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Proceedings ArticleDOI

A comparison between pulse compression options for NLC

01 Jan 1999-Vol. 1, pp 423-425

TL;DR: A comparison, between options for pulse compression systems that provide RF power to the main linac of the Next Linear Collider, and a cost model for each system as a function of compression ratio, number of RF sources per unit system, and storage line parameters is presented.

AbstractWe present a comparison, between options for pulse compression systems that provide RF power to the main linac of the Next Linear Collider (NLC). The parameters which are compared are efficiency, number of components and length of RF storage lines. Based on these parameters we produce a cost model for each system as a function of compression ratio, number of RF sources per unit system, and storage line parameters. The systems considered are delay line distribution systems, binary pulse compression, and resonant delay lines (SLED-II). For all these systems we consider possible improvements through the use of several modes, active switches, and circulators.

Summary (1 min read)

Jump to: [1 INTRODUCTION][2 COST MODEL] and [3 CONCLUSION]

1 INTRODUCTION

  • During the past few years high power rf pulse compression systems have developed considerably.
  • The SLED II pulse compression system is a variation of SLED that gives a flat output pulse [6].
  • The DLDS [8] is a similar system to BPC, but by sending the rf upstream twords the gun it utilzes the return delay of the electron beam to reduce the length of the over-moded waveguide assembly.
  • The system has an intrinsic efficiency of 100%, and the total over-moded waveguide length has been reduced considerably.
  • This will provide the basis for cost comparison.

2 COST MODEL

  • The NLC accelerator structure needs a pulse of 380 ns.
  • A fraction smk of the modulator cost is due to its energy storage elements [11].
  • The cost of the rf pulse compression and power transmission is divided into two parts: a part that is dependent on the storage line length L and diameter D, and a part that is dependent on the number of components per pulse compression system nc.
  • The maximum possible value is achieved with the DLDS using the TE01 mode in all waveguides.
  • Because components vary in their complexity the authors will give different weights to them.

3 CONCLUSION

  • For most systems there is a considerable cost reduction as one goes to higher compression ratios.
  • This implies the need for rf power sources that are capable of longer pulse width.
  • The development of high power circulators, multimoded technology and active super-high-power switches will result in a considerable cost reduction for the NLC.

