FEA
results
with
LEG
pulser
and
further
plans

FEA
results
with
LEG
pulser
and
further
plans


S.
Tsujino,
E.
Kirk,
P.
Helfenstein,
A.
Mustonen
(LMN
team)
 M.
Paraliev,
C.
Gough
(GFA)
P.
Beaud
(SYN)
B.
Oswald
(GFA)

 C.
Escher,
H.‐W.
Fink
(UniZ),
T.
Feurer
(UniBern)


Outline


1.  Sub‐nanosecond
pulsed‐field‐emission
in
LEG
pulser
 (single‐gate
FEA)


2.   HomogenizaVon
of
emission
distribuVon
 3.  Futher
plans


•  Two‐terminal
double‐gate
FEA
design


•  Sub‐micron
pitch
FEA
fabricaVon
(on
going)


10 µm 20 nm

Single‐gate

FEA
 5
µm‐pitch
 
1.2x10⁵‐Vp


Nanosecond
pulsed‐field‐emission
in
LEG
pulser
(prev.)


‐V_em

‐HV

Diode
gun A K

PSL

FEA

RF
cavity

DSL SCR/FC DP

SCR2 TR

Air‐core



criVcally‐coupled

 Transformer
for
for

 up
to
‐500
kV/250
ns
 cathode
voltage




Secondary
of
TR
is
a
semi‐rigid
co‐ax
cable:


Inner


==>


FEA
substrate
 Ground
==>
FEA
gate


4
ns


Diode
accelaraVon
of
~4
ns
FEA
beam


 
30
MV/m
surface
gradient


 
10
pC
charge


 
350
keV
beam
energy


Beam
imaging:
granular
paeern


Tsujino
et
al.
J.Vac.Sci.Technol.
B
(2011)


Sub‐nanosecond
pulsed‐field‐emission
in
LEG
pulser


10 µm 20 nm

Mo‐emieers Gate

SiON Ni-subst.

SiO₂

‐V_em

‐HV

Diode
gun A K

PSL

FEA

RF
cavity

DSL SCR/FC DP

SCR2 TR

V_dc

I_p e^‐

u t ^K

FEA gun

Air‐core



criVcally‐coupled

 Transformer
for
for

 up
to
‐500
kV/250
ns
 cathode
voltage




Secondary
of
TR
is
a
semi‐rigid
co‐ax
cable:


Inner


==>


FEA
substrate
 Ground
==>
FEA
gate


Single‐gate

FEA
 5
µm‐pitch
 
1.2x10⁵‐Vp


~50
%
reducVon
of
 capacitance
(~0.5
nF)
 by
SiON
inserVon


Tsujino
et
al.
Phys.
Plasmas
18
(2011)


Sub‐nanosecond
pulsed‐field‐emission
in
LEG
pulser


‐V_em

‐HV

Diode
gun A K

PSL

FEA

RF
cavity

DSL SCR/FC DP

SCR2 TR

V_dc

I_p e^‐

u t ^K

FEA gun

Air‐core



criVcally‐coupled

 Transformer
for
for

 up
to
‐500
kV/250
ns
 cathode
voltage




Secondary
of
TR
is
a
semi‐rigid
co‐ax
cable:


Inner


==>


FEA
substrate
 Ground
==>
FEA
gate


Field‐emission
pulse
~0.5
ns
 Pulsed
Vg‐e
~
1
ns


dc
Vg‐e


double
current
pulse
~
1ns


Tsujino
et
al.
Phys.
Plasmas
18
(2011)


with
RF
2MW
 focused
 Without
RF


200
keV,
imaging


Sub‐nanosecond
pulsed‐field‐emission
in
LEG
pulser


‐V_em

‐HV

Diode
gun A K

PSL

FEA

RF
cavity

DSL SCR/FC DP

SCR2 TR

V_dc

I_p e^‐

u t ^K

FEA gun

Air‐core



criVcally‐coupled

 Transformer
for
for

 up
to
‐500
kV/250
ns
 cathode
voltage




Secondary
of
TR
is
a
semi‐rigid
co‐ax
cable:


