Non-Evaporable Getter (NEG)
Coating
Narong Chanlek
• NEG is a Ti-Zr-V (Titanium
Zirconium Vanadium) alloy
film deposited inside
vacuum chamber walls.
NEG Coating
• Ti–Zr–V NEG films sorbs H2, CO, CO2, H2O, and N2
providing distributed pumping and also reduce
outgassing from the walls.
• Using for narrow and long vacuum chambers –
much easier and quicker to provide the required
vacuum
• Suppressing e-cloud
However
• Low pumping capacity
• Technical problems - design and operation
Coating Techniques
Coating Techniques
Chemical Vapour Deposition - CVD
• Creates thin films of material on a substrate via
the use of chemical reactions.
• Reactive gases are fed into a vacuum chamber
and these gases react on a substrate and form a
thin film or a powder.
XRD Technique
Detector
X-ray Source
d sin θ = n λ
Sample
X-ray Diffraction (XRD)
Technique
• Giving detailed information about the chemical
composition and crystallographic structure of
materials.
• A monochromatic X-ray beam is projected onto
a crystalline material diffraction occurs following
Bragg's Condition.
• Varying the angle, the Bragg's Law conditions
are satisfied by different d-spacings in
polycrystalline materials. Plotting the angular
positions and intensities of the resultant
diffracted peaks of radiation produces a pattern,
which is characteristic of the sample.
XRD result of Ti – Zr –V film growth by cylindrical magnetron
deposition
XRD result of Zr film growth by cylindrical magnetron
deposition
Pumping property measurements
Research Objectives
Two main objectives of the research are:
To analyse the impact of frequency errors in the cavities.

To obtain cavity misalignments from frequency spectrum.

Bands in 9-Cell Structure – Simulation vs Circuit Model
The simulation was performed in Poisson Superfish
and the points corresponding to resonant frequencies
were plotted on the graph (dots) along with
eigenmodes from circuit model (circles). Dispersion
curves of single cavity are plotted for comparison.
Legend
Solid
line – light line
Solid curves – dispersion
curves from circuit model
Dashed curves –
approximated dispersion
curves from circuit model
Circles – eigenfrequencies
from circuit model
Dots – resonant
frequencies from
simulations
Bands in Single Cell – Extended Circuit Model
The model was extended to include
coupling between cavity (n) and four
nearest cells (n-2, n-1, n+1, n+2).
Legend
Solid line – light line
Solid curves – dispersion
curves from circuit model
Dots – resonant
frequencies from
simulations
Last Measurements
The tuner plate has been machined and the cavity with its tuner has been measured
Measured frequency
100.885 MHz
Simulation
100.816 MHz
‐32 kHz (air)
+77 kHz (shorter antenna)
100.861 MHz
∆ Frequency
24 kHz
Goal frequency
~100.900 MHz
2
Comments
• The goal for the hot frequency has been fully achieved
• The tuner plate thickness of 0.35mm could give a possible sensitivity to the mechanical resonances
• Next tuner design will provide for a larger thickness in order to avoid the previous drawback
• The reduced coarse range of the new tuner design will be not a trouble as we have enough tuning range and also this will meet one of the suggestion of the review committee
• The last point will also make easier the LLRF controls 3
The line
2000
5
6
4
131
3
10
2
63
1
Top of the cryostat
The line has been divided in 5 pieces. The dimensions are in mm
6
Coupler
7
Q0 values
ISOLDE
(Eacc=6MV/m)
Pcav (W)
Rs (nΩ)
Q0=Γ/Rs
5
33
109
7
46
6.6∙108
10
65
4.6∙108
12
79
3.9∙108
15
98
3.1∙108
