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Test Results of the Fiber-based Beam Loss Monitor for PAL-XFEL

Pohang Accelerator Laboratory Nam-Suk JUNG, Rina Woo, Min-Ho Kim, Ilyou Kim, Juho Hong, Hee-Seock Lee

2015. 6. 3

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Contents

Introduction

: a PAL-XFEL and Radiation Protection Beam Loss Monitor & Interlock System

Fiber-based Radiation Protection Beam Loss Monitor (RP BLM)

: Concept and Test Results at Injector Test Facility of PAL-XFEL

Radiation Protection Beam-Off Detector (RP BOD)

: Detector, Configuration and Test Results at Injector Test Facility of PAL-XFEL

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BC1

330 MeV

XRF Gun BC2

Hard X-ray FEL10 GeV2.52 GeV

Laser Heater

3.45 GeV

Soft X-rayFEL

L1 L2 L3 L4BC3_H

BC3_S De-Chirper

kicker

710 m 780 m 1100 m1000 m

Linac BTL Undulator Hall Beamline

L3:S

3.15 GeV

Introduction

PAL-XFEL (Pohang Accelerator Laboratory X-ray Free Electron Laser)

• Schematic drawing of PAL-XFEL

• PAL-XFEL buliding

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Introduction

PAL-XFEL (Pohang Accelerator Laboratory X-ray Free Electron Laser) 2015.04.17

~ 2014. 12 : Finish a building construction 2015. 1 ~ 2015. 10 : Install the machine 2015. 10 ~ : Commissioning (RF commissioning of LINAC & Beam operation of injector part)

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Introduction

Main parameter and tunnel thickness of PAL-XFEL Linac Beam energy, GeV 10

Beam charge, nC 0.2

Slice emittance, mm-mrad 0.4 (0.6*)

Injector gun PC RF-gun

Peak current at undulator, kA 3

Repetition rate, Hz 60

Number of bunch Single or Two

Linac structure S-band

Undulator Undulator type Out-vacuum

HX undulator gap (min), mm 7.2

FEL Hard X-ray wavelength, nm

Soft X-ray wavelength, nm

1 ~ 0.06

10 ~ 1.0

FEL radiation power @ 0.1 nm

wavelength and 60 fs photon beam

length, GW

30

Photon flux @ 0.1 nm, photons/pulse > 1.0 E+12

Beam loss monitoring & interlock system is required for personal radiation protection.

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Introduction

Beam loss monitoring & interlock system of PAL-XFEL

• RP Fiber-based Beam Loss Monitor & RP Beam Off Detector

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Introduction

ITF : Injector Test Facility of PAL-XFEL

- Beam energy : 140 MeV

- Beam charge : 200 pC

- Repetition rate

: max. 60 Hz

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Schematics of RP BLM

Fiber-based Radiation Protection Beam Loss Monitor

PM

T

PM

T

Optical fiber×2

Tunnel

HV HV Ch.#1 Ch.#2

Trigger Interlock Personal Safety & Interlock System e- beam off

Digitizer Display Operation Room

Advantage of fiber-based BLM

- Long coverage

: installation along the accelerator

- Continuous monitoring by bunches

- Simultaneous acquisition of two

important information

: Signal arrival time → Loss position

: Signal amplitude → Loss amount

e- beam Accelerator

- Fiber : Fujikura SC400/440 (SiO2)

- PMT : Hamamatsu PMT H6780-02 (upstream only)

(Same combination with SACLA)

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Purpose & Set-up of Test

Osc

illosc

ope

Ch.

1 C

h.2

Ch.

