Method of the nanosecond microstructure creation of the negative ion beam
The method of the nanosecond microstructure creation of the negative ion beam with nanosecond edge times is presented. The method of creation does not destroy the beam compensation by the residual gas, so it is available for low-energy beams. Such effects as a beam divergence and, therefore, a bad b...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2001
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irk-123456789-792192015-03-31T03:02:00Z Method of the nanosecond microstructure creation of the negative ion beam Novikov-Borodin, A.V. The method of the nanosecond microstructure creation of the negative ion beam with nanosecond edge times is presented. The method of creation does not destroy the beam compensation by the residual gas, so it is available for low-energy beams. Such effects as a beam divergence and, therefore, a bad beam transport are overcome. The two-plate travelling wave chopper is used. The special shape of the plate deflecting voltage is needed. The estimations and a comparison with the existing methods of a beam deflection are presented. 2001 Article Method of the nanosecond microstructure creation of the negative ion beam / A.V. Novikov-Borodin // Вопросы атомной науки и техники. — 2001. — № 3. — С. 53-55. — Бібліогр.: 6 назв. — англ. 1562-6016 PACS numbers: 29.27.-a, 41.85.Ja, 52.65.Rr http://dspace.nbuv.gov.ua/handle/123456789/79219 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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The method of the nanosecond microstructure creation of the negative ion beam with nanosecond edge times is presented. The method of creation does not destroy the beam compensation by the residual gas, so it is available for low-energy beams. Such effects as a beam divergence and, therefore, a bad beam transport are overcome. The two-plate travelling wave chopper is used. The special shape of the plate deflecting voltage is needed. The estimations and a comparison with the existing methods of a beam deflection are presented. |
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Article |
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Novikov-Borodin, A.V. |
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Novikov-Borodin, A.V. Method of the nanosecond microstructure creation of the negative ion beam Вопросы атомной науки и техники |
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Novikov-Borodin, A.V. |
| author_sort |
Novikov-Borodin, A.V. |
| title |
Method of the nanosecond microstructure creation of the negative ion beam |
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Method of the nanosecond microstructure creation of the negative ion beam |
| title_full |
Method of the nanosecond microstructure creation of the negative ion beam |
| title_fullStr |
Method of the nanosecond microstructure creation of the negative ion beam |
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Method of the nanosecond microstructure creation of the negative ion beam |
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method of the nanosecond microstructure creation of the negative ion beam |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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2001 |
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http://dspace.nbuv.gov.ua/handle/123456789/79219 |
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Method of the nanosecond microstructure creation of the negative ion beam / A.V. Novikov-Borodin // Вопросы атомной науки и техники. — 2001. — № 3. — С. 53-55. — Бібліогр.: 6 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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AT novikovborodinav methodofthenanosecondmicrostructurecreationofthenegativeionbeam |
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2025-07-06T03:16:23Z |
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2025-07-06T03:16:23Z |
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1836865850320093184 |
| fulltext |
METHOD OF THE NANOSECOND MICROSTRUCTURE CREATION
OF THE NEGATIVE ION BEAM
A.V. Novikov-Borodin
Institute for Nuclear Research of Russian AS,
60-th Oct. Anniv.pr.7a, 117312,Moscow, Russia
e-mail: novikov@al20.inr.troitsk.ru
The method of the nanosecond microstructure creation of the negative ion beam with nanosecond edge times is pre-
sented. The method of creation does not destroy the beam compensation by the residual gas, so it is available for
low-energy beams. Such effects as a beam divergence and, therefore, a bad beam transport are overcome. The two-
plate travelling wave chopper is used. The special shape of the plate deflecting voltage is needed. The estimations
and a comparison with the existing methods of a beam deflection are presented.
PACS numbers: 29.27.-a, 41.85.Ja, 52.65.Rr
1 INTRODUCTION
The nanosecond microstructure beam production is
needed for physics experiments and/or during the injec-
tion from a Linac to ring machines. To form the beam
shape it seems much easier to use the low-energy beam.
The usual methods [1-3] destroy the beam neutralization
of the residual gas that, for low-energy beams (up to
200-300 keV), leads to a huge beam divergence and,
therefore, to the bad beam transport and beam losses up
to 50% for the 35 keV 100mA H– beam [1]. The neu-
tralization restore time constant is estimated from
2 - 5 µs [4] to 30-700 µs [5] and it may be considered as
a limitation to a beam microstructure edge times. This
process force people to use the higher energy beams for
deflection.
The proposed method lets to deflect the negative ion
beam without destroying the residual gas neutralization,
which overcomes the above-mentioned problems. The
two-plate travelling wave chopper is used. The special
shape of the plate deflecting voltage is needed. The esti-
mations and a comparison with the existing methods of
a beam deflection are presented in this paper.
Fig. 1. Principal scheme of the beam deflection.
2 PRINCIPLE OF THE NON-DESTROYING
DEFLECTION
The charged particle beam, moving in the beam
tube, produces the opposite charged ions from the resid-
ual gas molecules, which compensate partially or even
completely the beam charge. For positive charged
beams the compensation is made by the free electrons
and negative ions and for negative beams it is made by
the positive ions. The residual gas ions oscillate inside
the potential gap, created by the beam. It seems compli-
cated to deflect the beam and to keep the opposite
charged neutralized residual gas, but possible. In case of
the negative charged beams the travelling wave chopper
with a special way of operation is used for the non-de-
stroying beam deflection. The principal scheme of the
proposed installation is shown in Fig. 1.
Here A is the distance between the deflecting plates,
l is their length, L is the distance to the beam damp and
d is the vertical beam size at the input to the chopper. U
is the voltage between deflecting plates during the time
period (0 – T) when the beam needs to be deflected.
