METHOD AND APPARATUS FOR AN ABSOLUTE BEAM BRIGHTNESS

DETECTOR

INVENTOR:

Vadim Dudnikov, Ph.D.

J. Cross-Reference to Related Application

[0001] This application claims the benefit of U.S. Provisional Patent Application No.

61/578,222, filed December 20, 2011, which is hereby incorporated by reference in its entirety, as if set out below.

//. Field of the Disclosure

[0002] The present disclosure is generally related to an absolute beam brightness detector

(ABBD) and, in particular, to an ABBD that is useful for fast beam characterization and for beam formation-transportation optimization.

///. Summary

[0003] In generally accepted emittance measurements, the main attention is concentrated on emittance areas ε _χ , e _y occupied by a desired part of an ion beam in transverse phase space and the shape of these areas. The absolute beam phase density (brightness) usually is not measured directly and the average beam brightness B is calculated from a beam intensity I and the transverse emittances. In ion source optimization and low-energy beam transport (LEBT) optimization, it is important to preserve the beam brightness because some aberration of ion optics and/or beam instabilities can decrease the brightness of the central part of an ion beam significantly. For these measurements is convenient to use an Absolute Beam Brightness Detector (ABBD) with the brightness determination from one short measurement, as described herein.

[0004] A local beam brightness is an important beam characteristic that should be an invariant in conservative force fields without particle loss. The terms and definitions used herein are standard in the field and are as described, for example, in H. Zhang, Ion Sources, Springer, 1999, p. 432-444. [0005] The principles of the determination of the phase density distribution in four-dimensional phase space is well-known and is considered in detail in H. Zhang, Ion Sources, Springer, 1999, p. 432-444, for example, but until now it was used very little in the characterization of beams.

[0006] In order to measure the four-dimensional emittance, four moveable slits with a width of As may be used. The first two perpendicular slits at z=0, called the "position sampling-slits," select a surface element, As ² , of the beam having coordinates (xj,yi). After some drift space L, the momentum and phase-density distribution of the sampled element of the beam emerging from As ² are analyzed with two other perpendicular slits at z = L, X2, y _∑ called the "momentum measuring-slit." With a current I3 detected by a collector after the second slits are crossed, the phase current density is given by the expression: B4(xj,yj,xj ',yj ') ~ I3 (xj,yj,xj ',yj ') {L ² /(Asf}. A complete four-dimensional phase density distribution can be mapped and given, and the measured results possess direct physical meaning for the beam phase density (or brightness). It can be used to analyze the coupling interaction in the x, y direction and to study the change in the emittance (brightness) after the beam passes through a nonlinear transport system, and so forth. Unfortunately, this method involves the variation of four independent variables (four moving mechanisms) and leads to difficulty both in acquiring and handling the data.

[0007] More practical and more often used is the "two pairs of crossed-slits method" moving in one direction that measures the distribution: B2(x,x') _y =o, _y '=o ~ (x, x') {L/(As) ² J where B _∑ (x, χ') = Β^χ,χ',Ο,Ο), i.e,. B(r,r') for an axisymmetric beam, and gives the distribution in the two-dimensional trace plane corresponding to a section through the

four-dimensional domain. The sectional emittance is useful when the ion-optical quality of a system is to be tested and beam aberrations need to be seen clearly. This emittance can be directly compared to computer simulations.

[0008] In the "two-slits method," the two slits are extended "infinitely" in the _y-direction. In this way it is possible to obtain the integrated partial density function:

Ό(χ,χ') = a, ⁰⁰ . . ./oo ⁰⁰ B(x,x',y,y') dy dy '.

[0009] In many practical realizations of emittence detectors, such as pepper-pot (PP) emittance probes, as described, for example, in H. Zhang, Ion Sources, Springer, 1999, p. 432- 444, and D. Liakin, D. Selesnev, A. Orlov, R. kuibeda, G. Kropachev, T. Kulevoi, and P. Yakushev, Sci. Instrum., 81, 02B719 (2010), or in slit and multi-section collectors (BNL, Fermilab, as described, for example, in M. Stockli, S. Murray, T. Pennisi, M. Santana and R. Welton , AIP Conf. Proc. 639, 2002, 160-173), only relative

measurements of I ₃ (xi,yi,xi ',yi ') or I3 (x, x') are used.

[0010] Absolute measurements of current I 3 (x, x') are available with an electric (Allison)

scanner, as described, for example, in M. Stockli, S. Murray, T. Pennisi, M. Santana and R. Welton , AIP Conf. Proc. 639, 2002, 160-173, B. Han , M. Stockli, , R. Welton S. Murray, T. Pennisi, M. Santana and C. Long, Rev. Sci. Instrum., 81, 02B721 (2010), and M. Stockli, R. Welton S. Murray, T. Pennisi, M. Santana and C. Long, AIP Conf. Proc. 639, 2002, 135-159. However, even in measurements where it is possible to have the absolute current density distributions they were not used for beam characterization but were used only for determination of emittance contours relating to a desired fraction of the Brightness magnitude. Recently, the main attention was concentrated on the reproducible determination of emittance contours with a self-consistent separation of beam halo from background, as described, for example, in M. Stockli, S. Murray, T. Pennisi, M. Santana and R. Welton , AIP Conf. Proc. 639, 2002, 160-173, B. Han , M. Stockli, , R. Welton S. Murray, T. Pennisi, M. Santana and C. Long, Rev. Sci. Instrum., 81, 02B721 (2010), and M. Stockli, R. Welton S. Murray, T. Pennisi, M. Santana and C. Long, AIP Conf. Proc. 639, 2002, 135-159.

