Frédéric Bouly MAX 1 st Design Review WP1 Task 12 Bruxelles Belgium Monday 12 th November 2012 Starting point amp Objectives 2 Bouly F MAX 4 th General meeting Frankfurt ID: 389886
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Slide1
Beam tolerance to RF faults & consequences on RF specifications
Frédéric
Bouly
MAX 1st Design ReviewWP1 - Task 1.2
Bruxelles
, Belgium
Monday, 12
th
November 2012Slide2
Starting point & Objectives
2
Bouly F.
MAX 4th General meeting, Frankfurt12th
November
2012
INTRODUCTION
Evaluate the minimum RF power required to enable fault-recovery procedures.
Take Margins
as regard to control errors : cavity theoretical parameters (ex: (r/Q)), accuracy of control systems, measurement errors.
It
depends on coupling
(from the power couplers) - A choice has to be made for each section of the
linac
.
Re-tuning beam dynamic studies will give the new
V
cav
and ϕs for each compensation cavity. Carry out beam study based on the reference linac design to : Give an exhaustive list of critical retuning cases Evaluate the retuning feasibility From these typical scenarios evaluate the power consumption of recovery cavities in every linac sections Slide3
3
Introduction
Beam tolerance to RF Faults- Methodology
-Example : loss of a Spoke module- Status on different critical cases Couplings (Q
i) choices
- PRF &
Qi
are directly linked- Methodology- Results & consequences
RF specifications
- Statistical study of errors
- RF power required for each section
Summary & Prospects
Bouly F.
MAX 4
th
General meeting, Frankfurt
12
th
November
2012Slide4
4
Introduction
Beam tolerance to RF Faults
- Methodology-Example : loss of a Spoke module- Status on different critical cases Couplings (Qi) choices
- P
RF &
Q
i are directly linked
- Methodology- Results & consequences
RF specifications
- Statistical study of errors
- RF power calculation for each section
Summary & Prospects
Bouly F.
MAX 4
th
General meeting, Frankfurt
12
th
November
2012Slide5
Method
5
Bouly F.
MAX 4th General meeting, Frankfurt Beam tolerance to RF Faults
Simulations are based on the
linac
reference design (“strong focusing”option 1)
(J-L. Biarrotte, “SC linac
design & MEBT”)
I
0
= 4
mA
; Beam input parameters from injection line
(C. ZHANG, “Injector layout & beam dynamics”)
Local compensation -
E
acc nominal chosen to enable a ~30 % increase (based on the SNS): 1 failed cavity (or 1 Cryomodule) is compensated by 2 cavities (or 2 Cryomodules) placed upstream & 2 cavities (or
2 Cryomodules
) placed
downstream
.
Procedure developed during previous project :
PDS-XADS () : Procedure setup - Identification of the difficulty to apply local compensation below 15
MeV
.
(J-L. Biarrotte,
D.Uriot
,M.
Novati
, P.
Pierini
, H
Safa
“
Beam dynamics studies for the fault tolerance assessment of the PDS-XADS
linac
design
” , EPAC 2004).
EUROTRANS : Transient effect study - Definition of dynamic retuning scenario
(J-L. Biarrotte,
D.Uriot,“Dynamic compensation of an rf cavity failure in a superconducting linac” , Phy. Review, May 1998).
The synchronous phases are kept in a range similar to nominal conditions (i.e. -40° ≲ ϕs ≲ -15°), in order to try to keep the longitudinal acceptance of the linac.
12
th
November
2012Slide6
Example : Failure of a spoke cryomodule (1/6)
6
Bouly F.
MAX 4th General meeting, Frankfurt
Beam tolerance to RF Faults
Failed module (2 cavities)
4 re-tuned modules
(8 re-tuned cavities)
Energy & Phase diagnostics
Longitudinal size diagnostic
Energy diagnostic
SPOKE SECTION
5-CELL ELLIPTICAL (
β
0.47) SECTION
TraceWin
Calculations
12
th
November
2012Slide7
Example : Failure of a spoke cryomodule
(2/6)
7
Bouly F.