Inner


==>


FEA
substrate
 Ground
==>
FEA
gate


Beam‐energy


Tsujino
et
al.
Phys.
Plasmas
18
(2011)


Sub‐nanosecond
pulsed‐field‐emission
in
LEG
pulser


‐V_em

‐HV

Diode
gun A K

PSL

FEA

RF
cavity

DSL SCR/FC DP

SCR2 TR

V_dc

I_p e^‐

u t ^K

FEA gun

Air‐core



criVcally‐coupled

 Transformer
for
for

 up
to
‐500
kV/250
ns
 cathode
voltage




Secondary
of
TR
is
a
semi‐rigid
co‐ax
cable:


Inner


==>


FEA
substrate
 Ground
==>
FEA
gate


Field‐emission
bunch RF
field In‐phase

Out‐of‐phase

Tsujino
et
al.
Phys.
Plasmas
18
(2011)


LimitaVon
of
the
electrically
switched
FEA
pulse
duraVon


‐V_em

‐HV

Diode
gun A K

PSL

FEA

RF
cavity

DSL SCR/FC DP

SCR2 TR

V_dc

I_p e^‐

u t ^K

FEA gun

Air‐core



criVcally‐coupled

 Transformer
for
for

 up
to
‐500
kV/250
ns
 cathode
voltage




Secondary
of
TR
is
a
semi‐rigid
co‐ax
cable:


Inner


==>


FEA
substrate
 Ground
==>
FEA
gate


Field‐emission
pulse
~0.5
ns
 dc
Vg‐e


double
current
pulse
~
1ns


Should
be
shorter
 Pulsed
Vg‐e
~
1
ns


Required
amplitude


ProporVonal
to
Capacitance


Dispersion
through
20
m:
pulse
 broadening
from
600
ps
to
900
ps


Sub‐nanosecond
pulsed‐field‐emission
in
LEG
pulser


‐V_em

‐HV

Diode
gun A K

PSL

FEA

RF
cavity

DSL SCR/FC DP

SCR2 TR

V_dc

I_p e^‐

u t ^K

FEA gun

Air‐core



criVcally‐coupled

 Transformer
for
for

 up
to
‐500
kV/250
ns
 cathode
voltage




Secondary
of
TR
is
a
semi‐rigid
co‐ax
cable:


Inner


==>


FEA
substrate
 Ground
==>
FEA
gate


RF‐off
(0.86
pC)

T_FEA
=
590
ps

T_FEA
=
390
ps

T_FEA
=
90
ps Pulse‐off


Pulse&DC
off

‐35
Vdc,
2
MW‐RF

€

δQ² ~ dQ

dϕ2πf δt² ~40
ps,
jieer
of
pulser

Faster
pulser
(0.7
ns
=>
0.5
ns)



smaller
pulse
delay
(~1
ns
=>
~0.8
ns)


What
makes
FEA
beam
non‐uniform?


Sta,c
effect


•  
Emieer
apex
radius
of
curvatures
r

•  
Emieer
surface
issues:



contaminaVon


molecular
adsorpVon
 surface
oxidaVon


work
funcVon
distribuVon
(faceVng)
 Current
induced
effect


•  
surface
diffusion:
local
heaVng
and
Vp‐blun,ng


•  
field
forming:
Vp‐sharpening


•  
ion
bombardment:
spueering,
implantaVon

 
 
=>
Vp‐blun,ng,
work
funcVon
change


Emission‐current
induced


cleaning
(local
heaVng)


combined
with
careful


preparaVon



Anode


Field‐emieer


Subst.


Gate
(G_ex)


SiO₂ V_em V_a

noble‐gas
atom/ion
 electrons


equi‐potenVal

 lines


D

FEA
beam‐homogeneizaVon
by
noble‐gas
processing


Field‐emission
in
noble‐gas
environment


•  
Impact
ionizaVon
of
gas
molecules


•  
Cathode
bombardment
of
ions


•  
Tip
bombardment
only
by
locally
 generated
ions


•  
Ion
bombardment
to
the
Vp


proporVonal
to
the
emission
current
 (high
for
sharper
Vp)


=>
self‐consistent
,p‐distribu,on
control


HomogeneizaVon
of
field‐emission
distribuVon

 by
noble‐gas
processing


FEA‐1



(5µm‐pitch,
120k‐Vp)
 aper
several
“events”


FEA‐beam
imaging:


200
keV‐diode
acc.