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A COMPARISON BETWEEN PULSE COMPRESSION OPTIONS FOR NLC
*
S. G. Tantawi
#$
, R. D. Ruth, P. B. Wilson, SLAC, Stanford, CA
Abstract
We present a comparison, between options for pulse
compression systems that provide rf power to the main
linac of the Next Linear Collider (NLC). The parameters
which are compared are efficiency, number of
components and length of rf storage lines. Based on these
parameters we produce a cost model for each system as a
function of compression ratio, number of rf sources per
unit system, and storage line parameters. The systems
considered are Delay Line Distribution Systems (DLDS),
Binary Pulse Compression (BPC), and Resonant Delay
Lines (SLED-II). For all these systems we consider
possible improvements through the use of several modes,
active switches, and circulators.
1 INTRODUCTION
During the past few years high power rf pulse
compression systems have developed considerably. These
systems provide a method for enhancing the peak power
capability of high power rf sources while matching the
long pulse of that source to the shorter filling time of the
accelerator structure. In particular, future linear colliders,
such as the proposed NLC[1] require peak rf powers that
cannot be generated by current state-of-the-art microwave
tubes. The SLED pulse compression system [2] was
implemented to increase the gradient of the two-mile linac
at the Stanford Linear Accelerator Center (SLAC). One
drawback of SLED is that it produces an exponentially
decaying pulse. To produce a flat pulse and to improve the
efficiency, the Binary Pulse Compression (BPC) system
[3] was invented. The BPC system has the advantage of
100% intrinsic efficiency and a flat output pulse. Also, if
one accepts some efficiency degradation, it can be driven
by a single power source [4]. However, The
implementation of the BPC [5] requires a large assembly
of over-moded waveguides, making it expensive and
extremely large in size. The SLED II pulse compression
system is a variation of SLED that gives a flat output
pulse [6]. The SLED II intrinsic efficiency is better than
SLED, but not as good as BPC. However, from the
compactness point of view, SLED II is far superior to
BPC. Several attempts have been made to improve its
efficiency by turning it into a system using active
switching [7]. However, the intrinsic efficiency of the
__________________________________________________
*
This work is supported by Department of Energy Contract DE-AC03-
76SF00515.
#
Email: tantawi@slac.stanford.edu
$
Also with the Communications and Electronics Department, Cairo
University, Giza, Egypt.
active SLED-II system is still lower than that of the BPC.
The DLDS [8] is a similar system to BPC, but by sending
the rf upstream twords the gun it utilzes the return delay of
the electron beam to reduce the length of the over-moded
waveguide assembly. However it still uses more over-
moded waveguide than that required by SLED-II. To
further enhance the DLDS a variation on that system, the
Multi-moded DLDS (MDLDS) [9] was introduced, which
further reduces the length of the waveguide system by
multiplexing several low-loss rf modes in the same
waveguide. The system has an intrinsic efficiency of
100%, and the total over-moded waveguide length has
been reduced considerably.
We present a comparison, based on cost, for all various
compression schemes that are available for the Next
Linear Collider. In this comparison we do not describe the
systems involved at any level of detail. The reader is
referred to the cited references for details. However, it is
our purpose to give an accurate formulation for the system
efficiency, number of components, and length of delay
lines or storage lines for each of these schemes as a
function of compression ratio (the ratio of the source rf
pulse width to the compressed pulse width). This will
provide the basis for cost comparison. We will also
extrapolate on the potential to expand and/or improve
systems through the usage of
a.
Multi-moded structures,
b.
Active switching,
c.
Circulators.
2 COST MODEL
Basically, the rf sources available now or in the near
future will produce a pulse T of about 1.5
µ
s. The NLC
accelerator structure needs a pulse of 380 ns. Hence, a
pulse compression system which compresses the source rf
pulse by a factor C
r
=4 is required. The factor of 4 is the
minimum required compression ratio. If rf sources can be
improved to provide longer pulse lengths at the same peak
power, one might utilize a bigger ratio.
To achieve this pulse compression a storage system is
employed to store the rf power until it is needed. Different
portions of the rf pulse T are stored for different amount
of times. The initial portion of the rf pulse is stored for a
time period t
m
, the maximum amount of storage time for
any part of T. The maximum value for t
m
is
)1(
max
=
rm
Ct
τ
(1)
where
r
C
T
=
τ
is the accelerator structure pulse width,
and C
r
is the compression ratio. The value given in by
Eq.(1) is typical for most systems with the exception of
0-7803-5573-3/99/$10.00@1999 IEEE. 423
Proceedings of the 1999 Particle Accelerator Conference, New York, 1999