[0011] As described in various illustrative embodiments herein, we have invented the use of a map of the brightness magnitudes l3(xi,yi,xi ',yi ') _ma x distribution across the beam as an important beam characteristic. Degradation of the brightness magnitudes can be easy detected and can be used for correction of beam formation-transportation.

[0012] A diagram of an absolute beam brightness detector (ABBD) useful for such purposes is shown, for example, in Figure 1. The ABBD comprises a first collector (2) for registration of the full beam (1) current / with an aperture (s), for current density J registration by a second collector (3) with an aperture (si) for beamlet (4) sampling for brightness B detection; a vertical deflector (5) and an horizontal deflector (6) for steering and scanning of the beamlet (4); screen with aperture (s2), at a distance L for brightness B detection; a well-shielded third collector (8) collecting particle current I3 with a linear amplifier; where secondary emission may be suppressed by suppressor (9) for accurate absolute brightness B determination. The local absolute Brightness B ₄ (x,y) = (x,y) L ² /(sl s2), where I ₃ ~10 ^~7 A is a current of a third collector relating to the highest current density in the beamlet (4). By moving this ABBD across the beam it is possible to produce a distribution of the local absolute brightness that is useful for beam quality comparison and optimization.

[0013] A prototype of such an ABBD was used for H ^" beam characterization in the

development and characterization of high brightness surface plasma sources (SPS), as described, for example, in V. Dudnikov, Proc. 4 ^th All-Union Conf. on Charged Part. Accel., Moscow, 1974,V.l, p.323, G. Ye. Dereviankin, V. G. Dudnikov, and V. S. Klenov, Zhurnal Tekhnicheskoi Fiziki, 48, 404 (1978), G. Dimov, V. Dudnikov and G. Derevyankin, IEEE Trans. Nucl. Sci. NS-24,1545 (1977), G. Derevyankin , V.

Dudnikov, AIP conference proceedings, 111, p: 376-397,1984, V. Dudnikov, G.

Derevyankin, D. Kovalevsky, V. Savkin, E. Sokolovsky, S. Guharay, Rev. Sci.

Instrum. 67, 1614 (1996), V. Dudnikov, Rev. Sci. Instrum., 67, 915 (1996), G.

Derevyankin, V. Dudnikov, Instruments and Experimental Techniques, 30, 523- 528(1991), and G. Derevyankin, V. Dudnikov, AIP Conf. Proc. I l l, 376-397 (1984).

[0014] The actual design of this ABBD is shown, for example, in Figure 2. This assembly is movable for 20 cm along the ion beam on the Z axis and +/- 3 cm in the transverse directions X, Y. A front collector, numbered as (2) in Figure 1 , for example, of 7 cm diameter is plated by a thick multilayer mesh coated by aquadag for suppression of secondary electron emission. Collector heating by the ion beam was used for an indication of the beam current density distribution. The first aperture s of 0.8 mm diameter and the second collector (3) is used for the current density determination. The second aperture si of 0.12 mm diameter in the second collector is used for beamlet (4) sampling. A beamlet analyzer located at L = 240 mm from aperture si comprises four insulated segments for indication of the beamlet (4) position which is deflected by the scanners (5) and (6). The segments are plated by a thick multilayer mesh coated by aquadag mixture with luminescent powder for suppression of secondary electron emission and for precise beamlet (4) position visualization for the scanner calibration. Slits 0.2 mm between segments and relating collectors were used for beamlet size estimation. The beamlet current density distribution I 3 (xi,yi,xi ',yi ') was detected by scanning across a central aperture s2 of 0.2 mm diameter with collector (8) and a linear amplifier. All apertures were made with chamfered sharp boundaries to minimize secondary emission. Insulated segments may be used for automatic moving of the beamlet (4) to the central aperture s2.

[0015] This version of the ABBD was used for characterization of H ^" ion beams from Penning discharge surface plasma sources (SPS) with cesiation, as described, for example, in V. Dudnikov, G. Derevyankin, D. Kovalevsky, V. Savkin, E. Sokolovsky, S. Guharay, Rev. Sci. Instrum. 67, 1614 (1996), and as shown, for example, in Figures 3 and 4. Fast gas valve (17) was used for gas injection, as described, for example, in G. E.

Derevyankin, V. G. Dudnikov, and P. A. Zhuravlev, Prib. Teldi. Eksp., 5, 168 (1975); Instrum Exp Tech, 18 (5 pt 2), pp. 1531-1532 (1975). Compact Cs oven (16) was used for fast cesiation, as described, for example, in Yu. Bel'chenko, V. Davydenko,, G. Derevyankin, A. Dorogov, V. Dudnikov, Sov Tech Phys Lett, 3, pp. 282 (1977).

[0016] Figure 3 shows a schematic diagram of a Penning discharge SPS (a cross-section

perpendicular to the magnetic field). The essential components are: (1) a cathode, (2) a plasma electrode (anode), (3) an intermediate extraction electrode, (4) a grounded extraction electrode, (5) a magnet, (6) an anode-cathode insulator, (7) cathode cooling, (9) a high-voltage insulator, (12) a base plate, (16) a cesium supply, (17) a gas valve, and (18) valve cooling.

