Operation summary of Gun 4.5 and Gun 4.2 at PITZPage 2/12 Current setup of PITZ gun in 2018 (Gun4.5...

Operation summary of

Gun 4.5 and Gun 4.2 at PITZ

Igor Isaev

PITZ Collaboration Meeting

Zeuthen, 05.12.2018

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Current setup of PITZ gun in 2018 (Gun4.5 and Gun4.2)

Gun4.5 and Gun4.2 with ”contact stripe” spring design

2 Thales-type RF vacuum windows

(like 2014-2015 with Gun 4.2, but now optimized T-combiner)

T-Combiner has optimized RF design for best

window positioning for reflections + most compact

Features of the Guns setup

PMT – Photomultiplier tube

e-det – Electron detector

IR – Infrared sensor

IGP – Ion getter pump

(pressure reading)

PG – Pressure gauge

same

radiuses

Comparison with “watchband

reloaded” case at Gun 4.6

notice

radius of

3 mm

notice

different

radiuses

Cavity

backplane

Cathode plug

| Operation summary of Gun 4.5 and Gun 4.2 at PITZ | Igor Isaev | PITZ Collaboration Meeting | Zeuthen, 05.12.2018 |

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Operation history of Gun 4.5 (from 04.04.2018 to 27.07.2018)

1Hz 5Hz 5Hz 10Hz

* The power readings are presented from 10MW dir. coupler. The readings are not 100% reliable.

Restart after opening

DC measurements 1st trial of endoscopic

inspection

2nd endoscopic

inspection: successful begin of the

cathode

parts

exchange

The cathode spring was exchanged (the cathode holder is the same).

The z-Actuator was exchanged to brand new one (was backed, but vacuum was bad)

The z-Actuator

was exchanged

back to previous

Vacuum chamber heating

*

Have an

option of

volume

isolation


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Power and pulse length usage during operation of Gun 4.5 (all data with >100kW in gun taken into account)

DC check

03.05 09.05 23.05 06.06

• Conditioning with strategy:

reach maximum power for

100us pulse length and full

solenoid sweep, then

increase pulse length

• Different studies:

03.05.2018 DC imaging


with 1mm extracted

cathode

23.05.2018 First

photoelectrons

06.06.2018 Gun power

calibration (vs e-beam

momentum)

06-07.06.2018 DC images

correlation with

photoelectrons using grid

at BSA


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Dark Current of Gun4.5


0

500

1000

1500

2000

2500

3 4 5 6 7 8 9

Da

rk C

urr

en

t [u

A]

RF power in guin (MW)

Dark Current vs. RF Power

Ampl(max), cath.#700.1, 07.05.2018

Ampl(max), cath.#660.1, 08.05.2018

Ampl(max),cath#700.1, 20180727M

880

900

920

940

960

980

1000

1020

1040

1060

1080

20

-Ap

r

30

-Ap

r

10

-May

20

-May

30

-May

9-J

un

19

-Ju

n

29

-Ju

n

9-J

ul

19

-Ju

l

29

-Ju

l

8-A

ug

ma

xim

um

da

rk c

urr

en

t [u

A]

Dark Current at 6.5MW (amplitude value)

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Gun 4.5: visual inspection on 18.06.2018 Pictures taken from the cathode side using videoscope

• An attempt to touch and identify a ridge edge on the gun backplane

rounding was done: no tactile detectable edge was found.

• 2 leaves of the cathode spring more bended (?during inspection).

• Transition from flat wall to cylinder

• Flat wall of the Full cell

• RF coupler antenna


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Gun4.5: visual inspection in week 46/47 Pictures taken from the cathode side using a stiff videoscope provided by TH-Wildau

Shiny line on whole

circumference (ridge?)

Different roughness

not machined in one go

Possible step if machined

from both sides

Several scratches

on cylindrical part

Nonhomogeneous fade out of reflection

Steps on the radius curvature


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Gun4.5: visual inspection in week 46/47


Pictures taken from the cathode side using a stiff videoscope provided by TH-Wildau

Gun 4.5

Gun 3.2 April-August 2007

High dark current

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Operation history of Gun 4.2 (from 24.09.2018 to 26.11.2018)

* The power readings are presented from 10MW directional coupler. The readings are not 100% reliable.

Restart after opening

RF vacuum window First photo electrons

Problems with RF vacuum

window were noticed

High average

power tests

Operation with

high charge

>2nC

High average power tests


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Operation issue of Gun4.2 PMT interlocks on the air side of the upper of the two THALES

windows.

WG2 inspection:

• all screws were tightened normally, flange was mounted normally.

• ceramics evenly brown, but okay. No dust or dirt on ceramics. Looks

normal.

• parts of the standard WG (PDR14) contact plane sits on stainless steel

(bad conductivity)

• Waveguide part with PDR14 flange also damaged

Visible contact problem / damage on windows flange is due to too

small copper metallization on THALES-WG flange. It is led to

material melting.

Different technique to connect flanges was used.

Latest tests with maximum peak power and RF pulse length of

200μs did not show problems anymore.


THALES window air side flange

Waveguide flange air side

THALES window air side

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Gun 4.5 shows high dark current

The investigations showed that the dark current comes from the back plane of the gun

The visual inspection showed irregularities (scratches, varied machining steps etc.) at the cathode vicinity of

the Gun 4.5

The gun cavity was changed to Gun 4.2

The operation with the Gun 4.2 revealed problems with vacuum window flange

After reassembling short tests with high average power did not show problems at this place

The next plan is to operate the Gun 4.2 at 200us (enough for the experiments at PITZ)

Summary


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Thank You for your attention!