3 C

h.4

• Schematic diagram (plan view)

BAS0 dump BAM

Deflector (T-CAV)

Laser heater

L0b acc. col. + solenoid

L0a acc. col. + solenoid

e-gun

Beam

~ 130 m

~ 80 m

~ 30 m PMT

PMT

PMT

Installation start

Purpose : Check the characteristics of detector part (fiber & PMT) of fiber-based RP BLM

1) Relationship between the arrival Time and the loss Position

2) Attenuation & dispersion with the increase of the fiber length

Set-up at the ITF

- Fiber installation length : 14.6 m

☞ No.1 : 30~44.6 m from PMT

☞ No.2 : 80~94.6 m from PMT

☞ No.3 : 130~144.6 m from PMT

- Electron beam condition : 70 MeV, 200 pC, 10 Hz

Tunnel outside

Trigger

Tunnel

Mis-steered

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Time - Position Relation

8 ns = 0.96 m ⇒ 0.12 m/ns

e-beam

Upstream PMT

High-energy e- in vacuum

Cherenkov light in fiber

t = 0 [s] t = T [s]

L [m] L0 [m]

light

< Earlier e-beam loss > Occurrence time : 0 Arrival time of Cherenkov light : t1

t1, t2[s]

< Later e-beam loss > Occurrence time : T = L / c Arrival time of Cherenkov light : t2

𝒕𝟏 =𝑳𝟎𝒗

=𝑳𝒐𝒏𝒄

𝒕𝟐 = 𝑻 +𝑳𝟎 + 𝑳𝒗

=𝑳𝒄

+𝑳𝟎 + 𝑳 𝒏

𝒄=𝑳 𝒏 + 𝟏 + 𝑳𝟎𝒏

𝒄

< Arrival time interval at the upstream PMT >

∆𝒕 = 𝒕𝟐 − 𝒕𝟏 =𝑳 𝒏 + 𝟏

𝒄

L : distance bet. two loss points L0 : distance bet. earlier loss point & PMT c : speed of light in vacuum (= 3E+8 m/s) v : speed of light in medium (= c/n) n : reflective index (= 1.5, SiO2)

Time interval observed at the upstream PMT between 2 loss points

Governing Equation

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- Reference points for calibration

: 14 m away from installation start point

(over-steering point after the dipole,

70 MeV beam operation under

140 MeV dipole setting)

Time - Position Calibration

Time - Position calibration

Cross check with gate valve position 5.5 m (GV3), 9.5 m (GV4) & Screen 3 (1.87 m)

Gate Valve 4 (9.5m)

: Fiber : Loss positions

Gate Valve 3 (5.5m) Screen 3 (1.87m)

Beam Loss positions

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Observed Waveform, fiber 1

moved, hit thick Al frame

Inserted, hit thin screen

Time - Position Calibration

Over-steering, 14 m Screen 3, 1.87 m

GV3, 5.5 m GV4, 9.5 m

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Time - Position calibration

1) 1.87 m : Screen 3 Moved, hit the thick frame

2) 5.5 m : GV3 Closed

3) 9.5 m : GV4 Closed

4) 14 m : 70 MeV operation under 140 MeV

dipole setting (over-steering)

Results Time - Position Calibration

Slopes : 0.12 m/ns It is very well matched with governing equation.

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Attenuation GV3 (5.5 m) Closed

Fiber 1 : 35.5 m

Fiber 3 : 135.5 m Fiber 2 : 85.5 m

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Attenuation GV4 (9.5 m) Closed

Fiber 1 : 39.5 m

Fiber 3 : 139.5 m Fiber 2 : 89.5 m

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Averaged α = 71 ± 3 [dB/km] (similar with SACLA = 68 dB/km)

Attenuation

GV3 : α = 78 ± 0.3 [dB/km] GV4 : α = 64 ± 6 [dB/km]

α : attenuation coefficient [dB/km] : power transmission ratio = P(L)/P(0) L : length of fiber [km]

𝑷(𝑳) = 𝑷(𝟎) × 𝟏𝟎−𝜶𝒅𝒅𝒌𝒌 𝑳(𝒌𝒌)/𝟏𝟎

Attenuation coefficient

Attenuation coefficient of RP BLM

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Dispersion

FWHM of GV3, GV4 closed peak

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Signal Processing Algorithm

< Algorithm of the digitizer and its control PC >

- Low threshold level : Decision level for the attenuation correction Above the level : beam loss ⇒ Do correction Below the level : background ⇒ No correction

- Trip threshold level : Decision level for the beam off

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Polarity change

Attenuation correction Below low thres. level (background)

Trip!

