Proceedings of the 14th Annual Meeting of Particle Accelerator Society of Japan
August 1-3, 2017, Sapporo, Japan

PASJ2017 WEP080

MEASUREMENTS OF THE ENERGY DISTRIBUTION OF THE
ELECTRON CLOUD AT J-PARC MR
B. Yee-Rendon∗ , H. Kuboki, R. Muto, M. Okada, K. Satou, M. Tomizawa and T. Toyama
KEK/J-PARC, Tsukuba, Ibaraki, Japan
Abstract
The energy of the electrons plays a relevant role in theelectron cloud (EC) build-up, according to the Secondary
Electron Yield (SEY) curve. Different incident electronenergies create a distinct amount of secondary electrons at
the beam pipes. The Electron Cloud Detector (ECD) at JPARC MR is a Retarding Field Analyzer with a sweeping
electrode. The measurements of electron energy were doneby varying the voltage repeller of the grid of the ECD toselect the energy of the electrons that were collected on thedetector plate. The knowledge of the incident energy helps
to estimate the interaction between the EC and the beam
distribution, consequently, it allows us to develop a more
precise model of this phenomenon.

INTRODUCTION
In the last years, a series of EC surveys at the J-PARC MR
were done to understand the conditions of the EC build-up[1,2]. During this studies the ECD was the main device used
to collect signals of the electrons flux that impact the beamchambers. The ECD is a Retarding Field Analyzer with apulsed electrode developed at ANL [3, 4]. The detector is
located at the address 77 of the MR downstream of the SXElectro Static Septum (ESS), Figure 1 shows the actual setupof the ECD inside the MR tunnel.

these secondary electrons a voltage repeller is applied in agrid between the collector and the slot is added [5].

Figure 2: Schematic view of the ECD at J-PARC MR. Courtesy of R. J. Macek.
The EC simulations indicate that the low energy electrons
are the large population in the electron clouds, therefore, tocorroborate this result and understand more about the EC atMR, studies of EC changing the voltage repeller were done.

MEASUREMENTS
For this survey, the HV pulsed electrode is not used, thevoltage of the collector remain fixed at 60 V and the voltageof the repeller is changed from the nominal value of 30 V to-420 V. Due to the electron has negative charge, the positive
values of the voltage repeller has the function to attract theelectrons to the collector, on the contrary, for the negativevalues the electron must has an energy higher than the voltage
repeller to reach the collector plate.
Additionally, Table 1 presents the main parameters during
the study. During this survey the voltage repeller was only
the parameters that was changed.
Table 1: Relevant Parameters During the SX Survey at MR

Figure 1: The ECD installed at MR of J-PARC.
Figure 2 presents a diagram of the ECD, the electron passthrough the six slits (slot) on the top of the beam chamber.
The electron flux between the slot (grounded) and the collector slit is controlled by putting a bias voltage. The electrons
which have energy higher than the difference of voltage between the slot and the collector are detected by the collector
plate of stainless steels. Additional, the electrons that impact
the collector produce secondary electrons, thus, to trapped∗ byee@post.j-parc.jp- 1069 -Parameters

Units

ValueEnergyPowerIntensity
Phase offset
Q x ,Q yQs
Voltage collector
Voltage repellerGeVkW1013 ppp
degree––VV

30
374.2
722.3, 20.80.000119
60
30 to -420

Proceedings of the 14th Annual Meeting of Particle Accelerator Society of Japan
August 1-3, 2017, Sapporo, JapanPASJ2017 WEP080

RESULTS
Figure 3 shows a summary of the observations of theelectron flux peak during the debunching process for thedifferent values of the voltage repeller. For each of theconfigurations five measurements were done having similar conditions (some fluctuations in the beam power can beobserved in Figure 4 top) and the signal was average over100 turns. The electron cloud reached the maximum intensity about 75 ms after P3 (the time in which the debunchingstarted), when a significantly large signal is recorded fornegative low values of the voltage repeller.

estimation of the cumulative distribution of the electronenergy during the measurements can be done assuming thenext conditions:• The initial setting of the voltage repeller (30 V) provide
the maximum efficiency to collect electrons.
• The EC reached the highest signal at 75 ms.
• Taking only the signal of the highest peak.
Figure 5 presents the distribution of energy of the electron.
A fit with an exponential function was applied,y(x) = b0 ∗ exp(b1 ∗ x)(1)

where the values b0 = 0.760 and b1 = 0.003 were the parameters of the fit which provide a coefficient of determination (R2 ) of 0.856.

Figure 3: The surface map of the electron flux peak as afunction of debunching time and the voltage repeller.
In addition, the average value of the beam power (top)and the pressure rise close to the EC detector (bottom) for
the different setting of the measurements are presented inFigure 4. The beam power remained stable, except for theregion from -10 V to -180 V, in constrant the pressure risepresented more fluctuating behavior having a region of flatvalues from -180 V to -330 V.

Figure 5: The cumulative of the energy spectrum of theelectrons. The errors bars corresponded to the standarderror.

CONCLUSION AND OUTLOOK

Figure 4: The average beam power (red dot line) and the pressure rise (blue solid line). The errors bars were computed
using the standard error.
The values presented in Figure 3 are the cumulative energy
spectrum of the electron impacting the collector. A roughThe study proved that a significant fraction of the electron that impact the wall chambers corresponded to the low
energy regime from 0 eV to 180 eV (See Figures 3 and 5),
this support the preliminary results of the simulations andshown the importance of the low energy electron in the EC
build-up.
In Figure 5, the percentage of electron presented a decreased behavior (See the exponential fit) as the energy ofthe electrons increase, however, there are some high peaks
at 60 eV and 150 eV were observed. The possible reason ofthe peaks could be that the region from -10 V to -180 V in
Figure 4 presented variations in the beam power and the pressure rise, thus, this could affected the formation of the EC.
A detailed analysis of the measurements is under process.
Finally, the measurements of the SEY are under process,this is important to corroborate our assumption of the electron production ratio and help us to improve the simulation
model.

- 1070 -Proceedings of the 14th Annual Meeting of Particle Accelerator Society of Japan
August 1-3, 2017, Sapporo, JapanPASJ2017 WEP080

ACKNOWLEDGMENT
The authors thank the members of J-PARC Main Ring, in
specially to A. Kobayashi, Y. Sato for their support during
the measurements. This work was partially supported byJSPS KAKENHI Grant Number JP16H06288, Grant-in-Aid
for Specially promoted Research titled “Measurement of CP
symmetry of neutrino by upgrading T2K experiment”.

REFERENCES[1] B. Yee-Rendon et al., “Electron Cloud Measurements at JPARC Main Ring”, in Proceedings of the 7th International
Particle Accelerator Conference, Busan, Korea, May 8 - 13,
2016, pp. 4175–4177.
[2] B. Yee-Rendon et al., “Electron Cloud Study at SX Operation
Mode at J-PARC MR”, in Proceedings of the 13th Particle
Accelerator Society of Japan, Chiba, Japan, August 8 - 10,2016, pp. 149–151.
[3] The LANL, SPSS Project, LAUR-98-4172, 1998.
[4] R.J. Macek et al., “Electron Proton Two-Steam Instability atthe PSR”, in Proceedings of the 2001 Particle Accelerator
Conference, Chicago, U.S., June 18 - 22, 2001, pp. 688–692;
LA-UR-01-3034.
[5] T. Toyama et al., “Electron Cloud Observed During Debunching for Slow Beam Extraction at J-PARC Main Ring”, inMonitor group weekly meeting.

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