claire simon

16/01/12 DITANET Topical Workshop on Beam Position Monitors

Reentrant Beam Position

Monitors

DITANET Topical Workshop on Beam Position Monitors

16th – 18th January 2012

Claire Simon


IntroductionTwo types of BPMs based on a radiofrequency reentrant cavity are developed:One monitor is developed for the E-XFEL (Thirsty two of those monitors will be installed in E-XFEL cryomodules) :

aperture of 78 mm designed to work at cryogenic temperature in a clean environment can get a high resolution and the possibility to perform bunch to bunch measurements.

One prototype is installed in a warm part in the Free electron LASer in Hamburg (FLASH), at DESY.. and shown a resolution Resolution measured around 4 µm with 1 nC and dynamic range around ± 5 mm.

The second monitor is developed for the probe beam (CALIFES) of CLIC Test Facility (CTF3) at CERN:

aperture of 18 mm operated in single bunch and multi-bunches modes.

Re-entrant BPM (left) installed on the linac FLASH.


E-XFEL - Accelerator Complex 17.5 GeV

800 accelerating cavities1.3 GHz / 23.6 MV/m

25 RF stations 5.2 MW each

XFELX-Ray Free-Electron Laser

100 accelerator modules


Cold BPM (unit cell)XFELX-Ray Free-Electron Laser

100+1 (Injector) Modules along machine with 32 re-entrant BPMs Injector 1M+3rd: Button2x

Linac 1 4M: Button4x(1unit)

Linac 2 12M: 2xReentrant2x(1unit), 2xButton4x(1 unit)

Linac 3 84M: 14x Reentrant2x(1 Unit), 14 x Button 4x (2 Unit)

Schematic from D. Noelle


Cold Reentrant BPM for the E-XFEL

quadrupole

BPMbellows

HOM absorber

gate valve


Specifications

Single bunch resolution (RMS): 50 µm

Drift over 1 hour: 5 µmMax. resolution range: ± 3 mmReasonable signal range : ± 10 mmLinearity: 10%

Transverse alignment tol. (RMS): 300 µmCharge dependence : 50 µm

Collaboration between DESY, PSI and CEA Saclay


Design

Arranged around the beam tube and forms a coaxial line which is short circuited at one end. Cavity fabricated with stainless steel as compact as possible :

170 mm length (minimized to satisfy the constraints imposed by the cryomodule) 78 mm aperture.

Eigen modes

F (MHz) Ql (R/Q)l (Ω) at 5 mm

(R/Q)l (Ω) at 10 mm

Measured Measured Calculated Calculated

Monopole mode

1255 23.8 12.9 12.9

Dipole mode

1724 59 0.27 1.15

Twelve holes of 5 mm diameter drilled at the end of the re-entrant part for a more effective cleaning.

Feedthroughs are positioned in the re-entrant part to reduce the magnetic loop coupling and separate the main RF modes (monopole and dipole)


Signal from one pickup

Cu-Be RF contacts welded in the inner cylinder of the cavity to ensure electrical conduction.

Dowel pins to adjust transverse alignment with quadrupole


Test bench in CryHolab Test in a horizontal cryostat at Saclay (Cryholab)

He tube to cool down

BPM


BPM integrated in CRYHOLAB.

CRYHOLAB.

Frequency (MHz) QlMeasured in Cryholab at

300 K

Estimated at 6 K

Measured in Cryholab

at 6 K

Measured in Cryholab

at 6 KMonopole mode

1254 1257.7 1257.2 22.2

Dipole mode

1720.6 1725.8 1727.7 49

Reflection and transmission measurements


Feedthroughs

Feedthroughs mounted on BPM body with Conflat gaskets

Brazed ceramic

Manufacturing Process

1. Machining of feedthroughs (carried out by company)

2. Cryogenic test in N2 according to: (carried out by company and by CEA Saclay to check)

3. Transport of feedthroughs to DESY

4. Particle cleaning of feedthroughs

5. RGA and leak test of feedthroughs in clean room (ISO5) at DESY

Cold test procedure for feedthroughs

1. Feedthroughs leak tested

2. Feedthroughs plunged into LN2

3. Operation repeated 3 times

4. Feedthroughs leak tested



Process steps for the reentrant cavity BPM (1)


1. Firing at 950°C and machining body (carried out by company)

2. Copper coating (acid bath) of 2 parts (carried out by company). Using of tools to protect reentrant part and outside parts which are not copper coated.

