1

Status of the Phase I

of the SARAF Linac

L. Weissman, D. Berkovits, I. Eliyahu, I. Gertz, A. Grin,

S. Halfon, G. Lempert, I. Mardor, A. Nagler, A. Perry,

J. Rodnizki,

Soreq NRC, Yavne, Israel

K. Dunkel, M. Pekeler, C. Piel, P. vom Stein

RI Research Instruments, Bergisch Gladbach, Germany

A. Bechtold,

NTG, Gelnhausen 63571, Germany

LINAC 2010, Tsukuba, Japan

September 15, 2010

2

Presentation Outline

Overview

SARAF Linac Phase I components

ECR ion source + LEBT

RFQ

Prototype Superconducting Module (PSM)

Beam operation experience

Outlook

3

RFQ 1.5 MeV/u

PSM

p: 4 MeV, d: 5 MeV

EIS20 keV/u

Phase I

2009

Phase II

2015

5 × SC Modules 40 MeV

Radio

Pharmaceuticals

Radioactive

beams

Nuclear

Astrophysics

Thermal neutron

diffractionThermal neutron

radiography

ValueParameter

p / dIons

5 – 40 MeVEnergy

0.04 – 2 mACurrent

Hands-OnMaintenance

•Current upgradeable to 4 mA

Accelerator Parameters

SARAF LINAC Layout

44

SARAF Phase I – Upstream View

EISLEBT

RFQMEBT

PSM

A. Nagler, Linac-2006

C. Piel, EPAC-2008

A. Nagler, Linac-2008

I. Mardor, PAC-2009

5

ECR/LEBT

wire/FCslits

aperture

K. Dunkel PAC 2007

ECRIS

8 mA p/d

DC/pulsed

analyzer

magnet

Build by RI (ACCEL)

sol1

sol2 sol3

beam

blocker

5 mA proton

beam optics

RFQECR

Large beam

minimize

space charge

(TRACK)

See poster TUP74

L. Weissman et al.

6

LEBT aperture

-19 -4 11

-30

-5

21

x [mm]

x' [m

rad

]

50 mm

-19 -4 11

-30

-5

21

x [mm]

x' [m

rad

]

5 mm

-19 -4 11

-30

-5

21

x [mm]

x' [m

rad

]

25 mm

-19 -4 11

-30

-5

21

x [mm]

x' [m

rad

]

15 mm

-19 -4 11

-30

-5

21

x [mm]

x' [m

rad

]

10 mm

Manipulating beam size, current and emittance using the LEBT aperture

0

0.05

0.1

0.15

0.2

0.25

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

LEBT current (mA)

rm

s n

orm

em

i ( p

mm

mra

d)

50

55

60

65

70

75

80

85

Aperture diam. (mm)

Tra

ns

mis

sio

n (

%)

RMS norm emi

Transmission

5 10 15 20 25 50

7

RFQ Beam Properties

Beam Parameter Protons Deuterons

Energy (MeV) 1.5 (1.5) 3.0 (3.0)

Maximal current [mA] 4.0 (CW) (4.0) 2.5 (10-2) (4.0)

Transverse emittance, r.m.s.,

normalized, 100% [π·mm·mrad]

( 0.5 mA, closed LEBT aperture) 0.17 (0.30) 0.16 (0.30)

(4.0 mA, open LEBT aperture) 0.25 / 0.29 (0.30) NM

Longitudinal emittance, r.m.s.,

[π·keV·deg/u] (3.0 mA/0.4 mA)90 (120) 200 (120)

Transmission [%] ( 0.5 mA)

(2.0 mA)

( 4.0 mA)

80 (90)

70 (90)

65 (90)

NM

NM

70 (90)

RF Conditioning Status

Input Power

[kW]

Duration [hrs]

190 (CW) 12

210 (CW) 2

240 (CW) 0.5

260 (DC = 80%) 0.5

Deuteron CW operation

requires conditioning up

to 260 kW (65 kV)

Power density:

average ~ 25 W/cm2

I. Mardor, SRF 2009

176 MHz 4-Rod CW RFQ

Built by NTG/

Univ. Frankfurt

2006

2005

8

0

50

100

150

200

250

300

0 10 20 30 40 50 60 70 80 90 100

Duty Cycle (%)