Auto‐correlaVon


Same
FEA


(5µm‐pitch,
120k‐Vp)
 aper
DC
emission
 in
Ar
(10^‐5‐10^‐4
mbar)
 For
~1
hour
with
up
to



~
1
mA
dc
emission
 FEA‐beam
imaging

 w/same
condiVon:


200
keV‐diode
acc.


same
camera
parms.


Auto‐correlaVon
(0.7
pC)
 Auto‐correlaVon
(1.3
pC)


Tsujino
et
al.
submieed
to
APL
(2011)


HomogeneizaVon
of
field‐emission
distribuVon

 by
noble‐gas
processing


FEA‐3
(5µm‐pitch,
10k‐Vp)
 in
preparaVon
chamber
 (50
Hz
AC
bias)


€

I_a = A_FN

(

)

(

)

A_FN
:
~
total
emission
area
 
/work
funcVon


B_FN
:
~
emieer
apex
radius^1/2

 
×
work
funcVon^3/2

€

A

~ NS / Φ

€

B_FN ~ φ^{3/ 2}r_apex^0.5

in
Ne(10^‐4
mbar)
 Base‐pressure
 10^‐8
mbar


Increase
of
A_FN
and
B_FN

~
increase
of



apex
radius
&
total
area


Tsujino
et
al.
submieed
to
APL
(2011)


HomogeneizaVon
of
field‐emission
distribuVon

 by
noble‐gas
processing


FEA‐3
(5µm‐pitch,
10k‐Vp)
 in
preparaVon
chamber



Max
I_a
45
mA
&
4.5
µA/Vp
 Aper
Ne‐processing


(50
ns‐pulse
emission)



Before
Ne‐processing

 Max
I_a
~
0.5
mA


(without
local
arc)


Tsujino
et
al.
submieed
to
APL
(2011)


Improved
beam
homogeneity
of
field‐emission
distribuVon

 by
noble‐gas
processing


Tsujino
et
al.
submieed
to
APL
(2011)


FEA‐2
(5µm‐pitch,
40k‐Vp)
 in
LEG
gun


a:
(A,B)
=
(0.7×10⁴,
647)
 b:
(A,B)
=
(10.4×10⁴,
757)
 aper
Ar


c:
(A,B)
=
(8.7×10⁴,
677),
LEG


d:
(A,B)
=
(8.8×10⁴,
662),
LEG
aper
Ar


FEA
transfer


Through
air
&
re‐processing


Cathode
biased
by

 DCV
up
to
~100
keV


Upgrade
of
100
keV‐teststand
for
FEA
characterizaVon


20
ns


V_c
=

‐45
kV,

 F_acc
=
(1‐5)
MV/m


w177ch5b:



ϕ0.56
mm,
7.5
k‐,ps
 Vge
=
Vdc
+
Vpulse


Vpulse,set
=
‐19
V


New
FEA
holder
for
sub‐nanosecond
 electrical
switching
(same
as
LEG
pulser
 but
without
20
m‐transmission
line)


Indipendent
anode
voltage/current
meas,

 FC,
FEA
imaging,
&
emieance
monitor


cf.
Leemann
et
al.



Phys.
Rev.
ST.
(2007).


