spurce with the ZING-P and IPNS-I concepts. .... P where Bf is bunching factor of 0.45 rp is 1 54. (10-l*),. F is the form faitor of 1.5 .... George P. Lawrence, et al.,.
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IEEE Transactions on Nuclear Science, Vol. NS-30, No. 4, August 1983
2086
ASPUN, DESIGN FOR AN ARGONNE SUPER INTENSE PULSED NEUTRON SOURCE* T. K. Khoe and R. L. Kustom Physics Division Argonne National Laboratory 9700 S. Cass Avenue Argonne, IL 60439
i
Introduction Argonne pioneered the pulsed spallation neutron spurce with the ZING-P and IPNS-I IPNS-I is now a reliable and actively concepts. The used source for pulsed spallation neutrons. accelerator is a 500 MeV, 829 ma, 30 Hz rapid Other proton cycling proton synchrotron. spallation sources are now in operation or in These include KENS-I at the N tional construction. J the Laboratory for High Energy Physics in Japan, WNR/ SR at LOS Alamos National Laboaratory in the Appleton USA, e and the SNS at t e Rutherford !+ Laboratory in England. Newer and bolder concepts are for more intense pulsed spallation These inc ude SNQ at the sources. in Jiilich, Germany, '6 ASTOR at the for Nuclear Physics in Switzerland, Argonne concept.
being developed neutron KFA Laboratory Sh~iss Institute and ASPUN, the Fig.
ASP N is based on the Fixed-Field Alternating The design goal is to provide a Gradient 1 concept. time-averaged beam of 3.5 ma at 1100 MeV on a spallation target in intense bursts, 100-200 at a repetition rate of no more nanoseconds long, than 60 to 85 Hz. Fixed-Field
Alternating
Gradient
(FFAG)
Design
The design is based on 200 MeV H'- + H+ The linac must provide 32 stripping injection. milliamperes of H- beam for 500 nseconds at a A schematic view of the 220 Hz repetition rate. FFAG is shown in Figure 1 and the machine parameters are listed in Table 1. The injection radius is 17.5 meters. Acceleration is accomplished with 10 rf cavities symmetrically located around the circumference. The equilibrium radius grows to 18.75 m at time is 500 nseconds, capture 1100 MeV. Injection and acceleration time is time is 600 pseconds, Extraction is accomplished about 3400 nseconds. with one turn ferrite extraction kicker magners. The pulse width will be about 140 nanoseconds.
given
The guide by
B = Bo[+jk[l 0
field
in an FFAG accelerator
+ i fn cos nN(B-tan5 n=l
In F)]
(1)
0
The FFAG for ASPUN is designed with a relatively small spiral angle of 65" and a nearly
Work supported under Contract
by the U.S. Department W-31-109-Eng-38.
1.
Schematic
View
FFAG Accelerator
of
FFAG Ring.
Characteristics
Injection Energy Extraction Energy Injection Radius Extraction Radius Injection Field Extraction Field Number of Sectors Angular Width of Sectors Field Index, k Spiral Angle, 5 Radial Betatron Frequency, vx Vertical Betatron Frequency, vs Space Charge Limit Radial Beam Emittance @ 200 MeV Vertical Beam Emittance @ 700 MeV Frequency Range Maximum RF Voltage per Turn Harmonic Number Average Current Repetition Rage Output Energy Spread Output Bunch Length
200 MeV 1100 MeV 17.5 m 18.75 m 0.489T 1.281T 20 4.5" 14 65" 4.3 3. 5 >lO 14 7001 mm-mr 500n mm-mr 1.544-2.259 Mhz 300 kV 1 13.5 ma 220 Hz f19.5 MeV 136 ns
is
distance from the center of where r is the radial (dB/dr) is the mean field the machine, k = (r/B) index, B is the azumuthal angle, f, is the harmonic component of the azimuthally varying field, N is the number of identical magnets, and 5 is the spiral angle.