TRIUMF*: Q0=7∙108 with Pcav=7W and Eacc=8.5MV/m SPIRAL2**: Q0=109 with Pcav=10W and Eacc=6.5MV/m * V. Zvyagintsev et al., “Development, Production And Tests Of Prototype Superconducting Cavities For The High Beta Section Of The Isac‐ii Heavy Ion Accelerator At Triumf”, RuPAC 2008, Zvenigorod, Russia
** G. Olry et al., “Tests Results Of The Beta 0.12 Quarter Wave Resonators For The Spiral2 Superconducting Linac”, 8
LINAC 2006, Knoxville, Tennessee USA
Transmission Line Input parameters
Let us assume Q0=6.6x108, β=200 and a resonant frequency of 101.28MHz Δf
1
1
(1 + β ) ⇒ Δ f ≈ f 0 ≅ 30 Hz
≈
=
f 0 Qload Q0
Qload
Pf =
Pcav
⎛ β −1 ⎞
1 − ⎜⎜
⎟⎟
⎝ β +1⎠
2
= [for Pcav = 7 W ] = 350W
β −1
≡ ΓL = 0.98
β +1
9
The Model
2000
6
131
5
4
3
10
2
63
1
Top of the cryostat
The line has been divided in 5 pieces. The dimensions are in mm
We will propagate the reflection coefficient Γ along the line
Zg
Γ5
Γ4
Γ3
Γ2
Γ1
Vg
5
4
3
2
1
x L5
L4
L3
L2
L1
ΓL
0
10
1st block
V1+ = 2 Z L1 Pf
Propagation of the Reflection Coefficient
Γ1 ( x) = ΓL e −2γ 1 x
Voltage and Current in the line
⎧V1 ( x) = V1+ e γ 1 x (1 + Γ1 ( x) )
⎨
+ γ1 x
(1 − Γ1 ( x) )
I
(
x
)
I
=
1 e
⎩ 1
+
1
I = 2
With
Propagation coefficient
Attenuation Factor
γ 1 = α1 + j β1
α1 = α c1 + α d 1
Rs (1 / Rin ) + (1 / Rout )
α c1 =
2η ln( Rout / Rin )
Attenuation Factor of the conductors
β1 =
2π
λ0
Pf
Z L1
εr
Propagation constant
α d1 =
π f
c
tan δ
Attenuation Factor of the dielectrics
11
nd
2
block
The equations stay formally the same but the propagation coefficient γ is changing then we have to impose the continuity of the fields on the border surface
Zg
Γ5
Γ4
Γ3
Γ2
Γ1
Vg
5
4
3
2
1
x L5
L4
L3
L2
ΓL
L1
0
A1
Γ1 ( x) L = Γ2 ( x) L
1
1
⎧⎪V1 ( x) L = V2 ( x) L
1
1
⎨
⎪⎩ I1 ( x) L1 = I 2 ( x) L1
Γ2 ( x) = Γ1 ( L1 ) e 2γ 2 L1
V 2+
⎧V2 ( x) = V1+ e L1 (γ 1 −γ 2 )
⎨
+ L1 ( γ 1 −γ 2 )
I
(
x
)
I
=
1 e
⎩ 2
I 2+
∙
∙
∙
e −2γ 2 x
e γ 2 x (1 + Γ2 ( x) )
e γ 2 x (1 − Γ2 ( x) )
12
Total Voltage and Current in the line By generalizing from the previous results
Ai = Γi −1 ( Li −1 ) e 2γ i Li−1
Γi ( x) = Ai
⎧Vi + = Vi −+1 e Li−1 (γ i−1 −γ i )
⎨ +
Li −1 ( γ i −1 −γ i )
+
I
I
e
=
i −1
⎩ i
⎧Vi ( x) = Vi +
⎨
+
I
(
x
)
I
=
i
⎩ i
∙
e −2γ i x
∙
∙
e γ i x (1 + Γi ( x) )
e γ i x (1 − Γi ( x) )
From the full profile of the current and voltage in the line will get easily the dissipated power
n
⎧
⎪⎪V ( x) = ∑ Vi ( x)
i =1
⎨
n
⎪ I ( x) = ∑ I i ( x)
⎪⎩
i =1
1
Pactive ( x) = ℜ{V ( x) I ( x)}
2
This represents the total power dissipated: Line + Load dissipation; if we want only the line dissipation we have to subtract the load (7W)
13
Voltage, Current and Γ in the line
14
Power
15
Summary table
16
Comments
• We have not yet evaluated the contribution of the N connectors (4 connectors) as we have not yet decided their position
• Even if the total power is almost the double with respect for instance to the one dissipated on the Triumf coupler, we foresee a lower thermal charge on the cavity wall as we have only a thermal capacitance between internal and external conductor while in Triumf there is a direct contact (loop) giving a thermal resistance
• To use a thermal shielding material between the cavity wall and the coupler is always possible 17
CLIC Plans
19
Realization of RDDS structure (1)
• Presently the “0‐order” structures meet the design criterion
• Practical realization means to go to the “1st ‐
order” structures meaning to investigate the influence of the machining errors on the efficiency of the wake damping
• Powerful circuit model giving the opportunity of analyzing single cell frequency shift (machining errors)
20
Realization of RDDS structure (2)
• Understanding better the circuit model
• Interaction with Vasim (it would be nice to foresee a period here at CERN)
• Interaction with Walter Wuensch and Alexej
Grudiev.