DLDS, which stores the energy for only half the time. The
realization of the storage system is usually achieved using
low-loss waveguide delay lines. These lines are usually
guides that propagate the rf signal at nearly the speed of
light. The maximum length required for these guides, per
compression system, is
2
max
r
gm
C
vtl =
,(2)
where
g
v is the group velocity of the wave in the delay
line. The total number of rf pulse compression systems
required for the accelerator system is given by
crkk
aa
c
CnP
PN
N
η
=
,(3)
where
a
N
is the total number of accelerator structure in
the linac,
k
P
is the klystron (or the rf power source) peak
power,
a
P
is the accelerator structure required peak
power,
k
n
is the number of klystrons combined in one
pulse compression system, and
c
η
is the efficiency of the
pulse compression system. Thus the total length of
waveguide storage line for the entire linac is given by
l
gm
k
aa
ck
lc
R
vt
P
PN
n
RNlL
2
1
max
η
==
. (4)
where
l
R
is a length reduction factor which varies from
one system to another and in general is also a function of
the compression ratio. The total number of klystrons in the
system is given by,
k
aa
cr
k
P
PN
C
N
η
1
=
.(5)
The cost of the rf system is divided into three different
parts: cost of the klystron tube, the klystron power source
and modulator, and the rf pulse compression and
transportation system. The cost of the klystron tubes is
given by
k
a
r
r
k
k
aa
cr
kk
k
C
C
A
P
PN
C
ANS
==
0
0
1
η
,(6)
where
0k
A is the cost per klystron at a compression ratio
0r
C . The exponent
k
a is a number that depends on the
details of manufacturing klystrons. For our present
discussion we will assume that this number is 0.4 and
0r
C =4 [10].
The cost of conventional modulators is also dependent
on the compression ratio. If the klystron pulse width is
increased the stored energy in modulator is increased and
hence its cost. A fraction
s
m
k of the modulator cost is due
to its energy storage elements [11]. The rest of the
fractional cost,
s
m
k1 , is due to the rest of the system, in
particular the switching elements. Hence, a suitable model
for the modulator cost is
0
00
0
1
1
11
m
r
s
m
r
s
m
k
aa
cr
r
s
mmk
m
A
C
k
C
k
P
PN
C
C
kANS
+
=
+=
η
, (7)
where
0m
A is the cost of the modulator per klystron at a
compression ratio
0r
C .
The cost of the rf pulse compression and power
transmission is divided into two parts: a part that is
dependent on the storage line length L and diameter D,
and a part that is dependent on the number of components
per pulse compression system n
c
. The storage line cost is
divided into two parts: the cost of the vacuum system,
which is a very weak function of diameter, and the cost of
the pipes, which is directly proportional to the diameter.
The cost model is, then, given by
() ()
++
=++=
cc
r
p
l
v
ll
r
g
ckk
aa
ccc
p
l
v
l
c
nA
C
DAAR
C
v
Pn
PN
nANLDAAS
1
2
)1(
τ
η
(8)
where
v
l
A is the cost of vacuum system per unit length,
p
l
A is the cost of waveguide pipe per unit length and
diameter, and
c
A is the cost per component. The total
cost of the rf system normalized to the cost of one klystron
0k
A is given by
()
++
+
+
+
=
r
c
p
l
v
ll
r
k
c
r
s
m
r
s
m
m
a
r
r
rck
a
s
mc
v
l
p
lmlkrr
C
n
DkkR
C
n
k
C
k
C
k
k
C
C
CP
P
kkkkkRnDCS
k
2
)1(1
1
),,,,;,,,(
00
η
. (9)
The parameters
p
lc
v
lm
k
k
k
k
,,, are the normalized cost
factors and are given by
c
g
v
l
v
l
k
c
c
k
m
m
A
vA
k
A
A
k
A
A
k
τ
=== ,,
00
0
, and
c
g
p
l
p
l
A
vA
k
τ
=
cm-1 (10)
The cost of the modulators and components are
normalized to the cost of a klystron at a compression ratio
0r
C . However, the cost of the delay line is normalized to
the cost of a component. This is done because of the
nature of the information available for the cost estimates
at this time [12].
In the following we will compare all available pulse
compression techniques based on the above-described
criteria. To make the comparison more specific for the
proposed NLC design we will make the following
assumptions:
a.
The operating frequency of the system is 11.424
GHz
b. The duration of the accelerator rf pulse is 380 ns.
c. The basic waveguide delay system uses the TE
01
mode.
d. The next higher order modes that can be used are
the two polarizations of the TE
12
, and the two
polarizations of the TE
22
mode. Hence in
calculating the efficiency of the compression
system, the theoretical attenuation as a function of
diameter for these modes is considered.
e. The efficiency of transmission from the klystrons
to the pulse compression system and from the pulse
424
Proceedings of the 1999 Particle Accelerator Conference, New York, 1999