[0017] An H ^" beam with energy 10 kV and current 1=2.5 mA was extracted from noiseless discharge though emission aperture of 0.5 mm diameter. The beam current density distribution across the beam was close to Gaussian. The maximum beam current density of about J=10 mA/cm ² and a beam width full width at half maximum (FWHM) of about 3.5 mm is observed at a distance of 6 cm from the emission surface.

[0018] The normalized beam brightness B _n has been estimated by two ways: through

magnitude of I3 = 0.06 μΑ and from current density J and perpendicular ion temperature T following the relation: B _n = Mc ² J/4n T ^{Error! Bookmark not defined} \ Here, M is the mass of the ion species and c is the speed of light. The perpendicular temperature is obtained from the transverse angular spread a of the beamlet by T=eU a ² , where eU is the beam energy. The transverse angular spread is measured by a system comprising a circular aperture si of 0.12 mm diameter, following electrostatic beam deflectors, and the beamlet collector (8) after an aperture s2 of 0.2 mm diameter. The angular spread of the beamlet is determined from the current distributions measured by the beamlet collector for different voltages of the electrostatic deflectors. The full width of the beamlet distribution at lie level of the peak current is 1 mm in the most optimized case. This value can be significantly dominated by the instrument function as discussed in the context of error analysis in emittance measurements, as described, for example, in H. Zhang, Ion Sources, Springer, 1999, p. 432-444. The instrument function is dictated by the aperture size and the spacing between the aperture and the detector. The regular beam divergence at the aperture si is 17 mrad for X = 1 mm; the distance X is measured in the transverse direction with respect to the beam center. This divergence contributes a spread of about 0.4 mm to the aforementioned lie level beamlet width of 1 mm. The local transverse temperature angular spread is thus estimated to be 1.2 mrad, and the local perpendicular temperature of the 10 kV H- beam is Ti ~ 15 meV. Using this value of Ti and the corresponding Ji as 10 mA/cm ² for the core beam at 6 cm from the emission surface, the normalized beam brightness B _n is estimated to be about 0.5 A/(mm mrad) ² . The perpendicular temperature of the H ^" beam with current density J ₀ = 1.3 A/cm ² at the emission surface is calculated as about T ₀ =2 eV.

[0019] From direct measurement magnitude of h(x,y) by the ABBD, B x,y)= (x,y) l /fi ² (sl s2)=0.57 A/(mm mrad) ² . Here β ² =eU/Mc ² . Corresponding estimation of the transverse ion temperature on the emission surface is T ₀ =1.7 eV. Accuracy of the beamlet current density distribution may be relatively low because aperture s2 may be relatively large. But, for direct brightness detection, it is good enough.

[0020] In previous measurements, as described, for example, in G. Ye. Dereviankin, V. G.

Dudnikov, and V. S. Klenov, Zhurnal Tekhnicheskoi Fiziki, 48, 404 (1978), G. Dimov, V. Dudnikov and G. Derevyankin, IEEE Trans. Nucl. Sci. NS-24,1545 (1977), G. Derevyankin , V. Dudnikov, AIP conference proceedings, 111, p: 376-397,1984, apertures si and s2 of 0.05x0.05 mm ² were used, but the I3 current was very low and an electron multiplier was used for this current detection, which excludes absolute current measurements.

[0021] Other features of the above-described ABBD are a small dynamic range of electrostatic scanners and a possible aberration of the beamlet emittance by fields of scanner. It is attractive to replace the ordinary oscilloscopic scanning systems by an octupole deflector-corrector comprising eight parallel rods similar to those used in focused ion beam lithography systems, as described, for example, in A. Dubrovin, V. Dudnikov, D. Kovalevsky, and A. Shabalin, Instruments and Experimental Techniques, 34, 430-434 (1991). Other attractive versions of an ABBD scanner may use a diagonally- slit cylinder, used as a linear pick up electrode for beam position monitoring and shown, for example, in Figure 5.

[0022] Computer simulation of aberrations of such deflectors at low ion beam energy is

presented, for example, in P Mandal, G Sikler and M Mukherjee, Journal of

Instrumentation, 6, 10.1088/1748-0221/6/02/P02004 (2011). Further computer simulation may be useful for minimization of beamlet emittance aberrations. With a broad dynamic range linear (or logarithmic) amplifier, an improved ABBD may be a convenient and reliable instrument for fast beam characterization and beam

formation-transportation optimization.

[0023] In a particular embodiment, a device is disclosed that includes means for providing an absolute beam brightness detector (ABBD). The device also includes means for operating the ABBD for fast beam characterization and for beam

formation-transportation optimization.

[0024] In another particular embodiment, a method is disclosed that includes steps for

providing an absolute beam brightness detector (ABBD). The method also includes steps for operating the ABBD for fast beam characterization and for beam

formation-transportation optimization.

IV. Brief Description of the Drawings

[0025] The following figures form part of the present specification and are included to further demonstrate certain aspects of the present invention. The present invention may be better understood by reference to one or more of these drawings in combination with the description of embodiments presented herein.