Example Waveform correction

Above low thres. level (loss signal)

Trip!

1 2 3

𝟏

𝟏𝟎−𝜶𝒅𝒅𝒌𝒌 𝑳(𝒌𝒌)/𝟏𝟎

measured dose > criteria

measured dose < criteria

measured dose > criteria

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RP Beam Off Detector

Example of the position of Beam Off Detector (plan)

Near HX main beam dump

: BOD : RMS : Collimator : Safety magnet

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Schematics of Radiation Protection Beam Off Detector

BOD

4 ch negative HV

Preamp (max. 4 ea)

Discriminator & Interlock unit (max. 4 ea)

Tunnel

BOD cabinet

Signal to interlock PSIS e-beam OFF

BOD

Oscilloscope to set

discrimination level

RP Beam Off Detector

BOD : Toshiba E6876-600 proportional counter

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BOD test at ITF

Loss Point

BOD

Set-up & BOD installation

Set-up of test

- Electron beam condition : 70 MeV(L0a on, L0b off),

20, 50, 100 pC, 10 Hz

- Test condition : Screen 6 inserted

+ Gun Laser Shutter OPEN/CLOSED

Purpose of test

: performance check (trip generation time) of custom-made signal processing module

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Test results 20 pC

Shutter OPEN (beam + gun dark) Ch.2 amp : 5.2 ± 0.2 V

50 pC 100 pC

Shutter CLOSED (gun dark) Ch.2 amp : 4.7 ± 0.2 V

Shutter OPEN (beam + gun dark) Ch.2 amp : 5.4 ± 0.2 V

Shutter CLOSED (gun dark) Ch.2 amp : 4.0 ± 0.2 V

Shutter OPEN (beam + gun dark) Ch.2 amp : 7.0 ± 0.2 V

Shutter CLOSED (gun dark) Ch.2 amp : 4.0 ± 0.2 V

Ch2. amp output (unipolar shape)

Ch3. trip output (+12V to 0V)

Ch4. trigger from event timing system

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Test results

< Proportionality with various beam charge > < Fast trip output generation >

Only beam portion

- Rise time of the unipolar signal (10~90%) : ~ 6 μs - Delay time to make a point of contact : ~ 10 μs ※ Target time of the BOD-PSIS trip

: 16.67 ms (60 Hz)

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• The beam loss monitoring & interlock system of PAL-XFEL was designed and tested at the ITF.

< RP BLM >

• We determined the detector part (fiber and PMT) of fiber-based RP BLM with a several test; Fujikura SC400/440 & Hamamatsu H6780-02.

• We identified characteristics of the detector part of Fiber-based RP BLM

- Relationship of arrival time-loss position : well matched with governing eq.

- Attenuation of Cherenkov light : α = 71 ± 3 dB/km

• We made the signal processing algorithm of RP BLM.

• The determination of the trip threshold level is still challenge, it will be performed during the commissioning period.

< RP BOD >

• We designed and made the signal processing system of the RP BOD.

• We check the proportionality of system with a various beam charge.

• Trip generation time of RP BOD was short enough; ~ tens of μs.

Conclusion

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Thanks you for your attention nsjung@postech.ac.kr

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Back up slide

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Observed Waveform SC3(1.85 m) Moved & Inserted

No. 1 : 31.85 m

No. 3 : 131.85 m No. 2 : 81.85 m

moved, hit thick Al frame Inserted, hit thin screen

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Observed Waveform 70 MeV, Dipole ON (140 MeV), over-steered

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PMT bias

< Peak amplitude change with different PMT bias >

- Causes of amplitude change 1) Bunch charge itself, ~ 10 % 2) Gun dark-current change 3) Charge multiplication of PMT

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Attenuation coefficient