*
Table
1.
of
Energy
ge magnet so that the effective flutter, The betatron frequencies are is large. indgpendent of momentum.
$;174
The n and B functions for this design are with the shown in Figure 2. They are constant bending radius of the equilibrium orbit within the An Enge short tail fringing field is used magnet. to calculate the focusing or defocusing effects of The horizontal and vertical beam the magnet edges. envelopes for sx = 700 *mm-mr and E = 500 nmm-mr, The chosen respectively, are shown in Figure 3. values of Ed and sx are sufficiently small to avoid x and z coupling and destructive vertical spread due to the nonlinear magnetic field components present in the FFAG magnet.
OO18-9499/83/0800-2086$01.0001983
IEEE
2087 The incoperent space machine is 10 given by
N= where Bf (10-l*), 0.375 to will have frequency.
charge
T(E~ + /ml
this
of
B%uzBf
the
(2)
nF P is bunching factor of 0.45 rp is 1 54 F is the form faitor of 1.5, B-8*$ > angle errors maintain N > 10 . Spiral a large effect on the betatron The shift in tune is given by &v = 2 Lmsz?!E. v sin 25
For
limit
design
6v is
equal
(3) to 3.6
(A[)
rms.
The good field region of the magnet must extend from 17.4 to 18.9 meters. The field at the injection radius of 17.5 meters must be 0.4891' and and at the extraction radius of 18.75 m must be 1.281T. The magnet gap must allow for the betatron amplitude, field errors and misalignment, poleface windings, vacuum chamber walls, and some contingency. To within a 98% probability, the rms displacement of the equilibrium orbit will times the rms displacement of an individual where p is
P=*
be p magnet
B J-
--$-
e.(4)
The tolerances for rms displacement require a 1-b cm allowance in the gap. The total magnet gap at injection must be 20 cm which allows for 14.3 cm of betatron motion, 1.0 cm for field errors and misalignment, 1.7 cm for pole face windings, 2.0 cm for vacuum walls and 1.0 cm extra space. Tpe gross features of magnet are shown in section A-A of Figure 1. The 20 cm gap extends radially outward for 0.6 m and then tapers to 10.1 cm in another 0.9 m. Pole face windings extend over the inside 0.6 meters. The details of the magnet are given in Table 2. The injection system is shown in Figure 4. There are 4 programed bump magnets and one programed septum magnet. The stripper foil is located between the inside two bump magnets. Initially the foil edge is located at the center of the phase plane acceptance ellipse, and then it moves away during the 500 nsecond injection period. The vertical beam is also modulated during injection so that the total density distribution is as uniform as possible. The energy of linac beam is modulated to give a coasting beam energy spread of k3.2 MeV. This beam is adiabatically captured in a nonucket. At least 32 ma H- beam is accelerating rf per pulse. required for 10 18 protons Acceleration is accomplished with 10 cavities each capable of a peak value of 30 kilovolts. The beam is bunched adiabatically by instantaneously applying an rf voltage of 27 kilovolts and increasing the rf voltage to 150 kV in 250 useconds. After bunching, the rf voltage and frequency are programed to increase the en5rgy as linearly as possible while maintaining Bfy 8 > 0.375. The parameters of the accelerating system are given in Table 3. The rf voltage and frequency through out the cycle are shown in Figure 6. The kinetic energy and sin4, are shown in Figure 7.
Table
0
I 0
I 0.25
V/////A 0.5
I I.0
0.75
I I .25
S/f Fig.
2.
II
n and B functions
for
the
ASPlJN FFAG.
2.
Magnet
Minimum Pole Radius Maximum Pole Radius Spiral Angle Main Coil Ampere-Turns Pole Face Widning Ampere-Turns Weight of Yoke and Poles Weight of Coils Power Loss
Parameters 17.4 m 18.9 m 65" 9.7 x 104 4 4.8 x 10 68 Tons 2.5 Tons 140 kW
Ocm
I
5cm
-
/-----
.__--s(m)
I 0 -5
I I
-==---
I 2
I 3
I 4
I 5
---_ Z-envelope
X-envelope
-10 Fig.