[0026] Consequently, a more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which the leftmost significant digit(s) in the reference numerals denote(s) the first figure in which the respective reference numerals appear, wherein:

[0027] Figure 1 is a diagram illustrating a simplified conceptual scheme of an absolute beam brightness detector (ABBD);

[0028] Figure 2 is a diagram illustrating an absolute beam brightness detector (ABBD);

[0029] Figure 3 is a diagram illustrating a Penning discharge surface plasma source (SPS, showing a cross-section perpendicular to the magnetic field). The essential components are: (1) a cathode, (2) a plasma electrode (anode), (3) an intermediate extraction electrode, (4) a grounded extraction electrode, (5) a magnet, (6) an anode-cathode insulator, (7) cathode cooling, (9) a high-voltage insulator, (12) a base plate, (16) a cesium supply, (17) a gas valve, and (18) valve cooling;

[0030] Figure 4 is a diagram illustrating a Penning discharge surface plasma source (SPS);

[0031] Figure 5 is a diagram illustrating a simplified conceptual scheme of a diagonal-slit cylinder for beamlet scanning and position monitoring: Figure 5a showing one directional diagonal-slit cylinder, and Figure 5b showing a two directional diagonal-slit cylinder, as described, for example, in P Mandal, G Sikler and M Mukherjee, Journal of Instrumentation, 6, 10.1088/1748-0221/6/02/P02004 (2011);

[0032] Figure 6 is a diagram illustrating an embodiment of an apparatus including means for providing an absolute beam brightness detector (ABBD) and means for operating the ABBD for fast beam characterization and for beam formation-transportation optimization; and

[0033] Figure 7 is a flow diagram of an illustrative embodiment of a method including steps for providing an absolute beam brightness detector (ABBD) and steps for operating the ABBD for fast beam characterization and for beam formation-transportation optimization.

V. Detailed Description

[0034] Illustrative embodiments of the present invention are described in detail below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of the present disclosure.

[0035] Particular embodiments of the present disclosure are described with reference to the drawings. In the description, common features are designated by common reference numbers.

[0036] Referring to Figure 1 , a diagram illustrating a simplified conceptual scheme of an

absolute beam brightness detector (ABBD) is depicted and indicated generally, for example, at 100.

[0037] As described in various illustrative embodiments herein, we have invented the use of a map of the brightness magnitudes (xi,yi,xi ',yi ') _m ax distribution across the beam as an important beam characteristic. Degradation of the brightness magnitudes can be easy detected and can be used for correction of beam formation-transportation.

[0038] A diagram of an absolute beam brightness detector (ABBD) useful for such purposes is shown, for example, in Figure 1. The ABBD comprises a first collector (2) for registration of the full beam (1) current / with an aperture (s), for current density J registration by a second collector (3) with an aperture (si) for beamlet (4) sampling for brightness B detection; a vertical deflector (5) and an horizontal deflector (6) for steering and scanning of the beamlet (4); screen with aperture (s2), at a distance L for brightness B detection; a well-shielded third collector (8) collecting particle current I3 with a linear amplifier; where secondary emission may be suppressed by suppressor (9) for accurate absolute brightness B determination. The local absolute Brightness B x,y) = (x,y) L ² /(sl s2), where Fj-lO ⁷ A is a current of a third collector relating to the highest current density in the beamlet (4). By moving this ABBD across the beam it is possible to produce a distribution of the local absolute brightness that is useful for beam quality comparison and optimization. [0039] A prototype of such an ABBD was used for H ^" beam characterization in the development and characterization of high brightness surface plasma sources (SPS), as described, for example, in V. Dudnikov, Proc. 4 ^th All-Union Conf. on Charged Part. Accel., Moscow, 1974,V.l, p.323, G. Ye. Dereviankin, V. G. Dudnikov, and V. S. Klenov, Zhurnal Tekhnicheskoi Fiziki, 48, 404 (1978), G. Dimov, V. Dudnikov and G. Derevyankin, IEEE Trans. Nucl. Sci. NS-24,1545 (1977), G. Derevyankin , V.

Dudnikov, AIP conference proceedings, 111, p: 376-397,1984, V. Dudnikov, G.

Derevyankin, D. Kovalevsky, V. Savkin, E. Sokolovsky, S. Guharay, Rev. Sci.

Instrum. 67, 1614 (1996), V. Dudnikov, Rev. Sci. Instrum., 67, 915 (1996), G.

Derevyankin, V. Dudnikov, Instruments and Experimental Techniques, 30, 523- 528(1991), and G. Derevyankin, V. Dudnikov, AIP Conf. Proc. I l l, 376-397 (1984).

[0040] Referring to Figure 2, a diagram illustrating an absolute beam brightness detector (ABBD) is depicted and indicated generally, for example, at 200.