Ultrasonic bath + Heat treatment 300°C for 1 h + visual check Thickness measurement 12 µm ± 2 µm with 1 µm of Nickel to do the contact between stainless steel and copper

3. Welding of RF contacts and EB welding of 2 parts composing the BPM (carried out by company)

4. Cleaning, leak test and RGA (carried out by CEA/Saclay) Cleaning in US bath Leak test: leak rate must be <= 1*10-10 mbar l /s Residual gas analyze : sum of residual gases with mass < 45 not exceed 10-3 of total pressure which is ≤ 10-8 mbar

5. Process in clean room ISO5 (carried out by DESY) Particle Cleaning, Residual gas analyze, Transport to ISO3

6. Process in clean room ISO3 (carried out by DESY) Assembly of quad and BPM High pressure rinsing of quad-BPM assembly Assembly feedthroughs and checking Assembly of quad-BPM unit with valve and pump tube with valve Leak check and RGA spectrum total unit Packing and Transport to Saclay

BPM Mounting in an XFEL prototype cryomodule

16/01/12 DITANET Topical Workshop on Beam Position MonitorsFrame of re-entrant RFFE electronics

First RFFE prototype installed

First RFFE electronics prototype designed with a reference frequency of 9.028 MHz installed at FLASH

Digital electronics 8-channel Fast ADC with 14 bits resolution used.


BPMs in the linac tunnel

beam positionmonitor

x1

x2

y2

y1

180°hybrid

3 dBcombiner

x

y

Qx

ADC

Digital board

Ix

Qx

Iy

Qy

180°

hybrid

Ix

Qy

Iy

Low passFilter 70 MHz

Low passFilter 70 MHz

PLL

reference10 MHz1 Vpp

RF front-end

Band pass filter1724 MHz

110 MHz BW

Amplifier

Isolator

Detector

Isolator

LO

RF

LO

RF

90°hybrid

LO

RF

LO

RF

90°hybrid

Mixer

Mixer

3 dBsplitter

3 dBsplitter

3 dBsplitter

Phaseshifter

VideoAmplifier

Attenuator

Attenuator

control unitTo pilot

attenuators, switchs

PLL

3 dBsplitter

Attenuator

reference10 MHz1 Vpp

3 dBsplitter


110 MHz BW


110 MHz BW20 dBm leak.

20 dBm leak.

9.028 MHz

9.028 MHz


Calibration results from horizontal (left) and vertical (right) steering at 0.5 nC


Good linearity in a range ± 3 mm

RMS resolution ~ 10 µm on Y channel with beam jitter

~ 48 µm on X channel with beam jitter

Beam measurements with first RFFE prototype


Cavity BPM Hardware Concept

2 Reentrant Cavity RF front-ends, GPAC as digital back-end.

P2

RFFE2

P2

8 x MGT

P0

P0

Power GPACSFP/Trigger RFFE1

8 User IO2 Ctrl IO4 Trig IO

23 Special

Front EndBack End

2 SMB2 IPMB

3 Special P2

RFFE3

P2 P2

P2

User [32:47]

User [48:63]

Hot Swap Signals

P0 ADC

Ho

t S

wap

User [0:15]

User [16:31]

RFFE4

216.667 MHz

6 ch 160 MSa/s ADC GPACReentrant RFFEReentrant

Cavity

63 6 x 16 bit

160 MHz

ADC samples

I2C

MBU Backplane

6 ch 160 MSa/s ADC

Reentrant RFFE

63 6 x 16 bit

160 MHz

ADC samples

I2C

ReentrantCavity

Machine RF

160 MHz

160 MHz

By Courtesy of Raphael Baldinger, Goran MarinkovicMore information, please see E-XFEL/SwissFEL BPMElectronics‘ talk

PAUL SCHERRER INSTITUT




Second RFFE prototype

Option: for charge < 0.1 nC


E-XFEL infra- structure requirement: spacing will be N*111ns, with N=integer and >=2

Reference frequency : 216 MHz and then adding of a frequency divider to get 9 MHz

Adding of crystal oscillator on PCB board in backup if reference signal 216 MHz fails

Give a flag, showing something is wrong with the 216 MHz No exact value of the position – error position high

New design of sum channel with band pass filter at the dipole mode frequency and IQ demodulation Normalize position signal to reference (amplitude and phase) if small beam time arrival moved can be determined.

change of phase can be determined

Adding of ADC clock (design from M. Stadler/PSI)

Adding of Hot Swap control design with new components (design from R. Kramert and R. Baldinger/PSI)

Interfaces: “Two I2C buses” to control all RFFE functions

Differential outputs integrated on PCB board

Option 2 charge ranges: low charge (from 100 pC to 20 pC) adding switches, variable attenuator and amplifier on X and Y channels

Evolution of the second prototype



Damping time is given by using the following formula :

Time Resolution

BW*

1

ldQ

df

BW

Damping Time cavity only

Time resolutioncavity + electronics

BPM 9.4 ns 40 ns

With fd: dipole mode frequencyQld: loaded quality factor for the dipole mode

Considering the system (cavity + signal processing), the time resolution is determined, since the rising time to 95% of a cavity response corresponds to 3τ.