Fo

rwa

rd R

F P

ow

er

(kW

)

18.11 20.11 23.11 26.11

8.12 9.12 20.12 22.12

23.12 24.12 31.12 Goal

0

1

2

3

4

5

6

7

8

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300

Average power (kW)

Pre

ss

ure

(1

0^

-7 m

ba

r)

20.11 23.11 26.11 8.12

9.12 20.12 22.12 23.12

24.12 31.12 Goal

The objective of the RFQ

conditioning (260 kW CW)

has not been achieved yet

Example: campaign end 2009

RFQ conditioning

campaigns

Deuterons CW

Deuterons CW

RFQ issues which prevented

reaching deuteron CW power:Arching from back side of rods

Melted tuning plates

Melted plungers

Broken RF fingers

Warming of end flanges

Burning O-rings

…

See poster TUP095 J. Rodnizki et al.

9

0

50

100

150

200

250

300

0 50 100 150 200 250 300

FPower in pulse (kW)

Scale

d V

pic

ku

p^

2(k

W)

4-Jul

9July

10July

Linear

Non-linearity of voltage response,

High x-ray background

Discharge between back of the rods and stems

Discharge between the rods and stems

In spring 2009 the rods were modified

locally to reduce the parasitic fields.

This solved the problem of discharge.

However, field realignment was required

(later in the talk).

10

Burning of tuning plates

Contact springs of tuning plates were burned twice

New design :

massive silver plate for better current and

thermal conductivity,

mechanical contact with stems by a splint system

11

Melting of plunger electrode

The low-energy plunger electrode has been melted.

It was verified that this was not due to a resonance phenomenon.

New design:

plunger was reduced by size (twice less thermal load),

cooling capacity was improved (the plunger and cooling shaft made from one block)

12

Plungers RF sliding contacts

Broken and deformed RF fingers of the plunger sliding contacts.

The sign analysis of the finger surface showed melting signs.

New design :

new type of RF contact with more rigid fingers

shafts plated by rhodium to avoid cold welding

rigid alignment of the plunger providing uniform contact pressure

Cu/Be silver plated

13

Heating of end flanges

Heating of RFQ end flanges (not water cooled).

Coloration of flanges was observed.

New design:

efficient water cooling

improved RF contact between the flanges and the base plate

14

Failure of vacuum seals

Several times vacuum failure

occurs during conditioning

Damaged vacuum or water

o-rings

This probably happens due to

discharges of RF field leaked

along cooling tubes

vacuum

air

beam direction

wa

ter

15

40 39bt 39 38b 38 37b 37 36b 36 35b 35 34b 34 33 32b 32 31 30 29b 29 28 27tb 27 26tb 26 25 24 23 22 21b 21 20b 20 19b 19 18 17 16 15 14t 14 13t 13 12 11 10 9 8 7 6 5 4 3 2 1t

150 -300 mV

<150 mV

300-450 mV

450-600 mV

600-750 mV

750-1000 mV

>1000 mV

RF mapping of cooling channels

RF hot spots were observed by mapping RF fields (200 W)

on the cooling channels .

In many cases these positions corresponded to the failed o-

rings.

Solutions for better RF contact, not implemented yet.

16

RFQ stability/availability

Tri

ps/

hou

r

Avail

ab

ilit

y (

%)

Duty cycle (%)

Stability as a function of the duty cycle6 hours

DC 25% DC 30% DC 35% DC 40% DC 45% DC 50% DC 55%

RF power 200 kW

25 oC

30oC

17

RFQ Conditioning Summary

The objective to condition RFQ to CW deuteron

operation powers is NOT achieved yet

Next steps to improve RF performance

Redesign and replace water flanges to solve the vacuum

seals problem

Improve vacuum systems: additional pumps, centralized oil

free backing

Further improvement of the RFQ cooling

Additional diagnostics for RF conditioning (more vacuum

gauges, RGA, x-ray mapping, etc.)

18

RFQ beam steering effects

Observed strong dependence of the overall transmission and beam

profiles on the RFQ forward power.