Fig. 3.
Horizontal
and Vertical
Beam Envelopes
4.
Injection Magnets,
System Showing Four Bumper Foil. Septum Magnet, and Stripper
2088 from the second kicker. has a field is 2 m long, by 460 mrd. Table
3.
Accelerating
System
The final bending of 1.4T and bends
magnet the beam
ParametJrs Discussion
Number of Cavities Length of Cavity Maximum Cavity Voltage Total Volume of Ferrite Total 'Peak Ferrite Power Loss Cavity Shunt Impedance u at Injection p at Extraction Average rf Flux Density Maximum rf Flux Density DC Bias at Injection DC Bias at Extraction
10 1.9 m 30 11 kmY 1.25 MW 7200 Cl 26.8 12.5 0.012T 0.0145T 900 A/m 1800 A/m
The ASPUN conceptual design is by no means a It is, complete and final facility design. however, indicative of the potential of the FFAG An accelerator of this capability will concept. have very exciting possibilities as a driver for a The neutron fluxes from a spallation source. facility built around this concept should exceed by at least an order of magnitude the fluxes that will be possible with the facilities now under construction. The concept will be studied in considerably more detail at Argonne in the next few years. Clearly, beam lojses in this machine must be less than 10s4 or lo- . Preliminary calculations indicate that capture, acceleration, and extraction could achieve this efficiency, but his is an area that will receive considerable attention. Also, magnet design and beam orbit programs will be pursued.
References
Fig.
5.
RF Voltage Tune.
and Frequency
as a Function
1.
J. M. Carpenter and David L. Price, "An Intense Pulsed Neutron Source for Argonne National IEEE Transactions on Nuclear Laboratory," Vol. NS-22, No. 3, June, 1979, Science, p. 1768.
2.
"Intense Pulsed Neutron R. L. Kustom, IEEE Transactions on Nuclear Science, 28, NO. 3, June, 1981.
3.
"The Booser Synchrotron Utilization H. Sasaki, of the ICANS-IV Facility at KEK," Proceedings Meeting, KEK, Japan, October 20-24, 1980.
4.
George P. Lawrence, et al., "LASL High-Current Proton Storage Ring," Proceedings of XI International Conference on High Energy Accelerators, Geneva, Switzerland, July, 1980.
5.
Source for G. H. Rees, "A Pulsed Spallation Neutron Scattering Research, "IEEE Transactions on Nuclear Science, Vol. NS-24, No. 3, June, 1977.
6.
"A High Intensity Proton Linear J. E. Vetter, Accelerator for the German Spallation Neutron on Nuclear Source (sNQ) ;' IEEE Transactions Vol. NS-28, No. 3, June, 1981, Science, p. 3455.
7.
W. Joho, "Astor, Acceleration and Intense Pulsed or Neutrinos, Pions, this conference.
of
1‘(MeV sin 4,
IIO00
0.4-
800
600 400 200 5
Sources," Vol. NS-
t(msec) Fig.
6.
Kinetic Tune.
Energy
and sines
as a Function
of
Extraction elements are shown in Figure 1. The ferrite kickers have a peak field of 0.0625T The first kicker and 1.0 meter length of ferrite. kicks the beam inward by 10.34 mr and the second The kicker kicks the beam outward by 10.34 mrad. betatron phase advance between the two kickers is 180". The septum magnet is one meter long, has a magnetic field of 0.376T, and bends the beam by It is located 100" in betatron phase 62.3 mrad.
a.
F. T. Cole, Alternating 28, Instr.,
Concept of a Combined Storage Ring for Production Continuous Beams of Muons, Kaons, and Neutrons,"
of
"Electron Model Fixed Field et al., Gradient Accelerator," Rev. Sci. 1957, p. 403.