Time resolution for re-entrant BPM

RF signal measured at one pickup

ΔT =1µs

100 bunches read by the re-entrant BPM

20 ns

20 mV

40 ns

IF signal behind Lowpass Filter on

channel Δ



CALIFES linac – Probe Beam of CTF3

6 BPMs are installed on the CALIFES linac

15 MV/mcompression

17 MV/macceleration

17 MV/macceleration

LIL sections

beam dump

Focusing coils

K

quadrupoles

LaserRF pulse compression

2 x 45 MW

10202525

Profile monitor

Beam position monitor

Steerer

RF gun cavitySpect. magnet RF deflector

Bunch charge (single/multi bunch): 0.6 nC/ 6 nC/NbBunch length (rms) : 0.75psInitial /final bunch spacing :5.3/1.8 ps, 1.6/0.5 mmTrain length: 21 - 150 nsTrain spacing (rep. rate): 5 Hz

SpecificationsEnergy ~ 170 MeVEmittance < 20 .mm.mradCharge per bunch : 0.6 nCEnergy spread: <2%Number of bunches : 1- 32 – 226

Collaboration between CERN and CEA Saclay


Reentrant Part

Reentrant Cavity BPM for CALIFES

Bent coaxial cylinder designed to have:

a large frequency separation between monopole and dipole modes

a low loop exposure to the electric fields

Cavity fabricated with titanium and as compact as possible : ~125 mm length and 18 mm aperture 4 mm gap

BPM


E field

H field

RF Characteristics

With Matlab and the HFSS calculator, we computed R/Q Ratio.

and k=w/c R: the Shunt impedance and Q: the quality factor

Wf

V

Q

R

***2

²

dzezEV jkz*)(

Due to machining, dipole mode frequencies are different for each BPMs.

Standard deviation on the dipole mode: ~ 10 MHz

Eigen modes

F (MHz) Ql (R/Q) (Ω) (R/Q) (Ω)

Calculatedwith HFSS

in eigen mode

Measured in the CLEX

Calculatedwith HFSS

in eigen mode

Measuredin the CLEX

CalculatedOffset 5

mm

CalculatedOffset 10

mm

Monopole mode

3991 3988 24 26.76 22.3 22.2

Dipole mode

5985 5983 43 50.21 1.1 7


Signal Processing for CALIFES BPM

Hybrids installed close to BPMs in the CLEX

Multiport switches used to have one signal processing electronics to control six BPMs.

Analog electronics with several steps to reject the monopole mode

BPMs in the probe beam linac tunnel

beam positionmonitor 1

x1

x2

y2

y1

180°hybrid

180°

hybrid

phaseshifter

3 dBcombiner

beam positionmonitor 6

x1

x2

y2

y1

180°hybrid

180°

hybrid

3 dBcombiner

.

.

.

6 to 1multiportswitch

phaseshifter

x

y

6 dB

6 dB

18 dBm leak.

18 dBm leak.

Filter 5997 MHz600 MHz BW

0 to 70 dB

0 to 70 dB

18 dBm leak.

Lowpass Filter120 MHz

0 to 70 dB

3 dBsplitter

reference2.891 GHz

14 dBm

RF electronics in the hall

8channel

videoamp

Gv = 10

4channel10 bits2 Gs/sADC

2channel10 bits2 Gs/sADC

DAQ in the hall

control unit

VME Crate

signals for switchesand variable

attenuators control

Ix

Qx

Iy

Qy


RF

LO

II-Q

demodulator

Q

RF

LO

II-Q

demodulator

Q

Lowpass Filter200 MHz


AcqirisDigitizers

Hybrid

couplers

RF electronics used synchronous detection with an I/Q

demodulator.


Beam tests To calibrate the BPM:

Beam is moved with one steerer.

Calculate for each steerer setting, the relative beam position in using a transfer matrix between steerer and BPM (magnets switched off to reduce errors and simplify calculation).

Average of 15 points for each steerer setting.

Good linearity in a range ± 1.5 mm

RMS resolution: ~58 µm on the Y channel with beam jitter

~98 µm on the X channel with beam jitter

Calibration results from horizontal (left) and vertical (right) steering


Summary

E-XFEL reentrant BPM: Mechanics (BPM body/Cavity + feedthroughs) under construction Second RFFE prototype under construction Tests at FLASH going on

CALIFES re-entrant BPM: In using with beam

Special thanks to CERN, DESY, PSI and CEA/Saclay Colleagues for their collaboration to CALIFES and E-XFEL reentant BPMs

Thank you for your attention

claire simon

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