Transcript PAM - PEP SuperB RF

PEP Super-B High Power RF
Peter McIntosh
SLAC
Super-B Factory Workshop in Hawaii
20-22 April 2005
University of Hawaii
Stanford Linear Accelerator Center
Outline
RF Requirements
Cavity Limitations


Voltage
Power
Klystrons
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
1.2 MW
2.4 MW
Circulators
HVPS System
System Configurations
Conclusions
Stanford Linear Accelerator Center
RF Requirements
3 cavity solutions being investigated:

R/Q = 5, 15 and 30 W (see S Novokhatski’s talk).
The RF power required for L = 7e35 and 1e36 varies as
a function of cavity option as the R/Q impacts primarily
the HOM losses:

As R/Q goes up  cavity HOM losses go up!
The R/Q also impacts the cryogenic losses which affect
the Total AC power required:

As R/Q goes up  cavity cryogenic losses go down!
For the cavity options being investigated, the net
difference in Total AC power is almost zero!
Assuming the cavity to be used lies somewhere between
5 – 30 W we can see that ……
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RF and AC Power (5W)
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RF and AC Power (30W)
Increased
Reduced
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RF and AC Power Summary
To define the number of cavities required, have assumed that 1 MW can be
supplied to each RF cavity (see later).
For L = 7e35 using R/Q = 5 W cavity:


LER = 21.7 MW
HER = 16.2 MW
For L = 7e35 using R/Q = 30 W cavity:
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
LER = 22.1 MW
HER = 16.2 MW
For L = 1e36 using R/Q = 5 W cavity:
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
LER = 39.8 MW
HER = 24.9 MW
For L = 1e36 using R/Q = 30 W cavity:


LER = 42.0 MW
HER = 25.0 MW
Cavity HOM losses increase by 2.2 MW in the LER at 1e36.
Total AC cryogenic power however reduces considerably for the 30 W cavity
by 50% for both luminosity options compared to the 5 W cavity.
Net AC power difference is comparable (to within 2%) for each cavity option
at each luminosity.
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R/Q=15W Solution
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Cavity Limitations - Voltage
Practical achievable voltage/cell depends upon:
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Cavity Qo
Niobium purity
Cryogenic operating temperature
Cryogenic load
For the R/Q = 5, 15 and 30 W cavities:
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Required voltage per cell Vc = 1.25 MV, requiring Qo = 3e9, 1e9
and 1e9 respectively.
For feedback stability R/Q = 5 W preferable  lowest detuning
(see D. Teytelman’s talk)
For cryogenic reasons R/Q = 30 W preferable (see later).
Number of cavities required is the same for each @ L =7e35.
At L = 1e36, the cavity HOM losses in the LER require more RF
cavities (2) at R/Q = 30 W.
What cavity voltage can we expect to reach ….
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Voltage for R/Q = 5 W Cavity
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Voltage for R/Q = 30 W Cavity
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Voltage for R/Q = 15 W Cavity
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Cavity Epk and Hpk Parameters
S Novokhatski
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Voltage Overhead (for 30W)
Theoretical Quench Limit for Nb (Hpk = 1700 Oe or 135.281 kA/m)
Field Emission Onset (Epk > 10 MV/m)
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Voltage Overhead (for 5W)
Theoretical Quench Limit for Nb (Hpk = 1700 Oe or 135.281 kA/m)
Field Emission Onset (Epk > 10 MV/m)
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Voltage Overhead (for 15W)
Theoretical Quench Limit for Nb (Hpk = 1700 Oe or 135.281 kA/m)
Field Emission Onset (Epk > 10 MV/m)
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Cavity Limitations - Power
To minimize the number of RF cavities per ring:

Based on what has been achieved at ~ 500 MHz for
both KEK-B and CESR:
1 MW total RF input power per cavity has been chosen!
Cavity will employ dual RF feeds, each providing
up to 500 kW.
RF breakdown investigations need to be
performed to identify a system that can meet this
power requirement at 952 MHz.
Coaxial coupler arrangement  more compact.
Is this power level realistically achievable?
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Cavity Input Couplers
CESR (fRF = 500 MHz):
Aperture waveguide coupled
Operate typically up to 300 kW
Operated up to 360 kW
(through)
Superconducting Damped Cavity for KEKB
T. Furuya
DOOR KN OB TRAN SFOR MER
INPU T COUPL ER
KEK-B (fRF = 508 MHz):
Biased coaxial coupler
Operate typically up to 350 kW
For Super-KEKB hope to
reach 500 kW
Tested up to 800 kW (through)
GATE VAL VE
L He
GATE VAL VE
F REQU ENCY
TUN ER
HOM DAMPER
( SBP)
HOM DAMPER
(LBP)
Nb
CAV ITY
ION PUMP
N 2 SHIEL D
0
0.5
1m
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Klystrons – 1.2 MW
SLAC already produces 1.2 MW tubes at 476
MHz for PEP-II.
Each powered by a 2.5 MVA DC HVPS.
Tube operates at 83 kV and 24 A with perveance
of 1.004.
Maintaining these beam parameters for Super-B
@ 952 MHz would enable the same HVPS
system to be used.
Scale the cavity frequencies, drift tube spacing,
gap lengths, drift pipe and beam radii.
Magnetic field increases by factor of 2 
existing 476 MHz tube focus coil adequate.
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1.2 MW Klystron – Small Signal
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1.2 MW Klystron – Large Signal
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1.2 MW Klystron Specification
Parameter
Gun
Collector
(Full power)
Frequency (MHz)
952
Beam Voltage (kV)
83
Beam Current (A)
24
Perveance
140.0
Accelerating
Cavities
RF Output
(WR975)
Value
1.004
Bandwidth (MHz)
10
Gain (dB)
47
Efficiency (%)
70
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Klystrons – 2.4 MW
Doubling in RF power means that the existing 2.5 MVA
HVPS can no longer be used  now need a 4 MVA
HVPS.
Beam power characteristics increase up to 125 kV and
29.2 A with drop in perveance to 0.6607.
Higher beam voltage increases cavity spacing and gap
lengths  accelerating section ~ 20% longer than the
1.2 MW tube.
Magnetic field comparable to that of the 1.2 MW tube.
Thermal loading of the output circuit requires more
detailed investigation.
Suspect will most likely require a dual output to minimize
thermal loading at the RF windows.
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2.4 MW Klystron – Large Signal
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2.4 MW Klystron Specification
Gun
Collector
(Full power)
160.0
Accelerating
Cavities
Parameter
RF Output
(WR975)
Value
Frequency (MHz)
952
Beam Voltage (kV)
125
Beam Current (A)
29.2
Perveance (A/V3/2)
0.6607
Bandwidth (MHz)
8*
Gain (dB)
49.8
Efficiency (%)
70
* Needs further optimization
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Klystron Option Footprints
1.2 MW @ 476 MHz
83 kV and 24 A
Perveance = 1.004
210.07
1.2 MW @ 952 MHz
83 kV and 24 A
Perveance = 1.004
140.0
2.4 MW @ 952 MHz
125 kV and 29.2 A
Perveance = 0.6607
160.0
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2.4 MW AFT Circulator Layout
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Circulators Spec
1.7%
1 dry load, 1 water load
Full Reflection!
Klystron would see 2.4 kW in beam abort
x 4 increase c.f. 1.2 MW 476 MHz unit
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HVPS
Originally designed for a depressed collector klystron.
Existing 2.5 MVA HVPS has a primary SCR-controlled
rectifier operating at the existing site-wide distribution
voltage of 12.47kV:

control provides for fast voltage adjustment and fault protection.
Rectifier configuration prevents the dump of filter
capacitor stored energy into the klystron in the event of a
klystron arc.
12.47kV enters the circuit breaker and manual load
disconnect switch and provides a safety lock and tag
disconnect for maintenance.
Remote turn-on and turn-off is by a full, fault-rated
vacuum breaker used as a contactor.
A 12-pulse rectifier reduces power line harmonic
distortion to industrial standards.
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PEP-II/SPEAR3 2.5 MVA HVPS
FILTER RESISTORS
500 OHMS 1KW
CAPACITORS
8uFD 30KV
RECTIFIERS
30KV 30A
-90KV
TERMINATION
TANK
T2
FILTER RECTIFIERS
30KV 3A AVE
-77KV
RECTIFIER
TRANSFORMER
T2
CROWBAR
100KV 80A
12.47KV 3PH
3000 KVA
-52KV
THYRISTOR
CONTROLED
RECTIFIER
40KV 80A
DISCONNECT
& BREAKER
T1
PHASE SHIFTING
TRANSFORMER
-26KV
FILTER
INDUCTOR
SPEAR 3
KLYSTRON
POWER SUPPLY
T1
GRN
KLYSTRON
UP TO 90KV
UP TO 27 AMPS
Stanford Linear Accelerator Center
Super-B HVPS Options
1.2 MW Klystron:
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Existing 2.5 MVA HVPS system compatible.
No development overhead.
2.4 MW Klystron:

Same 2.5 MVA HVPS design, with larger transformers
to reach 4 MVA:
Applicable transformers are commercially available.

Higher voltage required (125 kV):
Makes HV connections more difficult/expensive.

Anticipate a 20 – 30% size and cost increase over the
existing 2.5 MVA unit.
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System Configuration 1
1.2 MW Klystron
Single
952 MHz
RF Cavity
1.2 MW
Circulator
WR975 Waveguide
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System Configuration 2
2.4 MW Klystron
2.4 MW
Circulator
Dual
952 MHz
RF Cavities
WR975 Waveguide
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System Configuration 3
1.2 MW
Circulator
Dual
952 MHz
RF Cavities
2.4 MW Klystron
1.2 MW
Circulator
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Conclusions
RF requirements for L=7e35 and L=1e36 identified 
need up to 190 MW site AC power!
Low R/Q cavities needed for stability control.
Cavity voltage and RF power limits identified  how far
can we push these?!?
High power klystrons (> 1 MW) at 952 MHz look to be
achievable.
High power circulators appear to be available from
industry.
HVPS systems for Super-PEPII klystrons are available
now at 1.2 MW, but require development at 2.4 MW.
Watch this space!
Thank You
Stanford Linear Accelerator Center
RF Parameters Summary