Backup Slides Gun 4.5


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Gun 4.5 History DC studies in KW18 (30.04. - 06.05.2018) - KW23 (04.-10.06.2018)


09.05.2018 DC imaging with 1mm extracted cathode

23.05.2018 First photoelectrons

06.06.2018 Gun power calibration (vs e-beam momentum)

06-07.06.2018 DC images correlation with photoelectrons using grid at BSA

KW24 (11.-17.06.2018) to KW30 (23.-29.07.2018)

13.06.2018 Start of shutdown

Gun4.5 endoscopic inspection (bucking solenoid was not moved, cathode holder was not dismounted)

o 14.06.2018 1st trial to make inspection (bellow, tube and valve were not dismounted): endoscope length was not

enough

o 18.06.2018 2nd attempt (bellow, tube and valve were dismounted): successfully finished. During the inspection the

pictures of the cathode vicinity and gun surface were taken. Additionally, an attempt to touch and identify a ridge

edge on the gun backplane rounding was done: no tactile detectable edge was found.

29.06.2018 begin of the cathode parts exchange:

o 02.07.2018 The cathode spring was exchanged (the cathode holder is the same)

o 02.07.2018 The z-Actuator was exchanged to brand new one (was backed, but vacuum was bad)

o 04.07.2018 The z-Actuator was exchanged back to previous (Problems with vacuum remained due to vacuum

chamber pollution by the brand new z-Actuator. Cycled heating was applied to overcome the problems.)

KW30 (23.-29.07.2018)

Measurements:

o from 24.07.2018 to 27.07.2018 Gun DC measurements

o 26.07.2018 the decision to exchange the gun was taken | Operation summary of Gun 4.5 and Gun 4.2 at PITZ | Igor Isaev | PITZ Collaboration Meeting | Zeuthen, 05.12.2018 |

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Evolution of interlocks for Gun 4.5

Latest stable run in June 2018 showed that the most ILs are vacuum pressure

related and light from Vacuum windows

(all data with >100kW in gun taken into account)


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Run time of Gun 4.5 at given Power

Average peak power: 4.77 MW

Average RF pulse length: 47.26 µs

Total operation time: 1197 h

9.7 GJ deposited

(based on average values)

(all data with >100kW in gun taken into account)


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Left picture on the 3rd slide

(in the red frame)

Dire

ctio

n o

f the v

ideo p

robe m

ovem

ent

Direction of view

Dire

ctio

n o

f the v

ideo p

robe m

ovem

ent

View1

View2

View3

View1

View2

View3

Surface1

Surface2

Surface3

Surface4

Surface5

Surface1

Surface3

Surface4

Surface1

Surface3

Surface4

Surface4

Surface3

Surface5

Transition from flat wall to

cylinder

Transition from flat wall to

cylinder

cylinder White (calcareous-like) spot was observed of

the rounding (surface 4) | Operation summary of Gun 4.5 and Gun 4.2 at PITZ | Igor Isaev | PITZ Collaboration Meeting | Zeuthen, 05.12.2018 |

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Surface1

Surface2

Surface3

Surface4

Surface5

Middle picture on the 3rd slide

(in the red frame)

Direction of view

Direction of the video probe

movement (rotation around the z-

axis)

Surface1

Surface2

Surface3

Surface4

Surface5

Cylinder of the

half cell

Surface1

Surface2

Surface3

Surface4

Surface5

Cylinder of the

half cell

Surface1

Surface2

Surface3

Surface4

Surface5

Cylinder of the

half cell

Surface color change (like from high temperature

gradient or from burning) was observed of the

rounding (surface 4)

View1

View2

View3


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Dark current of the Gun 4.5 Dark current investigations:

Cathode plug insertion orientation change: DC images at Low.SCR1. Imain = 380A

Left: normal cathode orientation; Right: rotated by 180deg similar DC

Cathode plug Z position of insertion change: DC images at Low.SCR1. Imain = 390A

Left: normal cathode positon; Right: cathode plug is out by 1mm 2 x DC

Main conclusion: High DC is coming from

back wall of the gun.


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Gun front view (via DDC mirror & light via laser mirror) Left: cathode out Middle: cathode out & close to spring Right: cathode in


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Gun front view (via DDC mirror & light via laser mirror) Left: cathode out Middle: cathode in Right: during assembly

Edge of gun backplane seems much

more pronounced/burned compared to

original

In left picture the edge is barely illuminated, in middle

picture reflections off the cathode’s edge shine light onto

the backplane edge. A sharp black ring around the edge is

clearly visible today, but not in original picture.


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Gun back view (via load lock mirror & light via laser mirror) Spring visible, no major damage obvious (Right: during assembly)


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PITZ photoelectron gun

PITZ photoelectron gun setup consists of:

> RF cavity

L-band 1.6-cell copper (OFHC) cavity

Dry-ice cleaning → low dark current (< 100 µA @ 6 MW)

Cs2Te photocathode (QE ~5 - 10 %)

with load-lock system

LLRF control for amplitude

and phase stability

> Solenoids

Dedicated for emittance

compensation

Max. on-axis field ~0.3 T

(500 A in the main solenoid)

Bucking solenoid for

compensation of field at cathode

> Photocathode laser

Pulse train structure

Micropulses temporally and spatially shaped

Watchband

spring

design

Mo plug

CuBe spring

Cs2Te

cathode

Watchband

Reloaded

spring

design Mo plug

CuBe spring

Cs2Te

cathode

Contact

stripe

design

Mo plug

CuBe spring

Cs2Te

cathode

RF cavity water cooling channels (Gun 4 type)

Three designs of the cathode area

RF cavity body

(top view)

Main solenoid

(reminder)


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Gun model


Operation summary of Gun 4.5 and Gun 4.2 at PITZPage 2/12 Current setup of PITZ gun in 2018 (Gun4.5...

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