Such strong effects were not observed before the modifications made in

the RFQ in the first half of 2009

0

10

20

30

40

50

60

70

80

90

100

50 52.5 55 57.5 60 62.5 65 67.5 70 72.5

RF power (kW)

Tra

ns

mis

sio

n (

%)

Nov-2009

Profile X

-2

-1

0

1

2

3

4

5

6

7

-12.5 -10 -7.5 -5 -2.5 0 2.5 5 7.5 10 12.5

Position (mm)

Cu

rre

nt

(au

. U

n.)

61 kW

56 kW

53 kW

Profile XMEBT

March 2010:

replaced the shims in the high-energy section to shift the rod electrodes in the vertical plain

additional tuning block was introduced to keep the resonance frequency in range

as result the field homogeneity was improved to a large extent (+/- 2.7 %)

80

85

90

95

100

105

110

115

0 5 10 15 20 25 30 35 40

Stem no

Fie

ld U

0 [

%]

Nov-2009 Apr-2010

beam

19

RFQ field homogeneity

Tuning block

Shim

20

After improving field homogeneity observe

much smaller RFQ power effects

We plan further improvements of rods alignment(with help of our colleagues from the optics department)

RFQ steering effects

0

10

20

30

40

50

60

70

80

90

100

50 52.5 55 57.5 60 62.5 65 67.5 70 72.5

RF power (kW)

Tra

ns

mis

sio

n (

%)

Apr-2010 Nov-2009

Profile X

-2

-1

0

1

2

3

4

5

6

7

-12.5 -10 -7.5 -5 -2.5 0 2.5 5 7.5 10 12.5

Position (mm)

Cu

rre

nt

(au

. U

n.)

61 kW

56 kW

53 kW

Profile X

-1

0

1

2

3

4

5

-12.5 -10 -7.5 -5 -2.5 0 2.5 5 7.5 10 12.5

Position (mm)C

urr

en

t (a

u. u

n.)

62 kW

56 kW

54 kW

Nov 2009

Apr 2010

21

Prototype Superconductive ModuleThe cryomodule houses six SC HWR

cavities and three SC solenoids

Separate beam and insulation vacuum

Operating temperature 4.2°K

six 2 kW solid state amplifiers

Designed to accelerate 2 mA protons or

deuterons beams

HWR Parameters

176 MHzFrequency

0.09Optimal β (protons)

0.15 mLacc=βλ

840 kV @ 25 MV/mDV @ Epeak

>4.7x108Q0@Epeak

< 70 WCryogenic load

~1.3x106

~130 Hz

Qext

Loaded BW

M. Pekeler, LINAC 2006

Build by RI (ACCEL)

22

Helium processing :

99.9999% purity,

4 10-5 mbar

up to 43 MV/m 10% DC

Reduced field emission from the

cavities and allowed stable

operation at the nominal fields.

However, simultaneous operation

of all cavities at the nominal field

was not achieved for long period.

0.01

0.1

1

10

100

1000

15 20 25 30 35

Epeak (MV/m)

Rad

iati

on

(m

R/h

)

HWR1

HWR2

HWR3

HWR4

HWR5

HWR6

0.01

0.1

1

10

100

1000

15 20 25 30 35

Epeak (MV/m)

Rad

iati

on

(m

R/h

)HWR1

HWR2

HWR3

HWR4

HWR5

HWR6

Before

After

PSM commissioning

A. Perry, SRF2009

nominal peak field

23

HWR Microphonics measurements*

HWRs are extremely sensitive to LHe pressure fluctuations (60 Hz/mbar)

Detuning signal is dominated by the Helium pressure drift

Detuning sometimes exceeds +/-200 Hz (~ +/-2 BW).

100 110 120 130 140 150 160 170 180 190 200-100

-80

-60

-40

-20

0

20

40

60

80

100

Time[Sec]

Fre

quency D

etu

nin

g [

Hz]

Frequency Detuning

* Performed in collaboration with

J.Delayen and K. Davis (JLab)

45 sec45 sec

24

HWR Tune*

Piezoelectric actuator provides fine tuning of the

resonance frequency

Range reduction of the piezoelectric elements

Were subsequently replaced

is used for coarse tuning.Stepper motor

Stepper motor movement induces instabilities

and is therefore disabled during RF operation

* Performed in collaboration with

J.Delayen and K. Davis (JLab)600 700 800 900 1000 1100 1200 1300 1400

700

750

800

850

900

950

1000

1050

1100

Piezo Amplifier applied voltage[scaled]

Fre

quency d

etu

nin

g[H

z]

Tuner Response Curve

1st cycle

2nd cycle

Response of the fine tuner is

highly non-linear.