21
Wakefield Monitors
• I saw Riccardo Zennaro who is (weakly) involved at present on this subject
• There is already some work done by F. Peauger at CEA in Saclay
• The main problem seems to be the (non) attenuation of the accelerating mode (antenna position?)
22
CLIC_DDS1 : Long iris thick. (4.0-0.7) & bigger iris ellipticity (1.0-2.0).: Presented at SLAC
CLIC_DDS2 : Short iris thick. (3.0-0.7) & bigger iris ellipticity (1.0-2.0).
CLIC_DDS3 : Short iris thick. (3.0-0.7) & smaller iris ellipticity (0.5-2.0).
CLIC_DDS4 : Short iris thick. (3.0-0.7) & smallest possible iris ellipticity (0.5-1.5)
CLIC_DDS4 simulations are in progress.
Short iris thickness structure results in a reduced dipole bandwidth by ~ 240 MHz
Yet, no dipole simulations are run except CLIC_DDS1
CLIC_DDS1
(SLAC_WS09)
CLIC_DDS: 2 & 3
CLIC_DDS1 : Black
CLIC_DDS2 : Red
CLIC_DDS3 : Blue
Surface fields
CLIC_DDS1 : Black
CLIC_DDS2 : Red
CLIC_DDS3 : Blue
Input power
P in =
2
E acc
vg
(
ω R' Q
CLIC_DDS1 : Black
CLIC_DDS2 : Red
CLIC_DDS3 : Blue
)
CLIC_DDS3
Dashed curve : Unloaded condition
Solid curve : Beam loaded condition
Esur (MV/m)
Eacc (MV/m)
Pin (MW)
∆T (K)
CLIC_DDS1 : Long iris thick. (4.0-0.7) & bigger iris ellipticity (1.0-2.0).: Presented at SLAC
CLIC_DDS2 : Short iris thick. (3.0-0.7) & bigger iris ellipticity (1.0-2.0).
CLIC_DDS3 : Short iris thick. (3.0-0.7) & smaller iris ellipticity (0.5-2.0).
CLIC_DDS4 : Short iris thick. (3.0-0.7) & smallest possible iris ellipticity (0.5-1.5)
CLIC_DDS4 simulations are in progress.
Short iris thickness structure results in a reduced dipole bandwidth by ~ 240 MHz
Yet, no dipole simulations are run except CLIC_DDS1
Parameters
CLIC_DDS1
CLIC_DDS2
CLIC_DDS3
Pin (MW)
72
75.5
73
Esurmax. (MV/m)
232
250
244
∆Tmax (K)
47.3
44
48.5
Rf‐to‐beam effi. (%)
24.11
23.61
24.24
Corrected
Rf‐to‐beam effi. (%)
26.62
25.85
26.61
24 cell structure
SALCWS09
CLIC_DDS1
Dashed curve : Unloaded condition
Solid curve : Beam loaded condition
Esur (MV/m)
Allowable
limit on
Esur
Eacc (MV/m)
Pin (MW)
∆T (K)
Avg.
Eacc
Allowable
limit on ∆T
CLIC_DDS2
Esur (MV/m)
Eacc (MV/m)
Pin (MW)
∆T (K)