[0041] The actual design of this ABBD is shown, for example, in Figure 2. This assembly is movable for 20 cm along the ion beam on the Z axis and +/- 3 cm in the transverse directions X, Y. A front collector, numbered as (2) in Figure 1 , for example, of 7 cm diameter is plated by a thick multilayer mesh coated by aquadag for suppression of secondary electron emission. Collector heating by the ion beam was used for an indication of the beam current density distribution. The first aperture s of 0.8 mm diameter and the second collector (3) is used for the current density determination. The second aperture si of 0.12 mm diameter in the second collector is used for beamlet (4) sampling. A beamlet analyzer located at L = 240 mm from aperture si comprises four insulated segments for indication of the beamlet (4) position which is deflected by the scanners (5) and (6). The segments are plated by a thick multilayer mesh coated by aquadag mixture with luminescent powder for suppression of secondary electron emission and for precise beamlet (4) position visualization for the scanner calibration. Slits 0.2 mm between segments and relating collectors were used for beamlet size estimation. The beamlet current density distribution I 3 (xi,yi,xi ',yi ') was detected by scanning across a central aperture s2 of 0.2 mm diameter with collector (8) and a linear amplifier. All apertures were made with chamfered sharp boundaries to minimize secondary emission. Insulated segments may be used for automatic moving of the beamlet (4) to the central aperture s2. [0042] This version of the ABBD was used for characterization of H ^" ion beams from Penning discharge surface plasma sources (SPS) with cesiation, as described, for example, in V. Dudnikov, G. Derevyankin, D. Kovalevsky, V. Savkin, E. Sokolovsky, S. Guharay, Rev. Sci. Instrum. 67, 1614 (1996), and as shown, for example, in Figures 3 and 4. Fast gas valve (17) was used for gas injection, as described, for example, in G. E.

Derevyankin, V, G. Dudnikov, and P. A, Zhuravlev, Prib. Tekh. Eksp., 5, 168 (1975); Instrum Exp Tech, 18 (5 pt 2), pp. 1531-1532 (1975). Compact Cs oven (16) was used for fast cesiation, as described, for example, in Yu. Bel'chenko, V. Davydenko,, G. Derevyankin, A. Dorogov, V. Dudnikov, Sov Tech Phys Lett, 3, pp. 282 (1977).

[0043] Referring to Figure 3, a diagram illustrating a simplified conceptual scheme of a

Penning discharge surface plasma source (SPS, showing a cross-section perpendicular to the magnetic field) is depicted and indicated generally, for example, at 300. The essential components are: (1) a cathode, (2) a plasma electrode (anode), (3) an intermediate extraction electrode, (4) a grounded extraction electrode, (5) a magnet, (6) an anode-cathode insulator, (7) cathode cooling, (9) a high- voltage insulator, (12) a base plate, (16) a cesium supply, (17) a gas valve, and (18) valve cooling.

[0044] Referring to Figure 4, a diagram illustrating a Penning discharge surface plasma source (SPS) is depicted and indicated generally, for example, at 400.

[0045] Figure 3 shows a schematic diagram of a Penning discharge SPS (a cross-section

perpendicular to the magnetic field). The essential components are: (1) a cathode, (2) a plasma electrode (anode), (3) an intermediate extraction electrode, (4) a grounded extraction electrode, (5) a magnet, (6) an anode-cathode insulator, (7) cathode cooling, (9) a high-voltage insulator, (12) a base plate, (16) a cesium supply, (17) a gas valve, and (18) valve cooling.

[0046] An H ^" beam with energy 10 kV and current 1=2.5 mA was extracted from noiseless discharge though emission aperture of 0.5 mm diameter. The beam current density distribution across the beam was close to Gaussian. The maximum beam current density of about J=10 mA/cm ² and a beam width full width at half maximum (FWHM) of about 3.5 mm is observed at a distance of 6 cm from the emission surface. [0047] The normalized beam brightness B _n has been estimated by two ways: through magnitude of I3 = 0.06 μΑ and from current density J and perpendicular ion temperature

T following the relation: B _n = Mc ² il n T Error! Bookmark not defined. _{is Q mass of} the ion species and c is the speed of light. The perpendicular temperature is obtained from the transverse angular spread a of the beamlet by T=eU a ² , where eU is the beam energy. The transverse angular spread is measured by a system comprising a circular aperture si of 0.12 mm diameter, following electrostatic beam deflectors, and the beamlet collector (8) after an aperture s2 of 0.2 mm diameter. The angular spread of the beamlet is determined from the current distributions measured by the beamlet collector for different voltages of the electrostatic deflectors. The full width of the beamlet distribution at lie level of the peak current is 1 mm in the most optimized case. This value can be significantly dominated by the instrument function as discussed in the context of error analysis in emittance measurements, as described, for example, in H. Zhang, Ion Sources, Springer, 1999, p. 432-444. The instrument function is dictated by the aperture size and the spacing between the aperture and the detector. The regular beam divergence at the aperture si is 17 mrad for X = 1 mm; the distance X is measured in the transverse direction with respect to the beam center. This divergence contributes a spread of about 0.4 mm to the aforementioned lie level beamlet width of 1 mm. The local transverse temperature angular spread is thus estimated to be 1.2 mrad, and the local perpendicular temperature of the 10 kV H- beam is Ti ~ 15 meV. Using this value of Ti and the corresponding Ji as 10 mA/cm ² for the core beam at 6 cm from the emission surface, the normalized beam brightness B _n is estimated to be about 0.5 A/(mm mrad) ² . The perpendicular temperature of the H ^" beam with current density J ₀ = 1.3 A/cm ² at the emission surface is calculated as about T ₀ =2 eV.

[0048] From direct measurement magnitude of (x,y) by the ABBD, B4x,y)= (x,y) L ² /fi ² (sl s2)=0.57 A/(mm mrad) ² . Here fi ² =eU/Mc ² . Corresponding estimation of the transverse ion temperature on the emission surface is T ₀ =1.7 eV. Accuracy of the beamlet current density distribution may be relatively low because aperture s2 may be relatively large. But, for direct brightness detection, it is good enough.