MAX 4
th General meeting, Frankfurt
Beam tolerance to RF Faults
Cavities voltage
Synchronous phase
Beam Energy
Cavities RF power (Beam loading)
12
th
November
2012Slide8
8
Bouly F.
MAX 4
th General meeting, Frankfurt
Beam tolerance to RF Faults
Example : Failure of a spoke cryomodule
(3/6)
Fault-recovery
Nominal Tuning
12
th
November
2012Slide9
9
Bouly F.
MAX 4th General meeting, Frankfurt
Beam tolerance to RF FaultsExample : Failure of a spoke cryomodule (4/6)
12
th
November
2012Slide10
10
Bouly F.
MAX 4
th
General meeting, Frankfurt
Beam tolerance to RF Faults
Example : Failure of a spoke cryomodule
(5/6)
Nominal Tuning
Fault-recovery
Emittances
(
rms
)
Emittances
(
rms
)
Lattices phase advanceLattices phase advance
12
th
November
2012Slide11
11
Bouly F.
MAX 4
th General meeting, Frankfurt
Beam tolerance to RF Faults
Example : Failure of a spoke cryomodule
(6/6)
Nominal Tuning
Fault-recovery
Longitudinal acceptance of the
linac
(SC
linac
+ MEBT + HEBT)
ε
acc
/
ε
RMS ≈ 5.25/0.075 = 70
ε
acc
/
ε
RMS
≈ 4.5/0.075 =
60
12
th
November
2012Slide12
12
Bouly F.
MAX 4
th General meeting, FrankfurtOctober 1st 2012
Beam tolerance to RF Faults
Summary :
studied scenarios
Spoke
β
0.35
5-cell
β
0.47
5-cell
β
0.65
- Failure of 1 cavity
- Failure of a Cryomodule
- Failure of the last cavity
- Failure of 1 cavity
- Failure of a Cryomodule
- Failure of 1cavity
- Failure of the last cavity
- Failure of the last Cryomodule
- Failure of 1 Cryomodule
- Failure of the 1
st
cavity
- Failure of the 1
st
Cryomodule (
in progress
)
11 identified scenariosSlide13
13
Introduction
Beam tolerance to RF Faults
- Methodology-Example : loss of a Spoke module- Status on different critical cases
Couplings (Q
i) choices
- PRF
& Qi
are directly linked- Methodology
- Results & consequences
RF specifications
- Statistical study of errors
- RF power required for each section
Summary & Prospects
Bouly F.
MAX 4
th
General meeting, Frankfurt
12
th
November
2012Slide14
Beam power & RF power amplifier
14
Bouly F.
MAX 4th General meeting, Frankfurt Q
i choice
Power delivered to the beam :
RF power required from the generator when cavities gets their optimal frequency tuning :
with
Optimum for coupling :
Ideally, each cavity would have its own power coupler with an optimised
Q
i
(in function of its (r/Q),
ϕ
s
,
V
cav
& I
b0
)
To find out the most adapted couplings :
we look for the value of
Q
i
which minimise P
g
/
P
b
(i.e. which minimise the total RF power in nominal configuration)
To calculate the RF power requirements, one has to first choose the coupling values for each of the 3
linac
sections.
12
th
November 2012Slide15
Couplings choice & bandwidth
15
Bouly F.
MAX 4th General meeting, Frankfurt Q
i choice
5-cell
5-cell
Spoke
Frequency bandwidth
Spoke (
β
0.35
) : BW = 160.2 Hz
5-cell (
β
0.47
) : BW = 86.05 Hz
5-cell (
β
0.65
) : BW = 102.2 Hz
12
th
November
2012Slide16
Impact on RF consumption
16
Bouly F.