compression system to the accelerator structure is
about 90%. Hence the total efficiency of the rf
system is,
itc
ηηη
9.0=
; where
i
η
is the intrinsic
efficiency of the system, and
t
η
is the efficiency of
the delay lines. The maximum possible value is
achieved with the DLDS using the TE
01
mode in all
waveguides.
f.
The number of accelerator structures
a
N is 9936
for 1 TeV collider, and the power needed per
accelerator structure
a
P is 170 MW.
g. Based on [12], we will assume that the ratios
012.0=
c
k
,
5.0=
m
k
,
36=
v
l
k
,
4.1=
p
l
k
cm
-1
,
3/1=
s
m
k
,
4
0
=
r
C
h.
The maximum amount of energy per rf pulse
max
E that can be handled by rf components limits
the maximum number of klystrons,
k
n , that can be
combined to provide power to a single pulse
compression system; i.e.,
)/(
max
τ
rkk
CPEn
.
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
4 6 8 10121416
Single Moded DLDS
M ulti-M oded DLDS (number of modes=3)
Active DLDS
M ulti-M oded BPC (A high power circulator and 3 modes)
M ulti-M oded SLED II (A high power circulator and 3 modes)
Active SLED II (One time Switching [7])
Multi-Moded DLDS (n
k
=4, number of modes =3)
Single-Moded DLDS (n
k
=4)
Relative Cost
Compression Ratio
n
k
=8
Fig. 1 Comparison between different pulse compression
schemes. The relative cost is normalized to the cost of a
single moded DLDS at a compression ratio of 4.
i. Because components vary in their complexity we
will give different weights to them. Hence in
counting the number of components
c
n
for each
system, we will assume that some complex
components are the equivalent of several simple
components.
Fig. 1 shows the relative cost for several systems vs
compression ratio. For each of these systems we
calculated a general expression for the number of
components, for the length reduction factor, and for the
efficiency as a function of compression ratio.
3 CONCLUSION
For most systems there is a considerable cost reduction
as one goes to higher compression ratios. This implies the
need for rf power sources that are capable of longer pulse
width.
The development of high power circulators, multi-
moded technology and active super-high-power switches
will result in a considerable cost reduction for the NLC
4 REFERENCES
[1] The NLC Design Group “Zeroth-Order Design Report
for the Next Linear Collider,” SLAC-Report-474, May
1996.
[2] Z. D. Farkas et. al., "SLED: A Method of Doubling
SLAC's Energy," Proc. of the 9th Int Conf. on High
Energy Accelerators, 1976, p. 576.
[3] Z. D. Farkas, "Binary Peak Power Multiplier and its
Application to Linear Accelerator Design," IEEE
Trans. MTT-34, 1986.
[4] P. E. Latham, "The Use of a Single source to Drive a
Binary Peak Power Multiplier," Linear Accelerator
Conference, Williamsburg, Virginia, 1988, CEBAF-R-
89-001, pp. 623-624.
[5] Z. D. Farkas, et . al., "Two-Klystron Binary Pulse
Compression at SLAC," Proc. of the IEEE Particle
Accelerator Conference, Wasington DC, May 1993, p.
1208.
[6] P. B. Wilson, Z. D. Farkas, and R. D. Ruth, "SLED II:
A New Method of RF Pulse Compression," Linear
Accl. Conf., Albuquerque, NM, September 1990;
SLAC-PUB-5330.
[7] S.G.Tantawi, et al. "Active High-Power RF Pulse
Compression Using Optically Switched Resonant
Delay lines" IEEE TRANSACTIONS ON
MICROWAVE THEORY AND TECHNIQUES
IEEE, Aug. 1997. vol.45, no.8, pt.2, p. 1486-92
[8] H. Mizuno, Y. Otake, “A New Rf Power Distribution
System For X Band Linac Equivalent To An Rf Pulse
Compression Scheme Of Factor 2**N,” 17th
International Linac Conference (LINAC94), Tsukuba,
Japan, Aug 21 - 26, 1994, KEK-PREPRINT-94-112,
Oct 1994. 3pp.
[9] S.G. Tantawi, et al. " A Multi-Moded RF Delay Line
Distribution System for the Next Linear Collider,” to
be published in the proc. of the Eighth Workshop on
Advanced Accelerator Concepts, Baltimore, MD, USA
6-11 Jul 1998.
[10] Robert M. Phillips, private communications.
[11] Richard Cassel, private communications.
[12] Michael L. Neubauer, private communications.
425
Proceedings of the 1999 Particle Accelerator Conference, New York, 1999
Citations
More filters

Journal ArticleDOI
Abstract: We describe development of semiconductor X-band high-power RF switches. The target applications are high-power RF pulse compression systems for future linear colliders. We describe the design methodology of the architecture of the whole switch systems. We present the scaling law that governs the relation between power handling capability and number of elements. We designed and built several active waveguide windows for the active element. The waveguide window is a silicon wafer with an array of four hundred PIN/NIP diodes covering the surface of the window. This waveguide window is located in an over-moded TE01 circular waveguide. The results of high power RF measurements of the active waveguide window are presented. The experiment is performed at power levels of a few megawatts at X-band.