P.
Helfenstein
et
al.
Appl.
Phys.
Lee.
(2011)



 
 
−V


(V)


Finite
anode
current


|V_col|
<
0.91
|V_em| Collimated
beam

 V_col
=
62
V


Uncollimated
beam
 V_col
=
0
V


No
emission


|V_col|
>
0.91
|V_em|

V_col
=
V_em

CollimaVon
of
field‐emission
beam:
double‐gate
FEAs
(prev)


Anode


Faraday
cup


I

I

I

+V

A
 I

I

V

V

Double‐

gate
FEAs
 G

‐contact


Ceramic
 spacer
 G

‐contact


Central
 conductor


Anode
 iris


Electron‐gun
with
convenVonal
double‐gate
FEAs


Double‐

gate
FEAs
 Outer
conductor


~
G


contact



Central
 conductor


Anode


I

I

Ceramic
 spacer


+V

V

V

Faraday
cup


A
 I

Anode


iris


Electron‐gun
with
two‐terminal
double‐gate
FEAs


Two‐terminal
double‐gate
FEA


Emieer‐Vp
 Insulator


Single
emieer


G

FEA‐R
contact
 R


G

‐R
contact
 Resistor
unit


G

G

FEA
substrate
 Z

t


Transmision
line


V

V

+

−

+ −

Z

Em
 G

G

C

C

I

I

I

I

R

Field
emieer
driver
 Field
emieer


Anode/Electron
beam
 transport
space


V

DC/slow
pre‐

charge
pulse


Short
emission‐trigger
pulse


V

+

− + −

Two‐terminal
double‐gate
FEA


V_col
(V)
 V_em
(V)


V_em
=
71.8
V


Vem
(71.8
V)
 OpVmum
collimaVon



when
V_col/
V_em
=
0.86


Two‐terminal
double‐gate
FEA


Two‐terminal
double‐gate
FEA


107


1011
 1020


Em:
102
 G

:104


G

:
106


w
 L
 Z

823


V

821
 822


V

+

−

+ −

(a)


(b)


(c)


(d)


k_col^(op)
=
0.86
 k_col^(th)
=
0.91


Two‐terminal
double‐gate
FEA:
simulated
I‐V


150
ns‐emission
 Switching
potenVal


PotenVal
at
FEA


RaVo
k_col
=
V_col/V_em k_col
≥
0.91:
no
anode
current



k_col
=
0.86:



maximal
beam
collimaVon
 Anode
current

(a)


(b)


(c)


(d)


k_col^(op)
=
0.86
 k_col^(th)
=
0.91


Two‐terminal
double‐gate
FEA:
simulated
I‐V


500
ps‐emission
 Switching
potenVal


PotenVal
at
FEA


RaVo
k_col
=
V_col/V_em k_col
≥
0.91:
no
anode
current



k_col
=
0.86:



maximal
beam
collimaVon
 Anode
current

Near
Infrared
Laser‐induced
Field‐emission
(prev)


‐ 
Infrared,
800
nm,

excitaVon


‐ 
Experiment
with
120
k‐Vp
array


‐ 
5
pC
maximum
charge


Three‐photon
 photoemission
 from
gate‐electrode


5
pC


91
Vge


87
Vge


Laser‐induced
 field‐emission
 from
emiXer
Vps
 1‐photon
emission


0
Vge


V_em

Bias-T Va

Oscilloscope

Δt = 50 fs Ti:S

800nm 1.56 eV

Ia


Iem


hν = 1.56 eV hν =

1.56 eV

Mustonen
et
al.
submited
to
APL
(2011)


Q.E.
limited
by


emieer
density
(5
µm‐pitch)


Prototype
high‐density
FEA


Sub‐micron‐pitch
FEA
(<300
nm‐base
size)



=>
Expected:
more
than
×20
Vmes
increase
of
the
Q‐efficiency
 
 




for
the
laser‐induced
field‐emission


Underdevelopment:
electron‐beam
lithogrpahy
based
gate‐aperture
 paeerning
process
including
the
second
gate
aperture


•  Pulsed‐field
emission
in
LEG
gun:


‐   Sub‐nanosecond
field
emission,
synchronized
to
OBLA
gun
HV
pulse


&
RF
cavity
accelera,on


‐  Down
to
370
ps
emission
demonstrated


‐  Beam
homogeneiza,on
by
noble‐gas
condi,oning
demonstrated


•  Double‐gate
FEA:



‐
Two‐terminal
device
concept,
design,
and
fabrica,on
concept
developed


•  Laser‐induced
field‐emission:



‐
High‐density
FEA
fabrica,on
under
development

Summary