Doppler-Shift Proton Fraction Measurement on a CW Proton Injector Page: 6 of 6
4 p.View a full description of this report.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
from 2.2 to 5 secm, beam current decreased from 92 mA
to 71 mA. As above, the currents to the two ECR
solenoids were adjusted to maintain stable source
operation.
It is important to note that the proton fraction
corresponding to the 2.2-scem data point in figure 3
(85%) does not agree with the 1000 W data point in
figure 2 (95%). Source microwave power and
throughput were the same in these two cases, but the
proton fractions differ by 10%. Inspection of the raw
data supports the measured difference. ECR solenoid
settings were slightly different. This observation,
together with the variations in figure 2, indicates that the
proton fraction is sensitive to minor variations in ion
source setpoints.
Figure 4 is a spectrum from 50 kV, 132 mA source
operation. The source is operating above its design-
matched perveance (110 mA at 50 kV). An important
difference between the way this spectrum was acquired
and all of those discussed so far is that the slit width was
reduced to 20 im.a
0
u5000 -
4000-
3000 -
2000
1000
0-0 100 200 300
400 500
channel
Figure 4. Spectrum taken at 132 mA with 20
gm slit width showing a non-
gaussian proton peak.
Note the non-Gaussian shape of the proton line.
Such a distribution is indicative of poor beam optics. In
this case, it can be attributed to overdense beam
extraction. Other data taken with 20- m slits show a
return to Gaussian shape as the current was reduced to
110 mA. The data taken with 50-pm slits is more
Gaussian because the natural line width is convolved
with a wider instrument function.
Data were also taken during several hours of ion
source operation at 75 keV. Immediately prior to when
this data was taken, the ion source was exposed to air for
accelerator maintenance. The spectrometer slit width
was back to 50 }im.
An interesting spectrum was noted and is shown in
figure 5. Situated at channel 300 is a line due to
hydrogen atoms extracted as water ions. The presence of
significant water in the beam is attributed to the fact that
the ion source was just beginning to be conditioned and
that water became absorbed on the source walls during
its exposure to air.Cross sections for the production of Ha from water
incident on hydrogen have not been measured. To
estimate the water fraction, the required cross sections
were estimated from cross sections for the production of
Ha for hydrogen atoms incident on water[7].a
a
a6000 -
5000-
4000
3000 -
2000
1000-
0-0 100 200 300 400
500
channel
Figure 5. Spectrum at 75 kV, just after the ion
source was open to air.
The proton fraction is estimated to be in the range of 30 to
40% while water is 40 to 25%, respectively. There is a
large uncertainty in the beam fractions in this case due to
the facts that protons are no longer the dominant line and
that estimates of the water cross sections differ by a factor
of two.
After approximately 10 minutes of cw operation, the
water level in the beam decreased by over an order of
magnitude. However, the proton fraction was still poor
due to the low source power. Residual gas analysis of the
injector vacuum always indicates the presence of water
contamination for several days after exposure to air.
Water in the ion source cleans up at a more rapid rate due
to its active removal by the plasma and the beam.
Acknowledgments
Funding for this work has been provided by the US
Department of Energy. We would also like to thank the
neutral beam operations group at the Princeton Plasma
Physics Laboratory for the loan of the Optical Multi-
channel Analysis system.
References
[1]J. Sherman et al., Rev. Sci. Instrum. 69, 1003 (1998).
[2] C. F. Burrell, W. S. Cooper, R. R. Smith, and W. F.
Steele, Rev. Sci. Instrum. 51, 1451 (1980).
[3]I. D. Williams, J. Geddes, and H. B. Gilbody, J. Phys. B
15, 1377 (1982).
[4] G. Bracco, C. Breton, C. de Michelis, M. Mattioli, and
J. Ramette, J. Opt. Soc. Am. 71, 1318 (1981).
[5IB. G. Chidley, F. P. Adams, G. E. McMichael, T. T.
Ngoc, and T. S. Bhatia, in Proceedings of the 1990 Linear
Accelerator Conference.
[6] J. H. Kamperschroer et al., Rev. Sci. Instrum. 58, 1362
(1987).
[7]F. B. Yousif, J. Geddes, and H. B. Gilbody, J. Phys. B.
19, 217 (1986).Hea
+
H +L
+ ; -
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Kamperschroer, J. H.; Sherman, J. D.; Zaugg, T. J.; Arvin, A. H.; Bolt, A. S. & Richards, M. C. Doppler-Shift Proton Fraction Measurement on a CW Proton Injector, report, December 31, 1998; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc688132/m1/6/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.