30 citations


Cites background from "A comparison between pulse compress..."

  • ...ζ is chosen for forward biased status as [3]...

    [...]

  • ...Several schemes of pulse compression systems [3] have been developed....

    [...]

  • ...The active pulse compression systems, which use high power RF switches, are an alternative scheme [3]....

    [...]


Proceedings ArticleDOI
24 Jul 2002
Abstract: In recent years, R&D for pulse compression and power distribution systems for the Next Linear Collider has led to the invention of many novel rf components, some of which must handle up to 600 MW of pulsed power at X‐band. These include passive waveguide components, active switch designs, and non‐reciprocal devices. Among the former is a class of multi‐moded, highly efficient rf components based on planar geometries with overmoded rectangular ports. Multi‐moding allows us, by means of input phasing, to direct power to different locations through the same waveguide. Planar symmetry allows the height to be increased to improve power handling capacity. Features that invite breakdown, such as coupling slots, irises and H‐plane septa, are avoided. This class includes hybrids, directional couplers, an eight‐port superhybrid/dual‐mode launcher, a mode‐selective extractor, mode‐preserving bends, a rectangular mode converter, and mode‐mixers. We are able to utilize such rectangular waveguide components in systems incorporating low‐loss, circular waveguide delay lines by means of specially designed tapers that efficiently transform multiple rectangular waveguide modes into their corresponding circular waveguide modes, specifically TE10 and TE20 into circular TE11 and TE01. These extremely compact tapers can replace well‐known mode converters such as the Marie type. Another component, a reflective TE01‐TE02 mode converter in circular waveguide, allows us to double the delay in reflective or resonant delay lines. Ideas for multi‐megawatt active components, such as switches, have also been pursued. Power‐handling capacity for these is increased by making them also highly overmoded. We present a design methodology for active rf magnetic components which are suitable for pulse compression systems of future X‐band linear colliders. We also present an active switch based on a PIN diode array. This component comprises an array of active elements arranged so that the electric fields are reduced and the power handling capability is increased. Novel designs allow these components to operate in the low‐loss circular waveguide TE01 mode. We describe the switching elements and circuits.

6 citations


01 Apr 2000
Abstract: We describe the potential of semiconductor X-band RF switch arrays as a means of developing high power RF pulse compression systems for future linear colliders. We describe design methodology of high power RF switches, and scaling law which governs the relation between power handling capability and number of elements. The design and implementation of the active waveguide window is presented. The waveguide window is a silicon wafer with an array of four hundred PIN/NIP diodes covering the surface of the window. This waveguide window is located in an over-moded TE01 circular waveguide. The results of low power and high power RF measurements of the active waveguide window are presented. The high power experiment is performed at power levels of several megawatts at X-band.

2 citations


References
More filters

01 Jan 1974
Abstract: Over the past few years, several schemes for *. making significant increases in the energy of the SLAC beam have been proposed. Two of the proposals, namely the use of superconducting accelerating sections1 and recirculation 1 of the beam for a second pass through the existing acceler. &or,’ have been abandoned for technical and economic reasons after extensive investigation. An on-going method of gradually raising the beam energy is the development and installation of 30and 40-MW klystrons by the SLAC Klystron Group. It is clear, however, that the accelerator would have to be completely refitted with klystrons producing about 100 MW in order that the present machine energy be approximate1 doubled. While such an approach is not inconceivable, 3 the realization of such klystrons and the modulators needed to drive them would require further years of development and a high initial capital investment.

165 citations


"A comparison between pulse compress..." refers methods in this paper

  • ...The SLED pulse compression system [2] was implemented to increase the gradient of the two-mile linac at the Stanford Linear Accelerator Center (SLAC)....

    [...]


Journal ArticleDOI
Z.D. Farkas1
TL;DR: A new method of pulse compression, the binary power multiplier (BPM), a device which multiplies RF power in binary steps which doubles the input power and halves the input pulse length is described.
Abstract: This paper describes a new method of pulse compression, the binary power multiplier (BPM), a device which multiplies RF power in binary steps. It comprises one or more stages, each of which doubles the input power and halves the input pulse length. Practical designs are described and expressions for their compression efficiency are derived. The usefulness of pulse compression for accelerator design is illustrated and compared with the pulse compression system currently in use at the Stanford Linear Accelerator Center.