25

HWR Couplers temperature

During operation significant

heating of coupler #4 was

observed

Operation of cavity 4 is

therefore limited to ~500 kV

to avoid overheating

0.E+00

1.E+05

2.E+05

3.E+05

4.E+05

5.E+05

6.E+05

7.E+05

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Time (h)

Vo

ltag

e (

V)

Voltage Cavity 4

60

65

70

75

80

85

90

95

100

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Time (h)

T(

K)

coupler 4

26

PSM Status

Reached stable long-term only at 60-70% of nominal gradients :

high-sensitivity to helium pressure fluctuations

problems with tuner response

warming up of some couplers

Work on implementing a new tuner control algorithm on a NI – CRIO FPGA core – improve the response time and account for the hard nonlinearities.

Upgrade of 2 kW amplifiers to 4.0 kW to provide additional RF power required for high current field stabilization.

HWR1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

-120 -95 -70 -45 -20 5 30 55 80 105 130 155

phase (deg)

En

erg

y (

Me

V)

27

Example of phasing cavities for

proton beam

Use low beam DC (10-2 %)

RFQ - 100 % (protons),

a few % (deuterons)

Measure energy of the protons scattered

on a 0.3 mg/cm2 gold foil as a function of

the cavities voltages/phases

Phasing cavities for pulsed beams

HWR 3

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2

-200 -170 -140 -110 -80 -50 -20 10 40 70 100 130

phase (deg)

En

erg

y (

Me

V) 200 kV

430 kV

HWR4

1.7

1.8

1.9

2

2.1

2.2

2.3

2.4

-260 -220 -180 -140 -100 -60 -20 20 60 100 140 180

phase (deg)

En

erg

y (

MeV

)

200 kV

450 kV

HWR5

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

-160 -120 -80 -40 0 40 80 120 160 200

phase (deg)

En

erg

y (

Me

V)

200 kV

460 kV

HWR6

2

2.2

2.4

2.6

2.8

3

3.2

-180 -140 -100 -60 -20 20 60 100 140 180

phase (deg)

En

erg

y (

Me

V)

200 kV

660

Final settings for 3.1 MeV

Cavity Set Voltage Real Voltage Set Phase Sync Phase

HWR1 120 kV 150 kV 80 -95

HWR2 off off off off

HWR3 430 kV 600 Kv 40 0

HWR4 490 kV 500 kV -170 -35

HWR5 400 kV 500 kV -50 -30

HWR6 660 kV 500 kV 20 0

Beam Dynamics calculations J. Rodnizki

L. Weissman,

DIPAC2009

The highest beam energies for low DC beam:

Protons – 3.7 MeV

Deuterons – 4.3 MeV

28See poster TUP091, J. Rodnizki et al

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5500

1000

1500

2000

2500

3000

3500

Energy Gain [keV/degree]

Energ

y V

ariance[k

eV

*keV

]

test

polynomial fitRFQ 237 kW

Long. Emittance

210 π deg keV/u

Example : Deuteron beam

RFQ + 1st cavity

The cavity was set to -90° (bunching mode) and its voltage is varied

Evaluation of longitudinal emittance via measuring energy width of the peak

as a function of the cavity voltage

0 0.5 1 1.5 2 2.5 3 3.5500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

Energy Gain [keV/degree]

Energ

y V

ariance[k

eV

*keV

]

RBS

polynomial fitRFQ 249 kW

Long. Emittance

365 π deg keV/u

0 0.5 1 1.5 2 2.5 3 3.5 41000

1500

2000

2500

3000

3500

4000

4500

Energy Gain [keV/degree]

Energ

y V

ariance[k

eV

*keV

]

RBS

polynomial fit

Long. Emittance

260 π deg keV/u

RFQ 227 kW

RFQ Longitudinal emittance measurement

29

CW beam: vacuum/cryogenics effects

LHe inlet valve

Dewar heater

Scaled is

blown up

First attempts to conduct ~ mA CW

strong effects in the PSM vacuum and in the cryogenics

In this example 1 mA beam is conducted through the cryomodule without acceleration and

some optics parameters were varied (RFQ power, MEBT steers).

