamma sensitivity


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


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)


High Level SoftwareLossviewer2 (XAL application)

BLM statistics web site


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


Thank you!

managed by ut-battelle for the department of energy sns blm system overview detectors, measurements,...

Documents