72 citations


"A comparison between pulse compress..." refers methods in this paper

  • ...To produce a flat pulse and to improve the efficiency, the Binary Pulse Compression (BPC) system [3] was invented....

    [...]


ReportDOI
01 May 1996
Abstract: This Zeroth Order Design Report (ZDR) for the Next Linear Collider (NLC) has been completed as a feasibility study for a TeV-scale linear collider that incorporates a room-temperature accelerator powered by rf microwaves at 11.424 GHz--similar to that presently used in the SLC, but at four times the rf frequency. The purpose of this study is to examine the complete systems of such a collider, to understand how the parts fit together, and to make certain that every required piece has been included. The design presented here is not fully engineered in any sense, but to be assured that the NLC can be built, attention has been given to a number of critical components and issues that present special challenges. More engineering and development of a number of mechanical and electrical systems remain to be done, but the conclusion of this study is that indeed the NLC is technically feasible and can be expected to reach the performance levels required to perform research at the TeV energy scale. Volume one covers the following: the introduction; electron source; positron source; NLC damping rings; bunch compressors and prelinac; low-frequency linacs and compressors; main linacs; design and dynamics; and RF systems for main linacs.

68 citations


01 Sep 1990
Abstract: In the SLED method of RF pulse compression, two high Q resonators store energy from an RF source for a relatively long time interval (typically 3 to 5 {mu}sec). Triggered by a reversal in RF phase, this stored energy is then released during a much shorter interval equal to the filling time of the accelerating structure. A peak power gain on the order of three and a compression efficiency on the order of 60% are typically attained. The shape of the output pulse is, however, a sharply decaying exponential. In SLED-II the two cavities are replaced by two lengths of resonant line, forming a Resonant Line SLED (RELS) and resulting in a flat output pulse. Therefore, RELS stages can be cascaded to give a greater peak power gain. Using two stages, a peak power gain greater than ten can be achieved with a reasonable compression efficiency. Unlike the BEC, the RELS compression factor per stage is not limited to two, albeit at the expense of intrinsic efficiency. Like the BEC, it uses long lines rather than short cavities.

66 citations


"A comparison between pulse compress..." refers background in this paper

  • ...The SLED II pulse compression system is a variation of SLED that gives a flat output pulse [6]....

    [...]


Journal ArticleDOI
Abstract: We present the design and a proof of principle experimental results of an optically controlled high-power RP pulse-compression system. In principle, the design should handle a few hundreds of megawatts of power at X-band. The system is based on the switched resonant delay-line theory [1]. It employs resonant delay lines as a means of storing RF energy. The coupling to the lines is optimized for maximum energy storage during the charging phase. To discharge the lines, a high-power microwave switch increases the coupling to the lines just before the start of the output pulse. The high-power microwave switch required for this system is realized using optical excitation of an electron-hole plasma layer on the surface of a pure silicon wafer. The switch is designed to operate in the TE/sub 01/ mode in a circular waveguide to avoid the edge effects present at the interface between the silicon wafer and the supporting waveguide; thus, enhancing its power handling capability.

54 citations


"A comparison between pulse compress..." refers background in this paper

  • ...Several attempts have been made to improve its efficiency by turning it into a system using active switching [7]....

    [...]

  • ...4 6 8 10 12 14 16 Single M oded DLDS M ult i-M oded DLDS (number of modes=3) Active DLDS M ult i-M oded BPC (A high p ower circulator and 3 modes) M ult i-M oded SLED II (A high p ower circulator and 3 modes) Active SLED II (One t ime Switching [7]) Multi-Moded DLDS (n k =4, number of modes =3)...

    [...]


Frequently Asked Questions (1)
Q1. What have the authors contributed in "A comparison between pulse compression options for nlc" ?

The authors present a comparison, between options for pulse compression systems that provide rf power to the main linac of the Next Linear Collider ( NLC ). For all these systems the authors consider possible improvements through the use of several modes, active switches, and circulators.