MAX 4th General meeting, Frankfurt
Qi
choice
Total RF power increase is negligible : 0.74%
(from 2.335 MW to 2.352 MW)
12
th
November
2012Slide17
Return on Spoke failure example
17
Bouly F.
MAX 4th General meeting, Frankfurt Q
i choice
Once the
Qi
has been chosen it is therefore possible to calculate
the RF power increase for the recovery
cavities
in the ideal case :
the cavities frequency are perfectly tuned, errors & attenuations are not taken into account.
12
th
November
2012Slide18
18
Introduction
Beam tolerance to RF Faults
- Methodology-Example : loss of a Spoke module- Status on different critical cases Couplings (
Qi
) choices
- P
RF &
Qi
are directly linked
- Methodology
- Results & consequences
RF specifications
- Statistical study of errors
- RF power calculation for each section
Summary & Prospects
Bouly F.
MAX 4
th
General meeting, Frankfurt
12
th
November
2012Slide19
RF Power - Errors & Attenuations
19
Bouly F.
MAX 4th General meeting, Frankfurt RF specifications
RF generator power - general formula
V
cav
:
± 2%
ϕ
s
: ± 2°
I
b0
: ± 2%
Δf : ± 20 Hz Qi : ± 2 mm (± 20%) (r/Q) : ± 10 % Errors taken into account for statistical errors studyExample : Cavity n° 76 (β 0.47) which is compensating a failure
22.35 kW
Maxi.
24.9 kW
+ 10 % margins
added
from errors study
to take into account attenuation and calibration errors.
2.10
6
draws
12
th
November
2012Slide20
Summary on RF needs
20
Bouly F.
MAX 4th General meeting, Frankfurt RF specifications
12
th
November
2012Slide21
21
Introduction
Beam tolerance to RF Faults
- Methodology-Example : loss of a Spoke module- Status on different critical cases Couplings (
Qi
) choices
- P
RF &
Qi
are directly linked
- Methodology
- Results & consequences
RF specifications
- Statistical study of errors
- RF power required for each section
Summary & Prospects
Bouly F.
MAX 4
th
General meeting, Frankfurt
12
th
November
2012Slide22
Conclusions
22
Bouly F.
MAX 4th General meeting, Frankfurt Beam fault-tolerance to a module failure has been demonstrated in each sectionSame simulation m
ethod applied in each scenario A special tool should be developed to enable the calculation of the retuning set-points during the
linac operation
One scenario to improve : failure of the 1
st Spoke cryomodule - More tricky because bunchers
before the failed module have to be retuned In progress
Carry out simulation with several fault-recoveries in the
linac
& include errors (misalignments ... )
The power coupler
Q
i
requirements have been calculated :
Spoke section (
β
0.35
) : Qi = 2.2 106 BW = 160.2 Hz Elliptical 5-cell (β 0.47) : Qi = 8.2 106
BW = 86.05 Hz
Elliptical 5-cell (
β
0.65
) :
Q
i
= 6.9 10
6
BW = 102.2 Hz
Evaluation of the power requirements to anticipate on control errors + attenuations + fault-recovery scenarios :
Study with faults showed that a reasonable choice for the RF amplifier power would correspond to take
a
minimum margin of
~
70 %
(75% foreseen)
compare to the nominal required Power (errors + attenuations + fault recovery).
Spoke section (
β
0.35
) : 15 kW
Elliptical 5-cell (β 0.47) : 30 kWElliptical 5-cell (β 0.65) : 55 kW
R&D activities for fault-recovery procedures study on a real scale experiment will be presented tomorrow.
(R. PAPARELLA, “SC elliptical cavities design & associated R&D” - F. BOULY, I. MARTÍN,
“
Fault
-
recovery
procedures
&
associated
R&D
”)
12
th
November
2012Slide23
23
THANK YOU !
Frédéric Bouly
MAX 3rd General meeting, Madrid12
th
November 2012