[0049] In previous measurements, as described, for example, in G. Ye. Dereviankin, V. G.

Dudnikov, and V. S. Klenov, Zhurnal Tekhnicheskoi Fiziki, 48, 404 (1978), G. Dimov, V. Dudnikov and G. Derevyankin, IEEE Trans. Nucl. Sci. NS-24,1545 (1977), G. Derevyankin , V. Dudnikov, AIP conference proceedings, 111, p: 376-397,1984, apertures si and s2 of 0.05x0.05 mm ² were used, but the I3 current was very low and an electron multiplier was used for this current detection, which excludes absolute current measurements.

[0050] Other features of the above-described ABBD are a small dynamic range of electrostatic scanners and a possible aberration of the beamlet emittance by fields of scanner. It is attractive to replace the ordinary oscilloscopic scanning systems by an octupole deflector-corrector comprising eight parallel rods similar to those used in focused ion beam lithography systems, as described, for example, in A. Dubrovin, V. Dudnikov, D. Kovalevsky, and A. Shabalin, Instruments and Experimental Techniques, 34, 430-434 (1991). Other attractive versions of an ABBD scanner may use a diagonally- slit cylinder, used as a linear pick up electrode for beam position monitoring and shown, for example, in Figure 5.

[0051] Referring to Figure 5, a diagram illustrating a simplified conceptual scheme of a

diagonal-slit cylinder for beamlet scanning and position monitoring is depicted and indicated generally, for example, at 500. Figure 5 a shows one directional diagonal-slit cylinder 510, and Figure 5b shows a two directional diagonal-slit cylinder 520, as described, for example, in P Mandal, G Sikler and M Mukherjee, Journal of

Instrumentation, 6, 10.1088/1748-0221/6/02/P02004 (2011).

[0052] Computer simulation of aberrations of such deflectors at low ion beam energy is

presented, for example, in P Mandal, G Sikler and M Mukherjee, Journal of

Instrumentation, 6, 10.1088/1748-0221/6/02/P02004 (2011). Further computer simulation may be useful for minimization of beamlet emittance aberrations. With a broad dynamic range linear (or logarithmic) amplifier, an improved ABBD may be a convenient and reliable instrument for fast beam characterization and beam

formation-transportation optimization.

[0053] Referring to Figure 6, a diagram illustrating an embodiment of an apparatus is depicted and indicated generally, for example, at 600. The apparatus 600 includes means for providing an absolute beam brightness detector (ABBD) 610 and means for operating the ABBD for fast beam characterization and for beam formation-transportation optimization 620. [0054] Referring to Figure 7, a flow diagram of an illustrative embodiment of a method is depicted and indicated generally, for example, at 700. The method 700 includes steps for providing an absolute beam brightness detector (ABBD) 710 and steps for operating the ABBD for fast beam characterization and for beam formation-transportation optimization 720.

[0055] Attached herewith as an Appendix to this specification is a document describing more details about various illustrative embodiments, which Appendix to this specification is incorporated by reference as if set forth below. More details about various illustrative embodiments may be found by referring to the Appendix.

[0056] The present invention is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as those that are inherent therein. While the present invention has been depicted, described and is defined by reference to exemplary embodiments of the present invention, such a reference does not imply a limitation of the present invention, and no such limitation is to be inferred. The present invention is capable of considerable modification, alteration, and equivalency in form and function as will occur to those of ordinary skill in the pertinent arts having the benefit of this disclosure. The depicted and described embodiments of the present invention are exemplary only and are not exhaustive of the scope of the present invention.

Consequently, the present invention is intended to be limited only by the spirit and scope of the appended claims, giving full cognizance to equivalents in all respects.

[0057] The particular embodiments disclosed above are illustrative only, as the present

invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of composition or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and intent of the present invention. In particular, every range of values (of the form, "from about a to about b," or, equivalently, "from approximately a to b," or, equivalently, "from approximately a-b") disclosed herein is to be understood as referring to the power set (the set of all subsets) of the respective range of values, in the sense of Georg Cantor. Accordingly, the protection sought herein is as set forth in the claims below.

[0058] The particular embodiments of the present invention described herein are merely

exemplary and are not intended to limit the scope of this present invention. Many variations and modifications may be made without departing from the intent and scope of the present invention. Applicants intend that all such modifications and variations are to be included within the scope of the present invention as defined in the appended claims and their equivalents.

[0059] While the present invention has been illustrated by a description of various

embodiments and while these embodiments have been described in considerable detail, it is not the intention of the Applicants to restrict, or any way limit the scope of the appended claims to such detail. The present invention in its broader aspects is therefore not limited to the specific details, representative apparatus, methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of Applicants' general inventive concept.

Appendix to the Specification

Absolute beam brightness detector ^a)

Vadim Dudnikov ^b)

Muons, Inc., Batavia, IL 60510 USA

(Presented XXXXX, received XXXXX, accepted XXXXX, published online XXXXX)

In generally accepted emittance measurement main attention is concentrated on emittances areas ε _χ , ε _γ occupied by desired part of ion beam in transverse phase space and shape of these areas. The absolute beam phase density (brightness) as usually is not measured directly and the average beam brightness B is calculated from a beam intensity I and the transverse emittances. In the ion source and LEBT optimization it is important to preserve the beam brightness because some aberration of ion optic and beam instabilities can decrease the brightness of the central part of ion beam significantly. For these measurements is convenient to use an Absolute Beam Brightness Detector (ABBD) with the brightness determination from one short considered in this article.