RFQ power

PSM pressure

~10-8 mbar

~10-10

mbar

30

CW beam (continued)Otimizing RFQ power and MEBT steering to minimize beam-induced effects

Managed to achieve stable operation for CW beam

RFQ power

RFQ vacuum

PSM vacuum

(different scale)

MEBT vacuum

There are still effects

on cryogenics

but operation Is stable

In this example, 1-1.3 mA 1.5 MeV drifted through the cryomodule.

Operation was stable for longer than 6.5 hours and

Operation was repeated during the two consequent days

LHe inlet valve

Dewar heater

PSM LHe pressure

1.5-2%

Plant return pressure

31

CW beam (continued)

RFQ power

RFQ vacuum

PSM vacuum

(different scale)

MEBT vacuum

D-plate vacuum

The effects of vary RFQ power on vacuum in the accelerator are observed

32

CW beam (continued)

RFQ power

RFQ vacuum

PSM vacuum

(different scale)

MEBT vacuum

1 mA 3 MeV

beam 9.3 h

heaters

ON heaters

OFF

RFQ trip

In this example:

Operation of ~1 mA, ~3 MeV accelerated proton beam.

Operation was stable for more than 9 hours.

Only one RFQ trip. Return to operation within minutes.

Effect on cryogenics is similar to 1.5 MeV beam.

So, probably, the loss of 2-3 mA happens at the entrance of the cryomodule.

Plan to introduce a beam scrapper in MEBT

24 h

LHe inlet valve

Dewar heater

PSM LHe pressure

Plant return pressure

PSM LHe level

Dewar LHe pressure

1.5-2%

33

Phase I Beam Operation Summary

Cavities 1 is used for bunching; cavity 2 is used as a drift

Operation at higher gradients is still limited by instabilities

Beam induced effects

CW (1 mA)

Proton

3.1 MeV

Low DC

Deuteron

4.3 MeV

Low DC

Proton

3.7 MeV

HWR #

Eacc

MV/m

Voltage

[kV]

Eacc

MV/m

Voltage

[kV]

Eacc

MV/m

Voltage

[kV]

11501.929011501

3.75603.959046303

2.74003.35003.75504

3.75503.35003.75505

3.55203.35005.99006

Lacc=βλ

Nominal voltage:

840 kV

Summary and Outlook

First proton and deuteron beams were accelerated by

a HWR based SC Linac

Proton and Deuteron low duty cycle beams were accelerated up to 3.7 MeV and 4.3 MeV

Protons CW ~1 mA beams accelerated up to 3.1 MeV

Phase I is still in its commissioning stage.

1. Actions to improve beam operation :RFQ alignment

MEBT scrapper

Upgrade of tuners control and cavities amplifiers

2. CW Deuteron operation has not been achieved yet

Design of Phase II is underway

35

Temporary beam line

Future

target

stations

Beam dump

Temporary beam line is being

commissioned in the accelerator

tunnel

Pilot project. Several beam lines

will be built for the Phase II

The first experiments in material

science and astrophysics

The first experiments should take

place until the end of the year

PSM

D-plate

VAT beam dump

Test station

36

People involved

SARAF team (including students, advisers and partially affiliated personal ) :

A. Nagler , I. Mardor, D. Berkovits,A. Abramson , A. Arenshtam, Y. Askenazi,

B. Bazak (until 2009), Y. Ben-Aliz, Y. Buzaglo, O. Dudovich, Y.Eisen,

I. Eliyahu, G. Finberg, I. Fishman, I. Gertz, A. Grin, S. Halfon, D. Har-Even,

D. Hirshman, T. Hirsh, A. Kreisel, D. Kijel, G. Lempert, A. Perry,

R. Raizman (until 2010), E. Reinfeld, J. Rodnizki, A. Shor, I. Silverman,

B. Vainas, L. Weissman,Y. Yanay (until 2009).

RI&Varian /(former ACCEL):H. Vogel, Ch. Piel, K, Dunkel, P. Von Stain, M. Pekeler, F. Kremer,

D. Trompetter, many mechanical and electrical engineers and technicians

NTG/ Frankfurt Univ:A. Bechtold, Ph. Fischer, A. Schempp, J. Hauser

Cryoelectra :B. Aminov, N. Pupeter, …

Red font : persons who joined recently