In the travelling wave chopper the deflecting field is
moving with the beam. Deflecting different parts of the
beam during deflection time period to the opposite di-
rections, it is possible to keep the residual gas ions in
the beam tube. For the structure and deflecting voltage,
shown in Fig. 1, the non-relativistic beam deflection (up
or down) will be described by the equation:
,121
2
1
2
−−
=∆
l
L
c
lwy bbeam β
,
A
U
m
qkw
b
b
b = (1)
where βc is the longitudinal velocity of the beam, qb, mb
are the charge and the mass of the beam particle, k is the
efficiency coefficient of the deflecting structure.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №3.
Серия: Ядерно-физические исследования (38), с. 53-55.
53
Fig. 2. Transverse motion distribution of the residual gas ions.
For the residual gas ions, their transverse motion
will be described as a system of equations:
∫+=
t
oi vdtyy , ∫+=
t
ioi dtwvv ,
,
A
U
m
qkw
i
i
i =
(2)
where yo, vo are the initial transverse position and veloc-
ity of the ions, qb, mb are the charge and the mass of the
ion.
The ionized residual gas initial position and velocity
distribution are defined by the influence of the beam
charge. Ions oscillate in the beam potential gap. For the
estimation we will consider, that the beam potential on
the beam diameter defines the maximum ion energy. So,
for the initial transverse position and velocity of the ions
we can get the estimation:
,21
4
2
max
−=
d
y
m
q
c
Iv i
i
b
o
b
o βπ ε
.
2max
dyo = (3)
It is seen from (2) that for the deflection voltage
from Fig. 1 the transverse velocity of the ions before
and after deflection is the same. Only the transverse po-
sition is changed during the deflection. We will consider
that the residual gas neutralization is not destroyed if the
transverse position of the ions during the beam deflec-
tion is less than the aperture.
3 NUMERICAL CALCULATIONS
AND ANALYSIS
We will estimate the non-destroying deflection for
l=38 cm, L=50 cm, Um=850 V, T=150 ns. We will ana-
lyze the H– beam deflection with the diameter 1 cm, the
energies around 35 keV and the current 20-100 mA. We
need to analyze the transverse motion of the residual gas
ions at the end of the periods of the voltage deflection.
The transverse velocity and position distribution is
shown on Fig. 2.
Fig. 3. Ion transverse distribution at the end of
deflection.
Here (vo,yo) is the initial distribution (at t=0),
(V1,R1), (V2,R2) and (V3,R3) are the distributions at
t=T/4, 3T/4 and T, respectively. It is seen that the maxi-
mum position distortion is at the end of the deflection.
For the 100 mA beam, the residual ion distribution
at the end of the deflection is shown in Fig. 3.
The transverse distortion of the residual gas is in-
creasing with the beam current increasing and the beam
energy decreasing that is illustrated in Fig. 4.
So, one can conclude, that for these beam parame-
ters the neutralization will be partially lost. This is not
the principal limitation, another parameters of the de-
flecting structure needs to be chosen.
54
Fig. 4. Ion transverse distribution at the end of deflection with different beam current and energy.
4 PRACTICAL REALIZATION
In practice, it is possible to create the deflecting
voltage by using two identical modulators for upper and
lower deflecting plates by applying the deflecting volt-
age consequently, as is shown in Fig. 5.
Fig. 5. Time diagramm of the fast modulators.
The number (N) of the meanders depends on the pa-
rameters of the deflecting structure and beam parame-
ters, but it needs to be taken into account that there will
be some non-deflected part of the beam at the meander
edges.
Fig. 6. Field distribution during deflection with 60%
beam compensation.
Another question to be mentioned about is a variable
transverse distribution of the deflecting field by the in-
fluence of the beam charge and the charge of the ionized
residual gas during deflection. When the beam is com-
pensated, we can consider the deflecting field as uni-
form, but during the deflection the beam and the residu-
al gas are displaced. Uncompensated charge effects to
the deflecting field distribution. The typical field distri-
bution (E(y)) with 60% beam compensation during the
deflection is shown in Fig.6. Here shown is also the av-
erage field (Eo) without the beam and the beam (q(y))
and ion (i(y)) charge distribution in relative units.
This picture is the first order approximation, the real
pictures are more complicated [6], but in practice it is
enough to project the system parameters with the de-
flecting field value much more than the field between
the beam and the ionized residual gas. It is a limitation
to the beam size, but usually for low-energy high-inten-
sity beams it is not very important.
REFERENCES
1. J.G.Alessi, J.M.Brennan, A.Kponou. H– source and
low energy transport for an RFQ preinjector // Rev.
Sci. Instrum. 61 (1), January 1990, p. 625-627.
2. A.V.Novikov, P.N.Ostroumov. Beam Chopper for
750 keV LEBT of MMF Linac // Proc. of PAC’97,
Vancouver, Canada, May 1997.
3. S.S.Kurennoy, A.J.Jason, et al. Development of a
Fast Traveling-Wave Beam Chopper for the Na-
tional Spallation Neutron Source // Proc. of
PAC’97, Vancouver, Canada, May 1997.
4. R.Ferdinand, J.Sherman, et al. Space-Charge Neu-
tralization Measurement of a 75 keV, 130 mA Hy-
drogen-Ion Beam // Proc. of PAC’97, Vancouver,
Canada, May 1997.
5. A.Jakob, et al. Diagnostic of the Compensation
Process of Ion Beams with a Time-Resolving Ion
Energy Spectrometer // Proc. of PAC’97, Vancou-
ver, Canada, May 1997.
6. I.Hofmann. Emittance Growth of Beams Close to
the Space Charge Limit // IEEE Trans. on Nucl.
Ph., v. NS-28, No.3, June 1981, p. 2399.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №3.
Серия: Ядерно-физические исследования (38), с. 55-55.
55
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