I INTRODUCTION B ₂ (x, x') = B ₄ (x,x',0,0), i. e. B(r,r') (3)

A local beam brightness is important beam characteristics for axisymmetric beam, and gives the distribution in the which should be an invariant in conservative forces fields two-dimensional trace plane corresponding to a section without particle loss. There will be used terms definitions through the four-dimensional domain. The sectional reproduced in ¹ . emittance is useful when ion-optical quality of a system

Principles of determination the phase density distribution are to be tested and beam aberrations need to be seen in four-dimensional phase space is well known and detail clearly. This emittance can be directly compared to considered in ¹ , but until now it was used very little in the computer simulations.

beams characterization. In the "two-slits method" the two slits are extended

For measure the four-dimensional emittance, four "infinitely" in the ^-direction. In this way it is possible to moveable slits with width of As should be used. The first obtain the integrated partial density function:

two perpendicular slits at z=0, called the "position

sampling-slit", select a surface element, As ² , of the beam D(x,x')= f_ _∞ ^∞ f_ _∞ ^∞ B(x,x',y,y ') dy dy ', (4) having coordinates (xj,yj). After some drift space L the

momentum and phase-density distribution of the sampled In many practical realizations of emittence detectors, such element of the beam emerging from As ² are analyzed with as pepper-pot (PP) emittance probes ^{1 2} or in slit and multithe other two perpendicular slits at z = L, x ₂ , j¾ called the section collector (BNL, Fermilab ³ ) is used only relative "momentum measuring-slit". With current I ₃ detected by measurements of I ₃ (x ₁ ,y ₁ ,x ₁ ',y ₁ ') or I ₃ (x, x').

collector after the second slits cross, the phase current Absolute measurements of current I ₃ (χ, χ') is available density is given by expression: with an electric (Allison) scanner ³ ' ⁴ ' ⁵ . However, in

measurements where it is possible to have the absolute

B ₄ (x],y],X] ',y] ') ~ I ₃ (xj.yj.Xi '.yi ') {L ² /(Asf} (1) current density distributions they were not used for beam characterization but were used only for determination of

A complete four-dimensional phase density distribution emittance contours relating to desired fraction of the can be mapped and given, and the measured results Brightness magnitude. Recently main attention was possess direct physical meaning of the beam phase density concentrated on the reproducible determination emittance (or brightness). It can be used to analyze the coupling contours with a self-consistent separation of beam halo interaction in the x, y direction and to study the change in from background ^{3 5} .

the emittance (Brightness) after the beam passes through a II ABSOLUTE BRIGHTNESS DETECTOR

nonlinear transport system, etc. Unfortunately, this method

involves the variation of four independent variables (four Here it is proposed to use a map of the brightness moving mechanisms) and leads to difficulty both in magnitudes I ₃ (x _h y _h xi ',yi ')max distribution across the acquiring and handling the data. beam as important beam characteristics. Degradation of Practically more often used "two pairs of crossed-slits the brightness magnitudes can be easy detected and can be method" moving in one direction measures the used for correction of beam formation -transportation. distribution: A diagram of absolute beam brightness detector (ABBD)

B(x,x') _{y=o =0} ~ I ₃ (x, x') {U(Asf} (2) is shown in Fig. 1. The ABBD as proposed comprises of a first collector (2) for registration full beam (1) current /

^Contributed paper published as part of the Proceedings of the 14th

International Conference on Ion Source, Giardini-Naxos, Sicily, Italy,

September, 2011.

¾>ndence should be addressed. Electronic mail: with the aperture (s), for current density J registration by 0.12 mm diameter in the second collector is used for second collector (3) with the aperture (si) for beamlet (4) beamlet sampling. A beamlet analyzer located at L=240 sampling for brightness B detection; vertical deflector (5) mm from aperture si is comprised of four insulated and horizontal deflector (6) for steering and scanning of segments for indication of the beamlet (4) position which beamlet (4); Screen with aperture ( s2 ), in distance L for B is deflected by the scanners (5), (6). The segments are detection, well shielded third collector (8) collecting plated by thick multilayer mesh coated by aquadag mixture particle current I ₃ with a linear amplifier; the secondary with luminescent powder for suppression of secondary emission must be suppressed by suppressor (9) for electron emission and for precise beamlet position accurate absolute brightness B determination. visualization for the scanner calibration. Slits 0.2 mm between segments and relating collectors were used for beamlets sizes estimation. The beamlet current density distribution I ₃ (x ₁ ,y ₁ ,x ₁ ',y ₁ ') was detected by scanning across a central aperture s2 of 0.2 mm diameter with collector 8 and linear amplifier. All apertures were made with chamfered sharp boundaries for minimizing a secondary emission. Insulated segments can be used for automatic moving of the beamlet to the central aperture s2. This version of the ABBD was used for characterization of

FIG. 1. (Color online) Diagram of the ABBD. H ^" ion beam from Penning discharge SPS with cesiation ¹⁰ shown in Fig. 3 and 4. Fast gas valve (17) was used for gas injection ¹⁴ . Compact Cs oven (16) was used for fast cesiation ¹⁵ .

s

SPS (a cross section perpendicular to the magnetic field). The essential components are: (1)

A front collector numbered as (2) in Fig. 1 of 7 cm

diameter is plated by thick multilayer mesh coated by

aquadag for suppression of secondary electron emission.

Collector heating by ion beam was used for indication

b eam current density distribution. The first aperture s of

0.8 mm diameter and the second collector (3) is used for FIG. 4. (Color online) High brightness PD SPS.

current density determination. The second aperture si of H ^" beam with energy 10 kV and current 1=2.5 mA was is attractive to replace the ordinary oscilloscopic scanning extracted from noiseless discharge though emission systems by octupole deflector-corrector comprising of aperture of 0.5 mm diameter. The beam current density eight parallel roads similar to used in focused ion beam distribution across the beam is close to Gaussian. The lithography system ¹⁶ . Other attractive version of scanner maximum beam current density of about J=10 mA/cm ² and is a diagonally-slits cylinder, used as linear pick up a beam width (FWHM) of about 3.5 mm is observed at a electrode for beam position monitoring and shown in Fig.

and position

[17].

deflector at Further computer of beamlet

range can be beam

between the aperture and the detector. The regular beam

divergence at the aperture si is 17 mrad ϊοχ Χ=\ mm; the 1 H. Zhang, Ion Sources, Springer, 1999, p. 432-444.

distance X is measured in the transverse direction with 2 D. Liakin, D. Selesnev, A. Orlov, R. kuibeda, G. Kropachev, T. respect to the beam center. This divergence contributes a Kulevoi, and P. Yakushev, Sci. Instrum., 81, 02B719 (2010).

spread of about 0.4 mm to the aforementioned 1/e level 3 M. Stockli, S. Murray, T. Pennisi, M. Santanaand R. Welton , AIP

Conf. Proc. 639, 2002, 160-173.

beamlet width of 1 mm. The local transverse temperatute 4 B. Han , M. Stockli, , R. Welton S. Murray, T. Pennisi, M. Santanaand angular spread is thus estimated to be 1.2 mrad, and the C. Long, Rev. Sci. Instrum., 81, 02B721 (2010).

local perpendicular temperature of the 10 kV H- beam is 5 M. Stockli , , R. Welton S. Murray, T. Pennisi, M. Santanaand C. Ti~ 15 meV. Using this value of T and the corresponding Long, AIP Conf. Proc. 639, 2002, 135-159.

6 V. Dudnikov, Proc. 4 ^th Ail-Union Conf. on Charged Part. Accel., Ji as 10 mA/cm ² for the core beam at 6 cm from the Moscow, 1974,V.l, p.323.

emission surface, the normalized beam brightness is 7 G. Ye. Dereviankin, V. G. Dudnikov, and V. S. Klenov, Zhurnal estimated as about 0.5 A/(mm mrad) ² . The perpendicular Tekhnicheskoi Fiziki, 48, 404 (1978.

temperature of the H ^" beam with current density Jo =1.3 8 G. Dimov, V. Dudnikov and G. Derevyankin, ΓΕΕΕ Trans. Nucl. Sci.

NS-24,1545 (1977).

A/cm ² at the emission surface is calculated as about To=2 9 G. Derevyankin , V. Dudnikov, ΑΓΡ conference proceedings, 111 , p: eV. 376-397,1984.

From direct measurement magnitude of l3(x,y) by ABBD 10 V. Dudnikov, G. Derevyankin, D. Kovalevsky, V. Savkin,

B ₄ (x,y)= I ₃ (x,y) L ² /fi ² (sl s2)=0.57 A/ (mm mrad) ² . Here E. Sokolovsky, S. Guharay, Rev. Sci. Instrum. 67, 1614

(1996).

β ² =eU/Mc ² . Corresponding estimation of the transverse 11 V. Dudnikov, Rev. Sci. Instrum., 67, 915 (1996).

ion temperature on the emission surface is To=1.7 eV. 12 G. Derevyankin, V. Dudnikov, Instruments and Experimental Accuracy of the beamlet current density distribution is Techniques, 30, 523-528(1991).

relative low because aperture s2 is relative large. But, for 13 G. Derevyankin, V. Dudnikov, ΑΓΡ Conf. Proc. I l l, 376-397 (1984).

14 G. E. Derevyankin, V. G. Dudnikov, and P. A. Zhuravlev, Prib. Tekh. direct brightness detection it is good enough. Eksp., 5, 168 (1975); Instrum Exp Tech, 18 (5 pt 2), pp. 1531-1532 In previous measurements ^7"9 were used si and s2 of (1975) .

0.05x0.05 mm ² but I ₃ current was very low and electron 15 Yu. Bel'chenko, V. Davydenko,, G. Derevyankin, A. Dorogov, V. multiplier was used for this current detection, which Dudnikov, Sov Tech Phys Lett, 3, pp. 282 (1977).

16 A. Dubrovin, V. Dudnikov, D. Kovalevsky, and A. Shabalin, excludes absolute current measurements. Instruments and Experimental Techniques , 34, 430-434 (1991). Other disadvantages of described ABBD is a small 17 P Mandal, G Sikler and M Mukherjee, Journal of Instrumentation, 6 , dynamic range of electrostatic scanners and possible 10.1088/1748-0221/6/02/P02004( 201 1).

aberration of the beamlet emittance by fields of scanner. It